Hydrogenation of aliphatic carboxylic acids to corresponding aldehydes over Cr2O3-based catalysts Original Research Article

Direct hydrogenation of aliphatic carboxylic acids to the corresponding aldehydes catalyzed by Cr–ZrO2 and supported Cr2O3 catalysts were investigated. A variety of Cr–ZrO2 catalysts were prepared by doping of Cr2O3 into ZrO2, which itself catalyzes the intermolecular ketonization of aliphatic carboxylic acids. This Cr–ZrO2 catalyst exhibited higher catalytic performance toward the hydrogenation of caprylic acid than pure Cr2O3, having maxima both of the catalyst activity and of specific surface area of the catalyst at Cr:Zr = 15:100 in atomic ratio. It is estimated that high dispersion of chromia on the Cr–ZrO2 catalyst surface will improve the catalyst performance. Furthermore, the α-Al2O3-supported Cr2O3 catalyst showed over 90% aldehyde selectivity in the hydrogenation of stearic acid. However, employment of other supports such as γ-Al2O3, SiO2 and TiO2 to Cr2O3 resulted in poor aldehyde selectivity and also encouraged undesirable ketonization to give predominantly C35-ketone species. Pre-treatment of the γ-Al2O3 support at or above 1080 °C, enabled the Cr2O3 (10 wt.%)/γ-Al2O3 catalyst to catalyze the hydrogenation over 90% selectivity. The novel catalyst of 10 wt.% Cr2O3 supported by commercial α-Al2O3 was found to hydrogenate various aliphatic carboxylic acids as well as benzoic acid and methyl nicotinate in moderate to high conversion and in high aldehyde selectivity. The effects of catalyst supports and their thermal pre-treatment in promoting the hydrogenation are also discussed.