Physicochemical properties of Ti-grafted SBA-15

Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al₂O₃ catalyst exhibited much better catalytic activity than the Rh-Ni/-Al₂O₃ catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe₃O₄—Cr₂O₃) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date.     

Oxygenation of Dimethylsulfoxide and Copper-Catalyzed Autoxidation of Substituted Benzoins

The catalytic activity of autoxidized copper (I) in the oxidation of para-disubstituted benzoins in dimethylsulfoxide by O₂ was studied both kinetically and by product analysis. Stoichiometry (1), accounts for more than 80% of the reaction. The catlytic oxydation was followed by monitering th consumption of O₂ manometrically by a fully automatic apparatus. (X = H, CH₃, OCH₃, C₆H₅ CI) A redox shuttle mechanism is proposed, where the rate-determining step is the autoxidation of Cu(I) followed by a rapid oxidation of the substrate by an oxocupric species. The redox stiochiometry (I) corresponds to that found for external monooxy-genases (or mixed-function oxidases), and the significance of our results with respect to analogous catalytic systems is discussed.     

Immobilization of transition metal ion complexes and their catalytic activity towards the activation of hydrogen peroxide

Transition metal ion-imidazole complexes have been immobilized on silica, silica–alumina (25%Al₂O₃), and alumina supports by adsorption and functionalization methods. The catalytic activity of these supported complexes in the decomposition of H₂O₂ has been studied. The reaction exhibits first-order kinetics with respect to [H₂O₂] and the quantity of catalyst. The rate of reaction decreases as [H₂O₂]₀ increases. The order of catalytic reactivity is strongly dependent on the type of metal ion, support, and the immobilization method. The complex anchored via adsorption exhibited a higher activity compared to the corresponding complex anchored via functionalization of the surface. The reaction proceed via formation of the peroxo-intermediate, which has an inhibiting effect on the reaction rate. The reaction is enthalpy-controlled as is concluded from the isokinetic relationship. A mechanism is proposed involving the generation of HO₂ radicals from the peroxo-intermediate in the rate-determining step.     

Synergistic effect for bimetallic Ru-Tc catalysts of cyclohexane dehydrogenation

Catalytic properties of the Ru-Tc/support (-Al₂O₃, Y₂O₃, and SiO₂) systems in the dehydrogenation of cyclohexane have been studied. The catalytic activity of the bimetallic catalysts depends on the nature of the support. A nonadditive increase in the catalytic activity of the bimetallic catalysts in comparison with monometallic samples was established. The value of the synergistic effect depends on the ratio between the amounts of the supported metals and the nature of the support. By using the diffuse reflectance spectra in UV- and visible regions and hydrogen chemisorption techniques, the modifying influence of the ionic metal species on the catalytic properties was shown.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1959–1963, August, 1996.     

Effects of gamma-irradiation and Li2O-doping on surface and catalytic properties of unloaded Co3O4 solid

The effects of -irradiation (20–160 Mrad) and lithium oxide doping (0.75–6 mol%) on the surface and catalytic properties of unloaded Co₃O₄ solid have been investigated. The surface characteristics of various solids were determined from nitrogen adsorption isothems taken at –196 °C and their catalytic activities were measured by following the kinetics of CO-oxidation by O₂ at 100–150 °C using a static method. The results showed that -rays brough about a decrease of 21% inS _BET of Co₃O₄ due to widening of its pores and led also to a considerable increase in its catalytic activity. A maximum increase of 91% was observed upon exposure to a dose of 80 Mrad. Lithium oxide-doping at at 500 °C resulted in an increase of 150% inS _BET of treated solid without changing its mean pore radius. This treatment was also accompanied by an increase of about 50% in its catalytic activity measured at 150 °C. Gamma-irradiation and Li₂O-doping of unloaded Co₃O₄ did not change the magnitude of apparent activation energy of catalysis of CO-oxidation by O₂ but increased the concentration of catalytically active sites contributing in the catalytic process. In other words, -rays and lithium oxide doping did not alter the mechanism of catalytic oxidation of CO by O₂ over unloaded cobaltic oxide solid.     

