Effect of gold on the HDS activity of supported palladium catalysts

The effect of gold on palladium catalysts supported on amorphous aluminosilicate was investigated in the hydrodesulfurization of thiophene. A series of bimetallic AuxPdy catalysts was prepared by the slow deposition-precipitation method with decomposition of urea. The structural and surface properties of the samples were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy techniques at different stages of the catalyst life. After calcination at 673 K, gold-enriched solid solutions of approximately Au90Pd10 and Au80Pd20 composition were formed for all samples of different Au/Pd ratios, along with free palladium phases. Au80Pd20 was the prevailing phase. Hydrogen treatment of the catalyst at 673 K before catalytic tests reduced free palladium oxide to free metallic Pd. An increase of the hydrodesulfurization activity with increasing gold amount up to 50 wt% was found. The structural analysis of the "aged" catalysts indicated formation of palladium sulfide, Pd4S, in the monometallic palladium and in the bimetallic palladium-rich samples but not in the gold-rich samples. The catalytic behavior of the catalysts was related to the formation of the AuxPdy clusters and to the inhibition of the sulfide-phase formation