Catalysis at Multiple Length Scales: Crotonaldehyde Hydrogenation at Nanoscale and Mesoscale Interfaces in Platinum–Cerium Oxide Catalysts

Abstract

Crotonaldehyde hydrogenation is carried out on a series of Pt–CeO2 catalysts to investigate the mechanism of enhanced C═O bond hydrogenation by an active oxide–metal interface. We show that deposition of CeO2 nanoparticles onto a Pt surface leads to two types of Pt–CeO2 interfaces: (1) the nanoscale interface defined by the contact of individual CeO2 nanoparticles with the Pt surface and (2) a larger, mesoscale interface defined by the boundary between domains of self-assembled nanoparticles and the surrounding clean Pt substrate. Surprisingly, although the nanoscale interface accounts for greater than 90% of the total number of 3-phase boundary sites in the catalysts tested as shown by TEM analysis, C═O bond hydrogenation kinetics scale exclusively with the larger, mesoscale interface. Using in situ ambient pressure XPS, we show that these kinetics are not the result of variations in the CeO2 oxidation state due to H spillover or the result of Pt decoration by the migration of reduced Ce atoms during rea...