Fe/FeOx embedded in LDH catalyzing C-C bond forming reactions of furfural with alcohols in the absence of a homogeneous base

Progress of Reactions between Furfural and Aliphatic Alcohols via Catalytic Oxidation Processes: Reaction Routes, Catalysts, and Perspectives

Furfural is one of the most important biomass platform compounds and can be used to prepare various high-value-added chemicals. The reactions of furfural with aliphatic alcohols via an oxidative esterification reaction or oxidative condensation reaction can bond two carbon molecules together and produce longer hydrocarbon chains chemicals, including methylfuroate and some low-volatility liquid biomass fuels. Thus, these reactions are considered significant utilization routes of furfural, and many inspiring catalytic systems have been designed to promoted these reactions. In this work, the reported catalytic systems for the oxidative esterification and oxidative condensation reactions are reviewed separately. The catalysts for the oxidative esterification reaction are reviewed for the classification of noble metal catalysts and non-noble metal catalysts, according to the active metals in the catalysts. For the oxidative condensation reactions, the studies using oxygen as the oxidant are reviewed firstly, and then the studies conducted using the hydrogen transfer process are analyzed subsequently. Furthermore, suggestions for future research directions for the oxidative esterification and oxidative condensation reactions are put forward.

Batch and Continuous-Flow Preparation of Biomass-Derived Furfural Acetals over a TiO2 Nanoparticle-Exfoliated Montmorillonite Composite Catalyst

Furfural acetals with high octane value, high calorific value and high oxidation resistance are considered promising biofuels or fuel precursors with huge potential demand. However, there are few studies on efficient scalable catalyst systems, including continuous-flow catalyst systems, for their preparation. In this work, TiO₂ nanoparticles supported on exfoliated montmorillonite, with strong Lewis acid sites and abundant accessible Brønsted acid sites, is used to catalyze the acetalization reactions of biomass-derived furfural and alcohols. Low dosage of the catalyst made the reaction reach equilibrium in a very short time (TOF=690-1305 min^-1 ) at room temperature with the acetal as the only product. In continuous-flow reactions, the catalyst showed a stable product output with conversion close to that for the batch reaction with a short catalyst-reactant contact time of 150 s. Contrast experiments revealed that both Lewis and Brønsted acid sites on the catalyst were indispensable for maximizing the catalytic performance, and simultaneously activating both furfural and alcohol on the adjacent Lewis and Brønsted acid sites was proposed to be responsible for the high catalytic performance.