The rate and consequences of future high latitude ice sheet retreat remain a major concern given ongoing anthropogenic warming. Here, new precisely dated stalagmite data from NW Iberia provide the first direct, high-resolution records of periods of rapid melting of Northern Hemisphere ice sheets during the penultimate deglaciation. These records reveal the penultimate deglaciation initiated with rapid century-scale meltwater pulses which subsequently trigger abrupt coolings of air temperature in NW Iberia consistent with freshwater-induced AMOC slowdowns. The first of these AMOC slowdowns, 600-year duration, was shorter than Heinrich 1 of the last deglaciation. Although similar insolation forcing initiated the last two deglaciations, the more rapid and sustained rate of freshening in the eastern North Atlantic penultimate deglaciation likely reflects a larger volume of ice stored in the marine-based Eurasian Ice sheet during the penultimate glacial in contrast to the land-based ice sheet on North America as during the last glacial. Stalagmites from NW Iberia record the rapid demise of large ice sheets during the penultimate deglaciation, and reveal decadal-scale feedbacks between warming and ice melting. The rapid retreat of ice sheets which yields high meltwater fluxes, can be caused by marine ice sheet instability, ice sheet saddle collapse and marine ice cliff failure2. While the timing and associated deglacial feedbacks have been extensively studied for the last deglaciation 3, knowledge of the insolation thresholds, rate of ice sheet melting, and feedback sequence of previous terminations is more limited due to the lack of direct absolute chronology for ice retreat and deglacial warming. Some studies suggest that the sequence of millennial feedbacks may be different in previous terminations5. The penultimate deglaciation, Termination II (TII), is of particular interest because orbital boundary conditions were different, and the termination was followed by an interglacial with a + 1.2 to 5.3 m sea level highstand - suggesting both Greenland and Antarctic ice sheets retreated further than during TI6, despite similar highs in atmospheric CO27. To fully understand the last interglacial highstand, clear knowledge of the ice sheets melting time and retreat rates during TII is needed9.During glacial terminations, retreating ice sheets release large meltwater fluxes into the ocean. This leads to rising sea level and can initiate strong climate feedbacks when sufficiently large meltwater fluxes reach regions of deepwater formation in the North Atlantic. These ocean-atmosphere interactions, together with associated ocean CO18O lower than the mean ocean, meaning the deglacial melting of the Northern Hemisphere (NH) ice sheets lowers the δ18O of the surface ocean (δ18Osw). For regions proximal to release of glacial meltwater, such as the North Atlantic, the rate of δ18Osw depletion and freshening can exceed the global average11, which has been useful in diagnosing meltwater routes during TI14. We propose that the evolution of the North Atlantic δ18Osw can be recorded in coastal European speleothems through the transfer of the δ18Osw signal of the ocean moisture source to the δ18O of rainfall, and thereby the δ18O of dripwater15 from which the speleothem is formed. We report on the North Iberian Speleothem Archive (NISA) from caves within 10 km of the Atlantic coast  with the δ18Osw on the Irish Margin16 and a low standard error indicates a consistent relationship throughout the deglaciation despite the potential for variation in atmospheric and surface ocean boundary conditions . Multiproxy process modeling suggests that this correlation arises because higher temperature strongly increases vegetation productivity in this biogeographic regime, enhancing soil CO2 production and oversupply of CO2 to karst waters, both factors which produce more negative δ13C in speleothems (δ13Cspeleo)31. We infer that the specific slope of the temperature vs δ13CNISA relationships may be specific to a given cave systems and host lithology, and may be sensitive to the degree of smoothing of millennial-scale changes which is affected by the speleothem growth rate and the years aggregated in each drilling increment.Additionally, we confirm that over TI, the δ18ONISA and δ13CNISA over TII as indicators of δ18Osw and temperature, respectively. Three 230Th–dated NISA stalagmites replicate the main features of the TII deglaciation between 135 and 129 ka  and its relationship with regional warming (δ13CNISA)  Fig. .32, we infer that the addition of meltwater is the main driver of rapid deglacial freshening and declines in the δ18Osw in the eastern North Atlantic. Both abrupt freshening pulses began during a period of rapid warming, then, after several decades of rapid freshening, temperatures cooled rapidly, consistent with freshening-induced AMOC slowdown  and AMOC slowdown, a North Atlantic freshwater δ18O anomaly persisted. Unusually, for ~ 3000 years, the δ18ONISA remained lower than the final interglacial state. The maintenance of a freshwater δ18O anomaly for so long in the surface eastern North Atlantic requires addition of meltwater at rates greater than it can be distributed through mixing with the global ocean. Thereafter, starting around 131 ka, the North Atlantic freshwater δ18O anomaly diminishes rapidly, which suggests that the rate of addition of meltwater into the eastern North Atlantic had slowed sufficiently so that ocean circulation homogenized the deglacial meltwater anomaly to the global ocean average. This decline coincides with a rapid decrease in IRD delivery in the Northeast Atlantic and Labrador Sea  on the Iberian margin also slowed significantly at 131 ka  for the Red Sea curve39, and our chronology implies the potential for an earlier and even more concentrated meltwater pulse than estimated from the derivative of the Red Sea sea level curve  , remains below −1‰ only between 16.4 and 15.2 ka (1.2 ky duration), whereas during TII it remains below −1‰ from 134.7 to 131.2  Fig. . Yet, th TI Fig. . During 18Osw anomaly coincides with the interval of fast melt rate of the Eurasian ice sheet according to recent sea level reconstructions41  would be diluted during advection across the Atlantic by the North Atlantic Drift42. These model simulations, albeit limited, suggest the potential for higher amplitude δ18Osw anomaly in the eastern North Atlantic during EIS melt than NAIS melt, given similar δ18Oice as assumed in previous studies43. Therefore, one explanation for the longer duration surface ocean δ18Osw anomaly during TII is a larger proportion of EIS-derived meltwater in TII compared to TI.During TI, this period of greatest regional δs41 Fig. . One int45. The potential for a larger PGM EIS ice sheet has been explored in dynamical ice sheet models with total EIS ice volumes of up to 70 m sea-level equivalent, nearly triple that of the LGM EIS46. Because of similar estimated PGM and LGM sea level and benthic δ18O, this simulated large PGM EIS likely coexisted with a smaller than LGM NAIS46. The ice sheet reconstruction featuring a large TII EIS46 encompasses a 2.5–3.5x greater volume of marine-grounded  EIS ice at the PGM, compared to the LGM (Methods) with thickest ice in the Fennoscandian sector. Because of isostatic loading and higher relative sea level caused by self-gravitation, the larger PGM EIS would have been even more sensitive to ocean forcing and marine ice sheet instability which could have contributed to a rapid retreat. Although the onset of modeled TII EIS retreat differs slightly from our record8, its duration is broadly consistent with the here documented duration of eastern North Atlantic δ18O anomaly.In support of this explanation, Eurasian PGM deposits are found well beyond the limit of ice extent from the LGM, with the largest expansion in the Barents-Kara sectors of northern Russia Fig. . However49. Based on our records, we cannot confirm nor rule out disintegration of such an ice shelf as a contributor to freshening at the onset of TII, leading the retreat of Northern sectors of the EIS. However, the modest magnitude of Arctic shelf ice volume suggests that this cannot be the only factor responsible for differences in the meltwater anomaly and rate of change in δ18Obenthic and sea level rise over TII  also coincides with a period of AMOC reduction inferred from proxies such as Pa/Th50 . Nonetheless, the temporal coincidence of reduced AMOC and the phase of most rapid EIS retreat in TI may not be coincidence. Simulations suggest that meltwater release from the Northern and western margin of the EIS (and the Mackenzie River outlet of the North Americans), is more effective at decreasing AMOC compared to North American melt routed through the Gulf of Mexico, Hudson Bay, or St. Lawrence outflows52, because the former meltwaters reach the locations of northern North Atlantic convection with lesser dilution by other surface waters53. Therefore, the strong surface meltwater δ18Osw between 16.4 and 15.2 ka in the eastern north Atlantic may be both a direct consequence of high EIS melt rates releasing water in the eastern North Atlantic, and an indirect consequence of the high EIS melt rates on AMOC stability and concomitant amplification of the surface meltwater δ18Osw. In and of itself, reduced AMOC intensity, such as that inferred to have occurred during the Younger Dryas according to Pa/Th   Model (Version 4.8)71 NW Iberian caves: Pindal Cave , La Vallina Cave , and Cueva Rosa . These stalagmites cover TI, Greenland Stadial 22 (GS22), and TII72. Additional growth phases have been studied in the stalagmite Candela since earlier publication72, and we report additional dates and higher resolution geochemical data. In Candela, A ~10 cm long basal growth phase (CANB) has been sampled along its main growth axis and redated, contrasting with strongly off-axis and condensed sampling of this phase in earlier work. Additionally, within the Bølling-Allerød, a transient 1.5 cm shift in growth axis has been resampled along its expanded central growth axis for 2.5 cm, expanding by 5-fold the record previously sampled in a lateral portion at only 0.5 cm thickness.Stalagmite samples were analyzed from the following previously described73 between 230Th dates, for intervals of rapid freshening in TI and TII, we refine age models by estimating stalagmite growth rates from the width of growth bands defined by fluorescent layers74 which have been described to result from seasonal delivery and/or incorporation of fluorescent organic substances in dripwater75.To account for variation in growth ratesStalagmite slabs were mounted in low-viscosity Laromin C260 epoxy , ground flat with SiC paper, and then polished with a diamond suspension to 0.25 µm in preparation for Confocal laser scanning microscopy (CLSM) and laser ablation ICP-MS. Imaging by CLSM was performed at the Scientific Center for Optical and Electron Microscopy (ScopeM) at ETH Hönggerberg using an OIympus Fluoview 3000. Here, a series of overlapping images were obtained under 100–200x magnification using an incident wavelength of 488 nm and measuring fluorescence in a 490–590 nm window. Images were obtained at 1024 × 1024 or 2048 × 2048 resolution, corresponding to 1.2 to 0.6 µm/pixel (respectively) under 100x magnification. Images were processed using Fiji/ImageJ, where the exact distances between growth layers were recorded on an absolute length scale and later cross-referenced to laser ablation and drilling  data. Confocal images were counted in stalagmite Garth section from 177.5 to 269.5 mm from the tip. Growth layer thickness was used to determine rates of isotopic change in sections which could be layer counted, and to develop accurate interpolation of ages between U/Th dates. In areas where annual layers were not immediately visible, typically when layer thickness was less than 3 µm, an average growth rate for that section was assigned in order to be consistent with the sequence of U/Th ages.230Th dating. New dating was completed using standard methods and analysis on MC-ICP-MS (Thermo-Finnigan Neptune)76 at Xi’an Jiaotong University and the University of Minnesota; some previously published aged used in this study also include determinations on SF-ICP-MS (Thermo-Finnigan ELEMENT77); results are given in Supplement Tables 14C ages were measured at ETH Zurich with a gas ion source in a Mini Carbon Dating System at the Laboratory of Ion Beam Physics, ETH, via on-line acid digestion78 and calibrated with INTCAL 202079 and results are given in Supplement Table 27. Because agricultural and pasture land uses became widespread in Northern Spain after 5.5 ka BP80 which may decouple the natural relationships between climate and vegetation over cave sites, we do not present or discuss speleothem records younger than 5 ka BP.Absolute chronology is based on subsamples drilled for 230Th ages are interpolated using the Bchron software82  whereas linear interpolation was employed for short growth phases bracketed only by basal and top U/Th dates . Two approaches are used to refine the age model within the 18 to 14 ka interval in Candela. Where visible growth laminae are present, their thickness is used to constrain growth rates , and advanced upwards ~90 year using width of fluorescent growth layers