A ternary composite oxides S2O82−/ZrO2–TiO2–SiO2 as an efficient solid super acid catalyst for depolymerization of lignin

Abstract

The solid, super, acid catalyst S₂O₈²⁻/ZrO₂–TiO₂–SiO₂, which has both a strong Brønsted acid and Lewis acid, was prepared and applied in lignin depolymerization. The results indicate that S₂O₈²⁻/ZrO₂–TiO₂–SiO₂ is an effective catalyst for lignin depolymerisation since the liquid product was almost completely dissolved in ethyl acetate, indicating that it was comprised of mostly oligomeric lignin degradation products. The effect of hydrogenation co-catalysts (Pd/C, Pt/C and Ru/C, Rh/C) were also studied and found to improve the yield of aromatic compounds and the petroleum ether soluble fraction, which are mostly monomeric and dimeric products. The resulting yields of aromatic compounds and petroleum ether soluble products were 14.8% and 46%, respectively, when S₂O₈²⁻/ZrO₂–TiO₂–SiO₂ and Pt/C mixed catalyst was used at 310 °C for 24 hours. These results show that the use of a combination Brønsted and Lewis acid catalyst in combination with a hydrogenation catalyst (S₂O₈²⁻/ZrO₂–TiO₂–SiO₂ together with a noble metal catalyst) opens a practical route for efficient lignin depolymerization.