An enhanced selective hydrogenation of methyl benzoate and impacts promoted by Al-modified KMn/SiO2†

Benzaldehyde plays a vital role as an essential organic building block in the synthesis of a wide range of chemicals, serving as a linchpin in the production processes of the chemical industry. The direct hydrogenation of methyl benzoate to produce benzaldehyde aligns more closely with the principles of green chemistry and atomic economy compared to the traditional benzyl chloride method. However, the design and preparation of effective catalysts have aroused increasing attention. Herein, aluminum has been infused into the KMn/SiO₂ catalyst, and its surface and physicochemical properties were scrutinized using characterization techniques including XRD, BET, TPR, NH₃-TPD, and XPS. The results have indicated a reduction in the average pore diameter of the Al-modified KMn/SiO₂ catalyst, leading to improved reduction performance and an augmentation in H₂ adsorption capacity. Furthermore, an elevation in the oxygen vacancy concentration, acid centers, and acid amounts on the catalyst surface leads to an increase in adsorption sites. These enhancements have improved the adsorption capacity of H₂ and methyl benzoate molecules, thereby elevating the conversion rate of methyl benzoate and the selectivity for benzaldehyde and simultaneously decreasing by-products such as benzene and toluene. The optimized catalysts with a 5% Al content have achieved a 24.7% conversion rate of methyl benzoate and exhibited a 53.9% selectivity for benzaldehyde, which provided valuable insights into the modification of Mn-based catalysts for the catalytic hydrogenation of methyl benzoate in the preparation of benzaldehyde.