In Situ X-Ray Absorption Spectroscopy Studies of Carbon Monoxide Oxidation in the Presence of Nanocomposite Cu–Fe–Al Oxide Catalysts

Abstract

Nanocomposite Fe–Al and Cu–Fe–Al oxide catalysts are studied in the CO oxidation reaction. It is shown that the introduction of copper leads to a more than two orders of magnitude increase in the reaction rate. The most active catalyst is a nanocomposite containing 5 wt % CuO, 78 wt % Fe2O3, and 17 wt % Al2O3. According to X-ray diffraction analysis, the catalysts consist of hematite nanoparticles, α-Fe2O3, and amorphous alumina. Copper is in a highly dispersed state to form CuO and CuFeOx clusters. Results of in situ X‑ray absorption spectroscopy studies suggest that the reduction of copper from Cu2+ to Cu1+ and Cu0 in a CO stream begins at a temperature of 200–250°C; at 400–600°C, copper is mostly in the metallic state; the Fe3O4 → FeO → Fe reduction begins at 400–500°С. In a stoichiometric mixture of CO and O2, Fe3+ does not undergo reduction; the reduction of copper oxide to metal occurs at temperatures above 400°C. In the presence of excess oxygen in a temperature range of 100–600°C, no changes in the chemical state of the catalysts are detected. The mechanism of CO oxidation in the presence of Cu–Fe–Al nanocomposites is proposed.