The mechanism of selective NO<Subscript>x</Subscript> reduction by hydrocarbons in excess oxygen on oxide catalysts: VI. Spectroscopic and kinetic characteristics of surface complexes on a Ni-Cr oxide catalyst

The reaction mechanism of the selective catalytic reduction of NO_x by propane in the presence of O₂ on a commercial Ni-Cr oxide catalyst was studied using in situ IR spectroscopy. It was found that nitrite, nitrate, and acetate surface complexes occurred under reaction conditions. Considerable amounts of hydrogen were formed in the interaction of NO + C₃H₈ + O₂ or C₃H₈ + O₂ reaction mixtures with the catalyst surface. The rates of conversion of the surface complexes detected under reaction conditions were measured. The resulting values were compared to the rate of the process. It was found that, at temperatures lower than 200°C, nitrate complexes reacted with the hydrocarbon to form acetate complexes; in this case, the formation of reaction products was not observed. In the temperature region above 250°C, two reaction paths took place. One of them consisted in the interaction of acetate and nitrate complexes with the formation of reaction products. The decomposition of NO on the reduced surface occurred in the second reaction path. Nitrogen atoms underwent recombination, and oxygen atoms reoxidized the catalyst surface and reacted with the activated hydrocarbon to form CO₂ and H₂O in a gas phase.     

Spectrokinetic study of the mechanism of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> reduction with propylene over ZrO<Subscript>2</Subscript> in excess oxygen

It has been demonstrated by quantitative spectrokinetic measurements that, on the surface of zirconia stabilized as a tetragonal phase, the rate-limiting step of the selective catalytic reduction of nitrogen oxides (SCR of NO _x ) with propylene is the interaction of surface nitrates with C₃H₆ yielding organic nitro compounds. It is hypothesized that propylene reacts not with the nitrates themselves but with the activated complex NO₂ ^ads whose structure is intermediate between the structures of the monodentate NO₃ ^? and NO₂ species. Deep C₃H₆ oxidation exerts an adverse effect on the rate of the SCR of NO _x with propylene, and the interaction between O₂ and NO, which yields NO₂ and NO₃ ^? stimulates further nitrogen reduction to N₂. The effect of the reaction between oxygen and O₂N?C _n H _m on the NO _x reduction rate is variable and is determined by the C₃H₆/NO _x ratio. A generalized scheme of the SCR of NO _x with propylene on the surface of ZrO₂ partially stabilized as a tetragonal phase has been developed by comparing experimental data of this study and data available from the literature.     

Selective oxidation of carbon monoxide in hydrogen-containing gas on CuO-CeO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts prepared by surface self-propagating thermal synthesis

The CuO-CeO₂/Al₂O₃ catalysts for the selective oxidation of CO in hydrogen-containing mixtures were prepared by surface self-propagating thermal synthesis (SSTS) with the use of cerium nitrate Ce(NO₃)₃, the ammonia complex of copper acetate [Cu(NH₃)₄](CH₃COO)₂, and citric acid C₆H₈O₇ as a fuel additive. The effect of the C₆H₈O₇/Ce(NO₃)₃ molar ratio on the catalyst activity and selectivity for oxygen was studied. The catalyst samples were studied by X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR-H₂), IR spectroscopy of adsorbed CO, and transmission electron microscopy (TEM). It was found that an increase in the C₆H₈O₇/Ce(NO₃)₃ ratio resulted in an increase in the degree of dispersion of the resulting CeO₂ phase. The greatest amount of dispersed CuO particles, which are responsible for catalytic activity in the oxidation of CO, was formed at C₆H₈O₇/Ce(NO₃)₃ = 1.     

Interactions in the system Mn(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-HCONH<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

Solubilities and solid phases in the system Mn(NO₃)₂-HCONH₂-H₂O were studied by an isothermal method at 25°C. The congruently saturating compound Mn(NO₃)₂ · 2HCONH₂ · 2H₂O was isolated; the concentration conditions for its crystallization in the system were determined. The solid phases of the system were characterized by physicochemical methods (X-ray powder diffraction, differential thermal analysis, IR spectroscopy, and crystal-optical analysis).     