Influence of MgO loading on the structure and catalytic performance of Pd/γ-Al2O3, I. Effect of interaction between MgO and γ-Al2O3

The influence of MgO dispersed on -Al₂O₃ in different amounts on the structure and performances of Pd/-Al₂O₃ catalysts has been studied by means of XRD, H₂–O₂ titration, BET and catalytic activity test for CO oxidation. It was found that introduction of MgO enhanced greatly the CO oxidation activity of catalyst. It seems that the enhanced activity stems from the stronger interaction between MgO and -Al₂O₃ at a given temperature (e.g. 450 °C).     

Catalytic Properties of the Fe2O3–Bi2O3 System in Ammonia Oxidation to Nitrogen Oxides

The catalytic properties of the Fe₂O₃–Bi₂O₃ system in ammonia oxidation are studied at 1073 K. The effect of phase composition on the physicochemical and catalytic properties of the system is determined. The catalytic properties of individual components of the system (-Fe₂O₃, Bi₂Fe₄O₉, BiFeO₃, and -Bi₂O₃) are studied.     

Spectral Investigation of the Interaction of Carbon Monoxide and Dioxygen with Low-Temperature Sublimates of Co(II) meso-Tetraphenylporphyrinate: Evidences for Oxidative Catalysis

The interaction of carbon monoxide and dioxygen with low-temperature (T= 77 K) sublimates of cobalt(II) meso-tetraphenylporphyrinate (CoTPP) is studied by IR spectroscopy using isotopically labeled compounds (¹³CO and ¹⁸O₂). The obtained data confirm the coordination of CO and O₂with the formation of axial complexes CoTPP · L (L = O₂, CO) and the mixed complex O₂· CoTPP · CO. The heating of the complex containing CO and O₂to 150 K leads to the appearance of lines in the IR spectrum corresponding to valence asymmetric (_asOCO) and degenerated deformation (OCO) vibrations of carbon dioxide. This is evidence for the oxidation of CO. The evacuation of CO₂at a higher, but still low, temperature and the addition of a new portion of CO and O₂mixture lead to the formation of new portions of CO₂. This demonstrates the catalytic character of the process. Only low-temperature sublimates have catalytic properties. Sublimates of CoTPP obtained on the surface at room or higher temperature demonstrate neither catalytic activity nor the ability to coordinate any amount of CO and O₂sufficient for the detection by spectroscopy.     

Unsymmetrical dinuclear cobalt and nickel trimethylacetate complexes

The reaction of the dinuclear complex Co₂(-OOCCMe₃)₂(²-OOCCMe₃)₂bpy₂ (1) with the polymer [Co(OH) _n (OOCCMe₃)_2–n ] _x afforded the unsymmetrical dinuclear complex bpyCo₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (2). The reaction of 2,2"-dipyridylamine with [Co(OH) _n (OOCCMe₃)_2–n ] _x gave rise to the analogous complex [(C₅H₄N)₂NH]Co₂(₂-O,²-OOCCMe₃)(-OOCCMe₃)₂(²-OOCCMe₃) (3). The reaction of complex 1 with Ni₄(₃-OH)₂(-OOCCMe₃)₄(OOCCMe₃)₂(MeCN)₂[²-o-C₆H₄(NH₂)(NHPh)]₂ (4) produced an isostructural heterometallic analog of complex 2 with composition bpyM₂(₂-O,²-OOCCMe₃)(₂-O,O"-OOCCMe₃)₂(²-OOCCMe₃) (5) (M = Co, Ni; Co : Ni = 1 : 1) and the dinuclear heterometallic complex bpy(HOOCCMe₃)M(-OH₂)(-OOCCMe₃)₂M(OOCCMe₃)₂[o-C₆H₄(NH₂)(NHPh)] (6) (M = Co, Ni; Co : Ni = 0.15 : 1.85). Compounds 2 and 5 exhibit ferromagnetic spin-spin exchange interactions.     

