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.     

Crystal structure of [Ir(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl]<Subscript>2</Subscript>[OsCl<Subscript>6</Subscript>]Cl<Subscript>2</Subscript>. Crystal-chemical analysis of the iridium-osmium system

The [Ir(NH₃)₅Cl]₂[OsCl₆]Cl₂ binary complex salt has been prepared, and its structure was investigated by single crystal X-ray diffraction. Crystal data: a = 11.1901(13) Å, b = 7.9138(13) Å, c = 13.4384(18) Å; β = 99.640(3)°, V = 1190.0(2), space group C2/m, Z = 2, FW = 1099.47, d _x = 3.068 g/cm³. Thermolysis products of [Ir(NH₃)₅Cl]₂[OsCl₆]Cl₂, [Ir(NH₃)₅Cl][OsBr₆], (NH₄)₂[OsCl₆]_x[IrCl₆]_1?x , and K₂[OsCl₆]_x[IrCl₆]_1?x were studied by X-ray phase analysis; the unit cell parameters were refined, and the dependence of volume per atom (V/Z) on the composition of the Ir Os_1?x solid solution has been plotted.     

Catalytic removal of soot particles over MnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts prepared by the auto-combustion method

Soot removal for exhaust gas from diesel engine has been addressed due to the more stringent legislation and environmental concerns. MnCo₂O₄ catalysts were systematically prepared using glucose as a fuel via the auto-combustion method and applied for soot removal. The as-prepared samples were characterized by X-ray diffraction (XRD), O₂-temperature-programmed oxidation (TPO) reaction and H₂-temperature-programmed reduction reaction (H₂-TPR). The catalytic activities for soot combustion were evaluated by micro activity test (MAT) with a tight contact mode between soot and catalysts. Compared with catalysts prepared by the solid state method without glucose, auto-combustion method in the presence of glucose can decrease the synthetic temperature, avoiding high temperature treatment and sintering. The catalysts prepared with glucose could catalyze soot oxidation effectively and the derived values of T₁₀, T₅₀, and T₉₀ were 326, 408, and 468 °C in a tight contact mode, respectively, showing a significant drop of T₁₀, T₅₀, and T₉₀ by 156, 177, and 178 °C for non-catalytic reaction.     

Promotional effect of Ce on the SCR of NO with NH<Subscript>3</Subscript> at low temperature over MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> supported by nitric acid-modified activated carbon

Different amounts of Mn and Ce oxides were loaded onto nitric acid-modified activated carbon (ACN) by wet impregnation. The series of catalysts were employed for the selective catalytic reduction of NO _x by NH₃ at temperatures between 100 and 250 °C. Cerium-modified catalysts exhibited higher de-NO _x performance than those modified with Mn/ACN, even with the same total loadings. The precursor solution with a molar ratio for Ce/(Mn + Ce) of 0.4 exhibited the highest catalytic activity. Enhanced resistance to SO₂ and H₂O and better stability were observed for 10%Mn–Ce(0.4)/ACN relative to 10%Mn/ACN. The catalysts were further characterized by N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The N₂ physisorption and XRD results suggested that co-doping Ce with Mn increased the surface area and promoted the dispersion of Mn–Ce binary metal oxides. H₂-TPR the NH₃-TPD results demonstrated that the interaction between manganese oxide and cerium oxide species enhanced the redox and surface acidity of 10%Mn–Ce(0.4)/ACN.     

Highly efficient mesoporous WO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/KIT-6 catalysts for oxidative desulfurization of dibenzothiophene with hydrogen peroxide

Oxidative desulfurization (ODS) of organic compounds containing sulfur element from a model oil was performed using tungsten oxide catalysts supported on mesoporous silica with cubic Ia3d mesostructure, well-defined mesopores (7.2 nm), high surface area (719 m²/g), and three-dimensional pore network (WO _x /KIT-6). The prepared WO _x /KIT-6 catalysts (5–20 wt% WO _x ) were characterized by X-ray diffraction analysis, N₂ sorption measurements, electron microscopy, H₂-temperature programmed reduction, Raman spectroscopy, and thermogravimetric analysis. Among the mesoporous catalysts, 10 wt% WO _x /KIT-6 exhibited the best catalytic performance. Sulfur-containing organic compounds, such as dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene, were completely (100 %) removed from the model oil over 10 wt% WO _x /KIT-6 catalyst in 2 h. In addition, the catalyst could be reused several times with only slight decrease in catalytic activity.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

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.     

