Tmperature programmed techniques study on the nature of the oxidant in/on V2O5catalyst ?

Summary The nature of the oxidising species in/on a vanadium pentoxide (V₂O₅) catalyst has been studied using a combination of transient techniques: (i) Temperature programmed desorption (TPD), (ii) Temperature programmed reduction (TPR), (iii) Temperature programmed oxidation (TPO) and (iv) Temperature programmed reaction (TPRn). Chemisorbed oxygen was found not to exist on a fully oxidised V₂O₅ catalyst by TPD. The TPR in CO over V₂O₅ catalyst gave three peak maxima at 930, 982 and 1043 K, indicating that three types of kinetically different oxygen states exist in/on the catalyst. Reoxidation of the CO reduced V₂O₅ catalyst by N₂O resulted in the quantitative replacement of the lattice oxygen. A further reduction of the N₂O reoxidised catalyst gave a significantly different TPR profile compared to the original material suggesting that a less crystalline material had formed. The presence of phosphorus in (VO)₂P₂O₇ was found to labilise the lattice oxygen.     

Carvone epoxidation by system “hydrogen peroxide-[Mn2L2O3][PF6]2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid”: a combinatorial approach to the process optimization?

Summary Epoxidation of natural terpene (+)-carvone by the system consisting of a catalyst, oxalic acid (co-catalyst) and H₂O₂ (70% aqueous solution; oxidant) was studied and factorial design methods were applied for the optimization of this reaction. A dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) was used as a catalyst, and acetonitrile was employed as a solvent. An analysis by methods of the complete 2⁴ factorial design showed that an increase in the catalyst concentration gives a strong positive effect on the carvone conversion and selectivity. Hydrogen peroxide has a smaller positive effect on the conversion, but at high concentration, H₂O₂ leads to some decrease in the selectivity. An increase in the oxalic acid concentration has a beneficial effect on the conversion, but does not affect the selectivity.     

Temperature-programmed desorption/pulse surface reaction (tpd/tpsr) studies of CH4, C2H6, C2H4, and CO over a cobalt/MWNTs catalyst

Summary Temperature-programmed desorption (TPD) of CH₄, C₂H₆, C₂H₄, and CO and temperature-programmed pulse surface reactions (TPSR) of CH₄, C₂H₆, C₂H₄, CO, and CO/H₂ over a Co/MWNTs catalyst have been investigated. The TPD results indicated that CH₄ and C₂H₆ mainly exist as physisorbed species on the Co/MWNTs catalyst surface, whilst C₂H₄ and CO exist as both physisorbed and chemisorbed species. The TPSR results indicated that CH₄ and C₂H₆ do not undergo reaction between room temperature and 450^oC. Pulsed C₂H₄ can be transformed into CH₄ at 400 ^oC whilst pulsed CO can be transformed into CO₂ at 100 or 150^oC. In gaseous mixtures of CO and H₂ containing excess CO, the products of pulsed reaction were CH₃CHO and CH₃OH. When the ratio of CO and H₂ was 1:2, pulsed CO and H₂ were transformed into CH₃CHO, CH₃OH and CH₄. In H₂ gas flow, pulsed CO was transformed into a mixture of CH₃CHO and CH₄ between 200 and 250^oC and was transformed into CH₄ only above 250^oC.     

Simultaneous propane dehydrogenation andco2hydrogenation overCrOx/SiO2catalyst

Summary Single reverse water-gas shift (RWGS) and dehydrogenation of propane with CO₂(DH-CO₂) reactions in the presence and absence of the CrO_x/SiO₂ catalyst have been studied between 673 and 873 K. It was found that the CrO_x/SiO₂ catalyst is active both in the dehydrogenation of propane and in the RWGS reactions. The obtained results suggest that the dehydrogenation of propane to propene in the presence of CO₂on CrO_x/SiO₂can be facilitated by the RWGS reaction.</o:p>     

Effect of additive in feedstock on performance of Ag-MoO3/ZrO2 catalyst for propylene epoxidation by molecular oxygen

Summary The performance of the Ag-MoO₃/ZrO₂ catalyst for propylene epoxidation by molecular oxygen is influenced obviously by the composition of feedstock. As an additive in feedstock, the presence of organic chloride, CO₂, NO_x or H₂ at a suitable concentration can improve the catalytic performance of Ag-MoO₃/ZrO₂ catalyst for the propylene epoxidation.      

On the reduction kinetics of coprecipitated NiO-Al2O3 and NiO-La2O3-Al2O3 catalysts

Summary Reduction kinetic studies reveal qualitative and quantitative information about reducible NiO species co in the nano-size, coprecipitated NiO-Al₂O₃ and NiO-La₂O₃-Al₂O₃ mixed oxides.      

