The effect of the modification conditions of natural mordenite on their catalytic characteristics in the selective reduction of NOx

The results of a search for optimum conditions for the modification of natural mordenites and the results of an investigation of their acidic characteristics by temperature programmed desorption of ammonia for the purpose of producing active and sulfur-resistant catalysts for the selective reduction of NO_x by lower hydrocarbons (C₁−C₄) are presented. It was shown that during the chemical modification of samples of mordenite-bearing rock, including acid treatment with 0.25–0.5 N sulfuric acid solutions, recationization, and subsequent decationization, the concentration of strong acid centers increases. Here the activity of the catalysts and the resistance to the effect of SO₂ in the selective reduction of NO_x to nitrogen by a propane-butane mixture are increased. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 125–129, March–April, 1999.     

Effect of the nature of the support on the activity of palladium catalysts for oxidation of carbon monoxide

We have studied the catalytic activity of TiN_0.65, TiO₂, Al₂O₃, and palladium catalysts supported on them in the oxidation of carbon monoxide. The order in which the activities of the supported catalysts vary, Pd/Al₂O₃>Pd/TiO₂>Pd/TiN_0.65, is the reverse of the activity series for the supports. This is explained by the effect of transfer of electron density from the palladium to the substrate. Taras Shevchenko Kiev University, 64 Vladimirskaya ul., Kiev 252033, Ukraine, G. V. Kurdyumov Institute of the Physics of Metals, National Academy of Sciences of Ukraine, 36 Akademika Vernadskogo bul’var, Kiev-142 252642, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 118–121, March–April, 1998.     

Stereochemical features of the synthesis and the structure of fullerenes

Details of the design of decaplet fullerenes are discussed. A model of the cluster assembly of C₆₀, C₇₀, and C₈₀ monomers from mono-, bi-, and trihexacyclic compounds of carbon was developed on the basis of the described structural and stereochemical concepts. The autoadhesion in the supermolecular structure, the cluster macrorecombination of the π radicals, and the contribution from spin-polymerization effects to regulation of the organic synthesis of C_n fullerenes were examined. V. N. Bakul Institute of Superhard Materials, National Academy of Sciences of Ukraine, 2 Avtozavodskaya ul., Kiev 254074, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 3, pp. 145–149, May–June, 1999.     

Influence of alkaline earth metals on the activity and sulfur stability of zeolites in the Nox−C3−C4 hydrocarbon selective reduction of no to nitrogen (SKV) process

The results of the influence of alkaline earth metal and magnesium cations on the activity and sulfur stability of catalysts based on synthetic mordenites and high-silicon zeolites with pentasil structures on the selective reduction of nitrogen oxides with C₃−C₄ hydrocarbons are presented. Doping the H-form of mordenite and pentasils with Ca, Sr, Ba, and Mg cations increased their activity and stability with respect to sulfur dioxide in the selective reduction of NO_x with a propane-butane mixture. L. V. Pisarzhevskii Institute of Physical Chemistry, Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 5, 317–321, September–October, 1999.     

The role of the geometric factor in the selective oxidation of lower paraffins at VPO catalysts

For the most widely published oxidation of n-butane at vanadium-phosphorus catalysts it was shown that the geometric factor plays a deciding role in the formation of the selective oxidation products. The mechanism proposed for the transformation of the paraffin at the [100] plane of the vanadyl pyrophosphate, which takes account of the geometry of the molecule being oxidized, explains the observed experimental facts, i.e., the increase in the oxidation rate with increase in the effective negative charge at the oxygen atoms of the catalyst, the positive effect of the hyperstoichiometric phosphorus on the selectivity of oxidation, the increased selectivity of oxidation with the introduction of additives that form phosphates, and the difference in the characteristics and mechanism of the oxidation of a paraffin and C₄ olefins. On the basis of the proposed mechanism suggestions are made about possible paths for the transofrmation of C₂−C₆ paraffins at VPO catalysts and the factors that could affect the selectivity of these processes. A number of the suggestions were confirmed by the author's own investigations and by published investigations. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 5, pp. 265–276, September–October, 1999.     

