Exploring the influence of magnesium addition on the catalytic performance of Cu–Al mixed oxides in benzaldehyde reduction

Abstract

The study investigates the impact of magnesium on the physicochemical properties of CuAlO_x oxide and its catalytic behavior in the benzaldehyde reduction reaction. A series of catalysts, including CuAlO and CuAl_1-xMg_xO (x = 0.05; 0.1), were synthesized through a hydrothermal method, characterized using multiple techniques: Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), laser Raman spectroscopy (LRS), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX), temperature-programmed reduction (RTP), and X-ray photoelectron spectroscopy (XPS). Their catalytic performance in the reduction of benzaldehyde to benzyl alcohol was evaluated under atmospheric pressure within a temperature range of 150–200 °C. Their structural properties during reduction and re-oxidation were examined through in situ X-ray diffraction (HT-DRX) and X-ray photoelectron spectroscopy (HT-XPS) following specific pretreatments. The baseline CuAlO_x system exhibits catalytic activity in the benzaldehyde reduction reaction, and these capabilities are significantly enhanced in the presence of magnesium. Indeed, with a high magnesium content, the CuAl_0.9Mg_O.1 system achieves a conversion rate exceeding 83% and an impressive benzyl alcohol selectivity of up to 95%. The exact role of magnesium remains unclear. However, its presence appears to influence the reducibility of the system, which is slowed down, as observed in temperature-programmed reduction (RTP). Additionally, XRD results suggest the formation of a Cu–Mg–O mixed phase during preparation, while X-ray photoelectron spectroscopy (XPS) indicates the stabilization of copper in the Cu(I) oxidation state on the material’s surface. During the catalytic reaction, a synergistic effect between CuO, Cu–Mg–O, and Cu₂O phases likely enhances the performance of CuAl_0.9Mg_0.1O compared to CuAlO.