| Autor: |
Swallow JEN; Department of Materials, University of Oxford, Parks Road, Oxford, Oxfordshire OX1 3PH, U.K., Jones ES; Department of Materials, University of Oxford, Parks Road, Oxford, Oxfordshire OX1 3PH, U.K., Head AR; Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton 11973, New York, United States., Gibson JS; Department of Materials, University of Oxford, Parks Road, Oxford, Oxfordshire OX1 3PH, U.K., David RB; Department of Chemical and Biological Physics, Weizmann Institute of Science, 234 Herzl Street, 76100 Rehovot, Israel., Fraser MW; Department of Materials, University of Oxford, Parks Road, Oxford, Oxfordshire OX1 3PH, U.K., van Spronsen MA; Diamond Light Source, Didcot, Oxfordshire OX11 0DE, U.K., Xu S; Catalysis Hub, Research Complex at Harwell, Didcot, Oxfordshire OX11 0FA, U.K., Held G; Diamond Light Source, Didcot, Oxfordshire OX11 0DE, U.K., Eren B; Department of Chemical and Biological Physics, Weizmann Institute of Science, 234 Herzl Street, 76100 Rehovot, Israel., Weatherup RS; Department of Materials, University of Oxford, Parks Road, Oxford, Oxfordshire OX1 3PH, U.K.; Diamond Light Source, Didcot, Oxfordshire OX11 0DE, U.K. |
| Abstrakt: |
The reactions of H 2 , CO 2 , 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 H 2 is introduced prior to the addition of CO 2 . Only on increasing the CO 2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO 2 is present, the surface oxidizes to Cu 2 O and CuO, and the subsequent addition of H 2 partially reduces the surface to Cu 2 O without recovering metallic Cu, consistent with a high kinetic barrier to H 2 dissociation on Cu 2 O. 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 CO 2 activation and subsequent conversion to CH 3 OH. These findings are corroborated by mass spectrometry measurements, which show increased H 2 O formation when H 2 is dosed before rather than after CO 2 . 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. |
