Heterogeneous Catalytic Conversion

Heterogeneous Catalytic Conversion of Dry Syngas to Ethanol andHigher Alcohols on Cu-Based CatalystsABSTRACT: Ethanol and higher alcohols have been identifiedas potential fuel additives or hydrogen carriers for use in fuelcells. One method of ethanol production is catalytic conversionof syngas (a mixture of CO, H2, CO2, and H2O), derived frombiomass, coal, or natural gas. Thermodynamics of CO hydrogenationshows that ethanol is favored as the sole product atconditions of practical interest, but if methane is allowed asproduct in this analysis, essentially no ethanol is formed atequilibrium. The kinetics of ethanol formation must therefore be maximized. Although rhodium-based catalysts give C2þoxygenates with high selectivity, their prohibitive cost has spurred research on less expensive copper-based alternatives. Copperbasedcatalysts require an optimum amount of promoter to suppress undesired reactions and maximize the yields of ethanol andhigher alcohols. Common promoters include alkali, transition metals and their oxides, and rare earth oxides. Careful selection ofoperating variables is also necessary to achieve the desired activity and selectivity. This review describes the effects of promoters,supports, and operating conditions on the performance of copper-based catalysts for conversion of dry syngas to ethanol and higheralcohols. Proposed mechanisms from the literature for ethanol and higher-alcohol synthesis are outlined.KEYWORDS: Cu-based catalyst, CO hydrogenation, syngas, ethanol, higher alcohols, fuel