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Abstract

The impact of CO on the activation and reaction characteristics of Au/ZnO catalysts in methanol synthesis from a CO₂/H₂ 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 CO₂/H₂ after exposure to a CO/H₂ reaction gas mixture, while the steady-state activity is similar to that observed directly after oxidative pretreatment. For the reaction in CO/H₂, the much longer activation phase is accompanied by formation of CO₂ 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 CO₂/H₂. The consequences of these findings on the mechanistic understanding of methanol formation from CO₂/H₂ on Au/ZnO and for ZnO-supported catalysts in general are discussed.