The Chemical Properties of Hydrogen Atoms Adsorbed on M⁰-Nanoparticles Suspended in Aqueous Solutions: The Case of Ag⁰-NPs and Au⁰-NPs Reduced by BD₄ ⁻

The nature of H-atoms adsorbed on M⁰-nanoparticles is of major importance in many catalyzed reduction processes. Using isotope labeling, we determined that hydrogen evolution from transient {(M⁰-NP)-H_n}ⁿ⁻ proceeds mainly via the Heyrovsky mechanism when n is large (i.e., the hydrogens behave as hydrides) but mainly via the Tafel mechanism when n is small (i.e., the hydrogens behave as atoms). Additionally, the relative contributions of the two mechanisms differ considerably for M=Au and Ag. The results are analogous to those recently reported for the M⁰-NP-catalyzed de-halogenation processes.