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 cobalt addition on catalytic performance of Ce<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>O<Subscript>2</Subscript> mixed oxide for diesel soot combustion

A series of Co-modified Ce_0.5Zr_0.5O₂ catalysts with different concentrations of Co (mass %: 0, 2, 4, 6, 8, 10) was investigated for diesel soot combustion. Ce_0.5Zr_0.5O₂ was prepared using the coprecipitation method and Co was loaded onto the oxide using the incipient wetness impregnation method. The activities of the catalysts were evaluated by thermogravimetric (TG) analysis and temperature-programmed oxidation (TPO) experiments. The results showed the soot combustion activities of the catalysts to be effectively improved by the addition of Co, 6 % Co/Ce_0.5Zr_0.5O₂ and that the 8 % Co/Ce_0.5Zr_0.5O₂ catalysts exhibited the best catalytic performance in terms of lower soot ignition temperature (T_i at 349°C) and maximal soot oxidation rate temperature (T_m at 358°C). The reasons for the improved activity were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These results revealed that the presence of Co could lower the reduction temperature due to the synergistic effect between Co and Ce, thereby improving the activity of the catalysts in soot combustion. The 6 % Co catalyst exhibited the best catalytic performance, which could be attributed to the greater amounts of Co³⁺ and surface oxygen species on the catalyst.     

Sm<Subscript>2</Subscript>S<Subscript>3</Subscript>-Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> phase diagram

The Sm₂S₃-Sm₂O₃ phase diagram was studied by physicochemical methods of analysis from 800 K up to melting. Two oxysulfides are formed in the system: Sm₁₀S₁₄O with tetragonal crystal structure (space group I41/acd; unit cell parameters: a = 1.4860 nm, c = 1.9740 nm; microhardness: H = 4700 MPa; solid decomposition temperature: 1500 K) and Sm₂O₂S with hexagonal structure (space group P-3m1; a = 0.3893 nm, c = 0.6717 nm; H = 4500 MPa; congruent melting temperature: 2370 K). Within the extent of the Sm₂O₂S-based solid solution (61–70 mol % Sm₂O₃) at 1070 K, a singular point appears at the compound composition on property-composition curves. The eutectic coordinates: 23 mol % Sm₂O₃ and 1850 K; 80 mol % Sm₂O₃ and 2290 K.     

Highly chemiluminescent magnetic mesoporous carbon composites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@void@C with yolk-shell structure

In this work, highly chemiluminescent magnetic mesoporous carbon with yolk-shell structure was synthesized by encapsulating N-(4-aminobutyl)-N-ethylisoluminol (ABEI) and Co²⁺ into the magnetic mesoporous carbon composites (Co²⁺-ABEI-Fe₃O₄@ void@C). The synthetic Co²⁺-ABEI-Fe₃O₄@void@C showed a good magnetic separation property, which could remove residual ABEI molecules and Co²⁺ in less than 3 min under an external magnet. Moreover, the synthetic Co²⁺-ABEI-Fe₃O₄@void@C demonstrated good chemiluminescence (CL) property and good stability when interacted with alkaline H₂O₂ solution. The CL intensity of such Co²⁺-ABEI-Fe₃O₄@void@C was about 120 times higher than that of ABEI-Fe₃O₄@void@C. The Co²⁺-ABEIFe₃O₄@ void@C also exhibited good electrochemiluminescence (ECL) property in alkaline solution. The outstanding CL/ECL performance of the Co²⁺-ABEI-Fe₃O₄@void@C was attributed to the Co²⁺ immobilized in the Co²⁺-ABEI-Fe₃O₄@void@C, which catalyzed the decomposition of H₂O₂ to generate O₂^?? and HO^?, expediting the CL/ECL reaction. The synthetic Co²⁺-ABEI-Fe₃O₄@void@C may be of great application for the development of new methodologies in bioanalysis.     

Supramolecular 2D structure of [Co(2-Me-Pyz)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

The complex [Co(2-Me-Pyz)₂(H₂O)₄](NO₃)₂ is synthesized and its structure is determined. The crystals are monoclinic: space group P2₁/n, a = 10.685(2) Å, b = 6.837(1), c = 12.515(3) Å, β = 91.84(3)°, V = 913.8(3) ų, ρ_calcd = 1.042 g/cm ³, Z = 2. The Co²⁺ ion (in the inversion center) is coordinated at the vertices of the distorted octahedron by two nitrogen atoms of methylpyrazine and four oxygen atoms of the water molecules (Co(1)–N(1) 2.180(3), average Co(1)–O(w) 2.079(3) Å, angles at the Co atom 87.9(1)–92.1(1)°). Supramolecular pseudometallocycles are formed in the structure through the O(w)–H…N(1) hydrogen bonds between the coordinated H₂O molecules and the terminal nitrogen atoms of the 2-methylpyrazine molecules. Their interaction results in the formation of supramolecular layers joined by the NO₃ groups into a three-dimensional framework.     

