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1.
The temperature dependence of the Fe-HZSM-5 activity and selectivity in the process of catalytic oxidation of ethane by the excess of N2O at 250–350°C exhibits a pronounced hysteresis. The oxidized catalysts free from condensation products are active only in the complete oxidation of ethane. At low temperatures of the reaction of the C2H6 + N2O mixture with the catalyst, coke formation takes place and the coordination state of iron ions differs from the initial sample. Under these conditions, the process of complete oxidation of ethane is essentially suppressed and the process of oxidative dehydrogenation dominates. The catalytic properties of iron-containing zeolites prepared either by direct synthesis or by introduction of iron ions into the cationic positions of H[Al]ZSM-5 are quite similar, because irreversible formation of new iron species considerably different from the initial species takes place during the catalytic reaction on both series of samples. The activity of HZSM-5 containing trace amounts of iron is much lower than that of iron-containing samples.  相似文献   

2.
Nanostructured cobalt molybdate catalysts supported on mesoporous silica SBA-15 with different loadings were prepared by citric acid coordination-impregnation method and characterized by XRD, TEM, and BET techniques. The characterization results showed that high loading of well-dispersed crystalline CoMoO4 may be achieved using citric acid coordination-impregnation method and the mesoporous structure of the support remained intact. The catalytic activity of these catalysts in the oxidative dehydrogenation of propane was investigated. The catalysts of nanostructured cobalt molybdate supported on mesoporous silica SBA-15 showed better catalytic performance than the corresponding bulk composite oxide and nanostructured CoMoO4 supported on SBA-15 with loading of 13% (mass fraction, w) displayed propene yield of 16.8% at 823 K.  相似文献   

3.
The catalytic properties of complex oxide catalysts with ABO3 perovskite structure (A = Sr, Ba, La; B = Mn, Co, Ni) in the oxidative coupling of methane were studied with separate introduction of methane and oxygen onto the catalyst. The greatest catalytic activity was found for the nickel-containing oxides but these catalysts have much lower operational stability than Mn- and Co-containing catalysts. Modification of the oxide systems studied by partial replacement of the strontium or transition metal ions by alkali metal ions considerably improves their activity and selectivity.__________Translated from Teoreticheskaya i Eksperimental’naya Khimiya, Vol. 41, No. 2, pp. 110–114, March– April, 2005.  相似文献   

4.
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.  相似文献   

5.
The catalytic activity of Fe(III)(acac)3 (Cat) in ethylbenzene oxidation with dioxygen is studied. 1-Phenylethyl hydroperoxide (PEHP), acetophenone (AP), and methyl phenyl carbinol (MPC) are the main products of the process throughout the Cat concentration range examined. Phenol (Ph) is formed in much smaller amounts. The highest PEHP selectivity, S PEHP = 65%, is observed at an ethylbenzene conversion of C ≈ 2% at low [Cat] values. PEHP and the other main oxidation products (AP and MPC) form by parallel reactions at any Cat concentration. Depending on [Cat], AP and MPC form by parallel or consecutive reactions. When [Cat] is high enough, AP results from MPC oxidation. At the initial stages of the reaction, the MPC selectivity (S MPC = 50%) exceeds the PEHP selectivity (S PEHP = 25–30%). The mechanism of ethylbenzene oxidation catalyzed by Fe(III)(acac)3 and the role of active complexes in its steps are considered.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 354–359.Original Russian Text Copyright © 2005 by Matienko, Mosolova.  相似文献   

6.
Recent progress on the bismuth molybdate catalysts for oxidative dehydrogenation of n-butene to 1,3-butadiene was reported in this review. A number of bismuth molybdate catalysts, including pure bismuth molybdates (α-Bi2Mo3O12, β-Bi2Mo2O9, and γ-Bi2MoO6) and multicomponent bismuth molybdates, were prepared by a co-precipitation method for use in the production of 1,3-butadiene from C4 raffinate-3 through oxidative dehydrogenation of n-butene. It was observed that multicomponent bismuth molybdate catalyst was more efficient than pure bismuth molybdate catalyst in the oxidative dehydrogenation of n-butene. Various experimental measurements such as temperature-programmed reoxidation, X-ray photoelectron spectroscopy, and O2-temperature-programmed desorption analyses were carried out to elucidate the different catalytic activity of bismuth molybdate catalysts. It was revealed that a bismuth molybdate catalyst with a higher oxygen mobility showed a better catalytic performance in terms of conversion of n-butene and yield for 1,3-butadiene. We have successfully demonstrated from experimental findings that oxygen mobility of bismuth molybdate catalyst played a key role in determining the catalytic performance in the oxidative dehydrogenation of n-butene to 1,3-butadiene.  相似文献   

