Structure and catalytic performance of Pt-promoted alumina-supported cobalt catalysts under realistic conditions of Fischer-Tropsch synthesis

摘要

The structure of alumina-supported cobalt catalysts promoted with platinum and their catalytic performance in Fischer-Tropsch synthesis were investigated under realistic reaction conditions (P = 20 bar, T = 493 K) using in situ time-resolved X-ray diffraction with simultaneous analysis of reaction products. The catalysts were prepared via incipient wetness impregnation and characterized by a wide range of ex situ techniques. Direct in situ measurements were indicative of considerable versatility of alumina-supported cobalt catalysts during Fischer-Tropsch synthesis. Cobalt sintering occurred at the first hours of the reaction and resulted in a significant drop of the catalytic activity. In addition to sintering, partially oxidized catalysts containing smaller cobalt particles (mean particle size <5 nm) were slowly reducing during Fischer-Tropsch reaction. Treatment of cobalt catalysts in pure carbon monoxide led to selective transformation of cobalt metallic phases to Co _2C cobalt carbide. Cobalt carbidization followed by hydrogenation selectively led to cobalt hcp metallic phase, which seems to be more active in Fischer-Tropsch synthesis than cobalt fcc phase. Cobalt oxidation by water was not significant in the catalysts with metal particles larger than 5 nm even at high water concentrations.