Catalytic aerobic oxidation of lignin-based vanillyl alcohol under base–free conditions over an efficient and reusable LaFeO3 perovskite for vanillin production

Abstract

Conversion of lignin feedstocks into aromatic chemicals is a highly desirable target for biorefineries, and their depolymerization often requires high temperatures and harsh conditions. In this work, a process optimization involving several factors, including catalyst dosage, reaction temperature, reaction time, oxygen pressure and solvent effect, towards vanillin production from the oxidation of lignin-based vanillyl alcohol in a base-free solvent over a LaFeO₃ perovskite was proposed. The results pronounced that the LaFeO₃ perovskite exhibited excellent catalytic performance for affording a 100.0% conversion rate of vanillyl alcohol and 33.0% vanillin yield with the addition of 0.1 g LaFeO₃ dosage at 180 °C for 2 h under 1.0 MPa O₂ supply in ethyl acetate solvent. Furthermore, the presence of oxygen vacancies (Fe³⁺–□–Fe²⁺) in the LaFeO₃ perovskite contributed to combining with molecular oxygen to generate the active species [Fe³⁺O₂⁻], which played a key role in the oxidation of vanillyl alcohol and dominated the formation pathway of vanillin. On the other hand, reusability tests manifested that the performance of LaFeO₃ decreased gradually with the increase of consecutive runs and was strongly negatively related to the amount of carbon deposits, as carbon deposits would prevent vanillyl alcohol from being accessible to active sites. Nevertheless, the performance of the spent LaFeO₃ catalyst could be easily regenerated by a simple calcination approach. Overall, this work provides the possibility of a scalable strategy for constructing LaFeO₃-based perovskites as efficient and reusable catalysts for vanillin production from biorefinery lignin.