Impact of nitrogen species and content on the catalytic activity to C–O bond cleavage of lignin over N-doped carbon supported Ru-based catalyst

Abstract

The selective cleavage of C–O bond in lignin is the key to convert them into aromatic compounds and then to produce liquid fuels and chemicals. N-doped carbon nanosheets were obtained by direct pyrolysis of glucosamine hydrochloride (GAH) and melamine. Highly-dispersed and small-sized Ru nanoparticles (NPs) supported N-doped carbon by impregnation method, which can efficiently convert lignin to obtain 40.70% aromatic monomers. It was 2.3 times than that of the commercial catalyst (Ru/C) and the catalyst could be used at least five runs with an insignificant loss in the yield of aromatic monomers. The morphology, specific surface area, nitrogen species and content of supports could be tuned by controlling the weight of melamine. The results showed that the melamine and GAH were condensed to form layered graphitic carbon nitride (g-C3N4) and a carbon skeleton at 600 °C, respectively. Then, the produced N from the decomposition of g-C3N4 at high temperature (>700 °C) could improve nitrogen concentration, increase the specific area and result in the graphene-like wrinkled morphology. The presence of pyridinic N not only served as metal coordination sites to stabilize and disperse Ru NPs but also enhanced the proportions of Ru0 through the electronic interactions. The DFT calculations implied that the pyridinic N contributed to the highest adsorption energy for 2-phenoxy-1-phenethanol (PPE) and a reduction of the disassociation energy for Calkyl–O bond compared with graphite N and pure C.