Studies on palladium based bimetallic catalysts Pd-M/TiO2 (M = Cu, Ag & Au): I-Selective hydrogenation of 1-heptyne

Abstract

Two series of palladium based bi-metallic catalysts, Pd (1-x)Aux (x = 0.1,0.12,0.15 and 0.2 ) and PdmMn (M = Cu/Ag/Au; m, n = 0.9, 0.1) supported on TiO2-P-25, have been prepared and characterized by X-ray diffraction (XRD), Diffuse Reflectance Spectroscopy (DRS), Transmission Electron Microscopy (TEM), X-ray Photo-electron Spectroscopy (XPS) and Temperature Programmed Reduction (TPR). DRS and XPS studies indicate formation of nano scale alloys involving redistribution of charges within the metals. Selective hydrogenation of 1-heptyne in liquid phase has been studied on these catalysts at atmospheric pressure and in the temperature range 293–313 K. In the Pd (1-x)Aux series, the catalyst composition Pd0.9Au0.1 displays maximum activity, expressed as TOF. Activity pattern in Pd0.9M0.1 series follows the trend, Pd-Au > Pd-Ag = Pd-Cu > Pd. Selectivity for heptene formation is maintained at > 95% on all catalysts up to 60 min reaction time. Interplay of ensemble as well as ligand effects, acting simultaneously, influences the adsorption and activation of 1-heptyne, leading to higher activity on Pd-Au bimetallic catalyst vis-à-vis other bimetallic and mono metallic catalysts.