Precise Control of Pt Particle Size for Surface Structure-Reaction Activity Relationship

The use of surface organometallic chemistry on metal (SOMC/M) allows the controlled and stepwise variation of the platinum particle size in Pt/SiO₂ catalysts. This SOMC/M method is possible thanks to the better affinity of most organometallic compounds with the surface of zerovalent metal particles covered with hydrogen than their support. In this paper, Pt(acac)₂ was used as the organometallic precursor, silica as a support, and then hydrogen to reduce the adsorbed organometallic layer on top of the starting Pt nanoparticle. We partially succeeded in adding one Pt layer with a stepwise particle size increase of around 0.6 nm when going from the first (1G) to the second (2G) refilling run, as obtained from TEM and H₂ chemisorption analysis and then confirmed by DFT calculations. The metal loading could be kept at a very low level (<1-2 wt %), which is relevant for catalytic applications. The particle size distribution remained relatively narrow even after two refilling runs, allowing more precise relationships between particle size and catalytic properties to be established. The TOR_H (for hydrogenolysis) dramatically decreased, while TOR_I (for skeletal isomerization) slightly increased with increasing the particles size. It is therefore suggested that hydrogenolysis might preferentially occur on low coordination surface platinum atoms (corners and edges), while isomerization occurs mostly on the facets.