Bimetallic Ni–Cu/CeO2–Al2O3 catalysts for conversion of ethanol to higher alcohols

A sustainable route for the synthesis of butanol and higher alcohols via condensation of bio-ethanol has been investigated on a series of modified nickel on alumina catalysts. To maximize the selectivity for butanol, alumina support has been modified with ceria (5 wt% of alumina) to enhance basicity. Copper is added as the second metal, to promote dehydrogenation-hydrogenation functionality. Ni–Cu bi-metallic catalysts with varying proportions of the metals, i.e., bimetallic 5.5% Cu-2.5% Ni, 4% Cu-4% Ni and 2% Cu-6% Ni catalysts and 8% Cu, 8% Ni (all wt%) mono metallic catalysts, supported on ceria modified Al2O3, have been prepared by wet impregnation and characterized by XRD, BET, TEM, NH3– and CO2 TPD, H2–TPR and XPS. Condensation of ethanol has been carried out in Parr reactor, in batch mode (8 h, at 200 °C, after pressurization with nitrogen (10 bar). Mono metallic Ni displays ethanol conversion of 41%, with butanol selectivity of 48.6%. Whereas, mono metallic Cu catalyst, under identical reaction conditions, displays high butanol selectivity (64%) but very low ethanol conversion (18%). Bimetallic catalyst with composition 5.5% Cu-2.5% Ni, displays higher butanol selectivity of 55.6% with conversion at 32.2%. Thus, by optimization of Cu and Ni composition and support acidity/basicity, it is possible to maximize butanol selectivity. XPS and TPR studies indicate Ni–Cu alloy formation, especially in the compositions, 4% Ni-4% Cu, and 2.5% Ni-5.5% Cu. Presence Ni–Cu alloys, moderation of acidity and increase in medium and strong basic sites facilitate higher butanol selectivity.