Operando high-pressure investigation of size-controlled CuZn catalysts for the methanol synthesis reaction

Abstract

Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu0.7Zn0.3 nanoparticles supported on ZnO/Al2O3, ¿-Al2O3 and SiO2 to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al2O3 and CuZn/SiO2, but the methanol yield decreases with time on stream for the latter sample. Operando X-ray absorption spectroscopy data reveal the formation of reduced Zn species coexisting with ZnO on CuZn/SiO2. Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO2. In this work we demonstrate the beneficial effect of Zn, even in diluted form, and highlight the influence of the oxide support and the Cu-Zn interface in the reactivity.

This work was funded by the European Research Council under grant ERC-OPERANDOCAT (ERC-725915) and the Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy—EXC 2008 – 390540038—UniSysCat and EXC 1069 - RESOLV. The majority of the XAS work was performed at Stanford Synchrotron Radiation Lightsource (beamline 2–2) of SLAC National Accelerator Laboratory, supported by the Office of Basic Energy Sciences of the US Department of Energy (DOE) under Contract No. DE-AC02-76SF00515 and by Co-ACCESS (Chemical Sciences, Geosciences, and Biosciences Division). Additional studies were carried out at the National Synchrotron Light Source II (NSLS-II, IOS and QAS beamlines) of Brookhaven National Laboratory supported by DOE under Contract No. DE-SC0012704. We also acknowledge MAX IV Laboratory (Sweden) for access to the Beamline HIPPIE and Andrey Shavorskiy for his assistance during the NAP-XPS measurements. Max IV is funded by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. We further thank Olaf Timpe, Stephanie Kühl, and Frank Girgsdies (FHI) for the ICP and some of the XRD measurements and Alba Titze Alonso (RUB) for her assistance with sample preparation.

Peer Reviewed

Postprint (published version)