to constrain growth rate. Growth layers are not countable in the following 7.7 mm of stalagmite  interval at the end of the δ13C maximum. The precision of the age model is lowest between 17.85 and 16.1 ka, and improves by 16 ka due to a 15.4 ka 230Th date and the 16.1 and 14.5 ka tie points with Laura. Following these tie points, the age model until the hiatus at 11.6 ka is established from 230Th tie points, with interpolation between dated points further constrained by counting of 600 annual layers (14.5 to 13.9 ka) during the Bølling-Allerød. This set of speleothem records chronicles the changes across TI in higher detail than previous records from the region, with the following average absolute 95% CI age uncertainties 20–18 ka ; 18–16 ka , 16–14 ka ; 14–12.5 ka (Candela +/− 260 years).Age models for stalagmites younger than 30 ky are illustrated in Supplementary Fig. Age models for stalagmites spanning TII and the Bchron uncertainty windows, are illustrated in Supplementary Figs. 83 and are reported in ‰ relative to the Vienna PDB Standard. Analytical uncertainties for calibration with two in-house carbonate standards and NBS-19 and NBS-18 international standard and were 0.08 ‰ for both isotopes. Samples for isotopes were micromilled at 0.1 to 0.5 mm increments, or drilled at 1 to 5 mm increments, from the central axis of stalagmites. Stalagmite δ18O and δ13C were screened for the coupled effects of CO2 degassing and prior calcite precipitation, as detailed below. A spliced record of δ18ONISA and δ13CNISA is compiled from stalagmites spanning 26–5 ka BP. Where multiple stalagmites grow synchronously, we employ for the splice, the stalagmite with best constrained chronology and the stalagmite in which there is the least variation in Mg/Caindex over the included time interval. The goal of this approach is to limit the potential influence of PCP on the inferred trends in δ18ONISA and δ13CNISA.New stable isotope determinations were measured at Scientific and Technologic Centers from the University of Barcelona with a Thermo-Finnegan MAT-252 coupled to a CarboKiel-II and at ETH Zürich with a Thermo-Finnegan Delta V Plus coupled to Gas Bench II72, and with similar standardization approaches at ETH Zürich (Agilent QQQ 8800); all ratios are reported in mmol/mol. Mg/Ca is widely used indicator of variation in PCP84 and we use speleothem Mg/Ca and the Mg/Caindex as a qualitative indicator of the influence of the coupled process of CO2 degassing and prior calcite precipitation (PCP) on isotope trends, hereafter referred to as PCP. To facilitate comparison across stalagmites from different portions of the cave, which sample stratigraphically distinct portions of the host limestone, we normalize the measured Mg/Ca in each sample (Mg/Casample) to the minimum Mg/Ca of that stalagmite (Mg/Camin), where high index suggests little loss of Ca due to PCP and a low index suggests significant loss of Ca due to PCP.Mg/Ca was measured on splits of the isotope samples, at the University of Oviedo (Thermo ICAP DUO 6300)13C of dripwater acquired through rain equilibration with soil gas and bedrock dissolution is the primary signal of interest, we plot stalagmite δ13C coded by the Mg/Caindex  mmol/mol)  and peak MIS 5e (127–123 ka) are less influenced by PCP in Gael. At the same time, the trend in δ13CNISA at the termination onset may be amplified in Gael by decrease in PCP between 135 and 134 ka. In stalagmite Neith, Mg/Ca and δ13CNISA correlate strongly within glacial and termination time windows  using crossplots of isotopic records with Mg/Ca  mmol/mol), suggesting that variation in PCP is not a significant influence on the trend in δ18ONISA in this time interval. Over the termination there is also no correlation between growth rate and δ18ONISA in Garth, the stalagmite for which growth rate is most precisely resolved due to annual layer counting. .During TII, we evaluate whether deglacial δ18O of surface seawater (δ18Osw) is commonly estimated from coupled Mg/Ca and δ18O of planktic foraminifera89. We compare published marine δ18Osw with δ18ONISA over the time interval from 25 to 5 ka BP in fixed 500 year time bins  relative to the benthic δ18Ocalcite on the Iberian margin, which can be precisely and independently tuned to speleothem chronology for TII. This metric is denominated (δ18ONISA-BC) or (δ18OSW-BC). Although the decrease in benthic δ18Ocalcite is driven by both deep ocean warming and decreasing deep ocean water δ18O components, high resolution OA GCM model simulations show that in the depth range of our Iberian Margin North Atlantic records, decreasing deep ocean δ18O and warming are closely temporally coupled when meltwater release decreases AMOC intensity, because shallowed North Atlantic winter mixed layer depth lead to mid-depth warming11.The calculation of regional surface ocean δ18Osw records for TII91 based on Mg/Ca SST and δ18Ocalcite and align the major depletion in both δ18Osw of ODP 97791 and in δ18ONISA in Garth, as illustrated in Supplementary Fig. 10, we extend the NW Iberian speleothem chronology by the additional alignment of three key cooling events in the δ13CNISA record with events identified in the alkenone-SST record also from ODP 97792. ODP 977 is the primary tuning target because is the only available δ18Osw record that matches exactly the amplitude of the initial speleothem freshening in both TI and TII  is somewhat attenuated, potentially due to low biogenic productivity and foraminiferal growth periods which are biased against extreme conditions98.The ODP 977 marine chronology is transferred to ODP 97699 and 984100 we align the major reduction in %N. pachyderma sinistral with the deglacial temperature rise in the Alkenone SST record from ODP 977, a clear structure that correlates well all along the Iberian margin cores, as well as a subsequent local maximum in %N. pachyderma sinistral evident as a local minimum in alkenone SST  is known to lead that of deep N Atlantic and S Atlantic and Pacific over the TI103 and the applied tuning suggests a similar pattern in the TII 93 exhibit divergent millennial structure and amplitude of SST change across H11 likely reflecting a seasonality control in the H11 temperature signal. More intense winter cooling but summer warming104 during cold reversals may lead to differences in rate of winter vs annual or summer warming, which may enhance discrepancies among proxies which may have differing influence of summer and winter seasons. An additional factor which has been documented to slow the manifestation of deglacial SST rise in alkenone records on the Iberian Margin is the transport of glacial-aged alkenones into sediments of deglacial and early interglacial age29.Within H11, we have not relied on temperature records for tuning, because the alkenone temperatures exhibit a slower rate of warming than implied by δ18Osw record during the termination and using its δ18Oplanktic record during the interglacial. δ18Osw tuning of TII is based on observed lags during TI. During TI, the δ18Osw of ODP 99967 is based on 14 C age model, updated to INTCAL2013 with constant 400 year reservoir age. During TI the W Iberian margin δ18Obenthic105 is on chronology tuned to GRIP106 and Hulu90. We observe that depletion of δ18Osw at ODP 999 lags that of W Iberian margin δ18Obenthic by an average of 1100 years  and western Caribbean (no cooling from AMOC shutdown). However, during the interglacial, these two subtropical locations may be expected to have similar evolution of SST and δ18Osw.Therefore we use the combined signal of δ18Oplanktic to serve directly for correlation during MIS 5e (Supplementary Fig. We tune ODP 999 using its δ61 and an ice history that is the same as ICE6G for T2108. The sea level history and glacial isostatic adjustment modelling is from8, using the same ice sheet histories. ‘Marine’ ice is defined here simply as the volume of ice that is grounded below the reconstructed sea level.We approximate the ‘marine’ proportion of the T1 and T2 Eurasian ice sheet using the ice sheet reconstructions ofFurther information on research design is available in the Supplementary informationReporting Summary


A long-standing human lifespan debate is revival, and the consensus is yet to come on whether the maximum human lifespan is reaching a limit or not. This study discusses how mathematical constraints inherent in survival curves indicate a limit on maximum lifespans, implying that humans would have inevitable limits to lifespan growth. The existence of the maximum human lifespan is an active debate issue. Recent estimations suggest a limit of the maximum human lifespan of around 125 years (s(x) is typically a monotonic decrease function of age x and a mathematical equivalent of the mortality rate as μ(x) = –dln(s(x))/dx. The first-successful Gompertz model (x) = aexp(bx) with two parameters a and b or equivalently ln(μ(x)) = ln(a)+bx, but proves not appropriate to describe the mortality rate at extreme ages (over 100 years). Generally, survival curves can vary by external  conditions under internal  constraints, which makes survival curves plastic, and the ultimate evolution of survival curves becomes rectangular  devoted by Max Planck Institute for Demographic Research (Germany), University of California, Berkeley (USA), and French Institute for Demographic Studies (France). The demographic information on supercentenarians is taken from the International Database on Longevity (IDL) (available at https://www.supercentenarians.org). The mortality database for women was chosen because of their longer lifespans and the usual representation of the highest life expectancy in each country, which is compatible with this study's critical purpose of addressing the limits of lifespan growth  = exp[−(x/α)x)β(] with the characteristic age α taken at s(α) = e−1 and the age-dependent stretched exponent β(x). The age dependence of the stretched exponent differs from the stretched exponential model fixed at constant β (≠1.0) and the simple exponential model at β = 1.0 (x) describes the actual survival or mortality curves at extreme ages, as illustrated in Biological survival curves look quite plastic to ecological or social conditions. The recent trends of human survival curves seem to have become plastic and rectangular since the survival strategies have become optimized and deaths occur predominately at higher ages. Such plasticity and rectangularity of human survival curves can be described by adopting the modified stretched exponential model  formula β = 1.0 . Practicx)≈7/ln(x) from the modified stretched exponential model, which corresponds to s(x)≈1 for x < α and s(x)≈0 for x>α (x), which are realistic regarding the plasticity and rectangularity of human survival curves  at ds/dx = 0. Defining ω at ds/dx = 0, which is equivalent to β(x) = γ(x) where γ(x) = −xln(x/α)(dβ/dx) for the modified stretched exponential model, we are able to estimate ω at the crossover of the plausible quadratic models of β(x) and γ(x), as illustrated in The monotonic decrease of survival curves is inherent as ds/dt < 0, indicating the existence of mathematical constraints around ~125 years (marked by the dashed red line). This consideration is consistent with the later plateau hypothesis of the maximum age at death (marked by the solid black line) among three possible expectations of the IDL data (dots) for supercentenarians  taken from periodic life table data for Sweden females and Japan females between 2010 and 2020 are almost constant as ω = 123.8 ± 2.3 years for Sweden females and ω = 125.4 ± 1.4 years for Japan females (ω= average ± a standard deviation), as demonstrated in enarians .The mathematical constraint presented here gives more malleability when predicting the future maximum human ages of death. Previously, researchers have identified a human lifespan plateau at around 115 years , 17, clads/dx = 0, narrows down the possibilities of human lifespan growth suggested by several mathematical models, agreeing well with a later plateau of around ~125 years, as indicated by other researchers (Furthermore, the existence of a mathematical constraint, as shown in earchers . This apearchers .The human lifespan limit remains one of the oldest research questions that spark heated arguments surrounding the possible answers. The rising number of supercentenarians has questioned the applicability of mathematical models like the Gompertz model. Various researchers may make different predictions because of the availability and reliability of data for older ages. Even for the same datasets, there may be discrepancies, mainly due to mathematical modeling and interpretation. Generally, a consensus regarding reliable databases and appropriate mathematical models will lead to predictions toward a more accurate lifespan limit.This study demonstrates that the mathematical constraints inherent in survival curves can predict the maximum human lifespan growth limit. This result implies that humans would reach an inevitable later plateau toward the actual maximum lifespan limits.The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.BW conceived the study and collected the data. MG and BW analyzed the data and interpreted the results, wrote, and reviewed the manuscript. All authors contributed to the article and approved the submitted version.


