Can the direct conversion of biomass-derived formic acid be efficient for hydrogen generation?†

The possibilities of hydrogen generation from renewable sources through the intermediate formation of formic acid (FA) (Biomass → FA → H₂, the BFH process) have been investigated. The commonly employed hydrolysis–oxidation of biomass in the presence of Mo–V–P heteropoly acids (HPAs) was used to produce FA, and the latter was further selectively decomposed to H₂ on a suitable Pd catalyst. The low concentration of FA in the solutions expectedly decreased the rate of its decomposition, but the strongest adverse effect was found from HPAs remaining in the solution after the first stage. The XPS study showed a strong interaction between HPAs and the Pd catalyst, which could cause complete oxidation and poisoning of the Pd surface. Given that such an interaction was minimized (via the nature of HPA and/or purification of the reaction mixture), the catalyst with Pd single atoms and nanoclusters on N-doped carbon nanotubes provided the initial rate as high as 120 L H₂/gPd h and complete conversion of FA into the targeted product even in dilute solutions (0.044 M, 50 °C). The results demonstrate efficiency of the BFH process and indicate the means for further improvements.