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Micron-sized supports of catalytically active nanoparticles (NPs) can become a good alternative to nanocarriers if their structure is properly tuned. Here, we show that a combination of simple and easily scalable methods, such as defect engineering and polyol synthesis, makes it possible to obtain Ag and MgO nanoparticles supported on defective hexagonal BN (h-BN) support with high catalytic activity in the CO oxidation reaction. High-temperature annealing in air of Mg-containing (

A new scheme is presented for obtaining a pure spin state for the one-determinant wave function built on Hartree–Fock or Kohn–Sham orbitals. In this scheme, the unrestricted determinant is expanded in restricted determinants constructed in the basis set of spin-paired orbitals. Using spin projection, one can determine spin density components corresponding to pure spin states and estimate the weight of spin contaminants in the spin density. The efficiency of this approach is demonstrated on the example of methane oxidation. It is shown that self-consistent solutions of Hartree–Fock or Kohn–Sham equations with broken spin symmetry are not an artifact of one-determinant approximation. The equations reflect real spin polarization that creates negative spin density in some parts of the molecular system.

The hydroisomerization of n-paraffins to mono-methyl branched isomers on bifunctional metal acid-zeolite catalysts has been commonly considered in terms of the heuristic pore-mouth catalysis model developed to explain the highly selective formation of the monobranched isomer with the methyl group at the C2 position. This work presents a theoretical support of the pore-mouth model on the basis of semi-quantitative estimates of the entropy change upon adsorption at the opening of the zeolite channel and inside the pore, and the DFT calculated enthalpy for 3-heptene adsorption on the ZSM-23 zeolite. A key prediction is the entropy-driven preference for alkene (assumed to be readily produced by metal particle on the zeolite surface) to adsorb and isomerize only at the mouth of the zeolite pore being trapped by the Bronsted acid site via the alkene double bond located near the end of the molecule. This effect explains the origin of the pore-mouth catalysis and positional selectivity of the skeletal isomerization.

The substitution of A and B cations in SrFeO3 and SrCoO3 oxides with the perovskite structure ABO3 is studied using ab initio DFT calculations in terms of their effect on the structural and electronic properties of these compounds. It is shown that the main effect of Nb, Ta, Mo, W substituents refers to the local increase of the cohesive energy (the decrease of the total energy) of the oxides. This change may reach 10 kJ/mol per 1% of the B dopant.

The O-O coupling process in water oxidation on the gamma FeOOH hydroxide catalyst is simulated by means of density functional theory using model iron cubane cluster Fe4O4(OH)4. A key reactive intermediate is proposed to be the HO-FeIV-O• oxyl unit with terminal oxo radical formed from vertex HO-FeIV-OH moiety by withdrawal of proton-electron pair. The O-O coupling goes via water nucleophilic attack on the oxyl oxygen to form the O-O bond with a remarkably low barrier of 11 kcal/mol. This process is far more effective than alternative scenario based on direct interaction of two ferryl FeIV=O sites (with estimated barrier of 36 kcal/mol) and is comparable with the coupling between terminal oxo center and three-coordinated lattice oxo center (12 kcal/mol barrier). The process of hydroxylation of terminal oxygen inhibits the O-O coupling. Nevertheless, being more effective for ferryl oxygen, the hydroxylation in fact enhances selectivity of the O-O coupling initiated by the oxyl oxygen.

Oxides with perovskite structure SrFeO3 and SrCoO3 are ancestors of wide range of technologically important substances, used as oxide ionic conductors. Previously we use the substitution of the cations in the B positions by high-charge ions Mo6+ W6+ Ta5+ Nb5+ to modify the properties of this class of oxygen-deficient oxides. Doping with these elements suppressed phase transitions in oxides based on cobalt-ferrite strontium-barium, reduced the size of nanodomains and rise chemical and structure stability of these oxides. Now we performed the theoretical study of the influence of A- and B- substitution on electronic structure of SrFeO3 and SrCoO3 in the order to clarify how the doping by high-charge cations affects the properties and electronic structure of oxides.