Eleven well-trained male CrossFit athletes  carried out a resistance exercise test after drinking 140 mL of beetroot juice (BJ) or placebo. The test consisted of repeating the same resistance exercise routine twice: wall ball shots plus full back squat with 3-min rest (1st routine) or without rest (2nd routine) between the two exercises. Higher NOx plasma levels were verified after BJ than placebo in the pretest and post-test (p < 0.001). A higher number of repetitions was observed after BJ intake compared to placebo in the full back squat exercise during the first routine (p = 0.004). A significantly reduced VO2 was detected after BJ intake compared to placebo during rest and full back squat execution in the first routine (p < 0.05). Plasma myoglobin concentrations were significantly increased with BJ compared to placebo (p = 0.036). These results showed that plasma NOx levels reduced VO2 after BJ intake during rest time. These reduced VO2 was a key factor for improving full back squat performance during the first routine.This study aimed to determine the effects of circulating nitrate plus nitrite (NOx) concentrations on resistance exercise performance, VO From a biochemical perspective, dietary inorganic NO3− ingested is reduced in the mouth by NO3− reductase to nitrite (NO2−) by commensal anaerobic bacteria. In the stomach, NO2− can be reduced to nitric oxide (NO) and other bioactive nitrogen oxides. NO3− and the remaining NO2− are absorbed from the intestine into the circulation1. NO3− and NO2− can be transformed to bioactive NO in blood and tissues1 via reactions with hemoglobin and molybdopterin-containing enzymes4.Beverages such as beetroot juice (BJ) with a high nitrate  environments7 such as when exercise is performed. Limited O2 availability increases the effects of8 NO2−, and the NO derived from NO2− is determinant in the compensatory vasodilation, in the delivery of O2 to working muscles9 and in regulating oxygen uptake (VO2)10.In relation to crucial physiological functions, NO has shown to be a powerful vasodilator3− has demonstrated to increase plasma concentrations of NO3− and NO2− and decrease O2 cost in endurance-type exercise, at several exercise intensities and using different supplementation protocols14. In some but not all studies14, a reduction in pulmonary VO2 was not related to an improvement in test performance15. Other studies did not find a decrease in VO2 and improvements in endurance performance after BJ intake during submaximal exercise16, and improvements in performance are even more controversial when referring to well-trained athletes during exercise at light-moderate and high intensity17.Acute and chronic supplementation with dietary NO2 closely reflects VO2 in exercising muscles19, and cardiopulmonary exercise testing (CPET) has been considered a fundamental tool to evaluate the effects of NO3− intake on the behaviour of VO2, especially in endurance-type exercise17.Pulmonary VO21. We concluded that the half-squat exercise produced a lower VO2 than the cycle ergometer exercise at the same relative intensity of the lactate threshold, with both exercises maintaining similar blood lactate concentrations in a predominantly aerobic metabolism. The fact that VO2 was lower in resistance exercise compared to endurance exercise and that both types of exercise had similar lactate concentrations could be attributable, at least in part, to the rest time.The nature of resistance exercise differs from that of a more endurance-type exercise, with local muscle fatigue making it necessary to rest between sets to continue exercising the same muscle mass. In endurance exercise, the effort could be sustained from a few minutes to hours without recovery time. Previous studies by our research group showed that rest was a key factor to maintain exercise tolerance using a vital aerobic energy support when the same resistance exercise was executed3− supplementation22. Other nutritional strategies such as L-carnitine L-tartrate supplementation have been shown to reduce muscle tissue oxygenation during occlusion and during recovery from resistance exercise23. Carnitine supplementation improved blood flow regulation and oxygen delivery to muscle tissue during and after exercise24. Precisely, the vasodilator effect of NO play a key role in the delivery of O2 to muscle tissue9 and in regulating oxygen uptake (VO2)10, in an acidic environment with low oxygen availability7. It is also tempting to speculate that BJ might be used as a nutritional strategy for decreasing VO2 and, consequently, for improving performance during strenuous resistance exercise due to the physiological properties of dietary NO3− during rest time.Curiously, the transition time from rest to exercise could be a key factor for enhancing high-intensity exercise tolerance due to increased oxidative energy turnover coupled with augmented muscle perfusion in response to NO-induced vasodilation after NO3− on VO2 during endurance-type exercise, to the best of our knowledge, no studies have explored the behavior of VO2 on exhausting anaerobic-type exercise (resistance exercise) by assessing the effect of recovery time between exercises after acute NO3− intake.While most studies have focused on evaluating the effects of dietary NO3− plus NO2− (NOx) plasma levels and VO2 and in well-trained CrossFit athletes. For this purpose, the incidence of rest time between exercises was analyzed. A secondary purpose was to assess the effect of BJ intake on biomarkers of muscle damage. We hypothesized that acute NO3− intake could contribute to a reduction in VO2 by increasing NO3− plus NO2− plasma levels and, consequently, improving anaerobic exercise performance after rest time.The main goal of this study was to determine the effects of acute BJ intake on resistance exercise performance by establishing a causal physiological relationship between NOEleven highly-trained male CrossFit practitioners were recruited for the study . The inclusion criteria were: no musculoskeletal injuries or other conditions that could affect test performance; more than two years of experience in CrossFit and resistance exercise training; one-repetition maximum (1RM) in full back squat full back squat greater than 120 kg; regional, national and/or international competition level; no smoking; no consumption of drugs or pharmacological treatment; and no consumption of any other supplement at the time of the study. The participants performed CrossFit workouts at least four times a week.17. Initially, 12 well-trained CrossFit athletes were recruited for the study. However, one participant was excluded from the final data analysis because he was taking medication/drugs at the time of testing.The sample size was determined from the results of a pilot study involving 10 well-trained students. The calculation of the sample size was carried out as follows: α = 0.05 (5% probability of a type I error) and 1 − β = 0.80 (80% power)Participation was voluntary and according to experimental procedures, each participant provided written informed consent to be included in the study. This investigation was approved by the Ethics Committee of the TecnoCampus, Pompeu Fabra University (Registration number: 56/2019) and was performed according to the principles and policies of the Declaration of Helsinki.https://www.randomizer.org.The trial was a randomized double-blind, crossover design of three weeks duration. Procedures description and randomization (2 weeks); washout (one-week). Well-trained CrossFit athletes were randomly assigned to BJ or placebo (PL) treatment. Figure Participants attended four testing sessions under similar ambiental conditions  and at the same time frame (± 30 min) of the day , a researcher explained all the experimental procedures to the athletes (session 1). In the second session, participants carried out a 1RM test in full back squat exercise (see below for details).17. Respiratory exchange and heart rate data were recorded during the resistance exercise test.Over the next two weeks (sessions 3 and 4), the participants completed the resistance exercise test to compare the two experimental conditions: BJ and PL. A one-week washout period was established between the two sessionsAt rest (pre-test) and after (post-test) the resistance exercise test, blood was collected to determine plasma concentrations of NOx and muscle damage biomarkers .From 72 h before the test session until the end of the study, the study subjects did not undertake any high-intensity physical exercise. The participants refrained from any type of physical exercise during the 24 h prior to starting each test session. Participants were allowed to perform regular workouts throughout the study. The workouts allowed were of low intensity (light load resistance training or low intensity aerobic workouts), except during 24 h before starting the test.25. The full back squat test included a general and specific warm-up for all participants. The 1RM test involved a gradual increase in load with an Olympic bar until 1RM was achieved. The 1RM was stated as the maximum weight (kg) lifted by the participant. A 4-min rest was made between each attempt.In the second session, a 1RM test in full back squat exercise was performed according to the guidelines established by Baechle and Earle26. In summary, two characteristic weightlifting exercises in CrossFit workouts were chosen: Wall ball shots and full back squat. A 10 kg medicine ball was used for the wall ball shots, and the full back squat exercise was performed with free weight (Olympic bar) at a loading intensity of 50% of 1RM. The objective was to reach the highest number of repetitions within a given time domain.In sessions 3 and 4, a resistance exercise test was carried out to compare the two experimental conditions: BJ vs. PL. The resistance exercise test was implemented as in a previous study established by our research groupAfter performing a general and specific warm-up, the resistance exercise test consisted of repeating the same routine twice. The first routine involved 90 s of wall balls plus 60 s of full back squat. A 3-min rest was applied between the two exercises. Afterwards, the second routine involved wall balls for 90 s plus full back squat for 60 s without rest between the two exercises. A 3-min rest was established between the first and the second routine.2, minute ventilation (VE), carbon dioxide production (VCO2) and the respiratory exchange ratio (RER) were monitored. The heart rate was checked every 5 s by telemetry .Respiratory exchange data were recorded during the resistance exercise test (sessions 3 and 4) using a breath-by-breath open-circuit gas analyzer  which was calibrated before each test according to the manufacturer's instructions. VO2− peak in blood occurs 2–3 h after NO3− intake27. Both beverages (BJ and PL) were provided in an unlabeled 140 ml garnet-red plastic bottle. The participants were provided with a randomly assigned bottle containing 140 ml  of BJ Beet-It-Pro Elite Shot concentrate  or PL. The BJ dose was doubled in the present study compared to previous studies by our research group with well-trained triathletes17, in order to perform an exhausting resistance exercise protocol with other metabolic characteristics related to a mixed aerobic-anaerobic energy contribution in highly-trained CrossFit practitioners.BJ or PL was administered 3 h before the start of the resistance exercise test. NO3−, Experience-Naturgreen, Murcia, Spain) in a liter of mineral water. Lemon juice was added to imitate the taste of the commercial supplement. PL and BJ had the same taste. A professional in nutrition