Low-temperature carbon monoxide oxidation over zirconia-supported CuO–CeO₂ catalysts: Effect of zirconia support properties

Highlights: • CuO-CeO₂/ZrO₂ materials were investigated in the low temperature CO oxidation. • High surface area ZrO₂ synthetized by sol-gel method. • Low ZrO₂ surface area synthetized by fast precipitation. • Sol-gel samples showed, after impregnation, a severe decrease of surface area. • CuO-CeO₂/ZrO₂ with precipitated ZrO₂ led to a very active catalyst. - Abstract: A study was conducted to investigate the effect of the preparation route of ZrO₂ in CuO–CeO₂/ZrO₂ catalysts for the oxidation of carbon monoxide at low temperature (COX). Four ZrO₂ supports were synthetized via either type sol-gel methodology or precipitation. The final Cu-Ce-Zr oxide catalysts were prepared by incipient wetness co-impregnation with copper and cerium solutions (with a loading of 6 wt% of CuO and 20 wt% of CeO₂). The catalyst crystalline phases, texture and active species reducibility were determined by XRD, N₂ physisorption at −196 °C and H₂-TPR, respectively; meanwhile the surface composition and copper-cerium electronic states were studied by XPS. The catalytic activity was evaluated in the oxidation of CO to CO₂, in the 40–215 °C temperature range. Catalytic results evidenced that the samples prepared by a sol-gel methodology showed, after the impregnation, a severe decrease of specific surface area and pore volume attributable to a wide degree of pore blockage caused by the presence of metal oxide particles and a collapse of the structure partially burying the active sites. A simple co-impregnation of a zirconia support, obtained through facile and fast precipitation, provided instead a catalyst with very good redox properties and high dispersion of the active phases, which completely oxidizes CO in the range 115–215 °C with T₅₀ of 65 °C. This higher observed activity was ascribed to the formation of a larger fraction of highly dispersed and easily reducible Cu species and ceria nanocrystallites, mainly present as Ce(IV), with an average size of 5 nm.