Mesoporous Ceria‐Supported Gold Catalysts Self‐Assembled from Monodispersed Ceria Nanoparticles and Nanocubes: A Study of the Crystal Plane Effect for the Low‐Temperature Water Gas Shift Reaction

Abstract

AbstractMesoporous CeO2 colloidal spheres were obtained by the assembly of CeO2 nanocrystals in two shapes: nanoparticles (NPs) and nanocubes (NCs). CeO2 colloidal spheres assembled by nanoparticles (NPCS) have predominantly exposed {1 1 1} surfaces and that assembled by nanocubes (NCCS) are terminated by {1 0 0} planes. The size and surface area of NPCS and NCCS are comparable. We compared the water gas shift reaction activity over Au/NPCS and Au/NCCS to clarify the nanoscale crystal plane effect of the CeO2 {1 0 0} and {1 1 1} crystal planes. Au/NCCS and NCCS show a better catalytic activity than Au/NPCS and NPCS towards the water gas shift reaction. We used in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to confirm that the water gas shift reaction over Au/NPCS and Au/NCCS follows a formate mechanism and to prove that the formation/decomposition rate of bidentate formates (intermediates) are faster on Au/NCCS and that less monodentate carbonates (inactive species) are accumulated over Au/NCCS. We used X‐ray photoelectron spectroscopy and DRIFTS combined with DFT calculations to demonstrate that more active Auδ+ species could be formed on NCCS than NPCS because of the crystal plane effect. The crystal plane effect is also embodied in the experimental phenomenon that H2O adsorption is more significant on Au/NCCS than Au/NPCS, which is in agreement with the calculation results that H2O adsorption is more facile on CeO2 {1 0 0} than {1 1 1} surfaces.