Separation of C1–C4 hydrocarbon gases on impregnated liquid membranes

Diffusion plays an important role along with complexation in the separation of C₁–C₄ hydrocarbon gases on copper-containing impregnated liquid membranes. The partition factor changes as the process goes from nonsteady-state to steady-state. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 191–195, May–June, 1998.     

Fischer–Tropsch Synthesis by Carbon Dioxide Hydrogenation on Fe-Based Catalysts

Impregnated and co-precipitated, promoted and unpromoted, bulk and supported iron catalysts were prepared, characterized, and subjected to hydrogenation of CO₂ at various pressures (1–2 MPa) and temperatures (573–673 K). Potassium, as an important promoter, enhanced the CO₂ uptake and selectivity towards olefins and long-chain hydrocarbons. Al₂O₃, when added as a structural promoter during co-precipitation, increased CO₂ conversion as well as selectivity to C₂₊ hydrocarbons. Among V, Cr, Mn and Zn promoters, Zn offered the highest selectivity to C₂–C₄ alkenes. The different episodes involved in the transformation of the catalyst before it reached steady-state were identified, on the co-precipitated catalyst. Using a biomass derived syngas (CO/CO₂/H₂), CO alone took part in hydrogenation. When enriched with H₂, CO₂ was also converted to hydrocarbons. The deactivation of impregnated Fe–K/Al₂O₃ catalyst was found to be due to carbon deposition, whereas that for the precipitated catalyst was due to increase in crystallinity of iron species. The suitability of SiO₂, TiO₂, Al₂O₃, HY and ion exchanged NaY as supports was examined for obtaining high activity and selectivity towards light olefins and C₂₊ hydrocarbons and found Al₂O₃ to be the best support. A comparative study with Co catalysts revealed the advantages of Fe catalysts for hydrocarbon production by F–T synthesis.     

Platinum nanoparticle size effect on specific catalytic activity in <Emphasis Type="Italic">n</Emphasis>-alkane deep oxidation: Dependence on the chain length of the paraffin

The specific activity of 0.8% Pt/Al₂O₃ catalysts in the deep oxidation of C₁–C₆ n-alkanes increases with an increase in the Pt particle size from 1 to 3–4 nm. Further coarsening of the particles insignificantly changes the specific activity. The size effect was studied for a series of catalysts containing platinum nanoparticles 1 to 11 nm in diameter. The specific catalytic activity variation range depends on the size of the reacting hydrocarbon molecules. As the platinum particle size increases, the specific catalytic activity increases 3–4 times for the oxidation of CH₄ and C₂H₆ and by a factor of 20–30 for the oxidation of n-C₄H₁₀ and n-C₆H₁₄.     

Factors determining selectivity of ethylene conversion to butadiene over aluminosilicate catalyst

A study has been made of the influence of temperature, partial pressure of C₂H₄, and contact time on the selectivity of direct conversion of ethylene to butadiene over an aluminosilicate catalyst. A critical analysis has been made of the competing directions of C₂H₄ conversion, which determine the selectivity of C₄H₆ formation under conditions of a heterogeneous-homogeneous mechanism in carrying out the process. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 78–82, March–April, 1997.     

Corundum impregnation conditions for preparing supported Ni catalysts for the synthesis of a uniform layer of carbon nanofibers

Impregnation techniques for corundum (S _BET = 0.5 m²/g) as a support for Ni catalysts for C₃–C₄ alkane pyrolysis into catalytic filamentous carbon (CFC) are compared. The effects of the following factors on the uniformity of the active component (Ni) deposition on the inert support and on the CFC yield (g CFC)/(g Ni) are reported: (1) pH of the nickel nitrate solution, (2) presence of aluminum(III) nitrate in the solution, (3) addition of viscosifying agents (glycerol, glucose, sucrose) to the solution, (4) catalyst calcination conditions before pyrolysis, and (5) catalyst drying technique. The surface morphology of the Ni catalysts and of the carbon deposits resulting from the catalytic pyrolysis of C₃–C₄ alkanes in the presence of hydrogen has been investigated by scanning electron microscopy. The optimum way of preparing the supported Ni catalysts is by carrying out the incipient wetness impregnation of corundum with a nickel nitrate solution (0.05–0.1 mol/l) containing glycerol (20–25 vol %), drying the product in a microwave oven, and burning away the glycerol before alkane pyrolysis.     

