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

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.