Fischer–Tropsch Synthesis: TPR-XAFS Analysis of Co/Silica and Co/Alumina Catalysts Comparing a Novel NO Calcination Method with Conventional Air Calcination

Abstract

A novel conversion of cobalt nitrate to cobalt oxide using nitric oxide (Sietsma et al., patent applications WO 2008029177 and WO 2007071899) was utilized to prepare silica- and alumina-supported cobalt catalysts, in order to evaluate the materials for their sensitivity to Fischer–Tropsch synthesis process parameters by kinetics. In the current contribution, TPR-XAFS was used to probe the differences in reducibility and crystallite size resulting from the two procedures over two catalysts having widely different degrees of support interaction with the cobalt oxides. The nitric oxide calcination method resulted in smaller cobalt oxide crystallites compared to the air calcination method, and their increased surface contact with the support resulted in a slower, more broadened, reduction profile. A much more significant impact on crystallite size and reducibility was observed for the more weakly interacting Co/silica catalyst. That is, the already existing strong interaction between alumina and cobalt oxides dictated a small crystallite size upon reduction of the air calcined catalyst, and a measurable but more modest decrease in crystallite size was afforded by the nitric oxide calcination procedure for the alumina supported catalyst.