7.
Molybdates are biocidal materials that can be useful in coating surfaces that are susceptible to contamination and the spread of microorganisms. The aim of this work was to investigate the effects of copper doping of hydrated cobalt molybdate, synthesized by the co-precipitation method, on its antibacterial activity and to elucidate the structural and morphological changes caused by the dopant in the material. The synthesized materials were characterized by PXRD, Fourier Transformed Infrared (FTIR), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), and SEM-Energy Dispersive Spectroscopy (SEM-EDS). The antibacterial response of the materials was verified using the Minimum Inhibitory Concentration (MIC) employing the broth microdilution method. The size of the CoMoO4·1.03H2O microparticles gradually increased as the percentage of copper increased, decreasing the energy that is needed to promote the transition from the hydrated to the beta phase and changing the color of material. CoMoO4·1.03H2O obtained better bactericidal performance against the tested strains of Staphylococcus aureus (gram-positive) than Escherichia coli (gram-negative). However, an interesting point was that the use of copper as a doping agent for hydrated cobalt molybdate caused an increase of MIC value in the presence of E. coli and S. aureus strains. The study demonstrates the need for caution in the use of copper as a doping material in biocidal matrices, such as cobalt molybdate.  相似文献   

8.
A catalytic kinetic method (CKM) is presented for the determination of mercury(II) based on its catalytic effect on the rate of substitution of N-methylpyrazinium ion (Mpz+) onto hexacyanoferrate(II). The progress of the reaction was monitored spectrophotometrically at 655 nm by registering the increase in absorbance of the product [Fe(CN)5(Mpz]2− under the reaction conditions: 5 × 10−3 mol L−1 [Fe(CN)6]4−), 5 × 10−5 mol L−1 [Mpz+], T = 25.0 ± 0.1°C, pH 5.00 ± 0.02 and ionic strength, I = 0.1 mol L−1 (KNO3). Quantitative rate data at specified experimental conditions showed a linear dependence of the absorbance after fixed time A t on the concentration of mercury(II) catalyst in the range 20.06–702.1 ng mL−1. The maximum relative standard deviations and percentage errors for the determination of mercury(II) in the range of 20.06–200.6 ng mL−1 were calculated to be 1.7 and 2.7% respectively. The detection limit was found to be 7.2 ng mL−1 of mercury(II). Accuracy (expressed in terms of recoveries) was in the range of 98–103%. Figures of merit and interference due to many cations and anions was investigated and discussed. The applicability of the method was demonstrated by determining the mercury(II) in different synthetic samples and confirming the results using atomic absorption spectrophotometry. The proposed method allowed determination of mercury(II) in the range 20.06–702.1 ng mL−1 with very good selectivity and an output of 30 samples h−1.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 654–661.Original English Text Copyright © 2005 by Surendra Prasad.This article was submitted by the author in English.  相似文献   

9.
Methane oxidation by an excess of N2O on the catalytic sites formed in HZSM-5 zeolite, silicalite, and SiO2 after modification with iron, silver, and gadolinium cations in different combinations is studied. Introduction of iron and silver ions into H[Al]ZSM-5 zeolite is shown to result in the formation of the sites that are active in methane oxidation, while the systems obtained on the basis of crystalline silicalite or amorphous SiO2 demonstrate poor or no catalytic activity, respectively. Complete oxidation of methane with 100% conversion is observed on the Fe/HZSM-5 and Ag/HZSM-5 catalysts at temperatures higher than 350 and 450°C, respectively. A decrease in the reaction temperature and in the methane conversion is accompanied by coking of the catalysts and, in the case of Fe/HZSM-5, by the appearance of trace amounts of methanol and formic acid in the gas phase. The temperature dependence of the activity and selectivity for the Ag/HZSM-5 and (Ag + Gd)/HZSM-5 catalysts exhibits a pronounced hysteresis at 330–480°C, and the formation of coke proceeds much faster than in the case of iron-containing samples. Catalytic properties of (Fe + Ag)/HZSM-5 are similar to those of Fe/HZSM-5. The introduction of Gd does not influence significantly the activity and selectivity of the catalysts. ESR and TG–DTA were used to determine the state and distribution of Fe, Ag, and Gd in the samples and to examine the processes of coke formation.  相似文献   

