High-efficiency oxidative esterification of furfural to methylfuroate with a non-precious metal Co-N-C/MgO catalyst

Abstract

From both fundamental and practical perspectives, the production of chemicals from biomass resources using high-efficiency non-precious metal catalysts is important. However, many processes require addition of stoichiometric or excess quantities of base, which leads to high energy consumption, leaching problems, and side reactions. In this study, we investigated the high-efficiency oxidative esterification of furfural to methylfuroate by molecular oxygen with a Co-N-C/MgO catalyst. The catalyst was prepared by direct pyrolysis of a cobalt(II) phenanthroline complex on MgO at 800 °C under N 2 atmosphere. From furfural, 93.0% conversion and 98.5% selectivity toward methylfuroate were achieved under 0.5 MPa O 2 with reaction at 100 °C for 12 h without a basic additive. The conversion and selectivity were much higher than those obtained with cobalt catalysts produced by pyrolysis of a cobalt(II) phenanthroline complex on activated carbon or typical basic supports, including NaX, NaY, and CaO. X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and experimental results revealed that the high efficiency of Co-N-C/MgO for production of methylfuroate was closely related to the cobalt-nitrogen-doped carbon species and its catalytic ability in hydrogen abstraction. In contrast, Co-N-C(HCl) that synthesized by removing MgO with HCl from Co-N-C/MgO, as the catalyst produced mainly an acetal as a condensation product, and chloride ions had a negative effect on the oxidative esterification. Although the catalytic performance of the cobalt-nitrogen-doped carbon species was greatly affected by HCl treatment, it could be recovered to a great extent by addition of MgO. Moreover, changes in the oxygen pressure hardly affected the oxidative esterification of furfural with Co-N-C/MgO. This study not only provides an effective approach to prepare methylfuroate, but also for designing high-performance non-precious metal catalysts for the oxidative esterification of biomass-derived compounds. The non-precious metal catalyst Co-N-C/MgO showed high efficiency in the oxidative esterification of furfural to methylfuroate (93.0% conversion and 98.5% selectivity). The reaction with the catalyst Co-N-C(HCl) proceeded via a condensation pathway with acetal as the dominant product.