and dietetics prepared the PL beverage. CrossFit athletes were advised of the potential side-effects of BJ, that include the red appearance of urine and feces.The PL beverage was prepared by dissolving 2 g of powdered BJ , 25% lipids, and 15% proteins. The diet was recorded by the athletes in food diaries 48 h before the first resistance exercise test (session 3). The same diet was repeated 48 h before the second test (session 4). Compliance with the dietary guidelines was evaluated by checking the participants' food diaries.Diet control was established according to the instructions established in previous studies3− content that they should avoid at least 72 h before the study. No caffeine, alcohol, or other supplement intake was allowed during the study. Twenty-four hours prior to the test sessions, the participants were asked to refrain from brushing their teeth or using a mouthwash, chewing gum or sweets that could contain a bactericidal substance such as chlorhexidine or xylitol29.Participants were also provided with a list of foods with high NOThree hours after BJ or PL intake (in the morning period), at rest (pre-test) and after (post-test) the resistance exercise test, blood was collected to determine plasma concentrations of NOx and muscle damage biomarkers.Blood samples were collected from the antecubital vein in a 10 mL EDTA Vacutainer tube. After, serum was obtained, centrifuged at 2500 × g for15 minutes, aliquoted and stored at − 80 °C until posterior analysis.NOx levels were measured in plasma previously centrifuged at 14,000 g for 60 min, and ultrafiltered by a 10-kDa cut-off filter . Nitrate was converted to nitrite using nitrate reductase, and the total nitrite amount was measured by the Griess reaction using a colorimetric assay kit . Values were expressed as NOx nmol per mL of plasma.−1. Serum LDH levels were determined by the lactate to pyruvate method according to International Federation of Clinical Chemistry (IFCC) reference procedures at 37 °C30. Values were expressed as U L−1. Serum CK concentrations were assessed by the creatine phosphate/nicotinamide adenine dinucleotide phosphate (NADPH)/N-acetylcysteine method according to IFCC reference procedures at 37 °C31. Values were expressed as U L−1. The coefficient of variation for the between and within assay replicates was less than 5%.Serum concentrations of myoglobin, LDH, and CK were analyzed in an Abbott Architect c8000 analyzer . Serum myoglobin concentrations were determined by immuno-luminescence methodology. Values were expressed as nmol Lp2). The scale for classification of ηp2 was trivial (< 0.20), small (ηp2 = 0.20–0.49), moderate (ηp2 = 0.50–0.79), and large (≥ 0.80)32.Data were reported as mean and standard deviation (SD), mean and confidence intervals (95% CI) or percentage (%). The Shapiro–Wilk test was applied to check normal distribution of the data. NOx, myoglobin and CK concentrations presented a skewed distribution and were log-transformed to approximate normality. A two-way analysis of variance (ANOVA) with repeated measures was applied  to compare the effects of the two experimental conditions (BJ vs. PL). When significant differences emerged, Bonferroni adjustments were implemented for multiple comparisons. The magnitude of the response to both experimental conditions was estimated by partial eta-squared (η32.The formula [(post-test—pretest)/pretest] × 100 was applied to calculate the percentage changes (Δ%) between the pretest and the post-test in muscle damage biomarkers . The Student’s t-test was applied to identify significant changes in percentage between the two experimental conditions. The magnitude of the response to BJ or PL conditions was analyzed by the effect size (ES) using Cohen's qualitative descriptors to indicate the changes Significance was set at p < 0.05. All statistical tests were performed using the software package SPSS version 25.0 for Mac .All participants signed for written informed consent.Participants reported drinking BJ or PL at the right time (3 h before the start of the tests). They had to return the bottle. CrossFit athletes maintained their dietary and exercise practices in accordance with the nutritional and exercise guidelines. BJ intake was well tolerated by all participants, with some presenting beeturia (red urine) and red stools.p2 = 0.66, SP = 0.98; p = 0.007, ηp2 = 0.53, SP = 0.86; p < 0.001, ηp2 = 0.98, SP = 1.00; respectively). Bonferroni correction showed higher NOx plasma levels after BJ than PL intake in the pretest  and post-test conditions  (p < 0.001) . In addition, significant effects were detected in the time and experimental conditions . Bonferroni adjustment determined a higher number of repetitions with BJ compared to PL in the full back squat exercise after rest during the first routine ). As expected, the number of repetitions was significantly decreased due to muscle fatigue in the second (without rest)  compared to the first routine (with rest)  in the wall balls and full back squat  exercises in the two experimental conditions (p ≤ 0.012)  was identified in relation to the number of repetitions performed , time and experimental condition effects were detected . Bonferroni test confirmed a significantly reduced VO2 after BJ intake compared to PL during rest  and full back squat execution  in the first routine (p < 0.05) . Bonferroni correction verified a significantly decreased VE after BJ intake compared to PL during rest  and full back squat  exercise in the first routine (p < 0.05), and during wall balls plus full back squat exercise in the second routine  , time and experimental condition effects were noted , in addition to a significant time effect . No experimental condition effect was observed (p > 0.05). Bonferroni test confirmed a significantly increased RER after BJ intake compared to PL during rest in the second routine .For RER, a significant interaction effect  was verified , a significant time effect was found .While no interaction or experimental condition effects were observed for VCOp2 = 0.71, SP = 1.00).Although no interaction  or experimental condition effects were observed for heart rate (p > 0.05), there was a significant time effect . No experimental condition effect was detected (p > 0.05). Bonferroni adjustment verified a significant increase in myoglobin values in both experimental conditions  . In this regard, myoglobin values were significantly higher with BJ (101.22%) compared to PL (36.9%)  . Significantly higher serum CK  and LDH levels  were observed at the end of exercise under the two experimental conditions. No significant differences (%) were observed in CK and LDH between BJ and PL (p > 0.05) ; however, a significant time effect was detected . However, no positive effect was observed after BJ ingestion on resistance exercise performance and VO2 reduction when the metabolic conditions of exercise (increasingly anaerobic without rest) were changed during the test protocol. It is likely that VO2 and resistance exercise performance were affected during rest time by higher NOx concentrations during the two proposed routines. In addition, both experimental conditions raised muscle damage biomarkers. Surprisingly, plasma myoglobin concentrations were significantly increased after BJ compared to PL ingestion.According to our study hypothesis, on comparing BJ with PL, the NOx levels after BJ intake demonstrated a causal physiological relationship between a reduction in VO2 was reduced in the first routine during the rest time between the wall balls and the full back squat exercises after acute BJ intake. Interestingly, the lower VO2 observed in the rest time had a determinant physiological influence on the increase in the number of repetitions in the full back squat exercise exclusively after rest period. The reduction in VO2 was maintained during full back squat exercise (only 1st routine) after BJ intake. In contrast, the physiological effects of plasma NOx levels on VO2 and exercise performance diminished in an increased anaerobic environment (2nd routine).VO2 response is not usually evaluated by CPET during strenuous resistance exercises after BJ intake, therefore, this discussion is based on other studies evaluating the same variables in endurance exercise after NO3− intake. Cermak et al. reported that lower plasma NO3− concentrations (30.1 M after 6 days of chronic BJ supplementation) than those found in our study reduced VO2 and improved 10-km time-trial performance in trained cyclists33. In contrast, Boorsma et al. did not find a positive effect on VO2 and performance in elite 1500-m runners despite significantly increasing plasma NO3− concentrations (from 37 μM to 615 μM) after acute and chronic BJ intake34. Other authors described higher NOx concentrations after PL intake  and lower NOx levels after chronic BJ ingestion (147 μM and 159 μM after 4 and 6 days respectively) than those found in our study35. Plasma NOx levels were not sufficient stimulus for improving VO2 and endurance performance in elite cyclists.VO36. The increase in plasma NOx concentrations after BJ intake probably contributed to improving the physiological mechanisms of aerobic energy supply during rest time, enhancing performance (number of repetitions) in the full back squat set. In the first routine proposed, oxidative phosphorylation was the main adenosine triphosphate (ATP)-forming process when wall balls exercise surpasses beyond 60 s (until 90–120 s)37, and intramuscular glycogen was the dominant fuel source38. O2 availability declined during wall balls (1st routine) in both experimental conditions; however, there was a significant trend (p = 0.09) to a reduction in VO2 during wall balls exercise after BJ intake. Plasma NOx levels likely produced an advantageous effect, justified at least in part, by a reduced ATP cost for a given rate of muscle contractions during wall balls11. A 3-min rest could have been sufficient to stimulate a faster NO3− to NO2− reduction to NO under an aerobic environment after BJ intake. This suggests that NO-induced vasodilation during rest enhanced oxidative energy turnover coupled with augmented muscle perfusion22 which upregulated the efficiency of mitochondrial oxidative phosphorylation39. These metabolic and biochemical advantages acquired during rest time were essential for increasing full back squat repetitions at the end of the first routine.Previously, we demonstrated that recovery time between sets was determinant to sustain resistance exercise tolerance in the same muscle mass by aerobic turnover mechanisms2 and exercise performance was observed. Chronic NO3− intake has demonstrated to be a suitable nutritional strategy to enhance resistance exercise performance in terms of total weight lifted, and repetitions until failure at 60% of 1RM40. NO3− in the potassium NO3− salt form did not improve specific performance during CrossFit workouts (Grace protocol) with a mixture of aerobic-anaerobic demand and muscular exhaustion41. Ranchal-Sánchez et al. concluded that acute BJ supplementation (120 min prior) improved muscular endurance in back squat exercise but not in bench press without any ergogenic effect on power output and movement velocity in healthy adult men42. However, Williams et al. indicated that acute BJ supplementation improved total repetitions, velocity and power during free bench press exercise in resistance-trained male subjects43. Perhaps, the differences found between the studies may be due to the resistance exercise protocols used, the dose of BJ (concentration and acute or chronic supplementation), or the level of experience of the participants . There are limited