Surface kinetics and transport phenomena modelling for furfural hydrotreatment over Pd/C in isopropanol and tetrahydrofuran

Highlights: • Hydrogenation, hydrodeoxygenation, oligomerisation and etherification reactions. • In-situ palladium on activated carbon (Pd/C) catalyst reduction of PdO to Pd(1 1 1). • Micro-kinetic model for surface reactions and adsorption kinetics on metal sites. • Same kinetic parameters used in both solvents with varying hydrogen solubility. • Favored ring hydrogenation at high and aldehyde group at low hydrogen availability. Extensive experimental and computational study of hemicellulose-derived furfural hydrogenation, hydrodeoxygenation, oligomerisation and etherification has been conducted over Pd/C catalyst. In-situ reduction of PdO surfaces was observed, forming predominately Pd(1 1 1). Tetrahydrofurfuryl alcohol was observed as the main product. Selected solvent (solventless conditions, tetrahydrofuran, isopropanol), atmosphere (nitrogen, hydrogen), temperature (100–200 °C), pressure (25–75 bar) and stirring speed were varied. A micro-kinetic model was developed incorporating thermodynamics (hydrogen solubility), mass transfer, adsorption, desorption and surface reactions. The above-listed phenomena and their contribution to the surface coverages, TOF's and global reaction rates were studied. Approximately 66% of active sites were estimated to be covered by the solvent, 5% by furanic species, while hydrogen coverage was low and limiting. Both furfural ring and aldehyde group hydrogenation have low activation energies (19.1 kJ mol⁻¹ and 23.5 kJ mol⁻¹), although subsequent hydrogenation of tetrahydrofurfural (E_a = 42.5 kJ mol⁻¹) is preferred at higher temperatures compared to furfuryl alcohol (E_a = 24.0 kJ mol⁻¹) hydrogenation. Complete hydrogenation can be achieved at room temperature, while deoxygenation becomes considerable above 150 °C (E_a = 59.6 kJ mol⁻¹), leading to complete conversion in most tests, yielding up to 77% tetrahydrofurfuryl alcohol at 75 bar in isopropanol.