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Domain boundaries in perovskite oxides often exhibit abundant physical properties and phenomena. Here, epitaxial LaTiO3 thin films on (100) SrTiO3 substrates are prepared by pulsed-laser deposition. X-ray diffraction and transmission electron microscopy investigations reveal that the epitaxial LaTiO3 thin films have good crystallinity but a high density of domain boundaries. Atomic-scale scanning transmission electron microscopy observations reveal that two types of domain boundaries are formed in the LaTiO3 thin films. The type I domain boundaries are formed on the {100} crystal planes, while the type II domain boundaries on the {110} crystal planes. Electron energy-loss spectroscopy analyses suggest that the valence states of Ti ions at the type I domain boundaries are +3, while those at the type II domain boundaries are +4. First-principles calculations reveal that the bandgap decreases at both domain boundaries compared to the bulk. The carrier concentration at the type I domain boundaries is significantly higher than that of the bulk, while the carrier concentration at the type II domain boundaries is lower. These findings suggest that domain boundaries play an important role in tailoring the electrical properties of the LaTiO3 thin films, thereby promoting the potential applications and property modulation of related materials and devices. [ABSTRACT FROM AUTHOR]

The MoS2 nanosheets are acquired via a facile hydrothermal strategy, and the M/MoS2 (M = Pt, Rh, Pd, Ru) samples are gained by impregnation. By comparing the catalytic behaviors of these catalysts for p-nitroacetophenone selective hydrogenation, it is found that the catalytic property and selectivity for one −NO2 group hydrogenation of Ru/MoS2 outperform those of other as-prepared catalysts. In addition, the Ru/MoS2 catalysts with various Ru contents (0.37, 0.88, or 2.45 wt %) are used for 3-nitrostyrene selective hydrogenation, and the results show that 0.88 wt % Ru/MoS2 displays the highest catalytic activity (turnover frequency) of TOF = 118.4 h–1 (TOF = 64.2 h–1 for 0.37 wt %Ru/MoS2 and TOF = 61.7 h–1 for 2.45 wt %Ru/MoS2) under the reaction conditions of 100 °C, 3.0 MPa H2, and 1 h. The nanostructure characterization of the as-prepared catalysts (XRD, XPS, TEM, HRTEM, H2-TPD, XAS, AC-STEM, AC-STEM-EDX elemental mapping, and line scanning) demonstrate that Ruδ+ single atoms and Ru clusters are well dispersed on the support. Moreover, 0.88 wt % Ru/MoS2 exhibits extremely high selectivity of one −NO2 group hydrogenation (∼100%) at high conversion for other selected nitroaromatics' hydrogenation, such as nitrobenzene, 2-chloronitrobenzene, 1,3-dinitrobenzene, 3-nitrostyrene, p-nitroacetophenone, and p-nitrobenzonitrile. This is mainly due to the fact that Ru is present with single atoms and clusters, producing the synergism of Ruδ+ single atoms, Ru clusters, and MoS2 nanosheets. And the synergism mechanism is given below: hydrogen is preferentially adsorbed and activated at Ru clusters (forming activated H* species), the −NO2 group is easily adsorbed and activated at Ruδ+ single atoms (charge interaction between electrons from O in −NO2 and positive charge from Ruδ+ single atoms), and H* transfers to Ruδ+ single atoms by the hydrogen spillover effect of the MoS2 nanosheets, reacting with the −NO2 group, forming desired aromatic amines. [ABSTRACT FROM AUTHOR]

To obtain a recyclable and environmentally friendly solid catalyst with excellent catalytic properties and selectivity for 4-nitrophenol (4-NP) hydrogenation, herein, covalent organic frameworks (COFs) are used as the support. Tiny PdCo alloy particles are confined in the pores of the COFs to acquire PdCo/COFs, with an extremely narrow PtCo size distribution (6.28 ± 2.85 nm). The effect of Pd+Co loading and the Pd/Co atomic ratio on the catalytic behaviors of PdCo/COFs for 4-NP hydrogenation is explored. The as-gained PdCo/COFs catalyst (Pd1.72, Co1.23 wt %) exhibits good catalytic behaviors (conversion90.5%, selectivity to 4-aminophenol (4-AP) > 99.0%, and conversion11.0%, selectivity to 4-aminophenol (4-AP) > 99.0%, TOFturnover frequency44.2 min–1) for 4-NP hydrogenation under quite moderate reaction conditions (40 °C, 3.0 MPa hydrogen pressure), and PdCo/COFs have superior stability. Additionally, the catalytic property of PdCo/COFs is better than that of monometallic supported catalysts (Pd/COFs or Co/COFs) and PdNi/COFs. It can be considered that the formation of the PdCo alloy particles is beneficial to the activation of 4-NP. The PdCo/COFs catalysts are analyzed by XRD, XPS, ICP-OES, SEM-EDX, BET, TEM, HRTEM, STEM-EDX elemental analysis, and aberration-corrected STEM (AC-STEM), confirming that tiny PdCo alloy particles are uniformly loaded on the COFs. The PdCo/COFs samples have the advantages of outstanding stability and thus their own desired industrial application potential. [ABSTRACT FROM AUTHOR]