Boosting Higher Alcohols Selectivity via Regulating Basicity of Ni/Hydroxyapatite in Ethanol Upgrading

Upgrading bioethanol to higher alcohols (C6+–OH) is an environmentally friendly process for the production of high-value-added chemicals. However, a low selectivity for C6+–OH is generally obtained due to the step-growth of the carbon chain, which leads to a preponderance of butanol in the product. In this work, we report base-Ni synergistic catalysis, with Niδ+ on hydroxyapatite (HAP). The results showed that ethanol could be quickly dehydrogenated, continuously condensed, and finally hydrogenated to C6+ alcohols under the synergistic action of Niδ+ and Ca–[O2–]–Ca active site pairs. The loading of Ni on the OH–-rich HAP4 surface promotes the formation of more Niδ+ and Ca–[O2–]–Ca, which has been shown to be beneficial for ethanol upgrading. Especially, the ethanol reaction rate and the yield of C6+–OH are directly proportional to the amount of Niδ+ and the concentration of Ca–[O2–]–Ca, respectively. The situ ethanol infrared results demonstrated the catalytic ability of different basic catalysts for intermediate aldehydes, which led to differences in the selectivity of C6+–OH. A selectivity of 62.4% to C6+–OH with an ethanol conversion of 63.6% has been achieved on HAP4–0.5Ni with abundant Niδ+ and Ca–[O2–]–Ca sites under optimized conditions. Combined with the physical and chemical properties of the catalyst and reaction results, the mechanism of upgrading ethanol to C6+–OH on Ni/HAP was also proposed.