The role of different state ZnO over non-stoichiometric Zn–Cr spinel catalysts for isobutanol synthesis from syngas

A series of Zn–Cr based catalysts were prepared using combustion method (Comb-ZC), impregnation method (Impr-ZC), coprecipitation method (Copr-ZC) and fractional precipitation method (Frac-ZC). The catalysts were then examined for their ability to selectively convert syngas into higher alcohol with a special alcohol distribution (high selectivity for isobutanol). CO conversion of ca. 25%, alcohol selectivity of ca. 49% and selectivity of ca. 26% for isobutanol was achieved over the Frac-ZC catalyst. The better performance of Frac-ZC catalyst could be explained by smaller zinc oxide particle size, the higher proportion of non-stoichiometric Zn–Cr spinel phase and the good synergic effects between zinc oxide phase and non-stoichiometric Zn–Cr spinel phase. The better reducibility as well as appropriate CO-absorption property of Frac-ZC catalyst also plays an essential role in the process of isobutanol synthesis. The study also shows the excess zinc oxide could aggravate the cation disorder distribution in non-stoichiometric Zn–Cr spinel structure that provide more defects and oxygen vacancies for boosting isobutanol formation.