Carbon modified Fe–Mn–K catalyst for the synthesis of light olefins from CO hydrogenation

Abstract

A novel carbon modified Fe-Mn-K catalyst for light olefin synthesis from CO hydrogenation was prepared by the sol-gel method. The effect of carbon contents on the structure and performance of the catalysts was investigated. With the incorporation of carbon, the catalysts showed much different morphology from that prepared by co-precipitation. At the carbon contents between 0.23 and 6.66 wt%, the catalyst particles were around 10 nm while the carbon phase was amorphous. The activity test results indicated that the catalysts (Fe/Mn/K molar ratio = 60/20/1) with carbon modification showed high conversion of CO and selectivity to light olefins with low CH 4 selectivity. At the carbon content of 2.43 wt%, the total C 2 -C 4 content in all hydrocarbons and O/P (olefin/paraffin) in the C 2 -C 4 fraction was 49 wt% and 4.89, respectively. Furthermore, when the K content in the catalyst was reduced by half, the C 2 -C 4 olefin yield raised from 60 to 71 g/Nm 3 syngas. The formation of carbon provided a more hydrophobic surface, which inhibited the water gas shift reaction (WGSR) and caused a decrease in CO 2 selectivity. The dispersion of carbon favored the formation and stabilization of small particles, and promoted the production of light olefins via suppressing the chain propagation.

Catalysts for Production of Lower Olefins from Synthesis Gas: A Review

“…Another strategy used by several researchers to improve the catalytic performance of catalysts for the direct production of lower olefins from synthesis gas is the use of Fe-based bimetallic catalysts. Among them, Co–Fe ,,− and Fe–Mn ,,,,− , catalysts are the most studied systems. In the case of Co–Fe catalysts, the researchers intended to improve catalytic stability and activity of the already olefin-selective Fe catalysts by alloying it with a more active Fischer–Tropsch catalyst like Co.…”

Recent Advances in Bifunctional Catalysts for the Fischer–Tropsch Process: One-Stage Production of Liquid Hydrocarbons from Syngas

“…For example, Cu improves metal reducibility through the hydrogen spillover mechanism. ,− It has been suggested in recent studies that alkali promoters transfer electrons to the Fe surface and facilitate the adsorption and dissociation of CO, suppressing H 2 adsorption, thus explaining the decrease in CH 4 selectivity . The most effective promoter for the suppression of methane production in the presence of Fe-based catalysts is K, which has been demonstrated to inhibit surface carbon hydrogenation and promote carbon chain growth. ,− Nevertheless, a major challenge in applied iron-based bifunctional catalysts for the one-stage FT process is to prevent migration of the alkali promoters from the FT site to the acid site. This migration implies that the alkali promoters neutralize the acid sites, leading to the deactivation of this part of the catalyst, which is undesirable .…”

N-doped graphene as an electron donor of iron catalysts for CO hydrogenation to light olefins

“…It is quite remarkable since iron based catalysts usually give a wide distribution of hydrocarbons with a low selectivity toward light olefins (usually no more than 40%) when directly supported on carbon materials without promoters like S, K and Mn. 10,12,14 The nitrogen here may play the role like that of the K and Mn promoters that inhibited the hydrogenation of olefins and thus increased the selectivity of olefins. In addition, as shown in Table S3, with the nitrogen content increasing from 4.5% to 16.4%, CH 4 selectivity will increase from 14.2% to 29.2%, while the selectivity of C 5+ will reduce from 39.4% to 15.5% at GHSV = 5000 h À1 , 340 1C and 1.0 MPa, indicating that the growth of carbon chain was also restrained by increasing the nitrogen content.…”

“…For example, Na and K additives can be used as the electron donor to increase the selectivity of the light olefins. [12][13][14] Different supports such as silica, alumina, magnesia, zeolite, carbon, SiC etc. also have a crucial effect on the selectivity of these catalysts due to the different electronic interactions between them.…”