10.
The structures of a complex multicomponent Co-Mo-Fe-Bi-K-Sb-O catalyst for the oxidation of propylene to acrolein and simpler catalysts from which some catalyst components were absent were studied by X-ray diffraction analysis. The phases of α-CoMoO4, β-CoMoO4, Fe2(MoO4)3, Bi2O3 ⋅ MoO3, Bi2O3 ⋅ 2MoO3, Bi2O3 ⋅ 3MoO3, oxidized molybdenum oxide, and reduced molybdenum oxide are the main components of the catalyst. Ternary compounds were not detected. Under catalytic reaction conditions, the relative amounts of the phases changed; this change suggests the occurrence of redox transformations with the participation of these phases, probably, at the interface.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 580–584.Original Russian Text Copyright © 2005 by Shashkin, Udalova, Shibanova, Krylov.  相似文献   

11.
Cluster models for sites on the {1 1 1} surface of Fe3O4 were used to study the strength of bonding of water-gas shift intermediates using density functional theory. Three site models were used, representing an unpromoted catalyst, a catalyst where copper cations substitute for iron cations below the surface and a catalyst where copper cations substitute in the surface. The strengths of bonding of oxygen, carbon dioxide, dissociated water and dissociated formic acid were all observed to decrease by less than 20 kJ mol−1 when copper substituted below the surface, but they decreased by 60–80 kJ mol−1 when copper substituted in the surface of the catalyst. A minimum energy structure for molecularly adsorbed water was not identified because all attempts to do so resulted in dissociation.  相似文献   

12.
The effect of the chemical and phase composition of the Fe2O3–MnO catalytic system for ammonia oxidation on its activity and selectivity to NO at 873–1273 K is demonstrated. The optimal parameters of the process over manganese ferrite, the most active and highly selective component of the system, are determined. The combination of the factors of chemical and phase transformations of the catalyst results in the formation of an inactive component (Fe3O4) and in the structural changes (recrystallization and cationic redistribution of spinel) and is the reason for the deactivation of manganese ferrite at 1273 K.  相似文献   

13.
We studied on the function of the metal in the sulfated zirconia(SO42–/ZrO2) catalyst for the isomerization reaction of light paraffins. The addition of Pt to the SO42–/ZrO2 carrier could keep the high catalytic activity. The improvement in this isomerization activity is because Pt promotes removal of the coke precursor deposited on the catalyst surface. Though this catalytic function was observed in other transition metals, such as Pd, Ru, Ni, Rh and W, Pt exhibited the highest effect among them. It was further found that the Pd/SO42–/ZrO2–Al2O3 catalyst possessed a catalytic function for desulfurization of sulfur-containing light naphtha in addition to the skeletal isomerization. The sulfur tolerance of catalyst depended on the method of adding Pd, and the catalyst prepared by impregnation of the SO42–/ZrO2–Al2O3 with an aqueous solution of Pd exhibited the highest sulfur tolerance.Further, we investigated the improvement in sulfur tolerance of the Pt/SO42–/ZrO2–Al2O3 catalyst by impregnation of Pd. The results of EPMA analysis indicated that this catalyst was a hybrid-type one (Pt/SO42–/ZrO2–Pd/Al2O3) in which Pt/SO42–/ZrO2 particles and Pd/Al2O3 particles adjoined closely. This hybrid catalyst possessed a very high sulfur tolerance to the raw light naphtha that was obtained from the atmospheric distillation apparatus, although this light naphtha contained much sulfur. We assume that such a high sulfur tolerance in the hybrid catalyst is brought about by the isomerization function of Pt/SO42–/ZrO2 particles and the hydrodesulfurization function of Pd/Al2O3 particles. Besides, since the hybrid catalyst also provides high catalytic activity in the isomerization of HDS light naphtha, we suggest that the Pd/Al2O3 particles supply atomic hydrogen to the Pt/SO42–/ZrO2 particles by homolytic dissociation of gaseous hydrogen and also enhance the sulfur tolerance of Pt/SO42–/ZrO2 particles. Finally, we also propose the most suitable location of Pd and Pt in the metal-supported SO42–/ZrO2–Al2O3 catalyst.  相似文献   

14.
Decompositon of 2-propanol has been carried out on the hydrogen storage material Mg2Cu and its modified form (OH–Mg2Cu) to study their catalytic behavior. The reaction was carried out in a continuous flow type reactor in the temperature range of 403–513 K at various flow rates. Mg2Cu showed good catalytic activity with large amounts of condensation products. Its modified form gave acetone as the only products. The reason for these differences is explained in terms of differences in the structure of the catalyst as determined by XRD and XPS, as well as by surface area measurements. The reason for the formation of condensation products is discussed.  相似文献   

