AuPd alloy formation in Au-Pd/Al2O3 catalysts and its role on aromatics hydrogenation

Alumina-supported bimetallic Au-Pd catalysts were prepared by the simultaneous reduction of palladium and gold precursors by ethanol in the presence of the polyvinylpyrrolidone (PVP) and classical incipient wetness co-impregnation method (iwi). The catalysts were characterized by a variety of techniques (AAS, N-2 adsorption-desorption, XRD, TEM, CO chemisorption, TGA, FHR-CO, DRIFTS-NH3, and XPS). According to X-ray diffraction measurements and FTIR-CO spectra, an AuPd alloy formed on the sample prepared by the PVP method, whereas distinct phases of gold and palladium metals formed on the iwi samples. The effect of the presence of the AuPd alloy on the catalytic activity was investigated in the simultaneous hydrogenation (HYD) of toluene (T) and naphthalene (NP) in the presence of dibenzothiophene (DBT) at P = 5.0 NlPa, T = 523 K, WHSV = 41.2 h(-1). Under the selected conditions, all the catalysts were resistant to poisoning with 113 ppm of S (as DBT). The enhancement in activity observed for the sample prepared by PVP method as compared to those prepared by impregnation is related to the geometric effect resulting from the dilution of the Pd ensemble in the AuPd alloy and also to the presence of smaller Pd-0 particles. (c) 2004 Elsevier B.V. All rights reserved.