Identifying the nature of the active sites in methanol synthesis over Cu/ZnO/Al2O3 catalysts

Abstract

The heterogeneously catalysed reaction of hydrogen with carbon monoxide and carbon dioxide (syngas) to methanol is nearly 100 years old, and the standard methanol catalyst Cu/ZnO/Al₂O₃ has been applied for more than 50 years. Still, the nature of the Zn species on the metallic Cu⁰ particles (interface sites) is heavily debated. Here, we show that these Zn species are not metallic, but have a positively charged nature under industrial methanol synthesis conditions. Our kinetic results are based on a self-built high-pressure pulse unit, which allows us to inject selective reversible poisons into the syngas feed passing through a fixed-bed reactor containing an industrial Cu/ZnO/Al₂O₃ catalyst under high-pressure conditions. This method allows us to perform surface-sensitive operando investigations as a function of the reaction conditions, demonstrating that the rate of methanol formation is only decreased in CO₂-containing syngas mixtures when pulsing NH₃ or methylamines as basic probe molecules.

Methanol synthesis has a high potential for global CO₂ reduction. Here, the authors identify the oxidation state of the zinc sites on the metallic copper particles as partially positive for an industrial Cu/ZnO/Al₂O₃ catalyst under high-pressure reaction conditions.