15.
A new catalytic reaction of the etherification of alcohols in the system ROH-PtCl 4 2− has been observed. At 70 °C in the presence of catalytic amounts of chloride complexes of platinum(II) methanol gave dimethyl ether. Methyl tert-butyl ether and di-tert-butyl ether were formed analogously from a mixture of methanol and tert-butanol. In the reaction with ethanol the products were diethyl ether and a π-ethylene complex of platinum(II). It is suggested that the step-wise mechanism includes the oxidative addition of the alcohol with the intermediate formation of an alkyl complex of platinum(IV), the decomposition of which by reductive elimination under the influence of a second molecule of alcohol or an alkoxide anion gives an ether and regenerates the catalyst, a chloride complex of platinum(II).__________Translated from Teoreticheskaya i Eksperimental’naya Khimiya, Vol. 41, No. 3, pp. 190–193, May–June, 2005.  相似文献   

16.
Summary Zirconium molybdate has been used as a support on which [Cu(NH3)4]2+ has been sorbed. Its catalytic activity has been studied through hydrogen peroxide decomposition at different temperatures, using different concentrations of hydrogen peroxide and different amounts of catalyst. A probable mechanism is suggested based on kinetic data.  相似文献   

17.
The effect of addition of Re, Zr, Sc, and Sn on an aluminoplatinum catalyst in the reaction of dehydrogenation of propane was investigated. It was shown that addition of 0.2–0.5% Zr, Sc, or Re virtually does not alter the catalytic properties of the aluminoplatinum catalyst (APC); addition of 0.2% Sn increases the activity, selectivity, and stability of Pt/Al2O3. The amount of coke deposited on the APC after the first 5 min of work decreases by three times in the presence of Sn. The coke is more enriched with hydrogen than the other systems formed on the surface of Pt-Sn/Al2O3.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 765–771, April, 1991.  相似文献   

18.
Polymerization of butadiene in toluene at 25°C in the presence of catalytic systems based on VOCl3 and various titanium compounds in combination with Al(i-C4H9)3 is studied. If the organoaluminum compound is added in portions to the VOCl3-titanium component mixture and the primary suspension of the catalyst is heat-treated, two maxima are observed in the dependence of the activity of the catalytic system on the size of the first Al(i-C4H9)3 portion. The kinetic parameters of the polymerization are determined. The difference in activity between the mixed catalytic systems is due to the difference in structure and reactivity between active sites containing atoms of both transition metals.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 394–398.Original Russian Text Copyright © 2005 by Mullagaliev, Kharitonova, Monakov.  相似文献   

19.
Karski  S.  Paryjczak  T.  Witonñska  I. 《Kinetics and Catalysis》2003,44(5):618-622
Catalytic properties of bimetallic Pd–Bi, Pd–Tl, Pd–Sn, and Pd–Co catalysts supported on C (from plum stones) and SiO2 were studied in the reaction of glucose oxidation to gluconic acid. Catalysts modified with Bi show the best selectivity and activity. The results obtained from research on 5% Pd–5% Bi/C and 5% Pd–5% Bi/SiO2 catalytic systems were compared with the results for a commercial catalyst containing 1% Pt–4% Pd–5% Bi supported on active carbon (Degussa). For both Pd–Bi/support catalysts and 1% Pt–4% Pd–5% Bi/C, similar selectivity in the reaction of glucose oxidation was observed. XRD studies proved the presence of intermetallic compounds BiPd and Bi2Pd, which probably increase the selectivity of PdBi/SiO2 catalysts.  相似文献   

20.
In this work it is shown that iron(III) and gold(I) triflimide efficiently catalyze the hydroaddition of a wide array of nucleophiles including water, alcohols, thiols, amines, alkynes, and alkenes to multiple C? C bonds. The study of the catalytic activity and selectivity of iron(III), gold(I), and Brønsted triflimides has unveiled that iron(III) triflimide [Fe(NTf2)3] is a robust catalyst under heating conditions, whereas gold(I) triflimide, even stabilized by PPh3, readily decomposes at 80 °C and releases triflimidic acid (HNTf2) that can catalyze the corresponding reaction, as shown by in situ 19F, 15N, and 31P NMR spectroscopy. The results presented here demonstrate that each of the two catalyst types has weaknesses and strengths and complement each other. Iron(III) triflimide can act as a substitute of gold(I) triflimide as a catalyst for hydroaddition reactions to unsaturated carbon–carbon bonds.  相似文献   

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