Water-Gas Shift Reaction on Metal Nanoclusters Encapsulated in Mesoporous Ceria Studied with Ambient-Pressure X-ray Photoelectron Spectroscopy

Metal nanoclusters (Au, Pt, Pd, Cu) encapsulated in channels of mesoporous ceria (mp-CeO2) were synthesized. The activation energies of water-gas shift (WGS) reaction performed at oxide metal interfaces of metal nanoclusters encapsulated in mp-CeO2(M@mp-CeO2) are lower than those of metal nanoclusters impregnated on ceria nanorods (M/rod-CeO2). in situ studies using ambient-pressure XPS (AP-XPS) suggested that the surface chemistry of the internal concave surface of CeO2 pores of M@mp-CeO2 is different from that of external surfaces of CeO2 of M/rod-CeO2 under reaction conditions. AP-XPS identified the metallic state of the metal nanoclusters of these WGS catalysts (M@mp-CeO2 and M/rod-CeO2) under a WGS reaction condition. The lower activation energy of M@mp-CeO2 in contrast to M/rod-CeO2 is related to the different surface chemistry of the two types of CeO2 under the same reaction condition.