The state of zinc in methanol synthesis over a Zn/ZnO/Cu(211) model catalyst

The active chemical state of zinc (Zn) in a zinc-copper (Zn-Cu) catalyst during carbon dioxide/carbon monoxide (CO2/CO) hydrogenation has been debated to be Zn oxide (ZnO) nanoparticles, metallic Zn, or a Zn-Cu surface alloy. We used x-ray photoelectron spectroscopy at 180 to 500 millibar to probe the nature of Zn and reaction intermediates during CO2/CO hydrogenation over Zn/ZnO/Cu(211), where the temperature is sufficiently high for the reaction to rapidly turn over, thus creating an almost adsorbate-free surface. Tuning of the grazing incidence angle makes it possible to achieve either surface or bulk sensitivity. Hydrogenation of CO2 gives preference to ZnO in the form of clusters or nanoparticles, whereas in pure CO a surface Zn-Cu alloy becomes more prominent. The results reveal a specific role of CO in the formation of the Zn-Cu surface alloy as an active phase that facilitates efficient CO2 methanol synthesis..

Automated summary

This study used X-ray photoelectron spectroscopy to investigate the active state of Zn in a Zn-Cu catalyst during CO2/CO hydrogenation and the nature of reaction intermediates. The results showed that CO2 hydrogenation preferentially formed ZnO clusters or nanoparticles, while pure CO hydrogenation resulted in the formation of a surface Zn-Cu alloy. CO played a specific role in the formation of the Zn-Cu alloy, which acted as an active phase in facilitating efficient CO2 methanol synthesis.