The effect of sulfur dioxide on the activity of modified mordenites in the selective reduction of Nox

The results of a comparative investigation into the activity of modified natural and synthetic mordenites in the selective reduction of NO_x by C₁ and C₃−C₄ hydrocarbons (methane and a propane-butane mixture), the effect of sulfur dioxide on the process, and the acidic characteristics of the mordenites by temperature programmed desorption of ammonia and IR spectroscopy are presented. Sulfur dioxide has practically no effect on the selective reduction of NO_x by C₃−C₄ hydrocarbons at the H forms of synthetic and previously recationized natural mordenites but substantially retards the process at the Cu-, Co-, and Cr-substituted forms and palladium-containing mordenites. The decrease in the concentration of the strong B centers in the transition from the hydrogen to the copper-containing form of the mordenites reduces their activity in selective reduction. Prior recationization of natural mordenites increases their activity, stability, and resistance to the action of sulfur dioxide. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 2, pp. 119–124, March–April, 1999.     

Rate constants for the formation and decomposition of the σ-adduct in the reactions of N-arylpyridinium salts

The rate constants for the formation (k₁) and decomposition (k ₋₁ ,k ₂ ,k ₃ ) of the σ-adduct were determined for the reactions of 4-R-N-(2,4-dinitrophenyl)pyridinium salts [R=Py, CON(C₂H₅)₂] with 4-methoxyaniline, which takes place by the ANRORC substitution mechanism. L. M. Litvinenko Institute of Physical Organic Chemistry and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 282–285, September–October, 1998.     

Kinetics and mechanism of the oxidation of arenes in the presence of heteropoly acids and palladium(II) complexes supported on silica gel

Pd(II) complexes and twelfth-series heteropoly acids (HPA) H₉[PMo₆V₆O₄₀] and H₃[PMo₁₂O₄₀] supported on silica gel oxidize benzene and toluene at 95°C. The formation of methyldiphenylmethane in the oxidation of toluene on HPA/SiO₂ and (PdCl₂−HPA)/SiO₂ catalysts, KIE>1 for the toluene/toluene-d₈ pair, and greater rate for toluene than for benzene are in accord with a one-electron transfer mechanism. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 249–252, July–August, 1999.     

Influence of H<Subscript>2</Subscript>O and SO<Subscript>2</Subscript> on the activity of deposited cobalt oxide catalysts in the processes of reduction of nitrogen(I), (II) oxides with carbon monoxide and C<Subscript>3</Subscript>-C<Subscript>4</Subscript> alkanes

It is shown that palladium–cobalt oxide–cerium catalyst deposited on cordierite catalyzes the reduction of nitrogen(II) oxide with carbon monoxide, and cobalt–iron catalysts in simultaneous reduction of NO + N₂O with C₃-C₄ alkanes retained high activity in the presence of water vapor and sulfur dioxide. The Pd-Co₃O₄/cordierite catalyst exceeds the Pt-Co₃O₄/codierite catalyst in the conversion of NO and CO in the reaction mixture CO + NO + O₂ + H₂O + SO₂. Modification of the Pd-Co₃O₄/cordierite with cerium oxide considerably increases its sulfur resistance.     

双配体CuFe@MOFs材料为前驱体的催化剂的组分调控对CO2加氢制C2+醇性能的影响

采用水热法制备了以对苯二甲酸和对氨基苯甲酸为配体的双配体Fe基MOFs材料(MIL-88B(Fe)),在浸渍一定量Cu物种后经氮气气氛焙烧得到活性组分均匀分散的CuFe基催化剂。通过改变2种配体的比例调控催化剂表面Fe活性物种的价态分布,并考察了其用于固定床反应器上CO_2加氢制C_(2+)醇的催化性能,结合X射线衍射(XRD)、H_2程序升温还原(H2-TPR)、N_2吸附-脱附、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)等表征结果发现,对苯二甲酸与对氨基苯甲酸物质的量之比为5∶2时,催化剂表面低价态铁原子占比为71.27%,催化剂展现最优的催化活性,CO_2转化率为8.80%,总醇选择性为31.52%,其中C_(2+)醇的物质的量分数达到94.70%。     

