Direct hydrogenation of aromatic carboxylic acids to their corresponding aldehydes with zinc oxide catalysts Original Research Article

High yields of aromatic aldehydes were obtained by direct hydrogenation of aromatic carboxylic acids over different zinc oxide catalysts having distinctive surface properties. The reaction is carried out in a fixed bed reactor in gas phase at 330–350°C. High selectivity of 96% of benzaldehyde at 100% conversion of benzoic acid was achieved using a zinc oxide catalyst having very weakly acidic surface properties in addition to basic sites. The catalysts were characterized by XRD and N2-adsorption isotherms for the determination of BET-surface and porosity. The strength of acid and basic sites was determined by titration in the presence of Hammett-indicators. Very weakly acid sites were identified by pyridine adsorption combined with FT-IR-spectroscopy.