Synthesis and crystal structure of the new complex cobalt and nickel oxide Sr<Subscript>2.25</Subscript>Y<Subscript>0.75</Subscript>Co<Subscript>1.25</Subscript>Ni<Subscript>0.75</Subscript>O<Subscript>6.84</Subscript>

The complex cobalt and nickel oxide Sr_2.25Y_0.75Co_1.25Ni_0.75O_6.84 has been synthesized by the citrate method. The oxygen content of the oxide has been determined by iodometric titration. The crystal structure of the compound has been refined using X-ray powder diffraction data (a = 3.7951(2) Å, c = 19.700(1) Å, χ₂ = 1.15, R _F ² = 0.0586, R _p = 0.0365, R _wp = 0.0462). Sr_2.25Y_0.75Co_1.25Ni_0.75O_6.84 has the structure of the second member of the Ruddlesden-Popper series A _{n + 1}B_nO_{3n + 1}.     

Selective catalytic oxidation of ammonia into nitrogen and water vapour over transition metals modified Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, TiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript>

Copper or iron supported on commercially available oxides, such as γ-Al₂O₃, TiO₂ (anatase) and monoclinic tetragonal ZrO₂ (mt-ZrO₂) were tested as catalysts for selective catalytic oxidation of ammonia into nitrogen and water vapour (NH₃-SCO) in the low temperature range. Different commercial oxides were used in this study to determine the influence of the specific surface area, acidic nature of the support and crystalline phases as well as of the type of species and aggregation state of transition metals on the catalytic performance in selective ammonia oxidation. Copper modified oxide supports were found to be more active and selective to nitrogen than catalysts impregnated with iron. Activities of both transition metal modified samples decreased in the following order: mt-ZrO₂, TiO₂ (anatase), γ-Al₂O₃. Quantitative total ammonia conversion was achieved with the Cu/ZrO₂ catalytic system at 400°C. Characterisation techniques, e.g. H₂-temperature programmed reduction, UV-VIS-diffuse reflectance spectroscopy, suggest that easily reducible copper oxide species are important in achieving high catalytic performances at low temperatures.     

Effect of the Support on the Nature of Metal-Promoter Interactions in Ru-Cs<Superscript>+</Superscript>/MgO and Ru-Cs<Superscript>+</Superscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Ammonia Synthesis

The Ru-Cs⁺/MgO and Ru-Cs⁺/γ-Al₂O₃ catalysts, which were prepared by an impregnation method using RuOHCl₃ and Cs₂CO₃ as precursor compounds and reduced with H₂ at 450°C, are characterized by X-ray diffraction, high-resolution transmission electron microscopy (with X-ray microanalysis), and X-ray photoelectron spectroscopy (XPS). The Cs⁺/MgO(Al₂O₃) systems, Ru-Cs⁺ black, and model systems prepared by cesium sputtering onto polycrystalline ruthenium foil are studied as reference samples. It is found that, in the Ru-Cs⁺/MgO sample, cesium is present as a Cs_{2 + x}O cesium suboxide, which weakly interacts with the support, localized on the surface of Ru particles or near them. In the case of Ru-Cs⁺/γ-Al₂O₃, cesium occurs as a species that is tightly bound to the support; this is likely surface cesium aluminate, which prevents promoter migration to Ru particles. The Ru-Cs⁺/MgO sample exhibits a considerable shift of the Ru3d line in the XPS spectra toward lower binding energies, as compared to the bulk metal. It is hypothesized that this shift is due to a decrease in the electron work function from the surface of ruthenium because of the polarizing effect of Cs⁺ ions in contact with Ru particles. Based on the experimental results, the great difference between the catalytic activities of the Ru-Cs⁺/MgO and Ru-Cs⁺/γ-Al₂O₃ systems in ammonia synthesis at 250–400°C and atmospheric pressure is explained.     

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.     

Refinement of LiFe<Subscript>5</Subscript>O<Subscript>8</Subscript> crystal structure

The crystal structure and the formation conditions of crystals of the LiFe₅O₈ ordered phase obtained from the solution-melt of the Bi₂O₃-Fe₂O₃-B₂O₃-LiCl quadruple system are refined. The crystals are black, octahedral, of cubic symmetry (space group P4₃32). Unit cell parameters: a = 8.3339(1) Å, V = 578.82(1) ų, Z = 4, d _calc = 4.753 g/cm³. From 6046 of the collected array I _hkl 358 are independent (R _int = 0.0321). As a result of anisotropic refinement of structural parameters, R ₁ factor is found to be 0.0186 (wR ₂ = 0.0467). Lithium atoms are in octahedral environment, Li-O is 2.109(1) Å; iron atoms are of two types: in octahedra with Fe-O (by two) distances of 1.9586(9) Å, 2.0152(9) Å, and 2.0652(10) Å and tetrahedra with Fe-O (three) 1.8848(10) Å and 1.914(2) Å. The structure is of inverted spinel type.     

