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