Fabrication and Mechanism Study of Clustered Au/CeO₂ Catalyst for the CO Oxidation Reaction^★

Abstract

Supported Au-based catalysts have been attracting continuous attention owing to their outstanding performance in various catalytic applications. However, the complicated environment on the catalyst surface severely hampered the unambiguous illustration of the structural-function relationship for Au-based catalysts. In this work, we developed a facile strategy to fabricate various Au species [Au n ＋ (n＞1), Au δ ＋ (0＜n＜1) and Au 0 ] onto the CeO2 support, which the Au/CeO2 interaction was distinctively modulated by the CeO2-x with different calcination temperatures. As-prepared Au/CeO2-x were valued as catalysts for CO oxidation reaction, which is important for both environmental application and model catalysis. The as-formed clustered Au with δ＋ oxidation state on CeO2-400 demonstrates the best catalytic performance at 50 ℃, while the Au nanoparticles with dominant Au 0 atoms are superior for catalyzing CO oxidation at room temperature. However, the monodispersed Au n ＋ single-sites with the highest dispersion are almost inactive for CO oxidation below 50 ℃. On the basis of structural characterizations and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results, we reasonably speculated that the electronic state of Au species plays a predominant role at room temperature for catalytic performance owing to the differentiated CO adsorption ability. This speculation is well in line with our former research finding that the Au n ＋ sites are weak in capturing CO molecules and Au 0 is favorable for CO adsorption. The surficial O atoms, especially the lattice O atoms, play a minor role in catalyzing CO oxidation for the Au particles within Au/CeO2-700, implying that the reactant molecules might prefer a L-H pathway at room temperature. In contrast, the clustered Au δ ＋ with moderate CO adsorption ability and abundant interfacial site was apt to participate in the surface reaction with a MvK pathway, in which the reaction between surficial lattice O atoms and adsorbed CO molecules significantly contribute to the catalytic activity. Therefore, the Au/CeO2-400 catalyst coupling with moderate CO adsorption ability and abundant active O atoms displayed the best catalytic efficiency at elevated temperatures. These findings in this work provided a facile route for the fabrication efficient Au/CeO2 catalyst, and shed light on the molecular understanding of the reaction path over various Au sites.