studies and some controversy over the benefits of BJ intake in resistance exercise performance. VO2 assessment is not usual in this type of exercise modalities. The behavior of VO2 and the exercise performance observed during both routines indicate a need for more studies to validate the effects of NO3− on resistance exercises (with or without rest).However, when the anaerobic conditions were increased due to muscular demands during the second routine (without rest time between exercises), no positive effect of NOx on VO. showed that chronic BJ supplementation did not alter the VE process during high-intensity knee-extensor exercise in healthy, recreationally active males11. In line with their arguments, in our study, VE was not modified by BJ intake during exhausting wall balls exercise (1st routine). Concretely, VE was decreased during the recovery time (1st routine) and the execution of full back squat in the first routine, coinciding with the reduction in VO2. Remarkably, there was a trend (p = 0.07) towards a reduction in VCO2 during rest in the first routine (aerobic conditions) but not during the execution of the exercises (anaerobic conditions). This suggests that the decrease in VO2 induced by NO3- during the rest period after exhausting exercise is, at least in part, a consequence of a reduction in the energy cost of respiration and is not exclusive to the muscle contraction process. In fact, this reduction in VE was maintained immediately after the recovery period during full back squat muscle contraction, which allowed improved full back squat performance.Interestingly, we found that VE was lower after BJ intake compared to PL. Bailey et al3− ingestion did not reduce biomarker values for estimating muscle damage assessed by LDH, CK and myoglobin concentrations. As in previous studies on resistance exercises or high intensity eccentric muscle actions46, the exhausting exercise established here was associated with an increase and release of these enzymes and protein into the blood.Finally, acute NO47. In our study, plasma myoglobin concentrations were increased after BJ intake coinciding with a higher number of repetitions. We found no evidence to clarify whether higher plasma myoglobin concentration is related to higher NOx expression and increased performance, despite the oxygen supply by myoglobin drives oxidative phosphorylation in exercising skeletal muscle48. Future studies should focus on the interactions between myoglobin and NO/NO2- via dietary NO3- consumption and determine how these interactions regulate cellular respiration processes in working muscle.However, plasma myoglobin concentrations were significantly raised after BJ compared to PL ingestion . Plasma myoglobin concentration is considered a marker of muscle damage and is usually increased after resistance exercise. Wells et. al demonstrated that plasma myoglobin concentrations were higher after a high-intensity resistance exercise protocol  compared to a high-volume resistance training protocol 2 and VE during the recovery process (first routine) and the coincident increase in full back squat performance immediately after rest (first routine).All these arguments suggest a physiological causal relationship, at least in part, between an increase in plasma NOx concentrations after BJ intake, a lower VO17. The results detected in this study cannot be extrapolated to subjects not trained in CrossFit exercise routines although BJ intake should be considered as nutritional strategy during high intensity CrossFit routines in a predominantly anaerobic metabolism.This study has some limitations. Although it was a very homogeneous sample, the sample size could be considered small. Therefore, the sample size should be increased in future research as it is usual to observe minimal changes in performance and physiological response in well-trained athletes after BJ intake2 during rest time and full back squat exercise in the first routine. Plasma myoglobin levels were increased after dietary NO3- intake in BJ compared to PL. The physiological causal relationship established between VO2, VE and NOx levels likely enhanced full back squat performance in the first routine. This study approach based on rest time opens future lines of research on the role of NO3- supplementation in the performance of strenuous effort. Further studies are needed to determine the influence of acute NO3− intake on VO2 for improving performance in CrossFit workouts or resistance exercise modalities that are prolonged over time.Our results show that plasma NOx levels after BJ intake reduced VO


Whereas, beyond surface doping, the specific activity drops substantially upon the formation of Ru cluster/nanoparticle, which challenges the classical view of allegorically higher activity of coordinated Ru atoms in cluster form (B5 sites) than isolated sites.Ammonia is regarded as an energy vector for hydrogen storage, transport and utilization, which links to usage of renewable energies. However, efficient catalysts for ammonia decomposition and their underlying mechanism yet remain obscure. Here we report that atomically-dispersed Ru atoms on MgO support on its polar (111) facets {denoted as MgO(111)} show the highest rate of ammonia decomposition, as far as we are aware, than all catalysts reported in literature due to the strong metal-support interaction and efficient surface coupling reaction. We have carefully investigated the loading effect of Ru from atomic form to cluster/nanoparticle on MgO(111). Progressive increase of surface Ru concentration, correlated with increase in specific activity per metal site, clearly indicates synergistic metal sites in close proximity, akin to those bimetallic N Ruthenium-based materials show promising performance for ammonia decomposition, yet the underlying mechanism remains to be further explored. Here the authors investigate atomically dispersed Ru atoms on polar (111) on MgO facets to show synergistic metal sites in close proximity are required for the stepwise dehydrogenation of ammonia to N2/H2. Ammonia can be easily liquefied at a pressure of 8 bar at 20 °C, leading to a high energy density (4.25 kWh/L)5. It circumvents the safety problem in long-distance transport of H2 and is readily available as C-free energy carrier to be used in stationary and mobile applications upon decomposition via wind and solar power6. However, catalytic sites and mechanism are yet far from clear. Many researchers commonly adopt fundamental steps from the reversed reaction: the ammonia synthesis from respective nitrogen and hydrogen despite the fact that the reaction conditions can be significantly different from each other. Many transition metals such as Ni can give good catalytic activity for NH3 decomposition at relatively evaluated temperatures and has been the focused for recent investigation due to low cost in large scale operation9. Ruthenium (Ru) has been well-studied as an efficient metal for ammonia decomposition at low temperatures due to its catalytic performance with many folds higher activity than other transition metals. Ilaria systematically summarized the recent progress in developing Ru based catalysts for ammonia decomposition and these Ru catalysts demonstrated a variety of catalytic performance due to their different supports, metal structure and particle size9. It is found that Ru is also very structure-sensitive for the ammonia decomposition12. The sensitivity is thought to be stemmed from the chemistry occurring primarily on Ru cluster: the B5-type sites, composed of three Ru atoms in the surface layer and two additional Ru atoms in a sub-surface layer, which ensures the activation of dinitrogen in stereospecific manner to atomic nitrogen species in line with the molecular orbitals (dissociative pathway). Previous studies demonstrated that the number of B5 sites is highly dependent on particle size and shape, reaching at the maximum values at 1.8–3 nm and ~7 nm for hemispherical nanoparticles (NPs) and elongated NPs, respectively15. Much effort has been devoted to enrich the number of B5 sites via particle control; nevertheless, the formation of Ru NPs lessens the atomic economy and limits the large-scale application due to the high cost of Ru19. In addition, traditional Ru-based catalysts are easily prone to hydrogen poisoning  in both forward and backward reactions under mild reaction conditions22. The typical hydrogen reaction orders for ammonia synthesis and decomposition over Ru catalysts are negative, indicating the blockage of Ru active sites by hydrogen adatoms and eventually preventing the chemisorption of nitrogen species26. Therefore, developing a reliable Ru catalyst and support such as carbon nanotubes to reduce strong hydrogen adsorption and maximize the efficiency in ammonia chemistry is of great importance27. On the other hand, reversible activation of N2/H2 to and from NH3 is a longstanding and significant research focus within homogeneous catalysis community, which depicts a very different discrete active sites from the Ru cluster B5 site in solid state. Ligand stabilized bi or multinuclear redox site systems to coordinate N2 via diazenido-, hydrazido-, or nitrido-metal species are identified28. It would be important to compare the activity of surface dispersed 2 or more Ru sites akin to homogenous bi or multinuclear sites with B5 sites and their hydrogen removal ability at the interface of support surface. Such approach may provide paramount hints to achieve higher activity and higher atom economy regarding the use of Ru atoms in catalysis.The ammonia decomposition has been subjected to a new opportunity for the potential use of NH2– and Mg2+) that can efficiently catalyze the decomposition of ammonia in highly hierological manner. It is presented that the atomically dispersed surface Ru ensembles on MgO(111) surface gives an optimal turnover frequency (TOF) value of 3.43 s–1 for ammonia decomposition at 400 °C, higher than those of allegorically more active Ru cluster/nanoparticle counterparts on MgO(111) (2.1–2.9 s–1) in classic view and the ultralow-loading Ru/MgO(111) with isolated Ru atoms (1.67 s–1). A series of characterizations including Scanning Transmission Electron Microscopy (STEM), X-ray diffraction (XRD), X-ray absorption fine structure spectroscopy (EXAFS), X-ray Photoelectron Spectroscopy (XPS), temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR), In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Ambient Pressure XPS (AP-XPS) and DFT calculations were employed to investigate the interactions between Ru and polar MgO(111) facet and with neighboring Ru sites. Results clearly demonstrate the synergetic roles of individual Ru atoms in close proximity for ammonia activation and hydrogen migration to MgO (111) facets.Herein, we report the detailed loading effect of an atomically-dispersed Ru atoms on polar MgO (111) facet support , such as C12A7:e–, BHA and CNTs, give higher activity than that of inert supports 42. As stated, the MgO is empirically found to give high activity in both ammonia decomposition and synthesis; however, the simple electrostatic attraction and repulsion of Mg2+ and O2– ions in NaCl structure with corresponding Madelung charge distribution without anticipated electronic interaction to give good support effect is not yet clear. Here, we have found that MgO(111) facet as support for Ru displays a superior activity: for 3.1wt.