Surface Electronic State Mediates Proton Transfer at Metal Nanoscale Interface for Catalytic Hydride Reduction of −NO2 to −NH2


Concerted electron and proton transfer is a key step for the reversible conversion of molecular hydrogen in both heterogeneous nanocatalysis and metalloenzyme catalysis. (Gabor A. Somorjai, et al. PNAS, 2016, 113, 5159–5166) However, the activation mechanism involving electron and proton transfer dynamic remains elusive. (Starla D. Glover and Leif Hammarström et al., J. Am. Chem. Soc. 2021, 143, 560−576.) With the most widely used catalytic hydride reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction, we evaluate the catalytic activity of noble metal NPs trapped in porous silica in aqueous NaBH4 solution. By virtue of a novel combination of catalyst design, reaction kinetics, isotope labeling, and multiple spectroscopic techniques, we counter-intuitively demonstrates that, the hydrogen resource of the final product of 4-AP by hydride reduction is not originated from the NaBH4 reduced, and that metal NPs (Ag/Pt/Pd) is not a real catalytic active site for surface electron mediation. (Avelino Corma etal., Angew. Chem. Int. Ed. 2007, 46, 7266 –7269; ACS Catal. 2015, 5, 7114−7121.). A completely new ‘Surface Electronic State Mediated Proton Transfer’ mechanism was proposed to understand the catalytic hydride reduction of −NO2 to −NH2 at metal nanoscale interface. The similar concerted electron and proton transfer dynamic was only recently observed in the [FeFe]-hydrogenases for reversible proton reduction. (Gregory A. Voth et al., J. Phys. Chem. B 2013, 117, 4062−4071; J. Chem. Phys. 2014, 141, 22D527; Juan C. Fontecilla-Camps et al., Chem. Rev. 2007, 107, 4273-4303.) We believed that current research provide a completely new insights into the working mechanism of nanocatalysis and metalloenzyme catalysis involved by electron and proton transfer.