The effect of the carrier nature and the method of preparation of oxide catalysts containing indium on their activity in the selective catalytic reduction of nitrogen monoxide with C<Subscript>1</Subscript>-C<Subscript>4</Subscript> hydrocarbons

The activity of samples containing indium in the selective catalytic reduction (SCR) of NO with C₁-C₄ hydrocarbons depends on nature of the carrier, Al₂O₃, ZrO₂, the quantity of indium oxide, and the method of its introduction. The most active catalysts (2.5–5.0% In₂O₃/Al₂O₃) are stable to water and are characterized by a large overall concentration of oxide centers. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 107–111, March–April, 2007.     

Influence of the composition of Co-containing perovskites on their catalytic properties in the conversion of methane into higher hydrocarbons in non-stationary conditions

The oxidative coupling of methane in a periodic regime was studied using Co-containing perovskites as solid oxidants. Partial substitution of strontium with alkali metals in the perovskite SrCoO₃ increased the activity and selectivity of the catalyst with respect to higher hydrocarbons. The substituted catalysts continued to work after many oxidation-reduction cycles. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 1, pp. 47–52, January–February, 2000.     

A Density Functional Investigation on C2Aun+ (n?=?1, 3, 5) and C2Aun (n?=?2, 4, 6): from Gold Terminals, Gold Bridges, to Gold Triangles

A systematic density functional theory investigation on C₂Au _n ⁺ (n = 1,3,5) and C₂Au _n (n = 2,4,6) indicates that gold atoms serve as terminals (–Au) in the chain-like C_s C₂Au⁺ (C=C–Au⁺) and D_∞h C₂Au₂ (Au–C≡C–Au) and as bridges (–Au–) in the side-on coordinated C_2v C₂Au₃ ⁺ ([Au–C≡C–Au]Au⁺) and C_s C₂HAu₂ ⁺([H–C≡C–Au]Au⁺). However, when the number of gold atoms reaches four, they form stable gold triangles (–Au₃) in the head-on coordinated C_2v C₂Au₄ (Au–C≡C–Au₃) and the side-on coordinated C_2v C₂Au₅ ⁺ ([Au–C≡C–Au]Au₃ ⁺). Similar –Au₃ triangular units exist in the head-on coordinated C_2v C₂HAu₃ (H–C≡C–Au₃) and D_2d C₂Au₆ (Au₃–C≡C–Au₃). The existence of stable –Au₃ triangular units in small dicarbon aurides is significant and intriguing. The high stability of Au₃ triangles originates from the fact that an equilateral D_3h Au₃ ⁺ cation possesses a completely delocalized three-center-two-electron (3c–2e) σ bond and therefore is σ-aromatic in nature. The extension from H/Au analogy to H/Au₃ analogy established in this work may have important implications in designing new gold-containing catalysts and nano-materials.     

The effect of encapsulated cyanide complexes on the localization of cations in faujasite

Features of the localization of various types of cations and their distribution between the structural elements of the framework of faujasite with encapsulated hexacyanide complexes of iron(II) and cobalt(III) were established. The content of the alkali-metal cations in the sodalite cells is increased compared with faujasite, and the cations of the transition metals are localized in the large cavities with the formation of Me(S_II)−NC−Fe(CN)₅ (Me=Cu, Co) and (NC)₅Fe−CN−Me(S_V)−NC−Fe(CN)₅ (Me=Ni, Cu, Co) fragments. L. V. Pisarzhevskii Institute of Physical Chemsitry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 56–61, January–February, 1999.     

Compounds of the [PMo12O40]3− anion with surfactant cations forming nanoperiodic structures

Phosphomolybdic acid forms compounds with surfactant cations in acid aqueous media (pH 1.0–2.5) to give compounds A₃[PMo₁₂O₄₀] or Etn₃[PMo₁₂O₄₀]₂·nEtnCl₂ (n=0−3) with various nanoperiodicity depending on the surfactant and synthesis conditions. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, 184–190, May–June, 1998.