% Ru, under WHSV of 30,000 mL gcat–1 h–1 at 425 °C, an equilibrium conversion is recorded and at 450 °C with higher WHSV of 60,000 mL gcat–1 h–1 the highest specific activity of 1777.4 mmol H2 gRu–1 min–1 with a TOF value of 4.91 is achieved as compared to all other support materials.Following these studies, it would also be exciting to carefully investigate the general support effect for Ru in varying loading on surface of different MgO facets in terms of specific activity in catalytic ammonia decomposition. In this regard, MgO nanosheets with preferential exposed (111), (110) and (100) facets were synthesized. MgO(111) faceted sample was prepared by integrated processes of surfactant-assistant hydrothermal treatment and controlled calcination as compared to MgO(110) and commercial MgO, see experimental for details. The catalytic performances of MgO supported Ru catalysts (Ru/MgO) in NH43. X-ray diffraction analysis confirmed the typical rock-salt structure of MgO  nanosheet, the top and bottom faces are the (111) planes while the side faces are (220) planes based on the Bragg’s law and scattered beam collection, indicating the successful synthesis of MgO with maximal exposed (111) facets  facets was imaged by TEM and depicted in Fig. S1aets Fig. . For com3(CO)12 onto MgO supports to avoid the deconstruction of MgO surface during Ru immobilization48. As shown in Fig. 3/2 peaks at 463.3 eV in Ru/MgO(111) sample, which is corresponding to Ru2+ species. On the other hand, Ru/MgO(110) and Ru/MgO(100) display peaks with lower binding energies at 462.1 eV and 461.9 eV, respectively, corresponding to metallic Ru0 species. The unique positive charge of Ru species in Ru/MgO(111) is due to the adaptation of the most stable configuration of Ru2+ with terminal O2– (charge transfer) in MgO(111) surface with strong affinity, resulting in atomically dispersion of Ru in MgO(111). For identification of precise position of Ru atoms on MgO(111), high angle annular dark field (HAADF) imaging by 60 kV STEM was carried out. Fig. SThe Ru supported MgO catalysts were synthesized via decomposition of Ru2 and H2. Although it begins to decompose at low temperatures as shown in Fig. Scat–1 h–1, manifesting the importance of surface property of MgO(111) and Ru chemical states. The effect of WHSV was further conducted. Figure 3 conversion decreases with the increase of WHSV, which is due to the shorter residence time for NH3 absorbed on active sites. Figure 3) gcat–1 s–1 at 400 °C, which is about 2.1 times and 3.3 times higher than those of Ru/MgO(110) and (100), respectively, which do not follow their surface area value  (0.90 s–1) and Ru/MgO(100) (0.59 s–1), manifesting the importance of exposed MgO facets on catalytic performance. The Ru supported on commercially available MgO sample (Ru/Com-MgO) displays a comparable reaction rate between Ru/MgO(100) and Ru/MgO(110). This finding reveals that the Com-MgO is predominantly composed of more stable (100) and (110) facets, which has lower surface energy.The catalytic performance of as-built hierological Ru/MgO catalysts was directly evaluated for the decomposition of ammonia under low temperatures. The ammonia decomposition is a mildly endothermic process that involves successive cleavage of N–H bonds and recombination of N and H atoms to form N49. Ru/MgO(110) and Ru/MgO(100) without significant exposure of polar surfaces exhibit Ea values of 105.5 and 119.2 kJ mol–1, which are in agreement with normal 110–130 kJ mol–1 over traditional Ru/MgO catalysts52. The Ea was significantly reduced to 71.3 kJ mol–1 over Ru/MgO(111). This finding posts the important nature of polar surface on promoting the chemical process of ammonia decomposition. For further understanding, the reaction orders were analyzed to obtain information on the rate-determining step and the poisoning species in ammonia decomposition  and Ru/MgO(100), the small—γ/α value over Ru/MgO(111) indicates that hydrogen adatoms do not block the active sites and the nitrogen species desorb more easily from the catalyst surface (Table Kinetic studies were performed to depict the peculiar effect of using polar MgO(111) as support. Arrhenius plots were firstly obtained by linear fitting of Ln (reaction rate) versus 1/T Fig. . The appon Table . The parts Fig. S. These rce Table . Figure 57. The MgO cube exposes all (100) facets and the cleavage allows the formation of (110) and then (111) facets. Thus, a series of Ru/MgO catalysts with different ratios of (100), (110) and (111) facets were successfully synthesized  varies as a function of chemical formulations, based on the analysis of exposed facets. It can be seen that (111) facet displays the highest performance in all cases, followed by that of (110) and (100) facets, based on the analysis between the activity and facet percentages. The promoting effect of polar (111) facet is superior at higher reaction temperatures. Figure 2 formation rates. Significantly, a 4.3-fold and 3.4-fold higher H2 formation rates were observed over the Ru supported on (111) facets than that of (100) and (110) facets even under low reaction temperature of 400 °C. These results post the importance of polar surface for efficient ammonia decomposition.It is worthwhile to note that despite Ru/MgO(111) with predominant exposure of the (111) facet, there are still a considerable amount of (110) and (100) facet in the same sample. For approaching quantitative analysis of individual contribution of the (111), (110) and (100) facet towards the ammonia decomposition rates, surface reconstruction strategy was employed to cleave MgO from cube to octahedron shape, see experimental for more detailsed Fig. S. Figure 3 gas was introduced into the reactor at 50 °C for 30 min for NH3 chemisorption on the catalyst surface. Argon was used as the purge gas and the temperature was increased to 800 °C at 5 °C/min. The production of H2 and N2 was immediately observed with the decreasing signal of NH3 for both Ru/MgO(111) and Ru/MgO(100) samples. Importantly, the decrease of NH3 signal over Ru/MgO(111) occurs at 198 °C while the NH3 starts to decompose at about 300 °C over Ru/MgO(100), indicating the superior activation of NH3 on the interface of Ru and MgO(111) surface. These results correspond to the lower Ea over Ru/MgO(111). Besides, the larger signals of detected H2 and N2 reveal higher capability for ammonia adsorption which is ascribed to the highly dispersion of active sites. Further H2-TPD with MS detector was investigated for understanding of the chemisorption behavior of the hydrogen species, as shown in Fig. 2 desorption peaks located at about 475 °C was observed over the Ru/MgO(110) and Ru/MgO(100) samples, corresponding to the strong adsorption of hydrogen. That is to say, hydrogen species are strongly bonding on the surface of Ru and results in severe hydrogen poison. On the contrary, the higher temperature desorption peak for Ru/MgO(111) has a significantly lower intensity relative to the lower-temperature peak at 125 °C and there is an additional shoulder peak at around 200 °C. This might again be indicative of the reversible transfer of surface H-species from Ru onto MgO(111) as demonstrated by aforementioned TPSR measurement. As a result, the adsorbed hydrogen atoms could be quickly transferred away from the Ru active sites once they are dissociated, which agrees coherently with the H reaction order kinetic study. This result reveals that the hydrogen species are more feasible to be removed from the Ru surface.To verify the N–H and Ru–N activation as well as the hydrogen removal ability of the polar MgO(111) demonstrated in the above kinetic studies, a range of dynamic characterization has been performed. Temperature-programmed surface reaction (TPSR) coupled with mass spectrometry (MS) was first employed to investigate the ammonia activation process, as shown in Fig. 3 decomposition is of great importance to understand the nature of reaction mechanism. Thus, the in‑situ DRIFTS analysis for ammonia transformation was employed. Figure –1) was immediately observed on Ru/MgO(111) and the signal intensity increase as the temperature increase from 300 to 350 °C and then levels off at 400 °C59. The lower Ru–N band intensity at 300 °C might not necessarily mean a drop in catalytic performance, instead, the adsorbed ammonia is swiftly activated and recombined with another N atom to form dinitrogen. Additionally, this can be attributed to the circumvention of kinetic barrier and hence enhancement of the ammonia adsorption, similar to the phenomenon observed in the temperature and WHSV dependence experiments. Instead of the observation of on-top Ru–H at 1802 cm–1, the peak at 1900 cm–1 assigned to the bending mode of [OH] was clearly seen; simultaneously, the intensity of the [OH] stretching band at 3300 cm–1 is also found to rise as the temperature increases  support as protons during the activation of the adsorbed ammonia, in consistent with the above kinetic analysis with a small hydrogen reaction order. In other words, it is the facile removal of hydrogen from Ru active sites to support from this strong metal support interaction that maintains the robust ammonia activation.The direct observation of the intrinsic species during NHes Fig. S18,60. Th2 species at 1573 cm–1 together with relatively smaller intensity of Ru–N peaks for Ru/MgO(100) implies the sluggish dehydrogenation/recombination of ammonia to form the end products of atomic nitrogen and hydrogen  from the Fig. SIn contrast, the observation of sharp intermediate NHen Fig. S18. The a3 uptake and the corresponding surface change of the MgO support, as shown in Fig. 3 appears at 3333 cm–1 assigned to the N–H stretching with the introduction of NH3 gas. Notably, an increasing absorbance of a broad peak at about 3300 cm–1 was found, which is attributed to the [OH] stretching region for Ru/MgO(111). From the kinetic point of view, it is impossible for MgO(111) itself to dissociate hydrogen, which implies the growth of surface [OH] is presumably be originated from the transfer of hydrogenic species from Ru during the ammonia decomposition. This finding implies that atomic H on Ru could be spilled favorably to the oxygen-terminated surface of MgO(111) to form protons (as hydroxyl species), correlated with the strong H removal ability of the support.Time-resolved DRIFTS was then performed to disseminate the relationship between NH3 signal was found (the red line in cycle 1). Upon passing argon, the [OH] peak diminishes, indicating that the migration of the proton on the oxygen-terminated surface is reversible, leading to spontaneous return onto vacant Ru to form H adatom which eventually recombines with another H adatom and desorbs as dihydrogen molecule. These results reveal that polar MgO(111) surface allows the protons transfer from Ru surface to bond with O2– during the decomposition of ammonia and these protons can also be reversibly removed from the MgO(111) surface for dihydrogen production, which prevents the hydrogen poisoning and facilitates the efficient decomposition of ammonia. When no further change is observed for the [OH] region, the gas feed was switched back to ammonia for second cycle measurement. The shape, peak position, and intensity of the peaks are in general similar to the first cycle, implying the reversibility of such hydrogen spillover process to maintain effective H removal to alleviate H poisoning and subsequent migration to form end-product dihydrogen. The third-cycle confirms the stability of reversible transfer of protons. All-in-all, this cycle-test has proved the sustainability of the spillover phenomenon to facilitate ammonia decomposition.To further confirm the reversible change of the [OH] species on the Ru/MgO(111) surface, the DRIFTS was further performed where the sample feed was dynamically switched between