Electron Beam Irradiation-Induced Deoxidation and Atomic Flattening on the Copper Surface

Orientation-dependent oxidation behavior of Cu under In-situ E-Beam irradiation

Herein, we present an atomic in-situ investigation of Cu oxidation along different orientations stimulated by high-energy electron beams (E-Beam) in transmission electron microscopy (TEM). By following the microstructural evolution of the Cu substrate in real time, high-resolution TEM (HRTEM) images reveal an orientation-dependent oxidation mechanism, whereby Cu along [110] zone axis migrates onto the surface and be oxidized while Cu along [100] zone axis is oxidized completely both in bulk and at the surface. The different oxidation mechanisms can be attributed to the differing diffusion rates of oxygen in Cu structures along directions. Moreover, the growth of Cu oxides is found to follow a layer-by-layer mechanism, where Cu mostly migrates onto nanocrystal {110} planes. This behavior would lead to the oxides wider in geometric shape and therefore promote the aggregation of adjacent oxides. These findings have important implications for the practical use of copper-based materials in oxidizing environments.

Calcium poisoning mechanism on the selective catalytic reduction of NOx by ammonia over the γ-Fe2O3 (001) surface

γ-Fe₂O₃ has an excellent low-temperature selective catalytic reduction (SCR) deNO_x performance, but its resistance to alkaline earth metal calcium (Ca) is poor. In particular, the detailed mechanism of Ca poisoning on the γ-Fe₂O₃ catalyst at the atomic level is not clear. Hence, the density functional theory method was used in this research to investigate the influence mechanism of Ca poisoning on the NH₃-SCR over the γ-Fe₂O₃ catalyst surface. The findings reveal that NH₃, NO, and O₂ molecules can bind to the γ-Fe₂O₃ (001) surface to generate coordinated ammonia, monodentate nitroso, and adsorption oxygen species, respectively. The main active site is Fe₁-top. For the γ-Fe₂O₃ with Ca poisoning, the Ca atom has a high adsorption energy on the surface of γ-Fe₂O₃ (001), which covers the catalyst surface and reduces the active sites. The presence of Ca atom decreases the adsorption performance of NH₃, while slightly improving the NO and O₂ adsorption. In particular, the Ca atom restrains the NH₃ activation and NH₂ formation, which is detrimental to the NH₃-SCR process.

Influence of sub-zero temperature on nucleation and growth of copper nanoparticles in electrochemical reactions

Cu metal nanostructures have attracted wide interest of study as catalysts for CO₂ reduction reaction and other applications. Controlling the structure and morphology of Cu nanostructures during synthesis is crucial for achieving desired properties. Here, we studied temperature effects on electrochemical deposition of Cu nanoparticles. We found the size, nucleation density, and crystallinity of Cu nanoparticles are strongly influenced by low temperature processing. The electrodeposition at low temperature (-20°C) results in clusters of assembled small Cu nanoparticles, which is distinctly different from the large individual highly crystalline Cu nanoparticles obtained from the room temperature process. The differences in Cu nanoparticle morphology and crystallinity are attributed to the variations in reduction reaction rate and surface diffusion. The limitation of the reaction rate promotes multiple nuclei, and low surface diffusion induces poor crystallinity. This study deepens our understanding of low-temperature effects on electrochemical processes assisting the design of diverse hierarchical catalytic materials.

Effect of doping Cr on NH3 adsorption and NO oxidation over the FexOy/AC surface: A DFT-D study

Activated carbon supported iron-based catalysts (Fe_xO_y/AC) show good deNO_x efficiency at low temperature. The doping of chromium (Cr) greatly improves the catalyst activity. However, the detailed effect of doping Cr over Fe_xO_y/AC surface at molecular level is still a grey area. In this study, the roles of Cr dopant on gas adsorption and NO oxidation were deeply investigated by a DFT-D3 method. Results show that the synergy of Cr-Fe bimetal improves the binding capacity of Fe₂O₃/AC and Fe₃O₄/AC surfaces after doping Cr. NH₃ can be adsorbed on Cr and Fe sites to form coordinated NH₃. Doping Cr greatly improves the NH₃ adsorption property on the Fe₃O₄/AC surface. NO molecule can combine with Cr, Fe, and O sites to form nitrosyl and nitrite. The doping of Cr increases the adsorption performance of NO on the Fe₂O₃/AC and Fe₃O₄/AC surfaces, especially for Fe₃O₄/AC surface. Furthermore, NO can be oxidized to NO₂ by adsorption oxygen or active O sites of Fe_xO_y clusters. The doping of Cr restrains the formation of insoluble chelating bidentate nitrates and greatly reduces the reaction energy barrier of NO oxidation on the Fe_xO_y/AC surface, which can promote the deNO_x reaction.

Adsorption mechanism of NH3, NO, and O2 molecules over the FexOy/AC catalyst surface: a DFT-D3 study

The surface model of the Fe_xO_y/AC catalyst was constructed and the adsorption mechanism of gas molecules on its surface was revealed.