Solvent effects in hydrodeoxygenation of furfural-acetone aldol condensation products over Pt/TiO2 catalyst

The solvent effects on hydrodeoxygenation (HDO) of 4-(2-furyl)-3-buten-2-one (F-Ac) over Pt/TiO2 catalyst were investigated at T = 200 degrees C and P(H-2)= 50 bar. The initial reactant is the main product of aldol condensation between furfural and acetone, which constitutes a promising route for the production of bio-based chemicals and fuels. A sequence of experiments was performed using a selection of polar solvents with different chemical natures: protic (methanol, ethanol, 1-propanol, 2-propanol, 1-pentanol) and aprotic (acetone, tetrahydrofuran (THF), n,n-dimethylformamide (DMF)). In case of protic solvents, a good correlation was found between the polarity parameters and conversion. Consequently, the highest hydrogenation rate was observed when 2-propanol was used as a solvent. In contrast, the hydrogenation activity in presence of aprotic solvents was related rather to solvent-catalyst interactions. Thus, the initial hydrogenation rate declined in order Acetone > THF > DMF, i.e. in accordance with the increase in the nucleophilic donor number and solvent desorption energy. Regarding the product distribution, a complex mixture of intermediates was obtained, owing to the successive hydrogenation (aliphatic C=C, furanic C=C and ketonic C=O bonds), ring opening (via C-0 hydrogenolysis) and deoxygenation reactions. Based on the proposed reaction scheme for the conversion of F-Ac into octane, the influence of the studied solvents over the cascade catalytic conversion is discussed. A significant formation of cyclic saturated compounds such as 2-propyl-tetrahydropyran and 2-methyl-1,6-dioxaspiro[4,41nonane took place via undesirable side reactions of cyclization and isomerization. The best catalytic performance was found when using acetone and 2-propanol as solvents, achieving significant yields of 4-(2-tetrahydrofury1)butan-2-ol (28.5-40.4%) and linear alcohols (6.3-10.4%). The better performance of these solvents may be associated with a lower activation energy barrier for key intermediate products, due to their moderate interaction with the reactant and the catalyst. In case of methanol and DMF, undesired reactions between the reactant and the solvent took place, leading to a lower selectivity towards the targeted hydrodeoxygenated products. (C) 2016 Elsevier B.V. All rights reserved.