Activity of Pd/C for hydrogen generation in aqueous formic acid solution

• A Pd/C was found to be highly active for production of H2 from HCOOH solution.
• The structural characteristics of Pd/C were investigated.
• Catalyst deactivation was studied and the poisoning species were revealed.
• The apparent deactivation energy was estimated and discussed.
• Elementary steps were proposed and used to understand particle size effect.

A commercial Pd/C catalyst was found to exhibit high activity for formic acid (HCOOH) decomposition into CO2 and H2 in aqueous solution at near ambient temperatures. The performance of the catalyst toward HCOOH decomposition in aqueous solution was investigated in a batch reactor at temperatures between 21 and 60 °C and HCOOH concentrations between 1.33 and 5.33 M. The apparent activation energy of the overall reaction for the production of H2 from aqueous HCOOH was determined to be 53.7 kJ/mol on the heterogeneous Pd/C catalyst. This is in good agreement with the previously reported theoretical energy barrier (∼52 kJ/mol) for H2 evolution on a Pd surface. Under the present experimental conditions, the catalyst lost activity continuously over time and the apparent deactivation energy was estimated to be 39.2 kJ/mol. Furthermore, the deactivated and spent catalyst was studied by temperature-programmed desorption experiments to reveal the possible species that caused the loss of the activity. Combining the results of our previous DFT calculations and the present experimental results, elementary steps of HCOOH decomposition on Pd in aqueous solution were proposed and discussed.