Base-Free Formic Acid Dehydrogenation with Metal Nanoparticles in a Nanoporous PPO Matrix

Hydrogen (H₂) is an attractive energy vector due to its high gravimetric and volumetric energy densities and clean combustion byproduct (water). However, the storage and transport of H₂ are challenged by its low ambient-pressure density and high flammability, requiring either high-pressure compression or cryogenic conditions. Liquid organic hydrogen carriers (LOHCs) such as formic acid (FA) offer practical alternatives by covalently binding H₂ in stable, easily handled liquids with high hydrogen content. The catalytic dehydrogenation of FA (FAD) to H₂ and CO₂ proceeds via a highly selective pathway (ΔG° = –20.7 kJ/mol) while avoiding the dehydration route (CO + H₂O, ΔG° = +32.9 kJ/mol) that generates CO and poisons downstream fuel cells. Gold nanoparticles (AuNPs) have garnered attention for FAD catalysis due to their resistance to poisoning and tunable activity when supported on various substrates (CeO2,[1] ZrO2,[2] SiO2[3]). However, these high-performance systems typically rely on co-catalytic bases or functionalized supports, adding complexity and cost. In this contribution, we present the design, synthesis, and thorough characterization of a robust heterogeneous catalytic system based on gold nanoparticles (AuNPs) immobilized within a nanoporous poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) matrix for the selective dehydrogenation of FA to produce H₂ and CO₂ with complete suppression of the undesirable dehydration pathway (CO + H₂O). FAD was systematically investigated in aqueous and water/co-solvent media, and by optimizing the FA/Au molar ratio to 2000, the system achieves a peak TOF of 600 molFA·molAu⁻¹·h⁻¹. Notably, the AuNPs-PPO catalyst demonstrates excellent recyclability: five consecutive FAD runs at 80 °C and FA/Au = 100 maintain full activity and selectivity, with no detectable nanoparticle growth or structural changes by post-reaction WAXD. These findings position AuNPs-PPO as a highly efficient, selective, and sustainable platform for on-demand H2 generation from FA, with significant implications for liquid H2 storage technologies and portable fuel-cell applications.