Selectivity Control and Catalyst Design in the Fischer-Tropsch Synthesis: Sites, Pellets, and Reactors

Abstract

This chapter focuses on selectivity control and catalyst design in the Fischer-Tropsch (FT) synthesis. Chain growth during the FT synthesis is controlled by surface polymerization kinetics that place severe restrictions on our ability to alter the resulting carbon number distribution. Intrinsic chain growth kinetics are not influenced strongly by the identity of the support or by the size of the metal crystallites in supported Co and Ru catalysts. Transport-limited reactant arival and product removal, however, depend on support and metal site density and affect the relative rates of primary and secondary reactions and the FT synthesis selectivity. Diffusion-limited removal of products from catalyst pellets leads to enhanced readsorption and chain initiation by reactive α -olefins. Diffusive and convective transport processes introduce flexibility in the design of catalyst pellets and in the control of FT synthesis selectivity. The model is proposed in the chapter that describes the catalytic behavior of more complex Fe based materials, where several chain termination steps and highly non-uniform and dynamic surfaces introduce additional details into the models required to describe FT synthesis selectivity models.