Methanol synthesis from CO₂and H₂using supported Pd alloy catalysts

Abstract

A number of Pd based materials have been synthesised and evaluated as catalysts for the conversion of carbon dioxide and hydrogen to methanol, a useful platform chemical and hydrogen storage molecule. Monometallic Pd catalysts show poor methanol selectivity, but this is improved through the formation of Pd alloys, with both PdZn and PdGa alloys showing greatly enhanced methanol productivity compared with monometallic Pd/Al₂O₃ and Pd/TiO₂ catalysts. Catalyst characterisation shows that the 1 : 1 β-PdZn alloy is present in all Zn containing post-reaction samples, including PdZn/Ga₂O₃, with the Pd₂Ga alloy formed for the Pd/Ga₂O₃ sample. The heat of mixing was calculated for a variety of alloy compositions with high values determined for both PdZn and Pd₂Ga alloys, at <i>ca.</i> -0.6 eV per atom and <i>ca.</i> -0.8 eV per atom, respectively. However, ZnO is more readily reduced than Ga₂O₃, providing a possible explanation for the preferential formation of the PdZn alloy, rather than PdGa, when in the presence of Ga₂O₃.