Pronounced Size Dependence in Structure and Morphology of Gas-Phase Produced, Partially Oxidized XXXX Nanoparticles under Catalytic Reaction Conditions.

@entity16773 @entity13479 @entity11710 @entity53919 @entity1953 @entity5383
UNASSIGNED: It is generally accepted that optimal particle sizes are key for efficient nanocatalysis. Much less attention is paid to the role of morphology and atomic arrangement during catalytic reactions. Here, we unravel the structural, stoichiometric, and morphological evolution of gas-phase produced and partially oxidized @entity1953 nanoparticles in a broad size range. Particles with diameters between 1.4 and 22 nm generated in cluster sources are size selected and deposited on amorphous @entity5383 ( @entity16773 ) and ultrananocrystalline @entity11710 (UNCD) films. A combination of different techniques is employed to monitor particle properties at the stages of production, exposure to ambient conditions, and catalytic reaction, in this case, the oxidative dehydrogenation of @entity13479 at elevated temperatures. A pronounced size dependence is found, naturally classifying the particles into three size regimes. While small and intermediate clusters essentially retain their compact morphology, large particles transform into hollow spheres due to the nanoscale Kirkendall effect. Depending on the substrate, an isotropic ( @entity16773 ) or anisotropic (UNCD) Kirkendall effect is observed. The latter results in dramatic lateral size changes. Our results shed light on the interplay between chemical reactions and the catalyst's structure and provide an approach to tailor the @entity53919 phase composition required for specific catalytic schemes.
