Understanding the formation of higher alcohols in the liquid-phase ethanol condensation over copper-loaded hydrotalcite-derived mixed oxides

Abstract

The production of higher alcohols (C≥4) via ethanol liquid-phase condensation over different Cu-based catalysts is studied in this work. Experimental results demonstrate that dehydrogenation steps are more relevant than hydrogenation steps, according to the lack of improvement in activity when a bimetallic (Pd-Cu) catalyst. Thus, the sequential hydrogenation via Meerwein-Ponndorf-Verley (MPV) and surface-mediated H-transfer is identified as active enough to obtain the desired alcohols. The best results were obtained with a 20 % Cu/MgAl catalyst, showing more than 10 % of ethanol conversion (free solvent conditions) and 60 % selectivity to higher alcohols (16 % to C6 and C8 ones). Experiments with different feed compositions, including C4 alcohols and acetaldehyde, and a comprehensive analysis of all the results in terms of a mechanistic oligomerization model, demonstrate that the C-C coupling follows a step-growth model where the condensation between monomers coexists with the one involving oligomers.