Lignin-derived 4-methylanisole hydrodeoxygenation under mild conditions over ruthenium phosphide carbon nanosphere catalyst

Abstract

(1:1), (1:3), and (1:5) RuP@C-N carbon nanosphere catalysts were synthesized by in situ method using a hydrothermal, carbonization, and reduction strategy with tannic acid as the biomass carbon source. The synthesized materials were well described using several instrumental methods, including XRD, which revealed ruthenium phosphide phase formation as well as graphitic carbon. BET surface area and BJH pore size distribution revealed that the materials had multiple meso and micropores. XPS measurements assess the oxidation states and bonding interaction between the carbon nanosphere and RuP in the catalyst. FE-SEM validates the material’s spherical morphology, whereas EDS mapping reveals the presence of Ru, P, C, O, and N. HR-TEM images reveal the high distribution of RuP particles on the carbon network. The induction of C and N in the catalyst impacted electron transport between ruthenium and phosphorus as evidenced by XPS analysis, leading to Ru^δ+/P^δ- active sites responsible for C-O bond breakage. Additionally, the high dispersion and small particle size of ruthenium phosphide in the carbon spheres, as well as its acidity, had a significant impact on its high activity. The study investigated the hydrodeoxygenation (HDO) of 4-methylanisole under mild reaction conditions, with isopropanol as a hydrogen donor. The optimal conditions were 180 °C and 4 h, and for the (1:3) RuP@C-N catalyst, a maximum of 4-methylanisole conversion was 42.5 %, and a toluene selectivity of 21.5 % was reached at TOF 45.35 h⁻¹. The (1:3) RuP@C-N catalyst was the most active, while the (1:5) RuP@C-N catalyst with a high P concentration had no added effect on activity. Demethylation/hydrogenolysis was the most selective reaction pathway for 4-methylanisole conversion. Furthermore, the catalyst was regenerated and reused for five consecutive runs, and maintained its activity without considerable loss.