Highly Dispersed Rh/NbOx Invoking High Catalytic Performances for the Valorization of Lignin Monophenols and Lignin Oil into Aromatics

Abstract

As fossil fuels are constantly depleted, valorization of lignocellulosic biomass into valuable aromatic compounds is of great significance but exceedingly challenging. In this work, the structure and catalytic performance of various Rh/Nb₂O₅ catalysts were studied in detail via the catalytic hydrodeoxygenation of a representative lignin monophenol compound 2-methoxy-4-propylphenol. The best catalytic performance was obtained over Rh/Nb₂O₅-400 (Nb₂O₅ calcined at 400 °C) with an exceptional 98% yield of propylbenzene under 0.5 MPa H₂, which was mainly due to the cooperation between highly dispersed Rh metals and NbOₓ species, in which Rh was responsible for dissociation of H₂ and NbOₓ for breaking of C–O bonds at the metal–support interface. Besides, the lignin oil obtained in depolymerization of raw pine wood was directly used as the substrate in the catalytic hydrodeoxygenation reaction over the Rh/Nb₂O₅-400 catalyst under 0.5 MPa H₂. Encouragingly, the liquid products were identified and found that lignin oil was completely converted into C₆–C₁₀ hydrocarbons (>99% selectivity) with an 80.1 mol % yield of aromatics. The results achieved in this work highlighted that high-value utilization of lignocellulosic biomass feedstocks to produce aromatic chemicals and liquid fuels could be achieved over Rh/Nb₂O₅ under a low hydrogen pressure.