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Ultrasmall Silver Clusters Stabilized on MgO for Robust Oxygen-Promoted Hydrogen Production from Formaldehyde Reforming.

Efficient molecular hydrogen generation from renewable biomass derived resources and water is of great importance to the sustainable development of future society. Herein, ultrasmall Ag nanoclusters supported on defect-rich MgO matrix (AgUCs/MgO) are synthesized by a facile impregnation/calcination method and are applied to robust oxygen-promoted formaldehyde reforming into H2 at room temperature. DFT calculations and experimental observations show that the catalyst spatially builds up a channel for directional electron transfer from electron-rich Ag sites to anti-bonding π orbital of chemisorbed bridged O2 molecules, leading to the implementation of low temperature O2 adsorption and activation. The catalytically active species, •OOH, is thus selectively generated via a preferential two-electron reduction of O2 with low energy barrier on Ag sites involving an unusual long-range proton coupled electron transfer process. The •OOH-AgUCs/MgO active center is efficient for the subsequent C-H activation and H2 generation, leading to a 3-fold improvement of turnover frequency as compared with its analogous AgNPs/MgO catalyst. Our atomic-level design and synthetic strategy provide a platform that facilitates construction of electron-proton transfer channel for catalysis, altered adsorption configurations of activated reactants and enhancement of catalytic hydrogen generation activity, extending a promising direction for the development of next-generation energy catalysts.