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

Núria J Divins,Janis Timoshenko,See Wee Chee,Hemma Mistry,Ioannis Zegkinoglou,Adam S Hoffman,Ilya Sinev,Osman Karslıoğlu,Beatriz Roldan Cuenya,Alexey Boubnov,Marc Heggen,Jian Qiang Zhong,David Kordus,Rafal E Dunin-Borkowski,Arno Bergmann,Mauricio Lopez Luna,J Anibal Boscoboinik,Simon Widrinna,Simon R Bare

doi:10.1038/s41467-021-21604-7

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, γ-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.

Highlights

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
Investigations on Cu/ZnO systems revealed the presence of poorly crystalline ZnO interacting with Cu15, reversible changes of the Cu NP morphology depending on the reaction conditions[17,23], CuZn bulk alloy formation under severe reduction conditions (600 °C in CO/ H2)[17,26], and ZnO reduction and a stronger CuZn interaction for catalysts supported on SiO219–21
Energydispersive X-ray spectroscopy (EDX) maps in Fig. 1c and d confirm that the Cu and Zn signals, respectively, originate from the same NP

Summary

Introduction

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. Despite the tremendous effort dedicated to the investigation of this reaction, questions still remain on whether metallic Zn/brass is present under industrially relevant reaction conditions, its role in the reaction selectivity, and whether ZnO is needed as a part of the support, or small ZnO ensembles in direct contact with Cu within a NP can serve to activate CO2 To address these questions, here we use morphologically and chemically well-defined Cu and CuZn NP catalysts that help close the materials gap between the heterogeneous industrial catalysts and the model single-crystal systems previously studied, while addressing the pressure gap through operando spectroscopic characterization at industrially relevant high-pressure conditions. We are able to shed light on the dynamic evolution of the metal NP/oxide support interface during CO2 + CO hydrogenation

Methods

Results

Conclusion