Cluster model studies on oxygen sites at the (010) surfaces of V2O5 and MoO3

Tuning electronic and magnetic properties of MoO3 sheets by cutting, hydrogenation, and external strain: a computational investigation

Density functional theory computations were performed to examine the electronic and magnetic properties of MoO3 two-dimensional (2D) nanosheets and their derived one-dimensional (1D) nanoribbons (NRs). The pristine 2D MoO3 sheet is a nonmagnetic semiconductor with an indirect band gap, but can be transformed to a magnetic metal when the surface O atoms are saturated by H. Depending on the cutting pattern, the pristine 1D NRs can be indirect band gap nonmagnetic semiconductors, magnetic semiconductors or magnetic metals. The fully hydrogenated NRs are metallic, while the edge-passivated NRs possess the nonmagnetic semiconducting feature, but with narrower band gap values compared to the pristine NRs. Both the 2D monolayer MoO3 sheet and the 1D nanoribbons maintain the semiconducting behaviors when exerting axial strain. These findings provide a simple and effective route to tune the magnetic and electronic properties of MoO3 nanostructures in a wide range and also facilitate the design of MoO3-based nanodevices.

Quantum Mechanical Study of Clean and H-Covered α-MoO3(100) Surface

Structure and electronic properties of the α-MoO3(100) surface, as well as H adsorption on the α-MoO3(100) surface have been studied with periodic slab Hartree–Fock calculations. Gradient corrected density functional calculations have been performed in this study. The structure and electronic properties of the (100) surface are in agreement with experimental and previous theoretical results. Local electronic structure near the different surface oxygen sites are analyzed with Mulliken Population Analysis. The oxide is partially ionic and the symmetrically oxygens exhibit more ionic feature while the terminal oxygens are more covalent. Electrostatic potentials show broad negative minima above the terminal oxygen centers, which suggest that electrophilic adparticles, like H, resulting from surface reactions, will be attracted preferentially at these sites. The results of the H adsorption on the (100) surface are interpreted based on charge-transfer interactions between the surface and H species. It is found that terminal oxygen sites are the most stable binding site. Ionic relaxation of the α-MoO3(100) surface for the adsorption of hydrogen has no effect on the chemical properties and hydrogen atoms adsorbed favorably on the α-MoO3(100) surface at full coverage.

Mechanisms of Initial Propane Activation on Molybdenum Oxides: A Density Functional Theory Study

We report the first detailed density functional theory study on the mechanisms of initial propane activation on molybdenum oxides. We consider 6 possible mechanisms of the C-H bond activation on metal oxides, leading to 17 transition states. We predict that hydrogen abstraction by terminal Mo=O is the most feasible reaction pathway. The calculated activation enthalpy and entropy are 32.3 kcal/mol and -28.6 cal/(mol/K), respectively, in reasonably good agreement with the corresponding experimental values (28.0 kcal/mol and -29.1 cal/(mol/K)). We find that activating the methylene C-H bond is 4.7 kcal/mol more favorable than activating the methyl C-H bond. This regioselectivity is correlated with the difference in strength between a methylene C-H bond and a methyl C-H bond. Our calculations suggest that a combined effect from both the methylene and the methyl C-H bond cleavages leads to the experimentally observed overall kinetic isotopic effects from propane to propylene on the MoO(x)/ZrO(2) catalysts.