Role of Bifunctionality of ZrO2-Based Oxide Systems in NO Reduction with Lower Hydrocarbons

The catalytic properties of transition metal oxides (Cr, Ce, and Co) supported on ZrO₂ synthesized by various methods, as well as the effect of rhodium on the performance of the e O _y /ZrO₂ oxide systems in NO reduction with hydrocarbons (methane, propane–butane mixture, and propene) were studied. The acidity of the surface of the catalysts was studied by IR spectroscopy and ammonia temperature-programmed desorption. The adsorption of NO, propene, and their mixture on the Rh–r₂₃/ZrO₂ and Rh–O₂/ZrO₂ catalysts at temperatures of 293–623 K was studied by IR spectroscopy. The adsorption and co-adsorption of the reactants was found to differ significantly depending on the nature of the surface. The activity of the catalysts studied in NO selective catalytic reduction with hydrocarbons is due to the presence of the acidic functional groups on their surface.     

Schiff base complexes of dioxouranium(VI). VII. Dioxouranium(VI) acetate complexes with monobasic bidentate and bibasic tridentateSchiff bases

11 and 12 molar reactions of dioxouranium(VI) acetate dihydrate with the monobasic bidentateSchiff bases,o-HOC₆H₄CH=NR oro-HOC₁₀H₆CH=NR (R=C₂H₅,n-C₃H₇,n-C₄H₉ or C₆H₅) and bibasic tridentateSchiff bases,o-HOC₆H₄CH=NR(OH) oro-HOC₁₀H₆CH=NR(OH) (R=–CH₂CH(CH₃)- or —CH₂CH₂CH₂–) have been studied and derivates of the type UO₂(OAc)₂(SBH), UO₂(OAc)₂(SBH)₂, UO₂(OAc)₂(SBH ₂) and UO₂(OAc)₂(SBH ₂)₂ (whereSBH andSBH ₂ represent monobasic bidentate and bibasic tridentateSchiff base molecules respectively) have been isolated. These have been characterized by elemental analysis, conductance measurements and IR spectral studies.

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UO₂ ²⁺-Komplexe von Schiff-Basen. VII. Uranylacetat-Komplexe mit monobasischen zweizähnigen und bibasischen dreizähnigen Schiff-Basen

Zusammenfassung Es wurden in 1:1- und 1:2-molaren Reaktionen von UO₂(OAc)₂·2H₂O mitSchiff-Basen (L) Komplexe des Typs UO₂(OAc)₂ L bzw. UO₂(OAc)₂ L ₂ isoliert. Die Komplexe wurden mittels Elementaranalyse, Leitfähigkeitsmessungen und IR-Spektren untersucht.

     

1,10-Phenanthroline catalysis of the chromium(VI) oxidation of alcohols: a kinetic and mechanistic study

Several primary, secondary and tertiary alcohols are oxidised in acidic solutions using Cr^VIas an oxygen donor and 1,10-phenanthroline (Phen) as catalyst. A large primary kinetic isotope effect, kie(k _H/k _D 10) suggests a linear transition state in the noncatalytic system, whereas a moderate kinetic isotope effect observedin the catalytic pathway can be associated with a cyclic transition state. The k _D2O/k _H2Oratio does not seem to indicate any significant solvent isotope effect. Cr^III inhibition, reflected in the firstorder plots, can be explained by exchange reactions. PhCH₂OH reacts ca. 7 times faster than MeOH. Moderately negative ^* values indicate ahydride abstraction mechanism. Imperfect correlation is observed in the LFER between catalytic and noncatalytic reaction systems.Enhanced reactivity has been observed in the presence of 2,2-bipyridyl, whereas the catalytic activity is insignificant with picolinicacid, imidazole and oxalic acid. Consideration of the kinetic behaviour of catalytic and noncatalytic reaction pathways provides valuable mechanistic insight into the systems studied.     

