Core-shell catalysts and bimodal catalysts for Fischer-Tropsch synthesis

In the past decades, numerous efforts have been made to develop efficient catalyst systems for Fischer-Tropsch synthesis (FTS) reaction. This chapter reviews two successful examples of catalyst design and development for FTS reaction: the core-shell catalyst and bimodal catalyst. Their preparation methods, structures and catalytic performances are introduced. The core-shell catalysts are designed by coating a zeolite membrane on the surface of pre-shaped catalyst pellet. The catalysts show excellent performance for the direct synthesis of isoparaffins based on the FTS reaction. The formation of heavy hydrocarbons is suppressed completely and the middle isoparaffins become the main products. This core-shell structure provides a tailor-made confined reaction environment that result in spatially confined effects and shape selectivity. The bimodal catalysts are prepared using oxide or active components as building blocks to produce small pores inside large pores of homo- or hetero-atom support. The large pore size of the bimodal catalysts can be successfully controlled. Both the experiment investigations and mathematical simulation have demonstrated that the bimodal pore structure can increase the FTS activity through higher diffusion efficiency in large pores and higher dispersion of active metal particles via increased surface area. Besides the spatial effect, new chemical effects might appear with the formation of hetero-atom structure. The concepts and preparation methods of core-shell catalysts and bimodal catalysts provide insight and inspiration for other catalytic reactions.