Ca Cations Impact the Local Environment inside HZSM-5 Pores during the Methanol-to-Hydrocarbons Reaction

Anna Liutkova; Hao Zhang; Jérôme F M Simons; Brahim Mezari; Marta Mirolo; Gustavo A Garcia; Emiel J M Hensen; Nikolay Kosinov

doi:10.1021/acscatal.3c00059

Ca Cations Impact the Local Environment inside HZSM-5 Pores during the Methanol-to-Hydrocarbons Reaction

ACS Catal. 2023 Feb 23;13(6):3471-3484. doi: 10.1021/acscatal.3c00059. eCollection 2023 Mar 17.

Authors

Anna Liutkova¹, Hao Zhang¹, Jérôme F M Simons¹, Brahim Mezari¹, Marta Mirolo², Gustavo A Garcia³, Emiel J M Hensen¹, Nikolay Kosinov¹

Affiliations

¹ Laboratory of Inorganic Materials and Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
² ESRF, The European Synchrotron, 71 Avenue des Martyrs, CS40220, 38043 Grenoble, Cedex 9, France.
³ Synchrotron SOLEIL, L'Orme des Merisiers, St Aubin, B.P. 48, 91192 Gif sur Yvette, France.

Abstract

The methanol-to-hydrocarbons (MTH) process is an industrially relevant method to produce valuable light olefins such as propylene. One of the ways to enhance propylene selectivity is to modify zeolite catalysts with alkaline earth cations. The underlying mechanistic aspects of this type of promotion are not well understood. Here, we study the interaction of Ca²⁺ with reaction intermediates and products formed during the MTH reaction. Using transient kinetic and spectroscopic tools, we find strong indications that the selectivity differences between Ca/ZSM-5 and HZSM-5 are related to the different local environment inside the pores due to the presence of Ca²⁺. In particular, Ca/ZSM-5 strongly retains water, hydrocarbons, and oxygenates, which occupy as much as 10% of the micropores during the ongoing MTH reaction. This change in the effective pore geometry affects the formation of hydrocarbon pool components and in this way directs the MTH reaction toward the olefin cycle.