Toward an Understanding of the Hydrogenation Reaction of MO2 Gas-Phase Clusters (M = Ti, Zr, and Hf) (original) (raw)
Related papers
A density functional theory study on the interaction of hydrogen molecule with MOF-177
Molecular Simulation, 2010
The binding energies of H 2 molecule with metal-organic framework MOF-177 clusters at various possible interaction sites have been calculated using density functional theory. The binding energy of adsorbed H 2 molecule in MOF-177 was investigated, with the consideration of the favourable adsorption sites and the orientations at the inorganic cluster Zn 4 O and organic linker (1,3,5-benzenetribenzoate) in order to evaluate the role of these two principal components in MOF for H 2 adsorption. Our results showed that both the inorganic connector and the organic linker play an important role in the H 2 adsorption. The binding energy calculated for the inorganic cluster is 2.96-4.50 kJ mol 21 and for the organic linker is 2.6-3.8 kJ mol 21 .
Density Functional Theory Study on Catalytic Dehydrogenation of Methane on Moo3 (010) Surface
Social Science Research Network, 2022
Methane conversion offers hydrocarbon building blocks of high market value, which are easier to transport than natural gas. Under non-oxidative conditions, the process can also produce clean hydrogen fuel. In this study, we explored the catalytic dehydrogenation of methane on molybdenum oxide (MoO 3) surface. Periodic density functional theory calculations were performed to study the adsorption of CH 4 on two different supercells of the MoO 3 (0 1 0) surface. It was found that CH 4 adsorption was more favorable on a smooth surface constructed of Mo and O network, rather than a surface made with dangling O atoms as thought before. A reaction mechanism for hydrogen formation was then proposed. The first energy barrier for the H-abstraction step was calculated to be 66.4 kJ/mol, which is lower than previously reported values obtained for simple Mo x O y clusters. The reactions were discussed using the two-state reactivity approach, where different electronic states can play a role in the Habstraction step. The mechanism also showed the formation of methyl radicals and ethylene, in addition to molecular hydrogen.
The Journal of Chemical Physics
Rational design of novel catalytic materials used to synthesize storable fuels via CO hydrogenation reaction has recently received considerable attention. In this work, defect poor and defect rich 2D-MoS2 as well as 2D-MoS2 decorated with Mo clusters are employed as catalysts for the generation of acetylene (C2H2) via CO hydrogenation reaction. Temperature programmed desorption is used to study the interaction of CO and H2 molecules with the MoS2 surface as well as the formation of reaction products. The experiments indicate the presence of four CO adsorption sites below room temperature and a competitive adsorption between the CO and H2 molecules. The investigations show that CO hydrogenation is not possible on defect poor MoS2 at low temperatures. However, on defect rich 2D-MoS2, small amounts of C2H2 are produced, which desorb from the surface at temperatures between 170 K and 250 K. A similar C2H2 signal is detected from defect poor 2D-MoS2 decorated with Mo clusters, which indicates that low coordinated Mo atoms on 2D-MoS2 are responsible for the formation of C2H2. DFT investigations are performed to explore possible adsorption sites of CO and understand the formation mechanism of C2H2 on MoS2 and Mo7/MoS2. The theoretical investigation indicates a strong binding of C2H2 on the Mo sites of MoS2 preventing the direct desorption of C2H2 at low temperatures as observed experimentally. Instead, the theoretical results suggest that the experimental data are consistent with a mechanism in which CHO radical dimers lead to the formation of C2H2 that presents an exothermic desorption.
