Synergistic Effect of the Catalytic Action of Copper and Cerium in the Oxidation of Carbon Monoxide on Modified Cu/Ce/ZSM-5 Zeolites

A series of mono- and bimetallic copper–cerium catalysts based on ZSM-5 zeolite with different aluminum content (SiO₂/Al₂O₃ = 30 and 55) was synthesized by incipient wetness impregnation. The copper content was 0–4.3 wt %, and cerium loading varied in a range from 0 to 6 wt %. The resulting composites were studied by low-temperature nitrogen adsorption–desorption, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, UV–Vis diffuse reflectance spectroscopy, and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of adsorbed CO and tested in the catalytic reaction of CO oxidation with oxygen. A pronounced synergistic effect of catalytic action of copper and cerium associated with the redox interaction between the metals was observed in the systems under study. The catalytic activity of the composites monotonically increased with the fraction of cerium in the bimetallic systems (as the Сu : Ce ratio was changed from 6 to 1). In the presence of the most active catalysts, the temperature at which CO conversion reached 50% was about 100°C. A decrease in the aluminum content of the zeolite contributed to higher catalytic activity. It was found that Cu⁺ ions bound to the surface of CeO₂ particles played a key role in catalysis.