Identifying the nature of the active sites in methanol synthesis over Cu/ZnO/Al(2)O(3) catalysts

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/Al(2)O(3) has been applied for more than 50 years. Still, the nature of the Zn species on the metallic Cu(0) 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/Al(2)O(3) 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 CO(2)-containing syngas mixtures when pulsing NH(3) or methylamines as basic probe molecules.