Carbene-like reactivity of methoxy groups in a single crystal SAPO-34 MTO catalyst

Ivalina B. Minova, Michael Bühl, Santhosh K. Matam, C. Richard A. Catlow, Mark D. Frogley, Gianfelice Cinque, Paul A. Wright, Russell F. Howe*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Synchrotron FTIR microspectroscopy coupled with mass spectrometric analysis of desorbed products has been used to investigate the initial stages of the methanol to olefins (MTO) reaction in single crystals of SAPO-34. Surface methoxy groups (SMS) are key to initial dimethylether (DME) and subsequent carbon-carbon bond formation. Deprotonation of SMS is the critical first step in direct olefin formation at low temperatures and DME is not involved in the carbon-carbon forming step. Experiments with CD3OH confirm the deprotonation step and show an inverse kinetic isotope effect consistent with irreversible deprotonation. The subsequent formation of alkoxide species, which are the precursors of the olefinic hydrocarbon pool present in working MTO catalysts, is initiated via insertion of surface carbene-like species into adjacent SMS. The observed induction period for this process is determined by the limited mobility of SMS and/or carbene species. Olefins formed from cracking of the alkoxide species then transmit carbon-carbon bond formation through the SAPO-34 by rapid diffusion and reaction with further SMS. Acetyl species seen with methanol at higher temperatures support the insertion of CO into SMS suggested in the literature, but these species do not play a role in direct olefin formation.

Original languageEnglish
Pages (from-to)2289-2305
Number of pages17
JournalCatalysis Science and Technology
Volume12
Issue number7
Early online date21 Feb 2022
DOIs
Publication statusPublished - 7 Apr 2022

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