Selective Synthesis of Methanol and Higher Alcohols over Cs/Cu/ZnO/Al2O3 Catalysts

A variety of catalysts for higher alcohol synthesis from syngas have been under development for potential commercial application, which are still facing challenges, including poor carbon efficiency due to low selectivity to desired products. In this contribution, we systematically studied the effects of temperature, loading of K and Cs, space velocity, and CO2 addition on the alkali-promoted Cu/ZnO/Al2O3 catalysts in order to achieve a high yield of desired higher alcohol products. Our particular focus was to maximize the carbon efficiency by restricting the amount of undesired byproducts, such as lower alkanes and CO2 that could be formed. Among K and Cs promoted Cu/ZnO/Al2O3 catalysts studied, Cs-promoted Cu/ZnO/Al2O3 catalysts exhibit better performance to higher alcohols and higher carbon efficiency than K-promoted counterparts under similar conditions studied. 1.64 mol % Cs-promoted Cu/ZnO/Al2O3 catalyst achieves the highest selectivity to higher alcohols (24.9%) at a CO conversion of 41.6% under 290 degrees C, 1875 mL g(cat)(-1)h(-1), 5.4 MPa. The presence of a small amount of CO2 of 2.5 mol % in the feed has negligible effect on the productivity of higher alcohols but significantly suppresses the formation of CO2 byproduct. With the further increase of CO2 in the feed, the formation of CO2 can be further suppressed but at the expense of productivity loss of higher alcohols, which is probably due to the neutralization of surface Cs sites. The best carbon efficiency can be achieved at 8% mol CO2 in the feed.