The Competition between 4-Nitrophenol Reduction and BH Hydrolysis on Metal Nanoparticle Catalysts.

Assessing competitive environmental catalytic reduction processes via NaBH is essential, as BH is both an energy carrier (as H) and a reducing agent. A comprehensive catalytic study of the competition between the borohydride hydrolysis reaction (BHR, releasing H) and 4-nitrophenol reduction via BH on M- and M/M' (alloy)-nanoparticle catalysts is reported. The results reveal an inverse correlation between the catalytic efficiency for BH hydrolysis and 4-nitrophenol reduction, indicating that catalysts performing well in one process exhibit lower activity in the other. Plausible catalytic mechanisms are discussed, focusing on the impact of reaction products such as 4-aminophenol and borate on the rate and yield of BH hydrolysis. The investigated catalysts were Ag, Au, Pt, and Ag/Pt-alloy nanoparticles synthesized without any added stabilizer. Notably, the observed rate constants for the 4-nitrophenol reduction on Ag, Ag-Pt (9:1), and Au are significantly higher than the corresponding rate constants for BH hydrolysis, suggesting that most reductions do not proceed through surface-adsorbed hydrogen atoms, as observed for Pt nanoparticles. This research emphasizes the conflicting nature of BH hydrolysis and reduction processes, provides insights for designing improved catalysts for competitive reactions, and sheds light on the catalyst properties required for each specific process.