Catalytic Hydrogenation of Acetylene and Ethylene by Palladium Complex Supported on Polyorganosiloxne

摘要

Various factors involving and affecting the activity of hydrogenation of acetylene and ethylene on polyorganosiloxane(POS)-bound palladium acetate (Pd(OAc)_2) or on palladium chloride (PdCl_2) catalyst have been investigated. The rate of acetylene hydrogenation on POS-bound Pd(OAc)_2 catalysts decreases as the catalyst P/Pd ratio (mole ratio of phosphine group on POS to palladium) increases. Ethylene selectivity (moles ethylene produced per mole acetylene converted) is 67.2% for P/Pd = 7.63 catalyst and 78% for P/Pd = 27.9 catalyst, respectively. It is found that the rate of ethylene hydrogenation on POS-bound Pd(OAc)_2 catalysts increases with increase in the catalyst P/Pd ratio, pass a maximum at P/Pd = 14.5, and then slightly decreases for further increase in P/Pd ratio. Although the behavior of the activity for POS-bound PdCl_2 catalysts is also the same as that for POS-bound Pd(OAc)_2 catalysts, the reaction rate for POS-bound Pd(OAc)_2 catalysts if ca. 10 times higher than thar for POS-bound PdCl_2 catalysts. The ethylene kinetic order is 0.5-0.78 for both catalysts, while the reaction order in hydrogen is 0.13-0.21 for POS-bound Pd(OAc)_2 catalysts and 0.78-0.8 for POS-bound PdCl_2 catalysts, respectively. High catalytic activity of POS-bound Pd(OAc)_2 is considered to arise from the formation of Pd-H species on the catalyst.