Chemical reactivity of (010)MoO3: a structural study of the MoO2 formation in molecular hydrogen
Surface Science, 1984
The reduction of (OlO)MoO, in molecular hydrogen under low pressure (3~10~' Pa) was investigated between 300 and 720 K by Reflection High Energy Electron Diffraction and Auger Electron Spectrometry. A three-dimensional MOO, structure was found to be directly formed from MOO,. MOO, nucleation took place through some MOO, crystallographic planes having the same MOO, octahedra arrangement as in the MoO,(OlO) plane. It is deduced that the mechanism of the transformation strongly depends on the layered structure of MOO,. This transformation might be initiated by a periodic defect detected along the MoO,[lOl] directions. Some modifications of properties of the MoO,(OlO) plane as induced by heating are also presented.
Electronic Properties of the Active Sites Present at the (011) Surface of MoO 2
Adsorpt Sci Technol, 2007
The DFT method was used to describe the electronic structure of the catalytically interesting (011) surface of molybdenum dioxide, with attention being particularly focused on the properties of the active sites, both molybdenum and oxygen, present at this surface. In addition, a comparison of (011)MoO 2 and (100)MoO 3 surfaces was undertaken since both surfaces contain not only differently coordinated oxygen sites but also the bare molybdenum centres. The electronic structures of both surfaces were obtained using the cluster method and DFT approach. The local properties of the different surface sites exposed at the (011)MoO 2 surface, viz. five-and six-fold coordinated Mo atoms and nucleophilic O sites with different coordination numbers, have been discussed using charge densities, bond-order indices and molecular orbital diagrams. * The program package StoBe is a modified version of the DFT-LCGTO program package DeMon, originally developed by A. St.-Amant and D. Salahub (University of Montreal), with extensions by L.
Hydrogen adsorption on a Mo27S54 cluster: A density functional theory study
Journal of Molecular Catalysis A: Chemical, 2006
Density functional theory computations have been carried on the hydrogen adsorption mechanism on a Mo 27 S 54 single layer cluster, which has a size (15-20Å) close to that of real catalysts. For one molecule of H 2 adsorption, the most stable adsorption form (E ads = −27.2 kcal/mol) is the homolytic dissociation on the S edge with the hydrogen atoms keeping away from the plane consisting of all Mo atoms, followed by the heterolytic dissociation (E ads = −26.1 kcal/mol) on the intersection of S and Mo edges with the formation of Mo c -H and S c -H bonds. At high coverage with two and three H 2 , however, dissociated hydrogen adsorption on the Mo sites are much more favored thermodynamically than on the S sites. Moreover, the corner sites are more favored thermodynamically for hydrogen adsorption and formation of coordinatively unsaturated sites than the edge sites. In addition, the activation energy of H 2 dissociation and hydrogen transfer processes have been computed to be 2.7-19.2 kcal/mol, and these rather low barriers indicate the enhanced mobility of the adsorbed hydrogen on the surface.
Russian Chemical Bulletin, 2008
Reduction of tetranuclear heterometallic complex Mo 2 Mg 2 was simulated using the B3LYP and PBE density functional methods. The results of geometry calculations of the initial complex [Mo VI O 2 Mg(MeOH) 2 (OMe) 4 ] 2 and a partially reduced Mo V complex are in good agreement with experimental data. The reduced Mo III complex is characterized by a decrease in the binding energy of aqua ligands. Structural rearrangement of the complex with release of a coordination position at the Мо atoms requires small energy expenditure. One can assume that the reduction of the polynuclear complex causes overcrowding of its coordination sphere, which favors formation of dinitrogen complexes.
