In situ synthesis of supported palladium complexes:Highly stable and selective supported palladium catalysts for hydrodechlorination of CC1_2F_2

摘要

Supported palladium phosphine complexes [Pd(PPh_3)_2X_2/MgF_2] (X = Cl or SCN) were prepared as precursor catalysts for hydrodechlorination of CC1_2F_2 by a method of in situ synthesis of palladium complex on support (ISPS) and using environmentally benign solvents.Their performance and activities were compared to those of catalysts prepared via traditional incipient wetness impregnation method by catalytic reaction and characterization results,including FT-IR,XPS,XRD and H_2-chemisorption.After an induction period,during which the Pd(II) precursors are converted to active species by being put in contact with substrate CC1_2F_2 and H_2,stable catalytic activities and improved selectivities to CH_2F_2 (>93% on Pd(PPh_3)_2(SCN)_2/MgF_2) are achieved.The improvement of catalytic performance was ascribed to the more homogenous distributing of catalyst precursor on the surface of the support,where the amounts of the sites that induce side reactions are decreased.The XPS results revealed that there exist two kinds of active Pd sites on the surface of catalysts.One is Pd(0) site for the activation of hydrogen,and the other is the Pd site of high electrovalence,i.e.electron-deficient palladium for the activation of CC1_2F_2 High dispersion (approx 90%) of Pd particles results in a strong interaction between Pd and the support,and creates electron-deficient palladium sites being of high selectivity to CH_2F_2.