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. Graphical Abstract: [Figure not available: see fulltext.]