Towards understanding the hydrodeoxygenation pathways of furfural–acetone aldol condensation products over supported Pt catalysts

Abstract

Aiming at the valorisation of furfural-derived compounds, the hydrodeoxygenation of furfural–acetone condensation products has been studied using supported platinum catalysts. The influence of the catalytic properties of different supports, such as SiO₂, Al₂O₃, TiO₂, hydrotalcite (HTC), Beta zeolite, Al-SBA-15 and WO₃–ZrO₂, was evaluated in a batch reactor for 480 min at 200 °C and 50 bar of H₂. The used feed consisted of a mixture of furfural–acetone adducts (C₈–C₁₉), obtained in previous experiments using a continuous flow reactor and hydrotalcite as a catalyst. Except for Pt/SiO₂, all catalysts showed high conversion of the reactants, especially due to the hydrogenation of all the aliphatic CC bonds. However, the extent of further hydrogenation (furan CC and ketone CO bonds) was limited, particularly when HTC and Al₂O₃ were used as supports. The higher accessibility of Pt/TiO₂ and the smaller Pt particle size shown by Pt/Al-SBA-15, Pt/WO₃–ZrO₂ and Pt/Beta in comparison with the other catalysts led to an improvement in the hydrogenation of furanic and ketonic groups, likely due to lower adsorption constraints. The higher acid character of the latter group of catalysts promotes dehydration and ring opening steps, thus enhancing the selectivity towards linear alcohols. Likewise, a significant increase in the extent of aldol condensation reactions was also observed with these catalysts, yielding longer carbon chain compounds. Based on this study, a reaction scheme for the transformation of 4-(2-furyl)-3-buten-2-one (C₈) into octane has been proposed in order to establish a valuable correlation between the main conversion pathways and the catalytic properties of the employed heterogeneous catalyst, thus contributing to further development of efficient deoxygenation catalysts.