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)Au_x (x= 0.1,0.12,0.15 and 0.2 ) and Pd_mM_n (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)Au_x series, the catalyst composition Pd_0.9Au_0.1 displays maximum activity, expressed as TOF. Activity pattern in Pd_0.9M_0.1 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.