Theoretical modeling of the mechanism of aniline oxidation by singlet O<Subscript>2</Subscript>

The mechanism of aniline oxidation by singlet oxygen was studied by the DFT-PBE/L2 method. According to the calculations, aniline endoperoxide cannot participate in the reaction because of its energy instability. The addition of ¹O₂ to aniline proceeds with the simultaneous proton transfer to the oxygen molecule from the NH₂ group (for the syn-approach of oxygen) or from the aromatic ring (for the anti-approach). For the syn-approach of the ¹O₂ molecule, the HNC₆H₄(H)OOH intermediate is formed, whose decomposition leads to aniline p-hydroperoxide (predominantly) or p-iminoquinone. In the case of the anti-approach, the ¹O₂ molecule is inserted at the C–H bond to form aniline p-hydroperoxide (H₂NC₆H₄OOH). The decomposition of aniline p-hydroperoxide with the formation of p-aminophenol and H₂O₂ molecule proceeds via concerted mechanism.     

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.     

Synthesis and structure of [UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>){CONH<Subscript>2</Subscript>N(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

The single crystals of [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 7.461(2) Å, b = 8.828(2) Å, c = 11.756(2) Å, β = 107.21(3)°, space group Pc, Z = 2, R = 2.94%. The structure comprises infinite chains [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] extended along [001] and corresponding to the AT¹¹M ₂ ¹ crystallochemical group (A = UO ₂ ²⁺ , T¹¹ = C₂O ₄ ^2? , M¹ = N,N-CONH₂N(CH₃)₂) of uranyl complexes. The chains are connected into a three-dimensional framework by hydrogen bonds involving the oxygen atoms of oxalate and uranyl ions and the N,N-dimethylcarbamide methyl groups.     

Structure and electrical conductivity of cobalt-doped Bi<Subscript>26</Subscript>Mo<Subscript>10</Subscript>O<Subscript>69</Subscript>

The existence boundaries, structures, and transport parameters of Bi_{1 ? x} Co _x [Bi₁₂O₁₄]Mo₅O_{20 ± δ} and Bi[Bi₁₂O₁₄]Mo_{5 ? y} Co _y O_{20 ± δ} solid solutions, which have a unique columnar structure, were studied. Electrical conductivity in these solid solutions was studied by impedance spectroscopy.     

Mechanism of the initiation of combustion in CH<Subscript>4</Subscript>(C<Subscript>2</Subscript>H<Subscript>2</Subscript>)/Air/O<Subscript>3</Subscript> mixtures by laser excitation of the O<Subscript>3</Subscript> molecules

The possibility of enhancing the ignition and combustion of the CH₄/air/O₃ and C₂H₂/air/O₃ mixtures by exciting the asymmetric vibrations of the O₃ molecule with CO₂ laser radiation is considered. Even the admixture of small amounts of O₃ (2.5–5.0 vol %) into the hydrocarbon/air mixtures intensifies ignition and shortens the induction period. The excitation of the O₃ molecules with 9.7-μm radiation speeds up the chain process and further reduces the induction period and the ignition temperature. The induction period can be shortened by a factor of 10–100 even at low radiation energies absorbed by the gas (E _S = 10^?3-10^?2 J/cm³).     

The first chromate containing both Cr<Subscript>2</Subscript>O<Subscript>7</Subscript> and Cr<Subscript>3</Subscript>O<Subscript>10</Subscript> groups,bis(1,3-bis(4-piperidinium)propane) dichromate trichromate monohydrate: Synthesis and crystal structure

A new organic-inorganic hybrid material (C₁₃H₂₈N₂)₂[Cr₂O₇][Cr₃O₁₀]·H₂O (1) was synthesized by slow solvent evaporation at room temperature, and its crystal structure was determined by single crystal X-ray diffraction. This compound crystallizes in the monoclinic space group P2₁/c. The asymmetric unit contains two crystallographically independent 1,3-bis(4-piperidinium)propane, (H₂bppp)²⁺ cations (A and B), one trichromate Cr₃O ₁₀ ^2? anion, one dichromate Cr₂O ₇ ^2? anion, and one water molecule. All these entities are interconnected into a complicated two-dimensional hydrogen bonded network via N–H?O and O–H?O hydrogen bonds. Furthermore, this structure is stabilized by a large number of C–H?O interactions, thus establishing a three-dimensional network structure. This compound appears to be the first example of chromates containing both Cr₂O₇ and Cr₃O₁₀ groups.     

