Vera P. Santos

Metal organic framework-mediated synthesis of highly active and stable Fischer-Tropsch catalysts

Depletion of crude oil resources and environmental concerns have driven a worldwide research on alternative processes for the production of commodity chemicals. Fischer-Tropsch synthesis is a process for flexible production of key chemicals from synthesis gas originating from non-petroleum-based sources. Although the use of iron-based catalysts would be preferred over the widely used cobalt, manufacturing methods that prevent their fast deactivation because of sintering, carbon deposition and phase changes have proven challenging. Here we present a strategy to produce highly dispersed iron carbides embedded in a matrix of porous carbon. Very high iron loadings (>40 wt %) are achieved while maintaining an optimal dispersion of the active iron carbide phase when a metal organic framework is used as catalyst precursor. The unique iron spatial confinement and the absence of large iron particles in the obtained solids minimize catalyst deactivation, resulting in high active and stable operation.

Insights into the Catalytic Performance of Mesoporous H-ZSM-5-Supported Cobalt in Fischer–Tropsch Synthesis

Mesoporous H‐ZSM‐5 (mesoH‐ZSM‐5) was used as a carrier for a series of bifunctional Co‐based catalysts for Fischer–Tropsch synthesis with ZrO2 and/or Ru added as promoters. The reducibility of the catalysts was studied in detail by using temperature‐programmed reduction and X‐ray absorption spectroscopy. A comparison of the catalytic performance of Co/mesoH‐ZSM‐5 and Co/SiO2 (a conventional catalyst), after 140 h on stream, reveals that the former is two times more active and three times more selective to the C5–C11 fraction with a large content of unsaturated hydrocarbons, which is next to α‐olefins. The acid‐catalyzed conversion of n‐hexane and 1‐hexene, as model reactions, demonstrates that the improvement in the selectivity toward gasoline range hydrocarbons is due to the acid‐catalyzed reactions of the Fischer–Tropsch α‐olefins over the acidic zeolite. The formation of methane over the zeolite‐supported Co catalysts originates from direct CO hydrogenation and hydrocarbon hydrogenolysis on coordinatively unsaturated Co sites, which are stabilized as a consequence of a strong metal–zeolite interaction. Although the addition of either ZrO2 or Ru increases the catalyst reducibility considerably, it does not affect the product selectivity significantly.