Effect of Nb on plasticity and oxidation behavior of TiAlNb intermetallic compound by density functional theory

Based on the pseudo potential plane-wave method of density functional theory （DFT）, Ti1-xNbxAk （x=0, 0.062 5, 0.083 3, 0.125, 0.250） crystals＇ geometry structure, elastic constants, electronic structure and Mulliken populations were calculated, and the effects of doping on the geometric structure, electronic structure and bond strength were systematically analyzed. The results show that the influence of Nb on the geometric structure is little in terms of the plasticity, and with the increase of Nb content, the covalent bond strength remarkably reduces, and Ti-Al, Nb-M （M=Ti, Al） and other hybrid bonds enhance; meanwhile, the peak district increases and the pseudo-energy gap first decreases and then increases, the overall band structure narrows, the covalent bond and direction of bonds reduce. The population analysis also shows that the results are consistent with the electronic structure analysis. The density of states of TiAINb shows that Nb doping can enhance the activity of Al and benefit the form of Al2O3 film. All the calculations reveal that the room temperature plasticity and the antioxidation properties of the compounds can be improved with the Nb content of 8.33%-12.5% （mole fraction）.

Pt/Nb‐WO_x for the chemoselective hydrogenolysis of glycerol to 1,3‐propanediol: Nb dopant pacifying the over‐reduction of WO_x supports

Selective hydrogenolysis of glycerol to 1,3‐propanediol（1,3‐PD） is an important yet challenging method for the transformation of biomass into value‐added chemicals due to steric hindrance and unfavorable thermodynamics. In previous studies, chemoselective performances were found de‐manding and sensitive to H2 pressure. In this regard, we manipulate the chemical/physical charac‐teristics of the catalyst supports via doping Nb into WOx and prepared 1D needle‐, 2D flake‐, and 3D sphere‐stack mesoporous structured Nb‐WOx with increased surface acid sites. Moreover, Nb dop‐ing can successfully inhibit the over‐reduction of active W species during glycerol hydrogenolysis and substantially broaden the optimal H2 pressure from 1 to 5 MPa. When Nb doping is 2%, sup‐ported Pt catalysts showed promising performance for the selective hydrogenolysis of glycerol to 1,3‐PD over an unprecedentedly wide H2 pressure range, which will guarantee better catalyst sta‐bility in the long run, as well as expand their applications to other hydrogen‐related reactions.

Nb-and Ta-doped(Hf,Zr,Ti)C multicomponent carbides with enhanced oxidation resistance at 2500℃

Enhancing oxidation resistance of multicomponent carbides above 2000℃is critical for their thermal protection applications.For this purpose,novel Nb-and Ta-doped(Hf,Zr,Ti)C multicomponent carbides were designed to improve their oxidation resistance at 2500℃.The results demonstrated that Nb and Ta doping reduced the oxidation rate constant by 16.67%and 25.17%,respectively,thereby significantly improving the oxidation resistance of(Hf,Zr,Ti)C.This enhancement was attributed to the changes in oxycarbide composition and distribution within the oxide layer by adding Nb and Ta.Owing to the different oxidation tendencies of the constituent elements,a distinctive structure was formed in which(Hf,Zr)O_(2)served as a skeleton,and various oxycarbides were dispersed throughout the oxide layer.The doped Nb and Ta were retained within oxycarbides,retarding the diffusion of oxygen into the lattice.More importantly,the addition of Nb and Ta reduced the size of oxycarbides,decreasing both size and quantity of the pores in the oxide layer and facilitating the formation of a more effective oxygen barrier.