Effect of Copper Particle Size on the Surface Structure and Catalytic Activity of Cu–CeO2 Nanocomposites Prepared by Mechanochemical Synthesis in the Preferential CO Oxidation in a H2-Rich Stream (CO-PROX)

Abstract

An effect of Cu powder dispersion and morphology on the surface structure and the physical–chemical and catalytic properties of Cu–CeO2 catalysts prepared by mechanochemical synthesis was studied in the preferential CO oxidation in a H2-rich stream (CO-PROX). Two catalysts, produced by 30 min ball-milling from CeO2 and 8 mass% of copper powders and with particle sizes of several tens (dendrite-like Cu) and 50–200 nm (spherical Cu obtained with levitation-jet method), respectively, were characterized by X-ray diffraction and electron microscopy methods, a temperature-programmed reduction with CO and H2, and with Fourier-transform infrared spectroscopy. The catalyst synthesized from the “large-scale” dendrite-like Cu powder, whose surface consisted of CuxO (Cu+) agglomerates located directly on the surface of facetted CeO2 crystals with a CeO2(111) and CeO2(100) crystal planes exposition, was approximately two times less active at 120–160 °C than the catalyst synthesized from the fine Cu powder, whose surface consisted of CuxO (Cu2+) clusters of 4–6 nm in size located on the steps of facetted CeO2 nanocrystals. Although a large part of CO2 reacted with a ceria surface to give carbonate-like species, no blockage of CO-activating centers was observed due to the surface architecture. The surface structure formed by the use of highly dispersed Cu powder is found to be a key factor responsible for the catalytic activity.