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

Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO(2) 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 Cu(0.7)Zn(0.3) nanoparticles supported on ZnO/Al(2)O(3), γ-Al(2)O(3) and SiO(2) to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al(2)O(3) and CuZn/SiO(2), 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/SiO(2). Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO(2). 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.