The oxidative coupling of methane using the MnNaW/SiO 2 catalyst was considered for the W-Mn two-metal-site model on the (111) surface of α-cristobalite by DFT means in the cluster approximation. The crucial step of this process, namely, the hydrogen abstraction from methane is assumed to proceed on whether the terminal W O or the Mn O group. The energy barrier for the methane dissociation on the tungsten species was predicted to be much higher than that for manganese. This allows one to suggest that the Mn species are responsible for hydrogen abstraction from methane. The W species are suggested to play a role in the ethane formation on the surface from tungsten bound methoxy group and govern selective oxidative dehydrogenation of ethane.

Surveyed in this review are the most important achievements in the research and development of catalysts based on Mn, Fe, Co, and Cu hydroxides for the oxidation of water to molecular oxygen by chemical oxidizing agents obtained, for the most part, at Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences. An analysis of the results of kinetic studies on water oxidation in the presence of the above-menthioned catalysts together with data obtained by quantum chemistry methods allowed us to make a conclusion on the general nature and process mechanism both in the presence of artificial catalytic systems based on metal hydroxides and the natural enzyme photosystem II of green plants. The most important properties of hydroxo compounds responsible for catalytic activity in the oxidation of water by one-electron oxidants are discussed, and a possible reaction mechanism is considered.

Reactivity of the [FeO]2+ group in the abstraction of hydrogen from methane is determined by metastable oxyl state FeIII O causing the negative spin polarization of the methyl moiety as was shown by quantum-chemical means with the use of model iron hydroxide species FeO(OH)2, Fe2O(OH)5, and Fe4O5(OH)3 as an example. The energy of the gap between the ground-state ferryl configuration FeIV O and the oxyl state correlates with the energy barrier of the H-abstraction from methane.

The rearrangement of the NO ligand in ruthenium nitrosyl tetraammine complexes trans-[Ru(NO)(NH3)4X]2+ (X = F―, Cl―, OH―, SH―) has been studied for metastable oxygen-coordinated NO complex by means of DFT. On base of obtained data this rearrangement is concluded to be caused by ligand-to-metal charge transfer of the p(X) → π*(Ru-ON) type. The excitation energy for electron transfer from p-orbital of ligand to LUMO correlates perfectly with the activation energy of isomerization. Found correlations are explained in terms of electronegativity of the trans ligand X.

This work is a brief review of the authors’ applications of Lowdin–Amos–Hall paired orbitals for the analysis of spin-polarized DFT solutions. The possibilities of this approach are demonstrated on the example (1) of models of Fe(III) hydroxocomplexes with two forms of the terminal oxo center, which are involved in the detachment of methane hydrogen, and (2) models of vanadium oxide experiencing the dissociation of the vanadyl group.

The abstraction of hydrogen from methane on the terminal iron-oxo group in the ferryl Fe IV O and oxyl Fe III O states, the hydrogen peroxide group Fe OOH and the peroxo group Fe OO Fe created in iron hydroxide was modeled by means of the density functional theory. The active groups were built using the Fe 4 O 4 (OH) 4 starting complex having one hydrogen removed imitating the effect of the external oxidizer. Among considered groups the oxyl group is predicted to have the highest reactivity. A clear distinction in reactivity between the Fe III O and Fe IV O quasi-degenerate states has been attributed to the sign of terminal oxygen spin polarization.

The formation of the O O bond in the water oxidation catalyzed by the iron hydroxides was modeled with the Fe 4 O 4 (OH) 4 and Fe 2 O 2 (OH) 4 complexes by means of the density functional theory. Consideration of the local minima and transition states for various routes of the association of oxo- and hydroxo-centers reveals a determinative role of the oxyl radical center Fe III O − in facilitating this process. The preferable scenario comprises two steps: (1) the abstraction of the electron and proton from the initial complex leaving behind a ferryl FeO group, and (2) the incorporation of ferryl oxygen into the tetramer edge to form peroxo group.