Systems Li<Subscript>2</Subscript>O(Na<Subscript>2</Subscript>O)-CdO-V<Subscript>2</Subscript>O<Subscript>5</Subscript>: Phase composition and phase diagrams

The subsolidus phase composition of the M₂O-CdO-V₂O₅ systems with M = Li or Na is studied. Double orthovanadates MCdVO₄ and MCd₄(VO₄)₃ form solid solutions of composition Li_{1 ? 2x/3}Cd _x/3CdVO₄ (0 ≤ x ≤ 1, orthorhombic space group Cmcm, modulation at x = 0.6) and Na_{3 ? 2x} Cd_{3 + x} (VO₄)₃ (0 ≤ x ≤ 0.10 and 0.30 ≤ x ≤ 1, orthorhombic space group Cmcm and Pn2₁ a or Pnma, respectively). In the range 0.10 < x < 0.30, the end-members of the solid solutions coexist. Isothermal sections of the systems are mapped.     

Molecular mechanism of propane oxidative dehydrogenation on surface oxygen radical sites of VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/TiO<Subscript>2</Subscript> catalysts

Minimum energy pathways of propane oxidative dehydrogenation to propene and propanol on supported vanadium oxide catalyst VO _x /TiO₂ were studied by periodic discrete Fourier transform (DFT) using a surface oxygen radical as the active site. The propene formation pathway was shown to consist of two consecutive hydrogen abstraction steps. The first step includes C_β–H bond activation of propane followed by the formation of a surface hydroxyl group V–O _t H and a propyl radical n-C₃H₇. This step with the activation energy E* = 0.56 eV (54.1 kJ/mol) appears to be rate-determining. The second step involves the reaction of the bridging O _b oxygen atom with the methylene C–H bond of propyl radical n-C₃H₇ followed by the formation of a hydroxylated surface site HO _t –V⁴⁺–O _b H and propene. The initial steps of the C–H bond activation during propane conversion to propanol and propene by ODH on V⁵⁺–(O _t O _b )^? active sites are identical. The obtained results demonstrate that participation of surface oxygen radicals as the active sites of propane ODH makes it possible to explain relatively low activation energies observed for this reaction on the most active catalysts. The presence of very active radical species in low concentration seems to be the key factor for obtaining high selectivity.     

Synthesis of an Ni<Subscript>2</Subscript>P catalyst supported on Na-MCM-41 with highly activity for dibenzothiophene HDS under mild conditions

A novel and simple method to synthesize supported Ni₂P/Na(x)-MCM-41 catalysts (where x is the mass fraction of Na-to-MCM-41 in terms of percentage) at a lower reduction temperature by incorporation of Na was described. The catalysts were characterized by H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD), N₂ adsorption–desorption, CO uptake, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The effect of Na on the structure of catalysts and catalytic properties for the dibenzothiophene (DBT) hydrodesulfurization (HDS) was investigated, which confirmed that a suitable amount of Na can promote highly dispersed Ni₂P particles. The Na preferentially interacts with phosphate to generate the sodium phosphate and therefore suppresses the formation of stronger P–O–P bonds, which enables the phosphide catalyst to be easily formed at a lower reduction temperature. Compared with conventional phosphate (973–1273 K), the reduction temperature of Ni₂P/Na(x)-MCM-41 catalyst was relatively low (773 K). The Ni₂P/Na(x)-MCM-41 catalyst with x?=?1.0 showed the maximum DBT conversion of 91.6%, which is higher than that of Ni₂P/M41 without Na (80.3%).     

