Oxidative dehydrogenation of propane to propylene over a monolayer vanadia-titania catalyst was studied in situ using Fourier transform infrared spectroscopy (FTIRS). It was found that two types of active species capable of activating C–H bonds exist on the catalyst surface: vanadyl oxygen species (V = O) and hydroxyl groups (V–OH). The adsorption of propane onto vanadyl oxygen activates a C–H bond, subsequently initiating the transfer of a proton from the methylene group to another vanadyl oxygen, which leads to the formation of a new hydroxyl group and an isopropyl group. Alternatively, propane can adsorb onto a surface hydroxyl group to form a hydrogen-bonded complex. This surface complex is unstable and can decompose via the cleavage of a C–H bond in a methyl group, transferring the proton to the nearest vanadyl oxygen to form a new hydroxyl group and hydrogen-bonded n-propyl group. These findings indicate that the dehydrogenation of propane over the monolayer V 2 O 5 /TiO 2 catalyst can proceed via at least two distinct reaction pathways, initiated either by the adsorption of propane onto vanadyl oxygen species or onto the surface hydroxyl groups. The energy profiles for these pathways were calculated using the density functional theory (DFT). The DFT calculations demonstrated that the pathway initiated by the formation of a hydrogen-bonded complex between surface hydroxyl groups and propane is more thermodynamically favorable than the pathway starting with the adsorption of propane onto vanadyl oxygen species. In both pathways, two C–H bonds are cleaved and two protons are transferred to the vanadyl oxygen species to form new hydroxyl groups and propylene.

Quantum chemical modeling of CO oxidation on the Cu12S6(PH3)8 and Cu12S6 clusters was performed in order to establish the general tendencies in the process on metal nanoclusters stabilized by ligands and to find out if the presence of a phosphine ligand is needed in the active site. The Langmuir–Hinshelwood mechanism was studied, which involves sequential oxidation of two CO molecules with oxygen. The calculated activation energies on Cu12S6(PH3)8 are lower than on Cu12S6 for all oxidation stages; therefore, the PH3 ligands have a positive effect on the catalytic properties of the copper sulfide cluster in the CO oxidation. A linear correlation was found between the energy of CO adsorption on various copper sulfide clusters and the activation energy of the oxidation stage: the lowest activation energy is observed for the cluster with a CO adsorption energy of 36 kJ/mol.

Density functional theory (DFT) (PBE) was used to simulate the breaking of C–H bond in methane on copper-enriched Ni–Cu clusters as the first step of dry reforming of methane. The models of catalysts were the nanoscale clusters NiCu11S6(PH3)8, NiCu11S6, NiCu11O6(PH3)8, and NiCu11O6. The binding energy of methane with the clusters was calculated, and the activation energy of the step CH4* → CH_3^* + H* was determined. It was found from the obtained data that the NiCu11O6 catalytic system is the most promising for CH4 activation in terms of both kinetics (activation energy is 99 kJ/mol) and thermodynamics (energy change of the step is –29 kJ/mol). The coking resistance of the NiCu11O6 cluster was estimated by simulating the CH adsorption followed by dissociation (CH* → C* + H*). The calculated activation energy of this step is rather high: 159 kJ/mol.

Density functional theory (DFT) (PBE) is used to calculate the structure of bimetallic clusters Cu@Au19(SCH3)16 and Ag@Au19(SCH3)16, which are of interest as precursors for obtaining nanoparticles of controlled size. It is shown that silver occupies a position in the core of a cluster, while copper can be found in both the core and its shell. Models of O2 and CO adsorption on Cu@Au19(SCH3)16 and Ag@Au19(SCH3)16 show that copper in a cluster’s shell promotes the activation of CO. In a cluster’s core, it has a positive effect on the gold atoms of the staple fragment, enhancing the activation of CO. O2 can be activated on Cu(shell)@Au19(SCH3)16, making the latter a promising catalytic system for reactions with the participation of O2 and SO.

