Mesostructured alumina and the state of Ni as promoter for Co Fischer-Tropsch synthesis catalysts
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Supported cobalt catalysts are widely studied and applied for conversion of synthesis gas in low temperature Fischer-Tropsch (FT) synthesis. It is common practice to add a noble metal promoter to optimize the performance of the catalysts. Recently, more attention has been directed towards a fundamental understanding of the promotion. This study approaches from two perspectives: i) the nature and location of the promoter itself is unclear, especially at reaction conditions, which leads to the utilization of in situ techniques; and ii) tailored mesostructured alumina is employed as more well defined support material for Co Fischer-Tropsch catalysts to decouple catalyst-support interactions and pore-size effects. Being able to control a uniform pore size within the support leads to a homogeneous metal distribution with the metal particles being more ideal and metal-metal interactions might vary to give new clues towards the state of promoters under Fischer-Tropsch synthesis conditions. The catalysts were studied with the help of a dedicated in situ setup to be used at synchrotron radiation facilities which enabled us to simultaneously monitor the catalyst with X-ray absorption spectroscopy and X-ray diffraction at reduction and Fischer-Tropsch synthesis conditions in order to elucidate the state of promoters. Catalysts were prepared by incipient wetness impregnation and with various amounts of catalytic active metal, promoter metal and on various alumina support materials to find their degree of interaction. In the present work we also prepared mesostructured alumina thin films and powders with pore sizes around 5 nm using triblock copolymers Pluronic P123 and Pluronic F127. In addition to being of interest in their own right, the organized aluminas provided highly interesting support systems for studies of catalysts, as they provide a more well-defined environment for the catalytically active particles.