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.

a b s t r a c tThe dynamics of oxidation of cobalt nanoparticles were directly revealed by in situ environmental transmission electron microscopy. Firstly, cobalt nanoparticles were oxidized to polycrystalline cobalt monoxide, then to polycrystalline tricobalt tetroxide, in the presence of oxygen with a low partial pressure. Numerous cavities (or voids) were formed during the oxidation, owing to the Kirkendall effect. Analysis of the oxides growth suggested that the oxidation of cobalt nanoparticles followed a parabolic rate law, which was consistent with diffusion-limited kinetics. In situ transmission electron microscopy allowed potential atomic oxidation pathways to be considered. The outward diffusion of cobalt atoms inside the oxide layer controlled the oxidation, and formed the hollow structure. Irradiation by the electron beam, which destroyed the sealing effect of graphite layer coated on the cobalt surface and resulted in fast oxidation rate, played an important role in activating and promoting the oxidations. These findings further our understanding on the microscopic kinetics of metal nanocrystal oxidation and knowledge of energetic electrons promoting oxidation reaction.

A good knowledge of nanophase diagrams is critical to understanding the performance of nanomaterials. Herein, we for the first time fabricate a AuPdPt ternary nanophase diagram at 800 °C by experimental means. The solid-state synthesis strategy enables a precise synthesis of AuPdPt trimetallic nanoparticles with a full range of compositions and desired size distributions. By studying the phase behavior of those TMNPs, we succeed in mapping out the boundary curve and tie lines. Interestingly, the AuPdPt nanophase boundary shifts obviously to the Au-rich region as compared to the case of the corresponding bulk diagram, likely due to the combination of size and composition effects. Besides, owing to the different solubility of Pd in Au-rich and Pt-rich matrix, some tie lines do not parallel the baseline. These observations greatly improve our basic understanding of nanophase diagrams and are expected to be valuable references for other systems. Moreover, the as-fabricated nanophase diagram is successfully applied to guide the optimization of AuPdPt TMNPs catalysts for n-hexane oxidation.

The oxidation of ZrB2 nanoparticles was observed at high temperature of 1500°C under low oxygen partial pressure of 5 × 10−2 Pa by an environmental transmission electron microscope. The results demonstrate that the oxidation starts on the surface of ZrB2 nanoparticles with decomposition of ZrB2 into ZrO2 and B2O3. The nucleation and growth of ZrO2 on the surface of ZrB2 proceed with B2O3 being evaporated.