ammonia and argon in operando, as evident in Fig. 3 (0.9 mbar), as shown in Fig. s spectrum shows a peak ascribed to the typical oxide with trace [OH] species. After switching the sample gaseous feed to ammonia, the binding energy of Ru shifts to lower energy from 281.1 to 279.9 eV, indicating the reduction of Ru2+ to Ru0  during ammonia decomposition. The retained electrons enrich the electron density of Ru and then render the activation of Ru–N bond by donating electrons to the antibonding orbital, which allows the atomically-dispersed Ru2+ to exhibit high efficiency on ammonia decomposition. The surface N species is also visible from the N 1 s profile  with surface Ru2+ with terminal O2– species of MgO(111) is also consistent with the heterolytic activation of ammonia over the mechanism of Frustrated Lewis Pair, FLP (as Ru2+–O2–)61, which explains the fact that such simple ‘NaCl’ structure of MgO can exert such significant support effect for Ru to this reaction.It is also essential to investigate the dynamic change of the oxidation state of Ru and surface oxygen species during the ammonia decomposition. AP-XPS was performed at an elevated temperature of 300 °C under dynamic switching between Ar (0.9 mbar) and NHRu0 Fig. . Notablyile Fig. . Interesd nor shape changes in the O 1 s profiles of Ru/MgO(100)  Figs. S and S14.61. It has been well established that ammonia decomposition is a structure sensitivity reaction and simple B5 step sites on Ru NPs surface are responsible for the activity of this reaction. These sites are composed of three atoms in one layer and two additional atoms above this at a monoatomic step on an Ru(0001) terrace, which could provide appropriate geometric orbitals for reversibly cleavage/construction of N2. Previous reports have shown that the activity of ammonia decomposition depends on the concentration of B5 sites and isolated single-atom sites perhaps without strong metal support interaction are not efficient for this reaction12. Interestingly, our Ru/MgO(111) (at below ca. 3.1 wt.% Ru loading) displays an atomic dispersion of adsorbed Ru without any sign for the formation of B5 sites or other Ru clusters as shown by STEM  surface becomes higher to form surface sites in vicinity such as 2×Ru atoms and 3×Ru atoms as the Ru loading increases  and Ru/MgO(100) with an ultra-low loading of 0.01 wt.% exhibit negligible activities compared with Ru/MgO(111) with the same loading  appears to be a superior configuration, which shows a more efficient catalytic performance than the classical stepped sites for ammonia decomposition to achieve the maximum utilization of noble metal.Given that the polar MgO(111) exhibits efficient reversible hydrogen migration (hopping) with atomic Ru incorporation, it is significantly important to study the synergy of Ru and the support at progressive increase in surface Ru concentrationEM Figs.  and S3 aEM Figs.  and S15,t.% Fig. . It is ises Fig.  ①–⑥. Thang Table , which r64. It is clear from the modelling that the Ru does not transfer charge to the opposite side of the slab. Instead, the electron density from Ru is donated to and shared by the surface O atoms in the periphery of Ru  with the optimized Ru–Ru distance determined to be 5.04 Å as the close by neighbor pair in this geometric model Fig. S. This at3 molecules to N2/H2 over this simple binuclear model where two surface Ru single atoms (2× Ru) in close proximity over MgO(111). Experiments suggest that the two NH3 molecules do not seem to adsorb only on a single Ru at the same time but on two separate atomic Ru sites. This suggests recombination of N2 is unlikely catalyzed by a single metal site, as similar to the findings in homogeneous counterparts28. Thus, a similar mechanism was assumed in the DFT elucidation of the NH3 decomposition pathway. Interestingly, stepwise dehydrogenation of ammonia is energetically favorable to take place as experimental data indicated, due to the strong affinity of H on polar O terminal MgO(111) in vicinity by electrostatic means, as previously discussed. Apparently, the final N–N recombination to N2 involves the synergetic coupling of two Ru≡N species on both neighbored surface metal sites in the close proximity without going to the pathways using single metal site or complex B5 in metal nanoparticle. Overall, the calculated activation energies of 0.19 to 1.21 eV are required  among all steps, which is consistent to the observed activation process  also assists the kinetics of dehydrogenation of ammonia by fast H migration from Ru metal to this particular polar support surface and to other metal sites for H2 recombination.Figure ed Fig. S. In N2 ress Fig.  in rate 3 decomposition reaction coordinate using models of (NH3-Ru)2 on MgO (100), (110) and (111) in Fig. 3 species are unfavorable. Furthermore, the H atoms, unable to spillover to MgO, crowd the atomically dispersed Ru catalyst. In contrast, the adsorption of NH3 on 2Ru/MgO(111) immediately leads to removal of H atoms and their migration to the MgO surface with a barrierless process. Subsequent removal of H atoms from NHx species are also thermodynamically favorable on 2Ru2/MgO(111) due to absence of crowding of the Ru catalyst and abundance of surface O atoms where H can migrate. We note that the removal of H from catalyst surface may not affect the rate-determining step of the reaction64. However, our experimental results show that the hydrogen migration step (avoid poisoning) is crucial in the overall kinetics when much milder conditions are used. As we have showed that at low pressures, which is more relevant for renewable energy transport, the support interaction becomes important. The use of polar MgO(111) surface could render the kinetics much less dependent on hydrogen (spillover readily achieved) under the milder conditions; on the other hand, hydrogen adatoms are strongly adsorbed onto the Ru surface, well-known as hydrogen poisoning, was further observed on both Ru/MgO(110) and Ru/MgO(100)  and 2Ru/MgO(110) and spillover H–O on Ru2/MgO(111) on the thermodynamics of the steps toward N–N recombination. We also examine the desorption of N2 from the surfaces in Fig. 2 is much more thermodynamically favorable in MgO(111), compared to the other non-polar (100) and (110) facets. In short summary, the current DFT work provides consistent structural, energetic and electronic structure properties that agree with experimental data.We further compared the complete NH00) Fig. , prevent00) Fig. , consist2 combination steps, we also analyze their partial density of state (PDOS) of these intermediates  in range of 0 eV to −6 eV with respect to the Fermi level. It is interesting to find that upon their recombination, an intermediate akin to typical binuclear µ‑ƞ1:ƞ2 nitrido-metal species in homogeneous complexes with comparable geometry, expected electron density and acceptable bond distances  within experimental error to the two Ru atoms, is identified. Such surface complex may have gone through to the transition state of the linear µ‑1,2 diazenido Ru–N≡N–Ru species since transition between diazenido-, hydrazido- and nitrido-metal has been reported in reversible N2/H2 activation in solution complexes28. This clearly suggests a similarity in N recombination chemistry as homogeneous counterparts with the important additional function of support in this single atom solid catalyst to remove the H in ammonia decomposition. Notice that the increasing interaxial overlap between 2p orbital electrons of two N at the expense of their overlap with 3d orbital electrons of Ru near the Fermi level indicating the multi bonding between two N but lesser bonding with Ru sites with expected bonding distances.To gain more insight into the detail in the Ntes Fig. . As we c3 activation and promoting the N–N recombination. Thus, the (111) facet of MgO is a more efficient surface to host Ru for ammonia decomposition, showing at least 4 times higher catalytic activity than those of (100) and (110) facets at a low temperature of 400 °C. Significantly, we have also found that this support surface can give atomically-dispersed Ru which displays superior performance in ammonia decomposition than Ru NPs.In this paper we demonstrate the strong metal support interaction of Ru on polar MgO(111) to suppresses hydrogen poisoning on Ru surface during ammonia decomposition hence enabling better heterolytic NH28. Based on our experimental and theoretical investigation, a new reaction mechanism is proposed. As the ammonia approaches the surface, it will be activated by the dispersed [Ru2+–O2−] ion pairs at the metal support interface via heterolytic cleavage of N−H bonds. These attained protons are preferentially and rapidly hopping across the oxygen-terminated MgO(111) surface for H to transfer across the oxygen sites65. Consequently, the retained electrons enrich the electron density of Ru site, which enables electronic back donation to Ru–N antibonding orbital to weaken the strength of Ru–N bond for fast recombination to N2 between the 2× surface Ru pairs. This mechanism clearly differs from the classical coordinated stepped Ru sites in cluster/nanoparticle and give hints to guide for better catalyst candidates with higher atom efficiencies. This class of attractive catalysts apparently achieves more superior catalytic performance in ammonia decomposition under low reaction temperatures. Importantly, our experimental and theoretical studies demonstrate a synergistic effect of the efficient hydrogen spillover and recombination of N atoms in closed Ru pairs with unique support interaction, which is beyond the capability of B5 cluster sites. Our finding posts the importance of the utilization of synergistic single-atom noble catalysts in ammonia synthesis and decomposition, which can efficiently use the noble metals at the greatest extent.Unexpectedly, the dispersed, isolated Ru atom at greater surface dilution does not demonstrate the highest specific activity per Ru as those typical single atom catalysts. The closed Ru pairs at optimal but moderate surface concentration without excessive coverage of the support exhibit even better specific activity. This finding enables us to confirm the cooperative single-atoms Ru solid catalysts in synergy in ammonia decomposition as akin to those of solution counterparts2 and 0.12 g benzoic acid were dissolved in 60 mL deionized water with sonication treatment at room temperature and then the obtained mixture was stirred for 10 min. 20 mL of 2 M NaOH solution was added drop by drop into the mixture with vigorous stirring, forming a white precipitate. The slurry was subsequently transferred to a 100 mL autoclave and gradually heated to 180 °C and maintained for 24 h. The obtained Mg(OH)2 precursor was washed with deionized water, and dried at 80 °C under vacuum overnight after filtration. The MgO(111) nanosheets were obtained after calcination of the Mg(OH)2 precursor in compressed air at 500 °C for 6 h43.MgO nanosheets with preferential exposed (111) facets, hereafter denoted as MgO(111), were prepared by using the hydrothermal method with the benzoic acid as the surfactant. In brief, 2.0 g MgCl45.MgO(110) with exposed (110) facets was synthesized by reconstruction of commercial MgO. The commercial MgO was purchased from Sigma Aldrich. Typically, 500 mg commercial MgO was boiled in water for 5 h with an oil bath, followed by drying at 120 °C overnight. The obtained precursor was calcined at 500 °C for 6 h under a vacuum system3)2 precursor directly at 500 °C for 5 h46.MgO(100) was obtained by traditional thermal decomposition of Mg(NO57.The MgO nano-cubes (denoted as MgO-cube) were prepared