Kinetics and reaction mechanism of phenol hydroxylation catalyzed by La-Cu<Subscript>4</Subscript>FeAlCO<Subscript>3</Subscript>

The present work synthesizes La-Cu₄FeAICO₃ catalyst under microwave irradiation and characterizes its structure using XRD and IR techniques. The results show that the obtained La-Cu₄FeAICO₃ has a hydrotalcite structure. In the phenol hydroxylation with H₂O₂ catalyzed by La-Cu₄FeAICO₃, the effects of reaction time and phenol/H₂O₂ molar ratio on the phenol hydroxylation, and relationships between the initial hydroxylation rate with concentration of the catalyst, phenol, H₂O₂ and reaction temperature are also investigated in details. It is shown the phenol conversion can reach 50.09% (mol percent) in the phenol hydroxylation catalyzed by La-Cu₄FeAICO₃, under the reaction conditions of the molar ratio of phenol/H₂O₂1/2, the amount ratio of phenol/catalyst 20, reaction temperature 343 K, reaction time 120 min, 10 ml_ distilled water as solvent. Moreover, a kinetic equation of v = k[La-Cu₄FeAlCO₃][C₆H₅OH][H₂O₂]. and the activation energy of E _a=58.37 kJ/mol are obtained according to the kinetic studies. Due to the fact that the HO-Cu⁺-OH species are detected in La-Cu₄FeAICO₃/H₂O₂ system by XPS, the new mechanism about the generation of hydroxyl free radicals in the phenol hydroxylation is proposed, which is supposed that HO-Cu⁺-OH species are transition state in this reaction.     

Glass formation in the Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>-Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system

Glass formation boundaries in the Al₂(SO₄)₃-Al(NO₃)₃-H₂O system were determined. IR spectra were studied. Schemes of structural rearrangements within the boundaries of a second glass formation region in the Al(NO₃)₃-H₂O binary subsystem are suggested. A structure is suggested for glassy Al(NO₃)₃H₂O.     

Tin trifluoroacetylacetonate [Sn(C<Subscript>5</Subscript>H<Subscript>4</Subscript>O<Subscript>2</Subscript>F<Subscript>3</Subscript>)<Subscript>2</Subscript>] as a precursor of tin dioxide in APCVD process

A new method of synthesis of volatile complex, tin trifluoroacetylacetonate [Sn(C₅H₄O₂F₃)₂], was proposed. The prepared compound was identified by IR spectroscopy, CH analysis, X-ray powder diffraction, and DTA/TGA, the composition was confirmed by MALDI-TOF mass spectrometry, crystal structure was established. Thin films of tin dioxide on silicon were obtained by atmospheric pressure chemical vapor deposition using [Sn(C₅H₄O₂F₃)₂] as a precursor. The morphology and composition of the films were studied by scanning electron microscopy, EDX elemental analysis, and X-ray powder diffraction. Surface resistance and light transmission in visible and near IR region were studied.     

Photochemical properties of mixed-ligand europium compounds of Eu(C<Subscript>10</Subscript>H<Subscript>11</Subscript>F<Subscript>7</Subscript>O<Subscript>2</Subscript>)<Subscript>3</Subscript>D composition

The intensively luminescing mixed-ligand europium compounds were synthesized of the composition Eu(C₁₀H₁₁F₇O₂)₃D, where C₁₀H₁₁F₇O₂ is heptafluorodimethyloctanedione, D is either 1,10-phenanthroline (C₁₂H₈N₂), triphenylphosphine oxide (C₁₈H₁₅PO), hexamethylphosphoramide (C₆H₁₈N₃PO), benzotriazole (C₆H₅N₃), or phenylguanidine [(C₆H₅NH)₂ =NH]. The luminescent properties of europium compounds in the crystalline state and in a polymer matrix of high-pressure polyethylene (HPPE) and polyvinyl chloride (PVC) and kinetics of the luminescence intensity decay under UV radiation were studied. The most photo-resistant in HDPE and PVC was found to be Eu(C₁₀H₁₁F₇O₂)₃Ph₃PO.     

