Mechanistic and kinetics insights into Cu size effects on catalytic hydrogen combustion

The removal of excess hydrogen in a catalytic process is a safety measure, which should be incorporated into fuel cell technologies. In this study, the size effects of Cu catalysts on the catalytic hydrogen combustion are examined by investigating the impact of Cu-Cu and Cu-O coordination numbers. A distinct volcano-shaped trend in catalytic performance is observed, reaching its peak when the Cu loading is at 5 wt% with a reaction rate of 0.55 mol(H2).mol(Cu)(-1).min(-1). It is found that the lower Cu loading leads to strong metal-support interactions and a high Cu-O coordination, whereas the higher Cu loading hinders reduction and increases the Cu-Cu coordination. DFT calculations emphasize the significance of Cu(111) facets in facilitating H-H bond dissociation and O-H bond formation. However, excessively large Cu nanoparticles limit catalytic activity due to the reduced active sites. As a result, the 5 wt% Cu/gamma-Al2O3 catalyst, which strikes a balance between Cu-Cu and Cu-O coordination numbers, exhibits the highest catalytic performance for this reaction. This study not only provides valuable insights into the size effects of Cu-based catalysts on hydrogen combustion, but also offers guidance for designing highly active Cu-based catalysts.