Au and Ag were deposited on TiO2 modified with Ce, La, Fe or Mg in order to obtain bimetallic catalysts to be used for liquid-phase oxidation of 1-octanol. The effects of the deposition order of gold and silver, and the nature of the support modifying additives and redox pretreatments on the catalytic properties of the bimetallic Au-Ag catalysts were studied. Catalysts were characterized by low-temperature nitrogen adsorption–desorption, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and ultraviolet-visible diffuse reflectance spectroscopy. It was found that pretreatments with hydrogen and oxygen at 300 °C significantly decreased the activity of AuAg catalysts (silver was deposited first) and had little effect on the catalytic properties of AgAu samples (gold was deposited first). The density functional theory method demonstrated that the adsorption energy of 1-octanol increased for all positively charged AuxAgyq (x + y = 10, with a charge of q = 0 or +1) clusters compared with the neutral counterparts. Lanthanum oxide was a very effective promoter for both monometallic and bimetallic gold and silver catalysts in the studied process.

The efficiency of Au/TiO2 based catalysts in 1-phenylethanol oxidation was investigated. The role of support modifiers (La2O3 or CeO2), influence of gold loading (0.5% or 4%) and redox pretreatment atmosphere, catalyst recyclability, effect of oxidant: tert-butyl hydroperoxide (TBHP) or O2, as well as the optimization of experimental parameters of the reaction conditions in the oxidation of this alcohol were studied and compared with previous studies on 1-octanol oxidation. Samples were characterized by temperature-programmed oxygen desorption (O2-TPD) method. X-ray photoelectron spectroscopy (XPS) measurements were carried out for used catalysts to find out the reason for deactivation in 1-phenylethanol oxidation. The best catalytic characteristics were shown by catalysts modified with La2O3, regardless of the alcohol and the type of oxidant. When O2 was used, the catalysts with 0.5% Au, after oxidative pretreatment, showed the highest activity in both reactions. The most active catalysts in 1-phenylethanol oxidation with TBHP were those with 4% Au and the H2 treatment, while under the same reaction conditions, 0.5% Au and O2 treatment were beneficial in 1-octanol oxidation. Despite the different chemical nature of the substrates, it seems likely that Au+(Auδ+) act as the active sites in both oxidative reactions. Density functional theory (DFT) simulations confirmed that the gold cationic sites play an essential role in 1-phenylethanol adsorption.

CO preferential (PROX) and total (TOX) oxidation were studied over Pt and Pt0.5Co0.5 nanopowders. Pt0.5Co0.5 exhibited much higher CO PROX performance than Pt, being highly active and selective at 0-80 degrees C. Low-temperature activity in CO oxidation was shown to be the key feature of bimetallic Pt-Co catalysts in comparison with monometallic Pt. Density functional theory calculations of the oxidation of CO on Pt-13 and Pt12Co clusters revealed that a better catalytic activity of bimetallic cluster is due to an electronic effect: the calculated atomic charges on platinum atoms change when cobalt is introduced into its composition. (C) 2019 Elsevier B.V. All rights reserved.

This study aims to identify the role of the various electronic states of gold in the catalytic behavior of Au/MxOy/TiO2 (where MxOy are Fe2O3 or MgO) for the liquid phase oxidation of n-octanol, under mild conditions. For this purpose, Au/MxOy/TiO2 catalysts were prepared by deposition-precipitation with urea, varying the gold content (0.5 or 4 wt.%) and pretreatment conditions (H2 or O2), and characterized by low temperature nitrogen adsorption-desorption, X-ray powder diffraction (XRD), energy dispersive spectroscopy (EDX), scanning transmission electron microscopy-high angle annular dark field (STEM HAADF), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy of CO adsorption, temperature-programmable desorption (TPD) of ammonia and carbon dioxide, and X-ray photoelectron spectroscopy (XPS). Three states of gold were identified on the surface of the catalysts, Au0, Au1+ and Au3+, and their ratio determined the catalysts performance. Based on a comparison of catalytic and spectroscopic results, it may be concluded that Au+ was the active site state, while Au0 had negative effect, due to a partial blocking of Au0 by solvent. Au3+ also inhibited the oxidation process, due to the strong adsorption of the solvent and/or water formed during the reaction. Density functional theory (DFT) simulations confirmed these suggestions. The dependence of selectivity on the ratio of Brønsted acid centers to Brønsted basic centers was revealed.

