THE USE OF COMPOSITE RUTHENIUM CATALYSTS IN FISCHER-TROPSCH SYNTHESIS.

摘要

The catalytic properties of various supported ruthenium catalysts were investigated in the Fischer-Tropsch synthesis reaction at low pressures (1-3 atm). Reaction products from these systems consisted of primarily linear olefins and paraffins ranging from methane to C(,10)+ long chain hydrocarbons. TiO(,2)-supported Ru was found to have higher selectivities to C(,2)-C(,4) olefins than the conventional Ru/SiO(,2) and Ru/Al(,2)O(,3) catalysts. Evidence from catalyst characterization by chemisorption and XRD indicated that Ru/TiO(,2), after high temperature reduction, exhibited strong metal-support interactions (SMSI).; Potassium was found to be a selective promoter for olefin production over supported Ru catalysts. The addition of potassium to Ru/SiO(,2) strongly reduced the ability of Ru to chemisorb H(,2) but enhanced its selectivity to olefins and higher hydrocarbon products. The suppression of hydrogen adsorption of Ru was attributed to the electron rich character of the K promoted surface Ru as indicated by the shifts in ESCA binding energies. Possible interpretations of the mechanism of K promotion were discussed. For the SMSI Ru/TiO(,2), potassium has an additive effect on increasing olefin selectivities.; Composite catalysts offer interesting possibilities for the modification of catalytic properties of Ru in the Fischer-Tropsch synthesis. When large pore zeolites such as NaX, CuX, HY, and H-mordenite were used as second components in the Ru/TiO(,2) composite mixture, the distribution of hydrocarbon products for the primary Ru catalysts was strongly modified. The resulting hydrocarbon distribution deviated from the normal Schulz-Flory model because zeolites can intercept the normal desorption-readsorption processes of (alpha)-olefins on adjacent Ru/TiO(,2) particles. It is concluded that zeolite provides a synergism to modify the properties of Ru/TiO(,2) in: (1) increasing overall CO conversion (2) increasing C(,4) hydrocarbon formation and (3) decreasing the relative rate of chain growth for C(,4)+ hydrocarbons according to the non-trivial reaction kinetics. The extent of this selectivity modification depends on such factors as the nature of zeolite catalysts and their activity of (alpha)-olefin conversion, hydrocarbon diffusion within zeolite pores, and reaction temperatures.