Understanding Mn-modulated restructuring of Fe-based catalysts for controlling selectivity in CO2 hydrogenation to olefins
Qingxin Yang, Elizaveta A. Fedorova, Dong‐Bo Cao, Erisa Saraçi, Vita A. Kondratenko, Carsten Kreyenschulte, Henrik Lund, Stephan Bartling, Jana Weiß, Dmitry E. Doronkin, Jan‐Dierk Grunwaldt, Angelika Brückner, Haijun Jiao, Evgenii V. Kondratenko
Abstract
Abstract For CO 2 hydrogenation over iron-based catalysts, revealing the promoting effect of manganese and the nature of catalytically active sites remains a challenge that hinders targeted catalyst design. Here we elucidate the manganese-modulated restructuring of such catalysts during preconditioning and CO 2 hydrogenation using in situ X-ray absorption spectroscopy. The reaction-induced decoration of the surface of iron carbide with a MnO-containing layer is essential to hinder methane formation in favour of C 2 –C 4 olefins and C 5+ hydrocarbons. The selectivity changes were rationalized via spatially resolved steady-state and time-resolved (micro)kinetic tests combined with density functional theory calculations. The promoter affects the ability of iron carbide to generate surface species from H 2 , CO 2 and C 2 H 4 , thus controlling the surface C/H ratio, which is decisive for product selectivity. Consequently, the design of efficient multi-component heterogeneous catalysts requires a thorough understanding of the optimal catalyst architecture and, in particular, how to generate and stabilize it under reaction conditions.