Influence of the ZnCrAl Oxide Composition on the Formation of Hydrocarbons from Syngas

Tobias Kull; Thomas Wiesmann; Andrea Wilmsen; Maximilian Purcel; Martin Muhler; Heiko Lohmann; Barbara Zeidler-Fandrich; Ulf-Peter Apfel

doi:10.1021/acsomega.2c05225

Influence of the ZnCrAl Oxide Composition on the Formation of Hydrocarbons from Syngas

ACS Omega. 2022 Nov 16;7(47):42994-43005. doi: 10.1021/acsomega.2c05225. eCollection 2022 Nov 29.

Authors

Tobias Kull¹, Thomas Wiesmann², Andrea Wilmsen², Maximilian Purcel³, Martin Muhler³, Heiko Lohmann², Barbara Zeidler-Fandrich², Ulf-Peter Apfel^{1

2}

Affiliations

¹ Inorganic Chemistry I, Ruhr-Universität Bochum, Universitätsstraße 150, D-44780 Bochum, Germany.
² Fraunhofer UMSICHT, Osterfelder Straße 3, D-46047 Oberhausen, Germany.
³ Laboratory of Industrial Chemistry, Ruhr-Universität Bochum, Universitätsstraße 150, D-44780 Bochum, Germany.

Abstract

The conversion of syngas into value-added hydrocarbons gains increasing attention due to its potential to produce sustainable platform chemicals from simple starting materials. Along this line, the "OX-ZEO" process that combines a methanol synthesis catalyst with a zeolite, capable of catalyzing the methanol-to-hydrocarbon reaction, was found to be a suitable alternative to the classical Fischer-Tropsch synthesis. Hitherto, understanding the mechanism of the OX-ZEO process and simultaneously optimizing the CO conversion and the selectivity toward a specific hydrocarbon remains challenging. Herein, we present a comparison of a variety of ZnCrAl oxides with different metal ratios combined with a H-ZSM-5 zeolite for the conversion of syngas to hydrocarbons. The effect of aluminum on the catalytic activity was investigated for ZnCrAl oxides with a Zn/Cr ratio of 4:1, 1:1, and 1:2. The product distribution and CO conversion were found to be strongly influenced by the Zn/Cr/Al ratio. Although a ratio of Zn/Cr of 1:2 was best to produce lower olefins and aromatics, with aromatic selectivities of up to 37%, catalysts with a 4:1 ratio revealed high paraffin selectivity up to 52%. Notably, a distinct effect of aluminum in the oxide lattice on the catalytic activity and product selectivity was observed, as a higher Al content leads to a lower CO conversion and a changed product spectrum. We provide additional understanding of the influence of different compositions of ZnCrAl oxides on their surface properties and the catalytic activity in the OX-ZEO process. Furthermore, the variation of the zeolite component supports the important role of the channel topology of the porous support material for the hydrocarbon production. In addition, variation of the gas hourly space velocity showed a correlation of contact time, CO conversion, and hydrocarbon selectivity. At a gas hourly space velocity of 4200 mL/g_cat h, CO conversion as high as 44% along with a CO₂ selectivity of 42% and a lower paraffin (C₂ ⁰-C₄ ⁰) selectivity of 41% was observed.