Forum for Basic Studies on Energy(VI): Selectivity regulation in Fe-based FTS catalyst
Prof. Ding Ma
College of Chemistry and Molecular Engineering, Peking University
Transformation of syngas (CO/H2) derived from shale gas, biomass and coal has been developed as a promising alternative to oil to prepare liquid fuels and commodity chemicals. The well-known process is Fischer-Tropsch synthesis (FTS). The product selectivity of FTS is limited by the polymerization law, i.e. Anderson-Schulz-Flory (ASF) distribution, which restricts the industrial application as the result of a very wide product distribution. Recently, different novel catalyst design strategies have been developed to confine the products into a narrow range by altering the electronic property of metal active sites and the steric structure of the catalyst.
Here we reported that Zn and Na modulated Fe catalysts can be fabricated through a simple co-precipitation/washing method. Zn greatly changed the size of iron species, serving as the structural promoter while the existence of Na on the surface of Fe catalyst alters the electronic structure of the catalyst, making it very active for CO activation. Most importantly, the unique electronic structure suppresses the hydrogenation of double bonds and promotes desorption of products, which confers the catalyst unexpected reaction patch towards the alkenes, especially C5+ alkenes, at the same time of lowering the selectivity towards underside products.
A combination of Na-Zn-Fe5C2 and hierarchical zeolite with uniform mesopores dramatically changed the product distri-bution of FTS, leading to 51% aromatic selectivity under the stable stage with CO conversion > 85%. C12+ heavy hydrocar-bons almost disappeared and the catalyst showed good stability. The hierarchical zeolitic structure and Brønsted acidity of zeolite can be precisely tuned by controlling alkali treatment conditions and ion-exchange degrees. It is the appropriate density and strength of the Brønsted acid sites and the hierar-chical pore structure of HZSM-5 that endows the catalyst un-precedented aromatics yield.
Venue: Conference Room of State Key Laboratory of Catalysis
Date and Time: May 3, 2017 15:00 p.m.