A Pinch of Salt Improves n-Butanol Selectivity in the Guerbet Condensation of Ethanol over Cu-Doped Mg/Al Oxides

Improvement of processes that utilize renewable feedstocks to produce chemicals ordinarily derived from fossil carbon feedstocks is paramount to creating environmentally sustainable chemical and fuel industries. Catalytic conversion of biorefinery-derived ethanol via the Guerbet condensation has the potential to serve such a purpose. In this contribution, we demonstrate marked selectivity changes in the ethanol condensation over a copper-doped porous metal oxide catalyst upon a single exposure to ppm quantities of a soluble chloride source. Without this modification, ethyl acetate is the major product, with the others being n-butanol (principally) plus some 1-hexanol, butyl acetate, and ethyl butanoate. A single exposure to chloride increases activity and, more importantly, dramatically changes selectivity to give n-butanol and 1-hexanol as the largest products. X-ray diffraction and basicity measurements pre- and post-reaction were used to examine how chloride alters the properties of this Earth-abundant catalyst prepared by calcining a Cu-doped Mg/Al hydrotalcite.