Bifunctional Platinum Catalysts on Sulfonated Porous Aromatic Frameworks for the Hydrodeoxygenation of Furanic and Cyclohexanone-Derived Precursors to Fuel-Range Hydrocarbons

The catalytic hydrodeoxygenation (HDO) of biomass-derived oxygenates requires bifunctional catalysts that combine acid and metal sites, yet the reaction networks of polyfunctional substrates remain incompletely understood. In this paper, two bifunctional catalysts based on sulfonated porous aromatic frameworks with different platinum loadings (PAF-30-SO3H–Pt(1) and PAF-30-SO3H–Pt(3)) were prepared and studied in the HDO of two model substrates: 1,1-bis(5-methylfuran-2-yl)cyclohexane (C6-(MF)2) and the condensation products of cyclohexanone. These two substrates represent two classes of biomass-derived SAF precursors─the furanic C6-(MF)2, obtained by alkylation of lignocellulose-derived 2-methylfuran with cyclohexanone, and the self-condensation products of cyclohexanone, a common model compound of lignin bio-oils accessible by partial hydrodeoxygenation of lignin-derived phenolics. Their hydrodeoxygenation yields fuel-range naphthenic hydrocarbons, suitable as SAF components. The catalysts were characterized by CHNS and ICP-AES analysis, FTIR, XPS, N2 adsorption, TEM, and SEM, and the reaction products were identified by GC-MS. The transformations proceeded through the combined action of the acidic SO3H groups and platinum. Additional reaction routes were identified for both substrates, including the formation of methyldecalins and an acid-catalyzed cyclization competing with hydrogenation, which was markedly more favorable for the cyclohexanone trimers, as supported by DFT calculations. Higher temperature, H2 pressure, and platinum loading increased the yield of hydrocarbons, which reached 91% for the cyclohexanone condensation products and 51% for 1,1-bis(5-methylfuran-2-yl)cyclohexane after 4 h of reaction at 250 °C and H2 pressure of 5 MPa. Upon reuse, the catalyst was substantially deactivated, mainly through the accumulation of carbonaceous deposits that blocked the pores, while the framework and sulfonic groups remained intact.