In situ generated electron-deficient metallic copper as the catalytically active site for enhanced hydrogen production from alkaline formaldehyde solution

Low-cost copper-based catalysts have attracted great interests as it is able to accelerate hydrogen evolution from formaldehyde solution at room temperature. However, there remains challenge to clarify the catalytically active site and the catalytic mechanism of Cu-based catalyst for formaldehyde dehydrogenation. Herein, we report a rational design of freestanding nanosized-Cu model catalyst coexisting both metallic Cu and CuO via an in situ spontaneous reduction reaction from CuO nanoparticles. The charge transfer processes among formaldehyde, Cu, and CuO during reduction results in the generation of positively charged metallic copper (Cuδ+, 0<δ<1), which strengthens the adsorption and activation of H2O as well as HCHO molecules. Therefore, the metallic copper coupled with peroxide radical act as active phase and enable the selective cleavage of the C–H bond and the O–H bond in HCHO and H2O. As a result, the optimal turnover frequency (TOF) of the reduced CuO catalyst composing of slightly electronic-deficient Cuδ+ species reaches 7242 h-1, ~2 times superior to its counterpart Cu catalyst. This work not only deepens our understanding on HCHO dehydrogenation pathway over Cu-based catalyst, but also provides an alternative methodology to improve the performance of heterogeneous catalysts.