Thermal decomposition of gallium nitrate hydrate Ga(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>×<Emphasis Type="Italic">x</Emphasis>H<Subscript>2</Subscript>O

The thermal decomposition of gallium nitrate hydrate (Ga(NO₃)₃·xH₂O) to gallium oxide has been studied by TG/DTG and DSC measurements performed at different heating rates. It is concluded that 8 water molecules are present in the hydrate compound. The anhydrous gallium nitrate does not form at any temperature as the reaction consists of coupled dehydration/decomposition processes that occur with a mechanism dependent on heating rate. TG measurements performed with isothermal steps (between 31 and 115°C) indicate that Ga(OH)₂NO₃ forms in the first stage of the reaction. Such a compound undergoes further decomposition to Ga(OH)₃ and Ga(NO₃)O, compounds that then decompose respectively to Ga(OH)O and finally to Ga₂O₃ and directly to Ga₂O₃. Diffuse reflectance Fourier transform IR spectroscopy (DRIFTIR) has been of help in assessing that the reaction consists of parallel dehydration/decomposition processes.     

Reaction of Organyltrifluorosilanes with Dimethylsulfoxide and Domethylformamide and Its Spectroscopic Investigation

Reaction of organyltrifluorosilanes RSiF₃ (R = C₆H₅, 3-O₂NC₆H₄, and C₆H₅CH₂) with DMSO and DMF (B) results in formation of the complexes 2B·SiF₄ and R₂SiF₂. Besides, biphenyl, benzene, methyl(fluoromethyl)sulfoxide, and S,S'-dimethyldisulfide-S,S'-dioxide CH₃S(O)S(O)CH₃ were either isolated or identified by chromatomass-spectrometry. Speculative mechanism of the reaction proceeding is discussed. IR spectra of the reaction mixtures and those of 2B·SiF₄ adduct were studied in details; they indicate octahedron structure of the complex with cis arrangement of B ligands.     

Über Cyanatverbindungen und deren reaktives Verhalten. IX. Reaktionsverhalten von Vanadin(III)-thiocyanat gegenüber Pyridin-N-oxiden

V(NCS)₃ or V(NCS)₃(THF)₃ reacts under various conditions with pyridine-N-oxide to oxovanadium(IV)-complexes of the type VO(NCS)₂ · 4C₅H₅NO and VO(NCS)₂ · 5C₅H₅NO. Reactions with 4-picoline-N-oxide lead to VO(NCS)₂(4-CH₃C₅H₄NO₂)₂. The prepared compounds are characterised by analytical data, their spectral and magnetic properties, and IR absorption spectra. The mechanism of the reaction is discussed.     

Sodium tris(glycinium) bis(hexafluorosilicate) glycine trisolvate

The title compound, Na⁺·3C₂H₆NO₂⁺·2SiF₆²⁻·3C₂H₅NO₂, arose from an unexpected reaction of glycine and HF with the glass container. It is an unusual hybrid organic–inorganic network built up from chains of vertex‐sharing NaF₄O₂ and SiF₆ octahedra. A pair of glycinium/glycine molecules bridges the chains into a sheet via a centrosymmetric O...H...O link. The other organic species interact with the network by an extensive N—H...F hydrogen‐bond network, including bifurcated and trifurcated bonds. Finally, an extremely short C—H...O interaction (H...O = 2.25 Å) is seen in the crystal structure. The Na atom has site symmetry .     

Calculations of the Bond Dissociation Energies for NO<Subscript>2</Subscript> Scission in Some Nitro Compounds

The X(C,N,O)—NO₂ bond dissociation energy (BDE) for CH₃NO₂, C₂H₃NO₂, C₂H₅NO₂, HONO₂, CH₃ONO₂, C₂H₅ONO₂, NH₂NO₂, (CH₃)₂NNO₂ are computed using the DFT (B3LYP, B3PW91), the single and double-coupled cluster excited (CCSD), and the complete basis set (CBS-Q) methods, with the 6-311G^** and cc-pVDZ basis sets. By comparing the computed energies and experimental results, we find that the DFT method can not give good results of BDE, but, the BDEs generated by the CCSD/cc-pVDZ, CBS-Q are in good agreement with experimental values.     

The mechanism of reduction of NO with H<Subscript>2</Subscript> in strongly oxidizing conditions (H<Subscript>2</Subscript>-SCR) on a novel Pt/MgO-CeO<Subscript>2</Subscript> catalyst: Effects of reaction temperature

Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments using on-line Mass Spectrometry (MS) and in situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS) have been performed to study essential mechanistic aspects of the Selective Catalytic Reduction of NO by H₂ under strongly oxidizing conditions (H₂-SCR) in the 120–300°C range over a novel 0.1 wt % Pt/MgO-CeO₂ catalyst. The N-path of reaction from NO to the N₂ gas product was probed by following the ¹⁴NO/H₂O₂ → ¹⁵NO/H₂/O₂ switch (SSITKA-MS and SSITKA-DRIFTS) at 1 bar total pressure. It was found that the N-pathway of reaction involves the formation of two active NO _x species different in structure, one present on MgO and the other one on the CeO₂ support surface. Inactive adsorbed NO _x species were also found on both the MgO-CeO₂ support and the Pt metal surfaces. The concentration (mol/g cat) of active NO _x leading to N₂ was found to change only slightly with reaction temperature in the 120–300°C range. This leads to the conclusion that other intrinsic kinetic reasons are responsible for the volcano-type conversion of NO versus the reaction temperature profile observed.     

Unusual transformations of difluorosilanone F<Subscript>2</Subscript>Si=O

The structure and properties of fluorosilicon polymer (fluorosil) formed by the reaction of phenyltrifluorosilane with aliphatic alcohols have been studied by the methods of IR, ¹⁹F, ²⁹Si NMR spectroscopy, high temperature mass-spectrometry, derivatography and atom emission analysis. Due to its high reactivity, this polymer readily reacts with glass of the reaction vessel extracting the ions of all metals entering into its composition. Fluorosil formed in a quartz, teflon or polypropylene reactors is characterized by low stability and is slowly decomposed to SiF₄ and SiO₂. Apparently, fluorosil is the product of incorporation of SiF⁴ into the SiO₂ matrix.     

Hydrogen‐bonded frameworks of bis(2‐carboxypyridinium) hexafluorosilicate and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate

In bis(2‐carboxypyridinium) hexafluorosilicate, 2C₆H₆NO₂⁺·SiF₆²⁻, (I), and bis(2‐carboxyquinolinium) hexafluorosilicate dihydrate, 2C₁₀H₈NO₂⁺·SiF₆²⁻·2H₂O, (II), the Si atoms of the anions reside on crystallographic centres of inversion. Primary inter‐ion interactions in (I) occur via strong N—H...F and O—H...F hydrogen bonds, generating corrugated layers incorporating [SiF₆]²⁻ anions as four‐connected net nodes and organic cations as simple links in between. In (II), a set of strong N—H...F, O—H...O and O—H...F hydrogen bonds, involving water molecules, gives a three‐dimensional heterocoordinated rutile‐like framework that integrates [SiF₆]²⁻ anions as six‐connected and water molecules as three‐connected nodes. The carboxyl groups of the cation are hydrogen bonded to the water molecule [O...O = 2.5533 (13) Å], while the N—H group supports direct bonding to the anion [N...F = 2.7061 (12) Å].     