Kinetics and mechanism of the decomposition of hydrogen peroxide catalyzed by Mn(II)-bis-salicylaldimine complexes

Summary The tetradentateSchiff bases N,N-bis(salicylidene) ethylenediamine (salen), N,N-bis-(salicylidene) hexylenediamine (salhex), and N,N-bis(salicylidene)-o-phenylenediamine (sal-o-phen) are very strongly adsorbed by cation exchange resins (Dowex-50W) with manganese(II) as a counter ion, forming stable complexes. The kinetics of the catalytic decomposition of H₂O₂ in presence of these complexes has been studied in aqueous medium. The decomposition reaction is first order with respect to H₂O₂ in the case ofsalen andsal-o-phen and third order in the case ofsalhex. The greater the ligand methylene chain length or the greater the steric effect of the ligand, the greater will be the rate of reaction. The reaction is governed by the entropy of activation. A reaction mechanism is proposed.

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Kinetik und Mechanismus der von Mn(II)-bis-Salicylaldimin — Komplexen katalysierten Zersetzung von Wasserstoffperoxid

Zusammenfassung Die teradentatenSchiffschen Basen N,N-bis-Salicyliden-ethylendiamin (salen), N,N-bis-Salicyliden-Hexylendiamin (salhex) und N,N-bis-Salicyliden-o-phenylendiamin (sal-o-phen) werden von Kationenaustauschen (Dowex-50W) mit Mangan(II) als Gegenion unter der Bildung stabiler Komplexe adsorbiert. Die Kinetik der katalytischen Zersetzung von H₂O₂ in Gegenwart dieser Komplexe wurde in wäßrigem Medium untersucht. Die Zersetzungsreaktion ist erster Ordnung bezüglich H₂O₂ in den Fällensalen undsal-o-phen und dritter Ordnung im Fall vonsalhex. Die Reaktionsgeschwindigkeit steigt mit der Länge der Methylenkette des Liganden und mit dessen Raumbedarf und wird von der Aktivierungsentropie bestimmt. Ein Reaktionsmechanismus wird vorgeschlagen.

     

Effects of Composition and Method of Preparation of Lead-Containing Oxide Systems on Their Catalytic Properties in the Oxidative Dimerization of Methane

The effects of the Pb-Sn-O composition, the method of precipitating the active components, and modification with alkaline earth metals on the physico-chemical and catalytic properties of lead-tin catalysts in oxidative dimerization of methane have been studied. The effect of the phases of lead orthostannate, Pb₂SnO₄, on the surface properties of the Pb-Sn-O system has been established. The most selective composition has a ratio PbO : SnO₂ = 80 : 20 mole % on -Al₂O₃ with divalent metal hydroxides. Introduction of alkaline earth metals into the Pb-Sn-O/-Al₂O₃ system leads to stabilization of lead in its 4-valent state with formation of metal orthoplumbates, M₂PbO₄, and to a decrease in selectivity with respect to C₂-hydrocarbons. The increased catalytic activity of the modified M-Pb-Sn-O/-Al₂O₃ samples (M = Ba, Sr, Ca, and Mg) is determined by the presence of tightly bound oxygen. Conclusions about the nature of the interaction of the reagents with the surface of the catalyst were reached.     

Methylpyrazine Ammoxidation over Binary Oxide Systems: V. Effect of Phosphorus Additives on the Physicochemical and Catalytic Properties of a Vanadium–Titanium Catalyst in Methylpyrazine Ammoxidation

Oxide vanadium–titanium catalysts modified by phosphorus additives (20V₂O₅–(80 –n)TiO₂–nP₂O₅, n = 1, 3, 5, 10, and 15 wt %) are studied in methylpyrazine ammoxidation. Two regions of compositions are found corresponding to radically different catalytic properties, namely, catalysts with a low (5 wt % P₂O₅) and high (10 wt % P₂O₅) concentration of the additive. In the first case, the introduction of phosphorus is accompanied by a gradual increase in the activity. In the second case, an increase in the additive concentration results in a decrease in the activity and selectivity to the target product, pyrazineamide, and a simultaneous increase in the selectivities to by-products, pyrazine and carbon oxides. The catalysts are characterized by X-ray diffraction analysis, differential dissolution, IR, and NMR spectroscopic data. As in the binary system, the active sites of the samples with a low concentration of phosphorus contain V⁵⁺ cations in a strongly distorted octahedral oxygen environment, which are strongly bound to a support due to the formation of V–O–Ti bonds. The catalytic properties of the samples containing 10 wt % P₂O₅ are due to the presence of the phase of a triple V–P–Ti compound with an atomic ratio V : P : Ti approximately equal to 1 : 1 : 1. The V⁵⁺ cations in this compound occur in a weakly distorted tetrahedral oxygen environment and are bound to the tetrahedral P⁵⁺ cations.     

