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

DOI: 10.1039/D1CY02361F DOI Help

Authors: Ivalina B. Minova (University of St Andrews) , Michael Bühl (University of St Andrews) , Santhosh K. Matam (UK Catalysis Hub, Research Complex at Harwell; Cardiff University) , C. Richard A. Catlow (UK Catalysis Hub, Research Complex at Harwell; Cardiff University; University College London) , Mark D. Frogley (Diamond Light Source) , Gianfelice Cinque (Diamond Light Source) , Paul A. Wright (University of St Andrews) , Russell F. Howe (University of Aberdeen)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Catalysis Science & Technology , VOL 25

State: Published (Approved)
Published: February 2022
Diamond Proposal Number(s): 18680 , 20906 , 22347 , 23081

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.

Subject Areas: Chemistry

Instruments: B22-Multimode InfraRed imaging And Microspectroscopy

Added On: 03/03/2022 09:26

Discipline Tags:

Physical Chemistry Catalysis Chemistry

Technical Tags:

Spectroscopy Infrared Spectroscopy Synchtron-based Fourier Transform Infrared Spectroscopy (SR-FTIR)