Infrared Study of Hydrogenation of Benzoic Acid to Benzaldehyde on ZrO2 Catalysts

Abstract
The selective hydrogenation of benzoic acid to benzaldehyde on ZrO2 and Cr2O3–ZrO2 at 523 K was studied by IR spectroscopy. An enhancement of the hydrogenation rate of benzoic acid by Cr2O3 doping to ZrO2 was observed. The main role of Cr2O3 was considered to be the step of activating hydrogen. An intermediate species was observed based on the IR bands during a transformation from the adsorbed benzaldehyde to the benzoate at lower temperatures. This is discussed in conjunction with the reaction mechanism of the hydrogenation. The intermediate species was regarded as being the chemisorbed benzaldehyde by an analysis of the observed IR bands.