Reduction of Propanoic Acid over Pd‐Promoted Supported WOx Catalysts

Silica‐, titania‐, and zirconia‐supported tungsten oxide catalysts were synthesized by wetness impregnation techniques. When promoted with Pd, these materials catalyzed the reduction of propanoic acid to 1‐propanol at 433 K with a selectivity of up to 92 % (13.5 % conversion) in atmospheric pressure of H2. Over Pd‐promoted WOx/TiO2, the observed orders of reaction were 0.2 in H2 and 0.7 in propanoic acid, and the apparent activation energy was 54 kJ mol−1. In situ X‐ray absorption spectroscopy of Pd‐promoted WOx/SiO2 revealed a slight reduction of the W from +6 to an average oxidation state of about +5 during H2 treatment above 473 K. In situ infrared spectroscopy indicated the catalyst surface was covered mostly by propanoate species during reaction. For comparison, supported phosphotungstic acid was also evaluated as a catalyst under identical conditions, but the resulting high acidity of the catalyst was deleterious to alcohol selectivity. Worthy WOx gets work done: Promoting supported WOx with Pd results in catalytic activity for the selective (up to 92 %) reduction of carboxylic acids to alcohols. Palladium‐promoted tungsten oxides were deposited on a variety of supports and characterized using steady‐state conversion of propanoic acid, X‐ray absorption spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy.