Theoretical studies on the pentacoordinate silylenoid PhCH<Subscript>2</Subscript>(NH<Subscript>2</Subscript>)CH<Subscript>3</Subscript>SiLiF

The structures of pentacoordinate silylenoid PhCH₂(NH₂)CH₃SiLiF were studied by density functional theory at the B3LYP/6-31G(d) level. Three equilibrium structures, the three-membered ring (1), the p-complex (2), and the σ-complex (3) structures, were located. Their energies are in the order of 2 > 1 > 3 both in vacuum and in THF. To exploit the stability of PhCH₂(NH₂)CH₃SiLiF, the insertion reactions of 1 and PhCH₂(NH₂)CH₃Si into C–F have been investigated, respectively. The results show that the insertion of PhCH₂(NH₂)CH₃Si is more favorable. To probe the influence of amine-coordination to the stability of PhCH₂(NH₂)CH₃SiLiF, the insertion reaction of PhCH₃CH₃SiLiF was also investigated. The calculations indicate that the insertion of PhCH₃CH₃SiLiF is more favorable than that of 1. So the N atom plays an important role on the stability of silylenoid PhCH₂(NH₂)CH₃SiLiF.     

Organic-inorganic hybrid perovskite (C<Subscript>6</Subscript>H<Subscript>5</Subscript>(CH<Subscript>2</Subscript>)<Subscript>2</Subscript>NH<Subscript>3</Subscript>)<Subscript>2</Subscript>CdCl<Subscript>4</Subscript>: Synthesis,structural and thermal properties

The present research work reports the study on crystal structure, vibrational spectroscopy and thermal analysis of organic-inorganic hybrid compound (C₆H₅(CH₂)₂NH₃)₂CdCl₄. Single crystals of bis(phenethylammonium)tetrachlorocadmate (C₆H₅(CH₂)₂NH₃)₂CdCl₄ (PEA–Cd) were obtained by diffusion at room temperature. This compound crystallizes in the orthorhombic space group C2cb with unit cell parameters a = 7.4444(2) Å, b = 38.8965(3) Å, c = 7.3737(2) Å and Z = 4. Single crystal structure has been solved and refined to R = 0.036 and wR = 0.092. The structure consists of an extended [CdCl₄]^2– network and two [C₆H₅(CH₂)₂NH₃]⁺ cations to form a two-dimensional perovskite system. The infrared (IR) spectrum of the title compound was recorded at room temperature. Differential scanning calorimetry (DSC) was used to investigate the phase transition; this compound exhibits a reversible single solid-solid phase transition.     

Synthesis,structure and thermal decomposition of [Ni(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>][VO(O<Subscript>2</Subscript>)<Subscript>2</Subscript>(NH<Subscript>3</Subscript>)]<Subscript>2</Subscript>

The compound [Ni(NH₃)₆][VO(O₂)₂(NH₃)]₂ was prepared and characterized by elemental analysis and vibrational spectra. The single crystal X-ray study revealed that the structure consists of [Ni(NH₃)₆]²⁺ and [VO(O₂)₂(NH₃)]⁻ ions. As a result of weak interionic interactions V′···O_p (O_p-peroxo oxygen), ([VO(O₂)₂(NH₃)]⁻)₂ dimers are formed in the solid-state. The thermal decomposition of [Ni(NH₃)₆][VO(O₂)₂(NH₃)]₂ is a multi-step process with overlapped individual steps; no defined intermediates were obtained. The final solid products of thermal decomposition up to 600°C were Ni₂V₂O₇ and V₂O₅.     

Selective Catalytic Reduction of NO by NH<Subscript>3</Subscript> over MoO<Subscript>3</Subscript> Promoted Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst

A series of MoO₃ doped Fe₂O₃ catalysts prepared by the co-precipitation method were investigated in the selective catalytic reduction of NO by NH₃ (NH₃-SCR). The catalysts displayed excellent catalytic activity from 225 to 400°C and high tolerance to SO₂/H₂O poisoning at 300°C. To characterize the catalysts the N₂-BET, XRD, Raman, NO-TPD, NH₃-TPD and in situ DRIFTS were carried out. It was found that the main reason explaining a high NH₃-SCR performance might be the synergistic effect between Fe and Mo species in the catalyst that could enhance the dispersion of Fe₂O₃ and increase NH₃ adsorption on the catalyst surface.     

Adsorption of NO,NH<Subscript>3</Subscript> and H<Subscript>2</Subscript>O on V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalysts

The adsorption of small molecules NO, NH₃ and H₂O on V₂O₅/TiO₂ catalysts is studied with the semiempirical SCF MO method MSINDO as pre-stage for the selective catalytic reduction of NO. The mixed catalyst is represented by hydrogen-terminated cluster models. The local arrangement of the cluster atoms is in accordance with available experimental information. Partial relaxation of cluster atoms near the adsorption sites is taken into account. Calculated adsorption energies are compared with experimental literature data. Rapid convergence of computed properties with cluster size is observed. A possible reaction mechanism for the catalytic reduction of NO with NH₃ and O₂ is outlined.     

Study of Fe-doped V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> catalyst for an enhanced NH<Subscript>3</Subscript>-SCR in diesel exhaust aftertreatment

Selective catalytic reduction (SCR) with ammonia has been considered as the most promising technology, as its effect deals with the NO_X. Novel Fe-doped V₂O₅/TiO₂ catalysts were prepared by sol–gel and impregnation methods. The effects of iron content and reaction temperature on the catalyst SCR reaction activity were explored by a test device, the results of which revealed that catalysts could exhibit the best catalytic activity when the iron mass ratio was 0.05%. It further proved that the VTiFe (0.05%) catalyst performed the best in denitration and its NO_X conversion reached 99.5% at 270 °C. The outcome of experimental procedures: Brunauer–Emmett–Teller surface area, X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction and adsorption (H₂-TPR, NH₃-TPD) techniques showed that the iron existed in the form of Fe³⁺ and Fe²⁺ and the superior catalytic performance was attributed to the highly dispersed active species, lots of surface acid sites and absorbed oxygen. The modified Fe-doped catalysts do not only have terrific SCR activities, but also a rather broad range of active temperature which also enhances the resistance to SO₂ and H₂O.     

Crystal and molecular structure of ammonium trinitratouranylate NH<Subscript>4</Subscript>[UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>]

Ammonium trinitratouranylate NH₄[UO₂(NO₃)₃] (I) single crystals have been synthesized by the reaction of aqueous solutions of diaquadinitratouranyl tetrahydrate and ammonium nitrate in the presence of nitric acid. The structure of the complex has been studied by X-ray diffraction analysis: space group \(R\bar 3c\), a = 9.361(2), c = 18.883(4) Å; V = 1433.0(5) ų, and Z = 6. The structural units of the NH₄[UO₂(NO₃)₃] crystal—NH ₄ ⁺ cations and [UO₂(NO₃)₃]^? complex anions with three bidentate cyclic nitrato groups—are on crystallographic axes \(\bar 3\). A complex three-dimensional packing arranged by the electrostatic attraction forces between counterions and the N-H...O hydrogen bonds between ammonium cations and trinitratouranylate anions is realized in the structure. X-ray diffraction analysis results are confirmed by IR spectra of NH₄[UO₂(NO₃)₃].     

Thermal decomposition of [Cd(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

Thermal decomposition of [Cd(NH₃)₆](NO₃)₂ was studied by thermogravimetry (TG) with simultaneous differential thermal analysis (SDTA) for two samples and at two different sets of measurement parameters. The gaseous products of the decomposition were on-line identified by evolved gas analysis (EGA) with a quadruple mass spectrometer (QMS). The decomposition of the title compound proceeds, for both cases, in the three main stages. In the first stage, deammination of [Cd(NH₃)₆](NO₃)₂ to [Cd(NH₃)](NO₃)₂ undergoes by three steps and 5/6 of all NH₃ molecules are liberated. At second stage the liberation of residual 1/6NH₃ molecules and the formation of Cd(NO₃)₂ undergoes. However, during this process simultaneously a two-step oxidation of a part of ammonia molecules also takes place. In a first step as a result a mixture of ammonia, water vapour and nitrogen is formatted. At the second step, subsequent oxidation of a next part of NH₃ molecules undergoes. As a result, a mixture of nitrogen oxide, nitrogen and water vapour is formatted, what for these both steps clearly indicates the EGA analysis. The third stage of the thermal decomposition is connected with the melting and subsequent decomposition of residual Cd(NO₃)₂ to oxygen, nitrogen dioxide and solid CdO. Additionally, third sample was measured by differential scanning calorimetry (DSC) and the results are fully consistent with those obtained by TG.     

Orientational disorder in crystal structures of (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>ZrF<Subscript>7</Subscript> and (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>NbOF<Subscript>6</Subscript>

Crystal structures of (NH₄)₃ZrF₇ (I) and (NH₄)₃NbOF₆ (II) are refined by X-ray diffraction at room temperature. The compounds are isostructural and belong to the structural type of elpasolite: space group F23; a(I) = 9.4185(3) Å, a(II) = 9.3371(5) Å; V(I) = 835.50(5) ų, V(II) = 814.02(8) ų; Z = 4; R(I) = 0.0145, and R(II) = 0.0138. The refinement of the structures in the space group Fm3m yields abnormally short X-X distances in the pentagonal bipyramid MX₇ (X = F, O). The oxygen atom in II is identified by Nb-X distances and occupies one of the axial vertices of the bipyramid. The Nb atom in II is statistically distributed over the position 24f, while Zr in I resides in the symmetry center. The pentagonal bipyramid MX₇ has six independent orientations in I and twelve in II. One of three crystallographically independent ammonium groups of the structures is disordered over six or twelve equivalent orientations.     

Crystal structure and properties of [M(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>, (M = Ir,Rh, Ru)

The crystal structures of compounds from the series [M(NH₃)₅Cl](NO₃)₂, (M = Ir, Rh, Ru) were described. The compounds crystallized in the tetragonal crystal system, space group I4, Z = 2. Crystal data for [Ir(NH₃)₅Cl](NO₃)₂ (I): a = 7.6061(1) Å, b = 7.6061(1) Å, c = 10.4039(2) Å, V = 601.894(16) ų, ρ_calc = 2.410 g/cm³, R = 0.0087; [Rh(NH₃)₅Cl](NO₃)₂ (II): a = 7.5858(5) Å, b = 7.5858(5) Å, c = 10.41357(7) Å, V = 599.24(7) ų, ρ_calc = 1.926 g/cm³, R = 0.0255; [Ru(NH₃)₅Cl](NO₃)₂ (III): a = 7.5811(6) Å, b = 7.5811(6) Å, c = 10.5352(14) Å, V = 605.49(11) ų, ρ_calc = 1.896 g/cm³, R = 0.0266. The compounds were defined by IR spectroscopy and XRPA and thermal analyses.     

The Reactions of Two New Alkoxy-silyl Functionalized Alkynes with M<Subscript>3</Subscript>(CO)<Subscript>12</Subscript> {M = Fe,Ru} and Co<Subscript>2</Subscript>(CO)<Subscript>8</Subscript>. Spectroscopic Identification of the Products

The new alkoxysilyl-functionalized alkynes [HC≡CCH₂N(H)C(=O)N(H)(CH₂)₃Si(OEt)₃] and [HC≡C(C₆H₄)–N(H)C(=O)N(H)(CH₂)₃Si(OEt)₃] have been synthesized using literature methods. These have been reacted with Fe₃(CO)₁₂, Ru₃(CO)₁₂ and Co₂(CO)₈. With the iron carbonyl only decomposition was observed: with Ru₃(CO)₁₂ splitting of the alkynes into their parent components and formation of the complexes (μ-H)Ru₃(CO)₉[HC=N(CH₂)₃Si(OEt)₃], (μ-H)Ru₃(CO)₉[C–C(C₆H₄)NH₂] and (μ-H)₂Ru₃(CO)₉[HC–CCH₃] occurred. Finally, with Co₂(CO)₈ formation of complexes Co₂(CO)₆(HC₂R) R=(C₆H₄)NH₂, CH₂NH(CO)NH(CH₂)₃Si(OEt)₃, (C₆H₄)NH(CO)NH(CH₂)₃Si(OEt)₃ containing the intact alkynes could be obtained.     

Insights into the selective catalytic reduction of NO by NH<Subscript>3</Subscript> over Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>(110): a DFT study coupled with microkinetic analysis

Nitric oxide (NO_x), as one of the main pollutants, can contribute to a series of environmental problems, and to date the selective catalytic reduction (SCR) of NO_x with NH₃ in the presence of excess of O₂ over the catalysts has served as one of the most effective methods, in which Mn-based catalysts have been widely studied owing to their excellent low-temperature activity toward NH₃-SCR. However, the related structure-activity relation was not satisfactorily explored at the atomic level. By virtue of DFT+U calculations together with microkinetic analysis, we systemically investigate the selective catalytic reduction process of NO with NH₃ over Mn₃O₄(110), and identify the crucial thermodynamic and kinetic factors that limit the catalytic activity and selectivity. It is found that NH₃ prefers to adsorb on the Lewis acid site and then dehydrogenates into NH₂* assisted by either the two- or three-fold lattice oxygen; NH₂* would then react with the gaseous NO to form an important intermediate NH₂NO that prefers to convert into N₂O rather than N₂ after the sequential dehydrogenation, while the residual H atoms interact with O₂ and left the surface in the form of H₂O. The rate-determining step is proposed to be the coupling reaction between NH₂* and gaseous NO. Regarding the complex surface structure of Mn₃O₄(110), the main active sites are quantitatively revealed to be O_3c and Mn_4c.     

Performance and characterisation of CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>-WO<Subscript>3</Subscript> catalysts for selective catalytic reduction of NO with NH<Subscript>3</Subscript>

Ce-Ti-W-O _x catalysts were prepared and applied to the NH₃-selective catalytic reduction (SCR) reaction. The experimental results showed that the Ce-Ti-W-O _x catalyst prepared by the hydrothermal method exhibited higher NO conversion than those synthesised via the sol-gel and impregnating methods, while the optimal content of WO₃ and molar ratio of Ce/Ti were 20 mass % and 4: 6, respectively. Under these conditions, the catalyst exhibited the highest level of catalytic activity (the NO conversion reached values higher than 90 %) across a wide temperature range of 225–450°C, with a range of gas hourly space velocity (GHSV) of 40000–140000 h^?1. The catalyst also exhibited good resistance to H₂O and SO₂. The influences of morphology, phase structure, and surface properties on the catalytic performance were investigated by N₂ adsorption-desorption measurement, XRD, XPS, H₂-TPR, and SEM. It was found that the high efficiency of NO removal was due to the large BET surface area, the amorphous surface species, the change to element valence states, and the strong interaction between Ce, Ti, and W.     

Mechanistic study of Ce-modified MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/TiO<Subscript>2</Subscript> catalysts with high NH<Subscript>3</Subscript>-SCR performance and SO<Subscript>2</Subscript> resistance at low temperatures

A series of Ce–MnO _x /TiO₂ catalysts were prepared using a novel sol–gel template method and investigated for low-temperature selective catalytic reduction (SCR) of NO with NH₃ at temperatures ranging from 353 to 473 K. The 0.07Ce–MnO _x /TiO₂ catalyst showed the highest activity and best resistance to SO₂ poisoning. The structure and properties of the catalysts were characterized using X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), thermogravimetry (TG)–differential scanning calorimetry (DSC)–mass spectroscopy (MS), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) measurements, H₂-temperature-programmed reduction (TPR), and NH₃-temperature-programmed desorption (TPD). The superior catalytic activity of the 0.07Ce–MnO _x /TiO₂ catalyst was probably due to a change in the active components, an increase in surface active oxygen and surface acid sites, and lower crystallinity and larger surface area with Ce doping. Furthermore, the reduction ability also became stronger. The SO₂ poisoning resistance of the 0.07Ce–MnO _x /TiO₂ catalyst improved because doping with Ce can effectively decrease the formation of ammonium salt on the catalyst surface and the sulfation of MnO _x . In situ diffuse-reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments indicated that addition of Ce could promote adsorption of NH₃ and inhibit generation of some nitryl species. The SCR reactions over the catalysts mainly followed the Eley–Rideal mechanism accompanied with a partial Langmuir–Hinshelwood mechanism.     

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.     

Synthesis and crystal structure of [Cr(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl][PdBr<Subscript>4</Subscript>]

A new binary complex salt — chloropentaamminechromium(III) tetrabromopalladate(II) [Cr(NH₃)₅Cl][PdBr₄] — has been synthesized. The compound was characterized by elemental, X-ray diffraction, and X-ray phase analysis. The salt is isostructural with the previously investigated compounds [M(NH₃)₅Cl][PtCl₄] (M = Ir, Rh, Ru, Co, Cr) and [CM(NH₃)₅Cl][PdBr₄] (M = Ir, Rh, Co). Crystallographic data: space group Pnma, a = 17.068(2) Å, b = 8.315(12) Å, c = 9.653(14) Å; V = 1370.0(3) ų, Z = 4, d _calc = 2.903 g/cm³.     

Synthesis and x-ray structural investigation of bismuth 2-methyl-8-quinolineselenolate Bi[C<Subscript>9</Subscript>H<Subscript>5</Subscript>(CH<Subscript>3</Subscript>)NSe]<Subscript>3</Subscript>

Bismuth 2-methyl-8-quinolineselenolate, Bi[C₉H₅(CH₃)NSe]₃, was synthesized. X-ray analysis was used to determine the structure of this complex. The crystal chemistry of bismuth(III), antimony(III), and arsenic(III) 2-methyl-8-quinolineselenolates and 2-methyl-8-quinolinethiolates was discussed relative to the effect of going from Se to S as the ligand atoms and presence of a methyl group at C-2 of the quinoline system and unshared electron pair of the central atom in the complex.     

Complex salts with participation of [Rh(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>]<Superscript>3+</Superscript> cations

Four complex salts with the polyatomic [Rh(NH₃)₆]³⁺ cation are synthesized and studied by X-ray diffraction. The crystallographic characteristics of [Rh(NH₃)₆](WO₄)Cl are determined and the structures of [Rh(NH₃)₆]Cl₃, [Rh(NH₃)₆](ReO₄)₃·2H₂O, and [Rh(NH₃)₆](MoO₄)Cl·3H₂O are solved. The features of mutual packing of the fragments are studied.     

Influence of Synthesis Conditions on the Morphology and Spectral-Luminescent Properties of Films of Organic-Inorganic Perovskite CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>2.98</Subscript>Cl<Subscript>0.02</Subscript>

The influence of the synthesis conditions (rotation speed used for spin-coating deposition of the film, film drying temperature, and the ratio of the PbI₂ and CH₃NH₃I reactants in solutions) on the microstructure, phase composition, and spectral-luminescent properties of films of organic-inorganic perovskite CH₃NH₃PbI_3–xCl _x (x = 0, 0.02) was elucidated.     

Crystal structures of Ti(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript> and Sn(NH<Subscript>4</Subscript>)<Subscript>2</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>

The characteristics of crystal structures of the titanium(IV) diammonium (Ti(NH₄)₂P₄O₁₃) and tin(IV) diammonium (Sn(NH₄)₂P₄O₁₃) tetraphosphates, which are isostructural with similar silicon(IV) and germanium(IV) salts, have been obtained by the Rietveld method using X-ray powder diffraction data. The compounds crystallize in the triclinic system, space group P \(\overline 1 \), Z = 2, a = 15.0291(7) Å, b = 7.9236(4) Å, c = 5.0754(3) Å, α = 99.168(3)°, β = 97.059(3)°, γ = 83.459(3)° for Ti(NH₄)₂P₄O₁₃ and a = 15.1454(7) Å, b = 8.0103(5) Å, c = 5.1053(3) Å, α = 99.898(6)°, β = 96.806(3)°, γ = 83.881(4)° for Sn(NH₄)₂P₄O₁₃. The structure is refined in the isotropic approximation using the pseudo-Voigt function: R _p = 0.077, R _Bragg = 0.045, R _F = 0.057 for Ti(NH₄)₂P₄O₁₃; R _p = 0.082, R _Bragg = 0.044, R _F = 0.046 for Sn(NH₄)₂P₄O₁₃. The hydrogen atoms of the ammonium cations are placed in the calculated positions. A comparative analysis of the structures of the compounds of the M^IV(NH₄)₂P₄O₁₃ (M^IV = Si, Ge, Ti, Sn) series has been carried out.