Selective oxidation of cellulose into formic acid over heteropolyacid-based temperature responsive catalysts

Formic acid (FA) is one of the most promising vectors for sustainable hydrogen energy and it can be synthesized from renewable biomass resources. In this work, a range of heteropolyacid derived temperature-responsive catalysts (Ch_nH_4-nPMo₁₁VO₄₀, n=1–3) were prepared by modifying H₃PMo₁₂O₄₀ heteropolyacid with an oxidation site V⁵⁺ and temperature-responsive monomer choline chloride (Ch⁺), and used for the cascade conversion of biomass derived cellulose into FA via hydrolysis-oxidation in water. The ChH₃PMo₁₁VO₄₀ with a Ch/H ratio of 1/3 exhibited an outstanding catalytic performance to give a 49.5% yield of FA at 165 °C after 3 h reaction time. Catalytic activity of Ch_nH_4-nPMo₁₁VO₄₀ was found to be related to its amount of H⁺ and V⁵⁺, while the recyclable ability of Ch_nH_4-nPMo₁₁VO₄₀ was found to be related to its amount of Ch⁺. The as-prepared catalyst could be perfectly recycled with a single decrease the temperature of reaction systems, and be reused four times with limit loss in catalytic activity. The developed temperature-responsive catalysts have both advantages of homogeneous catalyst and heterogeneous catalyst, which should have potential application in other reactions of lignocellulosic biomass valorization.