Coordination Chemistry of the Magic Inorganic Building Block {Fe<Superscript>II</Superscript>[Mo<Subscript>6</Subscript>P<Subscript>4</Subscript>O<Subscript>31</Subscript>]<Subscript>2</Subscript>}: Hydrothermal Synthesis and Crystal Structure of a New Reduced Ferrous Molybdophosphate

A new reduced ferrous molybdophosphate composite solid of the formula, [(C₁₀H₁₄N₂)H]₄[Fe^II ₁₀Mo^V ₂₄(H₂PO₄)₄(HPO₄)₁₂(PO₄)₄(H₂O)₁₆(OH)₁₆O₄₄]·12H₂O, has been synthesized from a reaction mixture of MoO₃, FeSO₄·7H₂O, C₂H₂O₄·2H₂O, nicotine, H₃PO₄, and H₂O under hydrothermal conditions. The crystal data: monoclinic, space group C2/m, a = 24.4349(124), b = 12.9935(66), c = 14.7281(74) Å, β = 104.87(1) Å, V = 4520(4) Å³, Z = 2, R ₁  = 0.0874, wR ₂  = 0.2179. The structure is built from the building blocks of the formula, {Fe^II[Mo₆P₄O₃₁]₂}, consisting of a network of MO₆ (M = Fe, Mo) octahedral and PO₄ tetrahedral linked through their vertices. The connectivity of the building blocks with two pairs of face-sharing dinuclear Fe(II) clusters of the formula of [Fe^II ₂(H₂O)₄O₅] on which a phosphate group is hanging gives rise to one-dimensional chains with eight-membered apertures. The remarkable hydrogen bonded interactions between the chains form a unique and interesting framework with three-dimensional intersecting tunnels where the protonated nicotine molecules as structuring templates and crystallization water molecules are situated.     

High-temperature heat capacity and thermodynamic properties of pyrovanadate Pb<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> and orthovanadate Pb<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The heat capacities of Pb₂V₂O₇ and Pb₃(VO₄)₂ as a function of temperature in the range 350–965 K have been studied by the differential scanning calorimetry method. The C_P = f(T) curve for Pb₂V₂O₇ is described by the equation C_p = (230.76 ± 0.51) + (73.60 ± 0.50)×10^-3T ? (18.38 ± 0.54)×10⁵T^-2 in the entire temperature range. For Pb₃(VO₄)₂, there is a well-pronounced extreme point in the C_P = f(T) curve at T = 371.5 K, which is caused by the existence of a structural phase transition. The thermodynamic properties of the oxide compounds have been calculated.     

Effect of phosphate doping on electric properties and chemical stability of Ba<Subscript>4</Subscript>Ca<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11</Subscript> protonic conductor

Conductivity of perovskite phosphate–substituted solid solutions of Ba₄Ca₂Nb_{2 –x} P _x O₁₁ (0.0 ≤ x ≤ 0.5) was studied as a function of temperature, partial pressure of oxygen and water vapors. It is proved that the studied systems are protonic conductors at the temperatures below 600°C in the atmosphere with elevated content of water vapors (pH₂O = 1.92 × 10^–2 atm). Introduction of the tetrahedral [PO₄] group in the complex oxide matrix of Ba₄Ca₂Nb₂O₁₁ results in an increase in the oxygen–ionic (dry air, pH₂O = 1.91 × 10^–4 atm) and protonic conductivities (wet air, pH₂O = 1.92 × 10^–2 atm). Is it found that the doping causes a considerable increase in chemical stability of phases with respect to carbon dioxide.     

Synthesis and magnetic properties of quasi-unidimensional oxide Sr<Subscript>6.3</Subscript>Rh<Subscript>2.35</Subscript>Mn<Subscript>2.35</Subscript>O<Subscript>15</Subscript>

Attempts of the synthesis in air of complex oxides Sr₃RhMnO_x and Sr₄Rh_1.5Mn_1.5O_x resulted in revealing formation of a new oxide phase Sr_6.3Rh_2.35Mn_2.35O₉ related to quasi-unidimensional family A_3n+3m A′ _n B_3m+n O_9m+6n at n = 1 and m = 1. Its structural characteristics and magnetic properties are studied. X-ray data of the obtained phase is indicated on the basis of trigonal cell (spatial group P321) with the parameters: a 9.6239(4) Å; c ₁ 4.1130(4) Å, c ₂ 2.4946(2) Å. Manganese and rhodium exist in the compound as the cations Mn⁴⁺, Rh³⁺ and Rh⁴⁺, as follows from the data of measuring of magnetic susceptibility in the range 2–300 K.