Surface And Interface Engineering Of ZnO-based Catalysts For Synergistic Catalytic Hydrogen Production From Formaldehyde Solution

Hydrogen?H₂?has been gaining increasing attention by virtue of its high energy efficiency and environmental friendliness compared with fossil fuels.However,the widely used technology of fossil fuels steam reforming to produce hydrogen will bring resource and environmental issues.As one of chemical hydrogen storage resources,aqueous formaldehyde solution yields a theoretical hydrogen weight efficiency of 8.4 wt%.Catalytic hydrogen production from formaldehyde solution provides a promising strategy for future hydrogen-based energy system,while almost all of the present catalytic systems are carried out in highly alkaline medium.Undoubtedly,the utilization of alkaline solution could cause secondary pollution to the water environment if not handled properly.In order to realize hydrogen production from formaldehyde solution catalyzed in base-free medium,two effective solutions are proposed in this project.On one hand,the morphology and electronic structure of ZnO-based catalysts were changed by introducing metal-support strong interaction?SMSI?to improve their catalytic performance.On the other hand,the catalytic performance is enhanced by the introduction of the ligand effects,ensemble effects and geometric effects of the core-shell structure.The research scheme of this study is as follows:?1?This study shows that the SMSI effect between Pd nanoparticles and ZnO nanorods allows electron transfer between Pd and ZnO,resulting in the formation of a unique Pd@PdO_x/ZnO core-shell structured catalyst and achieving efficient hydrogen production from base-free formaldehyde solution.Experimental and theoretical observations indicate the key factor of low-temperature catalytic hydrogen production from formaldehyde solution is the Cannizzaro intermediate from protonated hydrated formaldehyde could be catalyzed by Pd@PdO_x/ZnO.?2?ZnO/Pd@PdO_x/ZnO was prepared by photochemical underpotential deposition method,and the SMSI effect can be adjusted between Pd and ZnO by controlling the deposition amount of ZnO layer,thus enhanced the catalytic performance for dehydrogenation of formaldehyde solution.Moreover,the alloy catalysts?PdPt@PdO_x/ZnO,PdCu@PdO_x/ZnO?were prepared by photochemical reduction method.The addition of Pt with high work function or Cu with low electronegativity can change the electron distribution of the Pd/ZnO catalyst,thereby enhancing its catalytic performance.?3?This paper also reports non-noble metal Cu-supported ZnO to form a Cu@ZnO core-shell catalyst for base-free hydrogen production from formaldehyde.In this catalytic system,a highly efficient hydrogen production is realized using Cu@ZnO as the catalyst and formaldehyde solution as the substrate in a base-free medium under either aerobic or oxygen-free atmospheres.The synergistic interaction between Cu and ZnO is the key to formaldehyde dehydrogenation.This effect can promote the protonation of hydrated formaldehyde to form Cannizaro intermediates and activate oxygen molecules to produce superoxide radicals in anaerobic and aerobic conditions,respectively,which in turn react with formaldehyde to produce hydrogen.In summary,this study reports that ZnO-based catalyst with SMSI and its surface interface regulation can catalyze hydrogen production from formaldehyde solution in based-free medium,which provides new ideas for understanding the nature of heterogeneous catalysis and the development and design of highly active energy catalysts.