Fischer-Tropsch synthesis (FTS) is an important industrial process converting syngas to long-chain hydrocarbons and other chemicals. Cobalt is commonly applied as catalyst for FTS, in particular for hydrogen rich feed gas such as syngas derived from natural gas. Recently, there has been increased interest in applying FTS to produce light olefins. Manganese is reported to promote light olefin production; however, the effects varies. In the present study, we investigate the effect of Mn on alumina-supported cobalt FTS catalysts. We show that Mn promotes the specific activity compared to the unpromoted Co-reference catalyst, independent on the preparation method. In addition, the selectivity towards light olefins increased as expected, as does the selectivity to C5+ hydrocarbons, the latter at the expense of methane. These results are discussed together with detailed experimental and theoretical investigations. The Mn-promoted Co catalysts were supported on Al2O3, and prepared by the incipient wetness impregnation method, both co-impregnated and sequential impregnation was applied. The activity tests were performed at industrially relevant conditions, i.e. 250 °C, 5 bar and H2/CO = 2.1. The performance of the different Mn-promoted catalysts was investigated and compared to that of a Co reference catalyst. The catalysts were characterized using standard methods including BET, TPR, H2 chemisorption, H2- and CO-TPD and XRD. Surface coverages and intrinsic activities were explored using Steady State Isotopic Transient Kinetic (SSITKA) experiments. X-ray photoelectron spectroscopy (XPS) was applied to assess the state of the catalysts for the as-prepared samples, after reduction, and post reaction conditions without exposing the samples to air. Addition density functional theory (DFT) calculations was utilized to further elucidate the promotional role of Mn.

Mn-promoted cobalt catalysts for light olefin production

2019 Spring National Meeting

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