The changing nature of the active site of Cu-Zn-Zr catalysts for the CO2 hydrogenation reaction to methanol

The effects of the most largely employed preparation methods (i.e., coprecipitation with sodium bicarbon-ate, complexation with citric acid, gel-oxalate coprecipitation) on the structure and catalytic behaviourof Cu-Zn-Zr systems for methanol synthesis from hydrogenation of carbon dioxide have been studied.The characterization data of the dried, calcined and reduced catalysts showed that the physico-chemicalproperties can be controlled by varying composition and preparation method. The catalyst obtainedby the gel-coprecipitation procedure showed the highest catalytic activity in the TRrange 453-513 K,3.0 MPa and 10,000 h-1, due to a superior functionality in the CO2and H2activation. An adequate balancebetween metal and oxide surface sites, in correspondence of a well defined particle size, was proposedto be crucial to design active and selective catalysts for such reaction. The good performance of the gel-oxalate coprecipitated catalyst was confirmed by an endurance test (?200 h), in which a constant andremarkable methanol space-time-yield value of 1200 g kgcat-1h-1at ?10% CO2conversion was obtained(TR, 513 K; PR, 3.0 MPa).