Controlling Carbonization of Tannin for the Effective Pd Loading to Hydrogenate Lignin-Derived Aldehydes

Finding new catalytic applications for tannin, a biomass resource, exploiting its structural features and renewable nature, helps contribute toward carbon neutrality in catalysis. Herein, novel Pd-supported, carbon-neutral catalysts are synthesized using tannic acid. First, tannic acid is cross-linked and coated on the surface of nano-SiO₂. This material is then subjected to controllable carbonization, with the temperature being optimized, to obtain the catalyst support SiO₂@TA-T (T: carbonization temperature). Experimental results demonstrate that carbonizing at 400 °C remained part of the phenolic hydroxyls of tannin with satisfactory reducing ability. Meanwhile, the condensation and the deoxygenation of tannin increased the thermal stability of this support and introduced porous structures and abundant defect sites. This material is then used to adsorb and in situ reduce Pd²⁺ to develop Pd-based catalysts. To this end, this synthesized Pd/SiO₂@TA-400 catalyst is then used to hydrogenate vanillin, with a conversion of 99% to vanillyl alcohol at a pressure of 0.5 MPa initial H₂ and a temperature of 20 °C for 60 min. Such remarkable results are corroborated in the hydrogenation of several lignin-derived aromatic aldehydes, with the catalyst achieving high conversion and outstanding recyclability (5 recycles).