by combustion of Mg ribbons  in an adequate oxygen gas flow. These smoke crystals were collected by a glass plate and rapidly transferred into sample tubes with Ar protection to prevent the surface etching in wet environments. The water solution with different values (pH = 2–6.8) was used to cleave the MgO-cube in (110) and (111) cuts of the ridges by dissolution of MgO surfaces. A well-control of surface cut with identified (111), (110) and (100) facets can be obtained by controlling the treatment time from 2 min to 7 days, finally transforming MgO nano-cubes into octahedron shape. The obtained precursors were carefully calcined under vacuum to remove the surface hydroxyl function groups to obtain clean MgO surfaces with different facets3(CO)12 incorporation and decomposition of Ru3(CO)12. Briefly, Ru3(CO)12 was ultrasonic-dispersed in tetrahydrofuran (THF) solution to avoid the affection of water and then desired amount of MgO supports were added with vigorous stirring for 2 h at room temperature. After removing the solvent, the obtained orange powders were treated at 90 °C overnight under vacuum where pink or light grew powders were obtained (the color depends on the loading amounts of Ru and support choice). Then these precursors were heated and vaporized and deposited on MgO supports before reaching 300 °C with 2 °C/min for 3 h under Ar gas flow.Supported Ru catalysts with different MgO supports (~3 wt%) were synthesized by integrated methods including Ru2/He gas flow for 4 h. The gas was switched to NH3 stream and then the catalyst bed was adjusted to the target reaction temperature. All the activity tests were conducted in the temperature range of 200-600 °C with varied weight hourly space velocity (WHSV) under atmosphere pressure. After the stabilization, the gas composition was analyzed by an online gas chromatography (Agilent 7890 A) equipped with TCD detector and a HayeSep Q column. Kinetic study was performed with varied temperatures and WHSV to ensure that the reaction conditions was within the kinetic zone. The Arrhenius plots and activation energies for ammonia decomposition were calculated based on the activity evaluated under the same gas flow and compositions but at different temperatures with the conversion kept below 15% so they were far from equilibrium. The activity was therefore at the kinetic controlled steady state. All the catalysts were evaluated twice to ensure the accuracy of the measurements. The reaction orders were conducted by varying one gas concentration of N2, H2 or NH3 with He as the balance gas and measured at 350 °C.The ammonia decomposition was carried out in a purposely built continuous flow fixed-bed reactor with a computer-controlled auto-sampling system. Typically, 50 mg of catalyst was loaded in the center of the quartz tube sandwiched with quartz wools. Prior to the reaction, the catalyst was pretreated at 350 °C under 5%HIt is noted that the contribution of each facet towards the ammonia decomposition rate was obtained independently: we first synthesized MgO cube with exclusive (100) facet; then we cleaved these cubes to expose (110) and (111) facets at various proportions (11 samples) and compared to the synthesized octahedron sample with exclusive (111) facet. Each sample was followed with the same Ru immobilization and tested for ammonia decomposition. Thus, the overall activity of each sample can be derived from the individual contributions of (100), (110), and (111) facets by resolving the equation as below.By taken all 11 samples with comparable surface area into account, the activity for each facet can be derived, as shown in Fig. XRD patterns were performed on a PANalytical X’Pert Pro diffractometer operating at 40 kV and 30 mA with a step size of 0.004°. Samples were dusted and pressed onto either a glass or an aluminum preparative slide.TEM images were collected by using a Philips Analytical FEI Tecnai 30 electron microscope operated at an acceleration voltage of 300 kV. Fresh samples were dispersed ultrasonically, dropped and dried on copper grid with lacy support films.Z-contrast STEM imaging and condition was performed on a JEOL ARM-200F Cold field emission source (CFEG), equipped with a Cs probe corrector to give a probe size of 0.8 Å, using 200 kV acceleration voltage and 22 to 25 mrad convergence angle. An annular dark field detector at 8 cm camera length was used for signal acquisition, with inner and outer collection angles of 72.80 and 235.75 mrad for HAADF imaging, respectively. All alignments and focusing were completed away from the areas imaged to reduce electron beam damage to the material under emission current 7μA. All micrographs were obtained without tilting the sample . The HAADF-STEM mode uses an annular detector to capture the scattered electrons to high angles. Rutherford scattering from the atomic nuclei predominates of Ruthenium, with a cross-section proportional to Z2. A high-Z number a Ruthenium atom on a low-Z support MgO therefore gives a spot with high contrast.Microscopy for 66 has been applied to increase the quality and contrast of the image, a low-pass filter and a Wiener filter across the Fourier transformation (FT) of the real-space image before reconstructing the image from the filtered FT. It can efficiently reduce noise without noticeable artifacts. The simulation of the elastic interaction of electrons applying the multislice method67 to demonstrate HAADF-STEM imaging of MgO(111) catalyst, the contrast of Ru atoms and Mg atoms can be enhanced. Using supercells derived from DFT models (1x Ru on MgO(111), see Fig. SNon-linear filter3. The gas composition was continuously monitored by online mass spectrometry (MS). If not otherwise stated, Ru 3d, O 1 s, N 1 s and Mg 2 s spectra were recorded using a fixed photon energy of 950 eV. The binding energy (BE) scale was calibrated with respect to the Mg 2 s (88.1 eV) as internal standard. Normal XPS measurement was conducted on an Omicron Sphera II photoelectron spectrometer equipped with Al-Kα X-ray radiation source hν = 1486.6 eV. The spectrometer is connected to a in situ chamber which can pretreat samples with different temperatures under different gases.In-situ AP-XPS study were carried out by means of operando XPS measurements at the Diamond Light Source B07 beamline. The samples were dispersed in acetone and mounted on a silicon wafer, followed by heating at 110 °C to remove the solvent. The temperature was maintained at a constant throughout the testing at 300 °C. The measurements were performed either under 0.9 mbar Ar or 0.9 mbar NH−4. The Demeter software package (Athena and Artemis) was used for XAFS data analysis for the Ru data. To ascertain the reproducibility of the experimental data, at least two scan sets were collected. The spectra were calibrated with foils as a reference. And the amplitude parameter was obtained from EXAFS data analysis of the Ru foil, which was used as a fixed input parameter in the data fitting to allow the refinement in the coordination number of the absorption element. In this work, the first shell data analyses under the assumption of single scattering were performed with the errors estimated by R-factor.XAFS spectra was recorded at the Ru K absorption edge, in fluorescence mode using a Lytle fluorescence detector in B18, Diamond light source. A Si (111) Double Crystal Monochromator (DCM) was used to scan the photon energy. The energy resolution for the incident X-ray photons was estimated to be 2 × 102 (m/z = 2), NH3 (m/z = 17), and N2 (m/z = 28) were tracked during the investigation. H2-TPD was performed on the same Micromeritics Autochem II ASAP 2920 chemisorption analyzer and the signals of H2 (m/z = 2) was monitored during the measurement.Temperature programmed surface reaction (TPSR) measurement of samples were carried out on a Micromeritics Autochem II ASAP 2920 hemisorption analyzer with a mass spectrometer detector. The activation procedure of catalysts was the same as that used for activity evaluation. After ammonia adsorption, the sample was heated from 50 to 800 °C with the purge of Ar. The signals of H3 gas was passed through the sample holder for 30 min at 15 mL min−1 and in-situ sample spectra were recorded after purging out the exceed ammonia gas by Ar. For the cycle testing, the DRIFTS for NH3 transformation was collected under alternative sweeping between NH3 and Ar at at 300 °C.The in-situ DRIFTS experiments for ammonia decomposition were carried out by a Thermo Scientific Nicolet 6700 spectrometer, equipped with ZnSe windows and a mercury cadmium telluride detector cooled by liquid nitrogen. Spectra were obtained by collecting 32 scans at a resolution of 4/cm and are presented in absorbance unit. Fresh samples were loaded onto the in‑situ sample holder. The sample was then flushed with Ar for 30 min to clean the surface under required temperature. After collecting background spectra, NH68. While the interactions between the core electrons and nuclei were evaluated by the projector augmented wave (PAW)71, the valence electrons were explicitly considered as follows: Mg(3s2), O, Ru, N and H(1s1). The generalized gradient approximation (GGA) within Perdew–Burke-Ernzerhof (PBE) functional72 was applied to describe the exchange correlation of electrons. Furthermore, the van der Waals corrections with DFT-D3 scheme proposed by Grime et al. 73 was adopted to feature the interactions of atoms. The optimized structures were obtained by using a conjugated-gradient algorithm when the residue ionic forces are less than |0.01| eV/Å. A k-point grid of 1x1x1 and the plane wave basis set with a cutoff energy of 450 eV were used for all calculations. In addition, the maximally localized Wannier functions (MLWF) method using Wannier90 code has also been applied to plot the projected orbitals of considered atoms, see Fig. S13b74.Spin-polarized periodic density functional theory calculations were performed employing the Vienna Ab initio Simulation Package (VASP)100O100, Mg128O128, and Mg144O144 were adopted to model the MgO surfaces exposed in the experiments. The MgO(111) slab has eight alternating anionic oxygen and cationic magnesium layers with the top being terminated by O atoms and the bottom by Mg atoms. To minimize the interactions between slabs, a vacuum space of 15 Å was generated for all slab models. The models were then optimized with their bottom two layers fixed in their bulk position, whilst the rest atoms and adsorbed species are allowed to relax. Also, the dipolar correction along z direction was included.MgO (111), (100) and (110) slab models with formula of Mgf) of the MgO(111)-adsorbed and embedded Ru models:We compared the stability of an Ru atom adsorbed on the surface (adsorbed model) with that of an Ru atom substituted for a Mg atom (embedded model). The formation energies (g) refers to the total energy of a single NH3 molecule in gas phase. The adsorption energies of intermediates of the dehydrogenation of NH* and H spillover was also calculated on atomic Ru supported on MgO(111), (110) and (100) as follows:2)(g) and E(H2)(g) are the total energies of N2 and H2 gas molecules. Spillover barriers were calculated by using climbing-image nudged elastic band (CI-NEB) approach75. To obtain the transition state structures, six images were created in each path and optimized with force threshold of |0.02| eV/Å. The atomic charges were calculated by applying the Bader method suggested by Henkelman et al79.Two Ru atoms (2Ru) supported on the MgO(111), (100) and (110) slab models, denoted 2Ru/MgO(111), 2Ru/MgO(100) and 2Ru/MgO(110) Fig. S, were usSupplementary informationPeer Review File