Synergy of nanoconfinement and promotion in the design of efficient supported iron catalysts for direct olefin synthesis from syngas

Abstract

Light olefins are important building blocks in chemical industry. High temperature Fischer-Tropsch synthesis provides a remarkable opportunity for direct synthesis of light olefins from syngas derived from a wide range of alternative feedstocks (biomass, organic or plastic wastes, natural gas, shale gas or coal). The present work focuses on the combined effects of the iron nanoconfinement, on the one hand, and promotion with bismuth and lead, on the other hand, on the structure and catalytic performance of iron catalysts supported by carbon nanotubes in high temperature Fischer-Tropsch synthesis. A wide range of techniques (TEM, XRD, TPR, synchrotron-based XPS, in-situ XANES and in-situ magnetic measurements) was used to characterize the catalysts. Iron carbidization proceeds much easier for iron species confined inside carbon nanotubes and promoted with Bi and Pb. Iron nanoconfinement inside carbon nanotubes combined with the promotion with Bi or Pb result in a 10-fold higher yield of light olefins. Nanoconfinement in carbon nanotubes mostly leads to better iron dispersion and stability, while the intrinsic activity is only slightly affected. Promotion with Bi and Pb results in a major increase in the site intrinsic activity in both confined and non-confined catalysts. Moreover, over the optimised promoted and confined catalysts, Fischer-Tropsch synthesis occurs even under atmospheric pressure with high conversion and enhanced selectivity to light olefins.