Combination of Cu/ZnO methanol synthesis catalysts and ZSM-5 zeolites to produce oxygenates from CO2 and H2

Cu/ZnO methanol catalysts were deposited over several ZSM-5 acid zeolites to directly synthesise oxygenates (methanol and dimethyl ether) from a CO2/H2 feed. Catalysts were prepared by two different preparation methodologies: chemical vapour impregnation (CZZ-CVI) and oxalate gel precipitation (CZZ-OG). Chemical vapour impregnation led to Cu/ZnO being deposited on the zeolite surface, whilst oxalate gel precipitation led to the formation of Cu/ZnO agglomerates. For both sets of catalysts a higher concentration of mild and strong acid sites were produced, compared to the parent ZSM-5 zeolites, and CZZ-CVI had a higher concentration of acid sites compared to CZZ-OG. Nevertheless, CZZ-OG shows considerably higher oxygenate productivity, 1322 mmol Kgcat−1 h−1, compared to 192 mmol Kgcat−1 h−1 over CZZ-CVI (ZSM-5(50), 250 ℃, 20 bar, CO2/H2 = 1/3, 30 ml min−1), which could be assigned to a combination of smaller particle size and enhanced methanol mass transfer within the zeolites