Control of metal dispesion and structure by changes in the solid-state chemistry of supported cobalt Fischer-Tropsch catalysts

摘要

Controlling preparation variables in supported cobalt Fischer-Tropsch catalysts has a sramatic effect on the dispesion and distribution of cobalt,and determines how active and selective the resulting catalyst will be.We detail specific examples of catalyst synthesis strategies for modifying interactions between the support and the cobalt precursor,promoting reduciton,stabilizing catalysts to high-termperatue treatments,minimizing deleterious support emtalinteractions,and controlling the distribution of cobalt on large support particles.It is important to optimize the support metal interaction strength,so that it is strong enough to obtain good dispersion but not too strong to prevent low temperature reducition.We show examples in which formation of surface complexes and epitaxial matching of precursor and support structures improves dispersion dramatically.Reduction promoters can help in those cases where support-precursor interactions are too strong.We show how substitutions of silicon into a titania lattice stabilizes surface area and retards formation at high oxidative coke removal is nessary.in addition,surface treatment of TiO_2 with an irreducible oxide like ZrO_2 can inhibit deleterious support interactions that can block surface cobalt sites.selectivity can also be dramatically altered by catalyst synthesis.We illusrate a case of large (2mm)SiO_2 particles onto which cobalt can be added eithr uniformly or in discrete eggshells,with the eggshell catalysts having substantially higher C_5+ selectivity.These approaches can lead to optimal fischer-Tripsch catalysts with high activity and C_5+ selectivity,good physical integrity, and a long life.