Fischer-Tropsch Synthesis over Mo / Zeolite Catalysts

Conventional Fischer-Tropsch synthesis (FTS) over Feor Co-based catalysts produces linear alkanes/alkenes as the dominant products, and the product molecular weight distribution follows the Anderson-Schulz-Flory (ASF) law [1, 2]. It is a challenge to maximize the product selectivity towards a given hydrocarbon fraction such as gasoline or diesel. Composite catalysts combining the conventional FTS catalysts with acidic zeolites were investigated to overcome the limitations in both product selectivity and quality through secondary reactions of the linear hydrocarbons on the zeolites to form aromatic compounds and branched alkanes, but encountering problems such as catalyst deactivation and loss in CO conversion [3]. Another possible way to modify the ASF product distribution is to change the mechanism and kinetics of the chain-growth process. Incorporation of a FTS active component into the zeolite cage/channel to limit the reaction inside the micro-space of the zeolite may effectively modify the FTS products distribution. Mo/HZSM-5 is an active catalyst for the dehydroaromatization of methane [4]. Molybdenum carbide or oxycarbide formed during the reaction by methane reduction of molybdenum oxides anchored on the Brönsted acid sites of HZSM-5 is generally accepted as the active species. On the other hand, molybdenum carbides have been reported to be active for mixed alcohol synthesis [5], and they were also reported to be active catalysts for alkane isomerization [6]. Furthermore, Mo/HZSM-5 has been applied in the aromatization reactions of methanol and ethanol [7]. Dehydration of the alcohols on Mo/HZSM-5 was supposed to occur during the aromatization process. These literature results may be combined to pose the potential of applying Mo/HZSM-5 as an innovative catalyst for the FTS to produce high quality gasoline. This presentation will show the unique performance of Mo/HZSM-5 in FTS, most probably through a potential route that directly transforms mixed alcohols to branched alkanes and aromatics.