Nitrogen-Doped and Pt-Pd-Decorated Porous Carbon Catalyst Derived from Biotar for 2,5-Furandicarboxylic Acid Production from Selective Oxidation of 5-Hydroxymethylfurfural in an Alkali-Free Environment

High-value-added 2,5-furandicarboxylic acid (FDCA) produced from renewable biomass-derived 5-hydroxymethylfurfural (HMF) is a promising alternative to petroleum-based terephthalic acid. The key to this synthetic route is the construction of efficient, stable, and low-cost catalysts suitable for alkali-free hydrothermal conditions. Hence, we prepared nitrogen-doped porous carbon materials loaded with metals by using waste bio-tar as the carbon source for catalyzing the selective oxidation of HMF to FDCA under alkali-free hydrothermal conditions. We systematically investigated the effects of the nitrogen source type, carbonization temperature, and bimetallic ratio on the catalytic performance and revealed the synergistic catalytic mechanism involving the functional sites on the catalyst. Pt_0.5Pd_0.5/NPC-M-800 exhibited the best catalytic performance with 96.1% HMF conversion and 84.6% FDCA yield, benefiting from graphitic nitrogen activating oxygen, pyridine nitrogen providing base sites, and Pd and Pt playing a positive role in the conversion of aldehyde and hydroxyl groups, respectively. This work offers significant insight into the high-value usage of waste biotar as well as provides a sustainable application scenario for green synthesis of FDCA.