Synthesis of cyclohexanol and ethanol via the hydrogenation of cyclohexyl acetate with Cu₂Zn_x /Al₂O₃catalysts

Cyclohexanol (CHOL), as a value-added chemical, has attracted much attention due to its huge application market. The hydrogenation of cyclohexyl acetate (CHA), derived from the esterification of acetic acid and cyclohexene, not only provides a novel route to yield CHOL and ethanol (EtOH), but also rationally utilizes excess acetic acid. In this work, a series of Zn-promoted Cu/Al2O3 catalysts were prepared via a deposition-precipitation method for the liquid-phase hydrogenation of CHA to yield CHOL and EtOH. As a result, the addition of Zn species with an optimal amount greatly improved the activity and selectivity to CHOL and EtOH. A Cu2Zn1.25/Al2O3 catalyst, which contained 16.2 wt% Cu and 9.6 wt% Zn, exhibited superior catalytic performance with 93.9% conversion of CHA and 97.2% selectivity to EtOH along with 97.1% selectivity to CHOL in a batch reactor. The Cu2Zn1.25/Al2O3 catalyst also showed excellent stability and there was no deactivation after five runs. Based on detailed characterization, it was revealed that the addition of Zn species increased the dispersion of Cu particles, adjusted the strength and amount of acid sites, and changed the electronic properties of Cu species and thus the ratio of Cu+/(Cu0 + Cu+).