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

Abstract

The effects of the most largely employed preparation methods (i.e., coprecipitation with sodium bicarbonate, complexation with citric acid, gel-oxalate coprecipitation) on the structure and catalytic behaviour of 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-chemical properties can be controlled by varying composition and preparation method. The catalyst obtained by the gel-coprecipitation procedure showed the highest catalytic activity in the TR range 453–513K, 3.0MPa and 10,000h−1, due to a superior functionality in the CO2 and H2 activation. An adequate balance between metal and oxide surface sites, in correspondence of a well defined particle size, was proposed to 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 (≈200h), in which a constant and remarkable methanol space–time-yield value of 1200gkgcat−1h−1 at ≈10% CO2 conversion was obtained (TR, 513K; PR, 3.0MPa).