A simple solution route to control synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanomaterials at low temperature and their magnetic properties

A series of nanostructured iron compounds including cubic Fe₃O₄ and orthorhombic FeOOH were synthesized via a facile low temperature (in the range of 60?100°C) solution method. In the whole process, the interaction between FeCl₂·4H₂O and methenamine (C₆H₁₂N₄) was carried out through a reflux device under different reaction conditions such as temperature, solvent, and duration. The samples were detected by XRD, TEM, SAED, physical property measurement system, and Mössbauer spectroscopy, separately. The experiments showed that magnetic mixture nanoparticles had flake and rod morphologies, and cubic Fe₃O₄ took on grain nanostructure. Magnetism measurements indicated that the saturated magnetization of the as-obtained magnetic mixture was lower than that of the cubic magnetite. Mössbauer spectroscopy testified the sample consisting of cubic magnetite rather than γ-Fe₂O₃. In addition, a possible growth mechanism of cubic magnetic nanoparticles under different conditions was discussed.     

Effect of active impurities on the condensation of nanoparticles from supersaturated carbon vapor in the combined laser photolysis of C<Subscript>3</Subscript>O<Subscript>2</Subscript> and H<Subscript>2</Subscript>S

The effect of active H₂S, HS^·, and atomic hydrogen impurities on the condensation of highly supersaturated carbon vapor obtained in the combined laser photolysis of a mixture of C₃O₂ and H₂S diluted with argon was studied. The concentrations of carbon vapor, HS^·, and atomic hydrogen obtained in the laser photolysis of the mixture were determined using the absorption cross sections of C₃O₂ and H₂S molecules measured in this work and the measured amount of absorbed laser radiation. The time profiles of the sizes of growing nanoparticles synthesized in C₃O₂ + Ar and C₃O₂ + H₂S + Ar mixtures were measured using the laser-induced incandescence (LII) method. An improved LII model was developed, which simultaneously took into account the heating and cooling of nanoparticles and the temperature dependence of the thermophysical properties of nanoparticles, as well as the cooling of nanoparticles by evaporation and thermal emission. The size distributions of carbon nanoparticles formed in the presence and absence of active impurities were determined with the use of a transmission electron microscope. The final average size of carbon nanoparticles was found to decrease from 12 to 9 nm upon the addition of H₂S to the system, whereas the rate of nanoparticle growth decreased by a factor of 3, and the properties of nanoparticles changed. In particular, the translational energy accommodation coefficient for Ar molecules at the surface of carbon nanoparticles was found to decrease from 0.44 to 0.30. A comparison of the calculated total carbon balance at the early stage of nanoparticle formation with experimental data demonstrated that the reaction C + H₂S → HCS^· + H, which removes a portion of carbon vapor from the condensation process, has a determining effect on the carbon balance in the system. It was found that HS^· and atomic hydrogen affect the carbon balance in the system only slightly. Thus, the experimentally observed decrease in the rate of nanoparticle growth and in the sizes of nanoparticles can be explained by a decrease in the concentration of free carbon upon the addition of H₂S molecules to the system.     

Synthesis and study of sodium triuranate Na<Subscript>2</Subscript>(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>O<Subscript>3</Subscript>(OH)<Subscript>2</Subscript>

Sodium triuranate Na₂(UO₂)₃O₃(OH)₂ was synthesized by the reaction between aqueous uranyl acetate solution and aqueous sodium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the synthesized compound were determined, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis.     

[Co(solv)<Subscript>6</Subscript>][B<Subscript>10</Subscript>H<Subscript>10</Subscript>] (solv = DMF and DMSO) for low-temperature synthesis of borides

The synthesis and structure of complexes [Co(solv)₆][B₁₀H₁₀] (solv = DMF and DMSO) have been reported. Both complexes have been prepared in a high yield by the reaction between cobalt(II) salts and closo-decaborates Cat₂[B₁₀H₁₀] in the corresponding solvent. The complexes have been characterized by elemental analysis, IR and UV spectroscopy, X-ray powder diffraction, and X-ray crystallography. The thermal properties of the compounds have been studied in the temperature range 20–600°C under argon. The conditions to form cobalt borides have been determined based on the results of thermal analysis, subsequent annealing of the complexes in various conditions, and analysis of IR spectra of the resulting thermolysis products.