CO2 hydrogenation to methanol over Cu/ZnO catalysts synthesized via a facile solid-phase grinding process using oxalic acid

Reduced Cu/ZnO catalyst was synthesized through solid phase grinding of the mixture of oxalic acid, copper nitrate and zinc nitrate, followed by subsequent calcination in N-2 atmosphere without further H-2 reduction. The catalysts were characterized by various techniques, such as XRD, TG-DTA, TPR and N2O chemisorption. Characterization results suggested that during the calcination in N-2, as-ground precursor (oxalate complexes) decomposed to CuO and ZnO, releasing considerable amount of CO, which could be used for in situ reduction of CuO to Cu-o. The in situ reduced O/I-Cu/ZnO catalyst was evaluated in CO2 hydrogenation to methanol, which exhibited superior catalytic performance to its counterpart O/H-Cu/ZnO catalyst obtained through conventional H-2 reduction. The decomposition of precursor and reduction of CuO happened simultaneously during the calcination in N-2, preventing the growth of active Cu-0 species and aggregation of catalyst particles, which was inevitable during conventional H-2 reduction process. This method is simple and solvent-free, opening a new route to prepare metallic catalysts without further reduction.