Theoretical study of the influence of para- and meta-substituents on X-pyridineHF hydrogen bonding

The effects of O⁻, N (CH₃)₂, NH (CH₃), NH₂, C₂H₅, CH₃, OH, F, Cl, OF, Br, NO₂ and substituents in para- and meta-positions on X-pyridineHF hydrogen bond has been studied by HF, B3LYP and MP2 methods using 6-311++G(d,p) basis set. The relationship between hydrogen bond formation energy ΔE and electron donating (or withdrawing) of substituents has been investigated. In this respect, population analysis has been performed by atoms in molecules (AIM) and natural bond orbital (NBO) theories. The results of AIM and NBO analyses are in good agreement with calculated energy values. The relationship between Hammett coefficient and complexation energy has been established and the ρ constant has been calculated for hydrogen bonding. There is a relationship between σ and ΔE with a correlation coefficient equal to 0.94.     

Oxidation of Finely Dispersed Carbon on Coated Oxide Catalysts

The catalytic activity of soot filters for internal combustion gas exhausts made from synthetic cordierite with a catalytic covering of transition metal oxides (Co₃O₄, MnO₂, CuO, Cr₂O₃) or binary oxides (CuCr₂O₄, CuCo₃O₅, Co₃MnO₆, CuMnO₃) has been studied. The most active catalyst for the oxidation of CO and hexane and for the combustion of soot forming compounds in the exhaust gases is copper chromite. A secondary carrier based on -Al₂O₃ increased the soot capacity of the filters and increased the selectivity the process of combustion of soot to CO₂.     

The complete oxidation of a volatile organic compound (toluene) over supported metal oxide catalysts

The complete oxidation of a volatile organic compound (toluene) was carried out over oxides of various metals (Cu, Mn, Fe, V, Mo, Co, Ni and Zn) supported with -Al₂O₃ catalyst. It was found that Cu/-Al₂O₃ was the best catalyst among them. With increasing calcination temperature, the specific surface areas and the surface oxygen of the catalyst decreased and, as a result, the catalytic activity decreased. Copper loadings on -Al₂O₃ had an influence on catalytic activity, and it was observed that 5 wt% Cu/-Al₂O₃ catalyst was the most active. Using TiO₂ (rutile) and SiO₂ as support instead of -Al₂O₃, the sequence of copper crystallinity degree with respect to supports was SiO₂ > TiO₂ (rutile) > -Al₂O₃, which was the opposite of the catalytic activity sequence.     

“In-situ” monitoring activation and reaction on very absorbing catalytic solid by DRIFT spectrometer

The FTIR's well-known advantages are strongly shown by the use of new infrared techniques. Both advantages of FTIR and diffuse reflectance make this coupling particularly important in the development of infrared studies.Sensitivity and rapidity of the FTIR spectrometer, added to the extremely simple preparation of the sample, allowed by diffuse reflectance attachment, give a high performing tool particularly in catalysis in the view of understanding the catalytic reactions mechanisms. We have chosen thein-situ study of two catalytic systems active in selective hydrogénation of dienes: a copper-chromium oxide and Cu/Al₂O₃ .     

锶助剂对铂锡催化剂正丁烷脱氢催化性能的影响

负载型ＰｔＳｎ／Ａｌ２Ｏ３催化剂已广泛地应用于工业生产中［１］，人们正尝试着添加不同助剂以改变催化剂的反应性能。文献的工作主要集中在研究铂锡催化剂中添加助剂对载体表面酸性的调变作用。在烃类重整催化剂中，加入氟、氯等元素可增强载体的表面酸性［２］，提高...