Phase formation in the Ag<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-MgMoO<Subscript>4</Subscript>-Al<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> system

The subsolidus region of the Ag₂MoO₄-MgMoO₄-Al₂(MoO₄)₃ ternary salt system has been studied by X-ray phase analysis. The formation of new compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgMg₃Al(MoO₄)₅ has been determined. The Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ variable-composition phase is related to the NASICON type structure (space group R \(\bar 3\) c). AgMg₃Al(MoO₄)₅ is isostructural to sodium magnesium indium molybdate of the same formula unit and crystallizes in triclinic system (space group P \(\bar 1\), Z = 2) with the following unit cell parameters: a = 9.295(7) Å, b = 17.619(2) Å, c = 6.8570(7) Å, α = 87.420(9)°, β = 101.109(9)°, γ = 91.847(9)°. The compounds Ag_{1 ? x} Mg_{1 ? x} Al_{1 + x} (MoO₄)₃ and AgMg₃Al(MoO₄)₅ are thermally stable up to 790 and 820°C, respectively.     

Interactions in the Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript>-Ti<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Interactions in the Al₂TiO₅-Ti₂O₃ system were studied and the regions of existence of Al_2?2xTi _2x ³⁺ Ti⁴⁺O₅ solid solutions with a pseudobrookite structure were determined.     

Catalytic efficiency of cesium and potassium salts of dodecatungstophosphoric acid supported on silica and comparison with H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/SiO<Subscript>2</Subscript>

Pure tungstophosphoric acid, potassium tungstophosphate, and cesium tungstophosphate with varying extent of substitution of protons by Cs or K ions x (x = 1, 2, 2.5, and 3) have been prepared and are supported on silica by the wet impregnation method. The extent of loading was fixed at 20 wt %. For the sake of comparison, unloaded Cs _x and K _x (x = 1) salts of tungstophosphoric acid were prepared by the precipitation method. The supported catalysts were characterized by FT-IR, XRD, specific surface area measurements, and catalytic conversion of tert-butanol. The results revealed that the catalytic conversion of tert-butanol proceeds mainly via dehydration yielding isobutene. The Cs₁PW/SiO₂, HPW/SiO₂, and K₁PW/SiO₂ catalysts were more active than their unsupported samples. The previous solids showed greater catalytic activity and stability. Unexpectedly, substitution of one proton of tungstophosphoric acid by a cesium or potassium ion exerted no measurable effect on the catalytic activity of the treated solids, in spite of decreasing the Brønsted acidity of Cs₁PW/SiO₂ and K₁PW/SiO₂ indicating that the acidity of HPW/SiO₂ decrease may be due to the interaction between HPW and the SiO₂ surface. On the other hand, significant decrease in the catalytic activity took place upon increasing the cation content (x) to x = 2, 2.5, and 3.     

Thermolysis of [Pt(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][ReHlg<Subscript>6</Subscript>] (Hlg = Cl,Br). Structure refinement for [Pt(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][ReCl<Subscript>6</Subscript>]

Thermal decomposition of [Pt(NH₃)₄][ReHlg₆] binary complex salts (Hlg = Cl, Br) in a hydrogen atmosphere has been studied. Polycrystal X-ray diffractometry indicated that two-phase metallic systems are the final products of thermolysis. Structure refinement was performed for [Pt(NH₃)₄][ReCl₆] by the combined technique involving decomposition of the diffractogram into individual reflections, isolation of reflections most sensitive to the position of separate light atoms, and full-profile analysis. Crystal data for PtReN₄Cl₆H₁₂: a = 11.616(1) Å, b = 10.998(1) Å, c = 10.377(1) Å, V = 1148.1 ų, space group Cmca, Z = 4, d _x = 3.831 g/cm³. The indices are R_p = 5.48%, R_wp = 10.01%, R(F²) = 12.62%. The coordination polyhedron of Re is an almost regular octahedron: Re-Cl 2.34–2.36 Å, ∠ Cl-Re-Cl 86.9–90.3°; the coordination polyhedron of Pt is a square: Pt-N 2.04 Å, ∠N-Pt-N 90.4°.     

Effect of copper precursors on the catalytic activity of Cu/ZSM-5 catalysts for selective catalytic reduction of NO by NH<Subscript>3</Subscript>

The Cu/ZSM-5 catalysts prepared by different copper precursors were used for the selective catalytic reduction (SCR) of NO _x with NH₃. The Cu/ZSM-5 catalyst prepared by the copper nitrate (Cu/ZSM-5-N) presented the best performance among the Cu/ZSM-5 catalysts and showed above 90 % NO _x conversion at 225–405 °C. The average particle size of CuO was 5.82, 9.20, and 11.01 nm over Cu/ZSM-5-N, Cu/ZSM-5-S (prepared by copper sulfate), and Cu/ZSM-5-C (prepared by copper chloride), respectively. The Cu/ZSM-5-N catalyst showed the highly dispersed copper species, the strong surface acidity, and the excellent redox ability compared with the Cu/ZSM-5-C and Cu/ZSM-5-S catalysts. The Cu⁺ and Cu²⁺ existed in the Cu/ZSM-5 catalysts and the abundant Cu⁺ over Cu/ZSM-5-N might be responsible for the superior SCR activity.     

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.     

Thermal activation effect on catalytic systems MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for deep oxidation of hydrocarbons

The effect of thermal activation, sharp increase in the catalytic activity of the system MnO _x -Al₂O₃ in reactions of deep oxidation of CO and hydrocarbons after calcination of the catalyst at 900–1000°C was discovered and investigated. With the use of X-ray phase analysis, X-ray electron spectroscopy, EXAFS, IR spectroscopy, electronic spectroscopy of diffuse reflections, electron microscopy etc. it was established that the effect of thermal activation is related to reversible phase transitions in the system at heating and cooling. On cooling from 1100°C to 650°C disperse particles of cubic spinel of composition Mn_{2.1 ? x} · Al_{0.9 + x} O₄ are conserved on the corundum surface. On further cooling the spinel decomposes and finally the nanocristalline species of β-Mn₃O*₄ containing up to 15 at% of Al³⁺ form and govern the activity.The thermal activation effect was implemented in an industrial catalyst IK-12-40. Joint Stocks Co “KATALIZATOR” produced and supplied to customers hundreds of tons of this catalyst. The catalyst was awarded with a silver medal of the International exhibition EUREKA in Brussels (1995).     

CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript>-Based materials with variable copper content

The CaO-3 (1 + x)CuO-4TiO₂ system was studied using powder X-ray diffraction in the concentration region near calcium copper titanate. A single-phase material is formed in this system only when x ～ 0. An excess or deficit of copper gives rise to extra phases: CuO or CaTiO₃ and TiO₂, respectively. Impurities increase the dielectric constant of CaCu₃Ti₄O₁₂-based ceramics. An excess of copper oxide (x ～ 0.08) increases ? more than tenfold.     

X-ray diffraction study of the monoclinic modification of [Cu(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>](ReO<Subscript>4</Subscript>)<Subscript>2</Subscript> in the range 100-410 K

The monoclinic modification of [Cu(NH₃)₄](ReO₄)₂ complex salt in the range 100-410 K is studied by single crystal X-ray diffraction. The crystallographic data for 300 K are as follows: a = 10.6123(3) Å, b = 7.5443(2) Å, c = 15.2261(4) Å, β = 108.406(1)°, V = 1156.67(5) ų, space group Р2₁/n, Z = 4, d_x = 3.623 g/cm³. The coordination environment of the Cu atom, being a distorted square formed by four nitrogen atoms with Cu–N of 1.997-2.018 Å, is completed by the contacts with two oxygen atoms Cu…O of 2.472 Å and 2.598 Å. The comparative crystal chemical analysis with the triclinic modification of [Cu(NH₃)₄](ReO₄)₂ known in the literature is performed.     

High-pressure defect phase La<Subscript>x</Subscript>Cu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

Perovskite-like nonstoichiometric oxide La _x Cu₃V₄O₁₂ (space group Im \(\bar 3\), Z = 2, a = 7.313–7.354 Å) with cation-site vacancies has been prepared for the first time at high pressures (p = 6.0–8.0 GPa) and high temperatures (T = 700–1100°C). The compound has metal-type conductivity and paramagnetic properties, and undergoes a phase transition.