Pr2NiO4+δ oxide with a layered Ruddlesden–Popper structure is a promising material for SOFC cathodes and oxygen separation membranes due to a high oxygen mobility provided by the cooperative mechanism of oxygen migration involving both interstitial oxygen species and apical oxygen of the NiO6 octahedra. Doping by Ca improves thermodynamic stability and increases electronic conductivity of Pr2 − xCaxNiO4+δ, but decreases oxygen mobility due to decreasing the oxygen excess and appearing of 1–2 additional slow diffusion channels at x ≥ 0.4, probably, due to hampering of cooperative mechanism of migration. However, atomic-scale features of these materials determining oxygen migration require further studies. In this work characteristics of oxygen diffusion in Pr2 − xCaxNiO4+δ (x = 0–0.6) are compared with results of the surface analysis by X-ray photoelectron spectroscopy and modeling of the interstitial oxygen migration by the plane-wave density functional theory calculations. According to the X-ray photoelectron spectroscopy data, the surface is enriched by Pr for undoped sample and by Ca for doped ones. The O1s peak at ~531 eV corresponding to a weakly bound form of surface oxygen located at Pr cations disappears at ~500 °C. Migration of interstitial oxygen was modeled for a I4/mmm phase of Pr2NiO4+δ. The interstitial oxygen anion repulses the apical one in the NiO6 octahedra pushing it into the tetrahedral site between Pr cations. The calculated activation barrier of this migration is equal to 0.585 eV, which reasonably agrees with the experimental value of 0.83 eV obtained by the oxygen isotope exchange method. At the same time, for the model compound Ca2NiO4+δ, obtained by isomorphic substitution of Pr by Ca in Pr2NiO4+δ, calculations implied formation of the peroxide ion comprised of interstitial and lattice oxygen species not revealed in the case of incomplete substitution (up to PrCaNiO4+δ composition). Hence, calculations in the framework of the plane-wave density functional theory provide a realistic estimation of specificity of oxygen migration features in Pr2NiO4+δ doped by alkaline-earth metals. © 2019 Elsevier B.V. Russian Science Foundation, RSF: 16-13-00112 Support by Russian Science Foundation (Project 16-13-00112 ) is gratefully acknowledged.

A decomposition of the spin density into the net spin density and polarization density for the unrestricted Kohn–Sham (KS) determinant in the basis of Lowdin–Amos–Hall paired orbitals (PO) is derived. In PO basis set, the net spin part of spin density is only determined by the manifold of occupied α-spin orbitals which do not overlap with occupied β-spin orbitals. In its turn, the polarization part is associated with the pairs of overlapping α and β orbitals. The decreased overlap in these pairs corresponds to the increased degree of spin polarization. As an example of the developed spin density decomposition, the complex of FeO with nitrobenzene (taken in the state with spin projection of Sz = 2) is considered for the B3LYP solution revealing substantial spin contamination for the KS determinant. The spin density decomposition predicts for this complex appreciable polarization density over the whole complex while the net spin density remains counter intuitive almost intact at FeO center. This result changes presumed mechanism of metal-to-ligand transfer of unpaired electrons from paramagnetic center to diamagnetic ligand having a high electron affinity. © 2012 Wiley Periodicals, Inc.

The structure and stability of small neutral and positively charged zinc oxide (ZnO)n clusters (n = 2−9) have been studied within the density functional theory. For n ≤ 7, the most stable clusters are shown to be flat rings; for n = 8, 9, the clusters are mainly three-dimensional cage structures. The energies and main channels of fragmentation of the clusters have been determined. It has been found that the fragmentation of the charged clusters with n > 6 occurs predominantly with formation of a (ZnO)4+ ion, which explains the available mass spectrometric data on ionization of the zinc oxide clusters by electron impact.

