The surface oxidation of palladium nanocrystals plays an important role in changing the active sites and subsequently influencing the catalytic reactivity. Such a microscopy study on surface oxidation, down to the atomic scale, is essential for understanding the structure-property correlations of palladium nanocrystal based catalysts. Herein, we present an in situ atomic scale study on the surface oxidation behavior of palladium nanocrystals, which is induced by electron beam irradiation under low oxygen partial pressure and at room temperature inside an environmental transmission electron microscope. We found that: (i) surface oxidation initially started at the edge sites with atomic steps or vertex sites, which served as active sites for oxidation; (ii) the oxidation reaction proceeded with a much faster rate on the {111} surface, indicating a certain crystallography preference; (iii) nanometer-sized palladium monoxide islands were formed on the surfaces eventually. The results from our in situ studies provide insightful knowledge, and will be of certain importance for the design of improved functional catalysts in future.

Sub-10 nm AuPtPd alloy trimetallic nanoparticles (TMNPs) with a high oxidation-resistant property were prepared by photo-deposition followed by a high temperature (700-900 °C) air annealing process.

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Base-free hydrogen evolution from formaldehyde solution represents one of the most important reactions in the fuel cell based hydrogen economy. However, limited progresses have been made in the rational design of cheap and efficient heterogeneous catalysts for this reaction. Here, we for the first time propose a Lewis acid–base combination strategy to design efficient heterogeneous catalysts for HER from HCHO/H2O. By utilizing the Lewis acid/base properties of Bi­(NO3)3·5H2O/ZnO, we successfully fabricated core–shell structured ZnO@Bi­(NO3)3 composites. A strong interfacial electronic interaction between ZnO and Bi­(NO3)3·5H2O is evidenced by the unprecedented 3.3 eV upshift of Zn 2p and 0.5 eV downshift of Bi 4f, which boosts the HER activities of inert ZnO and Bi­(NO3)3·5H2O. Destroying the interfacial electronic interaction leads to a fast deactivation while increasing interfacial sites proportionally enhances the activity, indicating that interfacial sites are real active sites. DFT calculations confirm that ZnO@Bi­(NO3)3 composites greatly lower the activation barrier of H2 formation from two adsorbed H atoms and thus promote the H2 production. The Lewis acid–base combination strategy also applies to the TiO2@Bi­(NO3)3 system, further highlighting the importance of salt–metal oxide interface in heterogeneous catalysis.