Hydrogen Production from Formic Acid over Au Catalysts Supported on Carbon: Comparison with Au Catalysts Supported on SiO2 and Al2O3

Characteristics and catalytic activity in hydrogen production from formic acid of Au catalysts supported on porous N-free (Au/C) and N-doped carbon (Au/N-C) have been compared with those of Au/SiO2 and Au/Al2O3 catalysts. Among the catalysts examined, the Au/N-C catalyst showed the highest Au mass-based catalytic activity. The following trend was found at 448 K: Au/N-C > Au/SiO2 > Au/Al2O3, Au/C. The trend for the selectivity in hydrogen production was different: Au/C (99.5%) > Au/Al2O3 (98.0%) > Au/N-C (96.3%) > Au/SiO2 (83.0%). According to XPS data the Au was present in metallic state in all catalysts after the reaction. TEM analysis revealed that the use of the N-C support allowed obtaining highly dispersed Au nanoparticles with a mean size of about 2 nm, which was close to those for the Au catalysts on the oxide supports. However, it was by a factor of 5 smaller than that for the Au/C catalyst. The difference in dispersion could explain the difference in the catalytic activity for the carbon-based catalysts. Additionally, the high activity of the Au/N-C catalyst could be related to the presence of pyridinic type nitrogen on the N-doped carbon surface, which activates the formic acid molecule forming pyridinium formate species further interacting with Au. This was confirmed by density functional theory (DFT) calculations. The results of this study may assist the development of novel Au catalysts for different catalytic reactions.