Density functional theory in the plane wave basis set is used to study As adsorption on the Pd(111) surface in order to determine the action of a palladium chemical modifier used in electrothermal atomic absorption spectrometry (ETAAS). The calculated heat of desorption of the arsenic atom is 435 kJ/mole, which corresponds to the activation energy of arsenic atomization of 439 kJ/mole (in the range of high temperatures T > 1828 K), obtained by ETAAS. Based on the calculated data, the action of the palladium modifier for the determination of As is assumed to be controlled by the process of chemisorption.

Adsorption species of ethyl benzoate (EB) on the (104) and (110) MgCl2 surfaces have been studied within DFT. As a result, monodentate and bidentate complexes of EB were obtained on both the MgCl2 surfaces. The bidentate structures on the (104) MgCl2 surface proved to be stabilized by the decreased distance between neighboring adsorption sites (surface Mg cations). The different affinity of EB for the five- and four-coordinated Mg cations predicted was suggested to be the cause of changing the equilibrium shape of MgCl2 crystals upon growing in the presence of EB: EB chemisorption seems to stabilize the (110) MgCl2 surface to a greater degree as compared to the (104) MgCl2 surface. The influence of EB coordination mode on active site stereoselectivity is discussed.

A systematic consideration of different Ti(IV) and Ti(III) species on the (104) and (110) MgCl2 surfaces has been implemented within DFT using cyclic boundary conditions. Some new mononuclear and dinuclear surface complexes of Ti(IV) and Ti(III) were obtained due to implication of zip coordination mode. A possible spin state of dinuclear Ti(III) species was thoroughly studied: antiferromagnetic (ESR silent) state proved to be the most preferable in a number of cases. The zip antiferromagnetic Ti2Cl6 complexes residing on the dominant (104) MgCl2 surface make it possible to rationalize the fact that the most part of Ti(III) incorporated in activated MgCl2 is ESR silent. Besides, these species produce aspecific active sites, thus explaining that aspecific centers significantly prevail over stereospecific one according to kinetic data on the simplest TiCl4/MgCl2 + AlR3 system.

Atomic forms of oxygen on the (111) face of metallic silver are studied by the NDDO/MC semiempirical method. The surface (above the octahedral void) and subsurface (within the void) positions of oxygen between the first and second layers of the (111) face are investigated. The potential surface cross section is calculated for the subsurface position of oxygen. A new approach is used to take into account surface relaxation due to reaction with adsorbate. The barrier of atomic oxygen diffusion through the surface is much lower than the banier of its desorption from the surface. The correlation correction to the diffusion and desoption barrier energies is estimated by the double CI (DCIP) method. The greatest correlation effects are obtained in the desorption banier calculation.

Anion-radical form of the oxygen centers O − is predicted at the DFT level for small silver oxide particles having the AgO stoichiometry. Model clusters (AgO) n appear to be ferromagnetic with appreciable spin density at the oxygen centers. In contrast to these clusters, the Ag 2 O model cluster have no unpaired electrons in the ground state. The increased O/Ag ratio in the oxide particles is proved to be responsible for the spin density at oxygen centers.

Eigenvalue-type equations for Lowdin-Amos-Hall spin-paired (corresponding) orbitals are developed to provide an alternative to the standard spin-polarized Hartree-Fock or Kohn-Sham equations in dealing with broken-symmetry (BS) states. To derive paired orbitals for different spins (PODS) equations there has been applied Adams-Gilbert "localizing" operator approach. The PODS equations contain different operators for different spins the eigenvectors of which are paired orbitals associated with the same eigenvalue for each pair. Preliminary applications to simple systems show viability of this approach. Although the spectrum of possible applications of the PODS equations seems to be quite wide, they would be especially useful for obtaining and analyzing the S(z) = 0 BS solutions for the systems with antiferromagnetic structure.