Energetic and topological analysis of the reaction of Mo and Mo2 with NH3, C2H2, and C2H4 molecules
Journal of Computational Chemistry, 2004
The Density functional theory has been applied to characterize the structural features of Mo 1,2 -NH 3 ,-C 2 H 4 , and -C 2 H 2 compounds. Coordination modes, geometrical structures, and binding energies have been calculated for several spin multiplets. It has been shown that in contrast to the conserved spin cases (Mo 1,2 -NH 3 ), the interaction between Mo (or Mo 2 ) and C 2 H 4 (or C 2 H 2 ) are the low-spin (Mo-C 2 H 4 and -C 2 H 2 ) and high-spin (Mo 2 -C 2 H 4 and -C 2 H 2 ) complexes. In the ground state of Mo 1,2 -C 2 H 4 and -C 2 H 2 , the metal-center always reacts with the COC center. The spontaneous formation of the global minima is found to be possible due to the crossing between the potential energy surfaces (ground and excited states with respect to the metallic center). The bonding characterization has been performed using the topological analysis of the Electron Localization Function. It has been shown that the most stable electronic structure for a -acceptor ligand correlates with a maximum charge transfer from the metal center to the COC bond of the unsaturated hydrocarbons, resulting in the formation of two new basins located on the carbon atoms (away from hydrogen atoms) and the reduction of the number of attractors of the COC basin. The interaction between Mo 1,2 and C 2 H 4 (or C 2 H 2 ) should be considered as a chemical reaction, which causes the multiplicity change. Contrarily, there is no charge transfer between Mo 1,2 and NH 3 , and the partners are bound by an electrostatic interaction.
Study of the interaction between hydrogen and the MoO3–ZrO2 catalyst
2012
The interaction of molecular hydrogen with the surface of MoO 3-ZrO 2 was observed using infrared IR and electron spin resonance (ESR) spectroscopy, and the hydrogen adsorption was quantitatively evaluated in the temperature range of 323-573 K. The hydrogen adsorbed IR results confirmed the formation of a new broad band in the range of 3700-3400 cm −1 , which corresponds to hydrogen-bonded OH groups. A decrease in the ESR signals indicated the formation of electrons that have been trapped by the electrondeficient metal cations and/or oxygen radicals. The hydrogen adsorbed IR and ESR results suggested that the protons and electrons were formed on the surface of MoO 3-ZrO 2 from molecular hydrogen enhancing the isomerization of n-heptane. A quantitative study of the hydrogen adsorption showed that the rate of hydrogen uptake was high for the first few minutes at 473 K and above, and the rate reached an equilibrium value within 10 h. At 423 K, different features of the hydrogen adsorption were observed on MoO 3-ZrO 2 , where the hydrogen uptake increased slowly with time and did not reach equilibrium after 10 h. The rate of hydrogen adsorption increased slightly at 373 K and below. Hydrogen adsorption on MoO 3-ZrO 2 involves two successive steps. The first step involves hydrogen dissociation on a specific site on the MoO 3-ZrO 2 catalyst to form hydrogen atoms, and the second step involves the surface diffusion of the hydrogen atoms on the MoO 3-ZrO 2 surface. Then the hydrogen atom becomes a proton by donating an electron to an adjacent Lewis acid site. The rate-controlling step involves the surface diffusion of hydrogen atoms and has an activation energy of 62.8 kJ/mol. A comparison of the hydrogen adsorption on SO 4 2−-ZrO 2 , WO 3-ZrO 2 and MoO 3-ZrO 2 catalysts is discussed.
Density functional theory calculation for H2 dissociation on MoS2 and NiMoS cluster models
Journal of Molecular Structure: THEOCHEM, 2005
Quantum chemical calculations for H 2 dissociation on NiMoS and MoS 2 catalysts were carried out using the ab initio density functional theory and the pseudopotential approaches. The catalysts were modeled by XMo 4 S 17 H 16 , XZNi, Mo cluster models. Two dissociation route, the heterolytic and the homolytic, were studied on the MoS 2 cluster model. The results show that the homolytic dissociation is favored over the heterolytic route. On the NiMoS cluster model, the homolytic route is less favored thermodynamically than in the MoS 2 . The topological analysis of the electron density indicates the presence of S 2 groups on the MoS 2 and NiMoS surfaces, as well as a Mo-Mo bond in the MoS 2 model. No Ni-Mo bond was found in the NiMoS cluster model. The presence of Ni activates the Mo-S bond, produces a polarization at this bond and decreases the chemical hardness of the solid. q