Selective hydroconversion of lignin-derived compounds over a Ni/hydroxyapatite

Abstract

Catalytic hydroconversion (CHC) of lignin-derived compounds (LDCs) to cyclanes and cyclohexanol (CHII) promotes the value-added utilization of LDCs. Nevertheless, designing a highly active and selective catalyst for this purpose remains a challenge. Herein, Ni/hydroxyapatite (HAP) was fabricated by a slightly modified deposition–precipitation approach and employed for the CHC of benzyloxybenzene (BOB) and phenethoxybenzene (PEOB) under different conditions. Consequently, BOB was fully converted with CHII and methylcyclohexane (MCH) as the main products (MPs) in the yield of 94.8 and 100 % under the optimum conditions of 20 mg Ni15/HAP, 140 °C, 4 MPa H2, and 4 h, while complete conversion of PEOB to CHII and ethylcyclohexane (ECH) as MPs proceeded under initial hydrogen pressure of 4 MPa at 180 °C for 4 h. In addition, other lignin-related model compounds can also be selectively hydrogenated to cyclanes and CHII, suggesting the high activity and selectivity of Ni15/HAP. Meanwhile, based on the product distribution and Ni15/HAP characterization, relevant mechanisms were proposed. Specifically, BOB conversion to CHII and MCH via the >CH–O– bond cleavage induced by H− addition, abstraction of H+ by the resulting phenoxy anion from the catalyst surface, and benzene ring hydrogenation, whereas conversion of PEOB to CHII and ECH was similar to BOB. Furthermore, Ni15/HAP displays an excellent reusability.