Influence of CO on the Activation, O-Vacancy Formation, and Performance of Au/ZnO Catalysts in CO Hydrogenation to Methanol.

The impact of CO on the activation and reaction characteristics of Au/ZnO catalysts in methanol synthesis from a CO/H mixture was studied by kinetic, near ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy at the O K-edge, together with in situ Foureir transform infrared measurements. Transient measurements under up to industrial reaction conditions (50 bar, 240 °C) show a pronounced transient increase of the activity for methanol formation from CO/H after exposure to a CO/H reaction gas mixture, while the steady-state activity is similar to that observed directly after oxidative pretreatment. For the reaction in CO/H, the much longer activation phase is accompanied by formation of CO due to reaction of CO with the ZnO catalyst support. This leads to O-vacancy formation on the support at an extent significantly higher than in CO/H. The consequences of these findings on the mechanistic understanding of methanol formation from CO/H on Au/ZnO and for ZnO-supported catalysts in general are discussed.