Revealing the role of CO during CO2 hydrogenation on Cu surfaces with in situ soft X-ray spectroscopy

DOI: 10.1021/jacs.2c12728

Authors: Jack E. N. Swallow (University of Oxford) , Elizabeth S. Jones (University of Oxford) , Ashley R. Head (Brookhaven National Laboratory) , Joshua S. Gibson (University of Oxford) , Roey Ben David (Weizmann Institute of Science) , Michael W. Fraser (University of Oxford) , Matthijs A. Van Spronsen (Diamond Light Source) , Shaojun Xu (Catalysis Hub, Research Complex at Harwel) , Georg Held (Diamond Light Source) , Baran Eren (Weizmann Institute of Science) , Robert S Weatherup (University of Oxford; Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society , VOL 10

State: Published (Approved)
Published: March 2023
Diamond Proposal Number(s): 25834

Abstract: The reactions of H2, CO2, and CO gas mixtures on the surface of Cu at 200 °C, relevant for industrial methanol synthesis, are investigated using a combination of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and atmospheric-pressure near edge X-ray absorption fine structure (AtmP-NEXAFS) spectroscopy bridging pressures from 0.1 mbar to 1 bar. We find that the order of gas dosing can critically affect the catalyst chemical state, with the Cu catalyst maintained in a metallic state when H2 is introduced prior to the addition of CO2. Only on increasing the CO2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO2 is present, the surface oxidizes to Cu2O and CuO, and the subsequent addition of H2 partially reduces the surface to Cu2O without recovering metallic Cu, consistent with a high kinetic barrier to H2 dissociation on Cu2O. The addition of CO to the gas mixture is found to play a key role in removing adsorbed oxygen that otherwise passivates the Cu surface, making metallic Cu surface sites available for CO2 activation and subsequent conversion to CH3OH. These findings are corroborated by mass spectrometry measurements, which show increased H2O formation when H2 is dosed before rather than after CO2. The importance of maintaining metallic Cu sites during the methanol synthesis reaction is thereby highlighted, with the inclusion of CO in the gas feed helping to achieve this even in the absence of ZnO as the catalyst support.

Subject Areas: Chemistry


Instruments: B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS

Added On: 15/03/2023 09:34

Documents:
jacs.2c12728.pdf

Discipline Tags:

Earth Sciences & Environment Climate Change Physical Chemistry Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Near Edge X-ray Absorption Fine Structures (NEXAFS)