Features of various Fe-containing nanosized slurry Fischer-Tropsch catalysts, obtained in situ by thermolysis, were investigated experimentally (catalytic tests, XRD, hermomagnetometric methods) and theoretically (DFT ab initio calculations, regression analysis). XRD patterns of the samples reveal the presence of preferentially single Fe7C3, Fe5C2 and Fe2C. A quantitative correlation was found between the values of the most important hydrocarbon group selectivity at 260 degrees C and the residual magnetization of the spent samples, regardless of promoter nature and amount. The Fe7C3 model clusters, according to the DFT results, prefer to be in high-spin states and substantiate the preference of associative coordinated CO. Because the CO associative sorption is unfavourable for chain growth on Fe Fischer-Tropsch catalysts and the carbides have Curie points <260 degrees C, the presence of nanosized paramagnetic carbide particles has been suggested to cause the abovementioned correlation. (C) 2019 Elsevier Inc. All rights reserved.

The oxidation of CO over Pt and Pt–Co catalysts was studied both experimentally and by quantum-chemistry calculations. Density functional theory simulation shows that CO is oxidized on Pt13 via dissociative oxygen adsorption. The calculated activation energy for the dissociation of O2 on Pt13 is 56 kJ/mol. It is found that when a cobalt atom is introduced into the cluster, the activation energy falls for the stages of CO oxidation and the dissociation of O2. Catalytic tests performed on Pt and Pt0.5Co0.5 nanopowders confirm the Pt–Co system displays high activity in the oxidation of CO.

The structure and reactivity of rhombic Au4 cluster protected by bis(dimethylphosphinomethyl) and phenylacetylide ligands towards CO and O2 were studied in scalar-relativistic DFT/PBE approach. The cluster is inert to noticeable CO binding or activation, while it reacts with O2 and forms peroxide [O2Au4(dmmp)2(С ≡ CCH3)2]2+ complexes. The CO oxidation on the cluster was simulated. According to the calculation and analysis of different pathways of reaction, the Au–P fragments of the cluster are the most probable active sites. The protected gold clusters are predicted to be promising heterogeneous catalysts in CO oxidation.

The interaction of CO and O 2 and the subsequent oxidation of CO in the presence of cyclic thiolate and dithiolate complexes of Au(I), which represent the model fragments of thiolate-protected gold clusters, were studied using the density functional theory (PBE). On the basis of the calculated values, it was shown that O 2 and CO were weakly bound to a cyclic thiolate complex of Au(I). In the presence of a dithiolate complex, the activation of O 2 and CO and the subsequent oxidation of CO occurred with low activation energies. The results obtained demonstrate the important role of ligands in the catalytic process.

The article is devoted to results of systematic study of the structure transformation of V2O5 supported on TiO2 (anatase). The effect of (001) TiO2-anatase on the structural properties and morphology of V2O5 was analyzed using the spin-polarized density functional theory (DFT) in the periodic approach. The calculations were performed using the VASP code with PBE energy functional and plane wave basis set. The catalyst is represented as a periodic surface. The supercell includes four Ti – O layers and the top V2O5 layer. A lot of different forms of V2O5 (monomeric and polymeric structures, individual crystallites) on the TiO2 surface were considered. According to the calculations of the adsorption energy, vanadium oxide on the oxide composite surface can form various forms. The monomeric form is the most stable. Calculated value of adsorption energy is -1.16 eV. The ionic interaction causes a significant change in the interatomic distances between the vanadium atom and the oxygen atom from the support d (V – O (Ti)) for all active forms. The highest value d (V – O (Ti)) was found for catalyst with the polymeric active form. It suggests that the binding of the form with the anatas is the smallest. Theoretical studies have shown that the V2O5/TiO2 system is dynamic and can change the surface structure under the different conditions.

A procedure based on density functional theory is proposed for calculation of Au20(ХCH3)16 (Х = S, Se, Te) isomers. It is established that the most stable isomer for all X has a core‒shell structure: Au7@(AuXCH3)8(XCH3(AuXCH3)3)(XCH3AuXCH3)2. Optical and IR spectra, ionization potential, and electron affinity are calculated for the first time for all clusters. It is shown that a cluster protected by thiolate ligands has the greatest electronic and thermodynamic stability.