Absolute rate constants for the reactions ofOHradicals withCH3CH2OH, CF2HCH2OHandCF3CH2OH

Summary Pulsed laser photolysis with resonance fluorescence monitoring of OH radicals was applied at T = 300±2 K to obtain the rate constants of k₁= (3.38±0.60)x10^-12, k₂= (2.52±0.44)x10^-13and k₃ = (1.06±0.30)x10^-13cm³molecule^-1s^-1with 2σprecision given for the overall reactions OH + CH₃CH₂OH (1), OH + CF₂HCH₂OH (2) and OH + CF₃CH₂OH (3), respectively. k₂is the first direct kinetic data for the reaction of OH radicals with CF₂HCH₂OH reported in the literature.</o:p>     

Direct synthesis of dimethyl carbonate ?from CH3OH AND CO2 by H3PW12O40/CexTi1-xO2 catalyst

Summary Ce_xTi_1-xO₂ and H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ catalysts were prepared using a sol-gel method, and applied to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ showed a better catalytic performance than the corresponding Ce_xTi_1-xO₂, due to the bifunctional catalysis of Br?nsted acid sites (provided by H₃PW₁₂O₄₀) and base sites (provided by Ce_xTi_1-xO₂). H₃PW₁₂O₄₀/Ce_0.1Ti_0.9O₂ showed the highest catalytic performance among the H₃PW₁₂O₄₀/Ce_xTi_1-xO₂ catalysts.     

Selective catalytic reduction of nitric oxide with propane over Ni-Al2O3: effect of Ni loading

Summary The SCR of NO by propane in excess oxygen was studied on a Ni-Al₂O₃ catalyst prepared by a coprecipitation method. The effect of Ni loading on the catalytic performance was studied and the optimal Ni loading was found to be 4 % (wt.%). Based on characterization results, highly dispersed nickel species in surface aluminate phase was regarded as the active site for NO reduction by C₃H₈ and NiO phase was the active site for C₃H₈ oxidation by oxygen.     

An investigation of the promotional effect of propylene or propane traces on the activity of sulfatedPt/g-Al2O3andPt-Sn/g-Al2O3inCH4combustion

Summary A strong promoting effect of the presence of C₃H₈or C₃H₆was determined for the combustion of CH₄in excess oxygen, over pre-sulfated 1%Pt/g-Al₂O₃and pre-sulfated 1%Pt-2%Sn/g-Al₂O₃catalysts.</o:p>     

Preparation and application of Ce-doped mesoporous TiO2oxide

Summary Mesoporous TiO₂-CeO₂mixed oxides (m-TiO₂-CeO₂) were synthesized under easy-operating neutral conditions. The structure was characterized by means of FT-IR, XRD, and N₂adsorption methods. For methanol decomposition to CO and H₂, the catalytic activity of the Ru/ m-TiO₂-CeO₂ catalyst was higher than that of the Ru/ m-TiO₂.</o:p>     

Preparation and catalytic oxidation performance andOF Pr2-xSrxCoO4+λwithK2NiF4structure

Summary A series of Pr_2-xSr_xCoO_4+λmixed oxides were prepared and used successfully for oxidation of CO and C₃H₈. The results show that Pr_2-xSr_xCoO_4+λdisplay K₂NiF₄-type structure and their catalytic activities are closely correlated with the concentration of Co³⁺, mobile lattice oxygen and oxygen vacancy.</o:p>     

Novel KF-TiO2catalysts for oxidative dehydrogenation of isobutane

A novel type of catalysts, KF-TiO₂, efficient for the oxidative dehydrogenation (ODH) of isobutane is presented. The effect of KF content and calcination temperature was studied. In the reaction conditions explored, the best performance (73 % selectivity to isobutene at 10.5 % conversion of isobutane) was observed over a catalyst with KF/TiO₂ = 0.2 (mol/mol). The surface properties of the catalysts were investigated by SPS (Surface Photo-voltage Spectroscopy) and XPS. The promotion effect of KF in the catalysts can be attributed to the formation of an oxyfluoro-compound, K₂Ti₄O₈F₂.     

Study of CuO/Ce0.8Zr0.2O2 catalysts for low-temperature CO oxidation

Summary Copper oxide catalysts supported on Ce_0.8Zr_0.2O₂ were prepared via an impregnation method and characterized by XRD and H₂-TPR techniques. The catalytic activity of the samples for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The influence of calcination temperature, calcination time and different CuO content on the catalytic activity was studied. TPR analysis indicated that well-dispersed CuO was responsible for the low-temperature CO oxidation. The results of the investigation showed that the calcination temperature and CuO loadings had larger influence than the calcination time.     

Study on the catalytic reduction mechanism of SO2 by CO over doped copper perovskite catalyst in presence of oxygen

Summary The reduction mechanism of SO₂ by CO using LaCoO₃ and doped copper as catalysts was investigated. The activity, selectivity of sulfur and the COS amount under various reaction conditions were tested. The results showed that the Cu doped catalysts were better than the undoped catalyst and 10% copper-doping gave the optimum catalyst.     

Methanol dehydration to produce dimethyl ether over g-Al2O3

Summary The kinetic data of about 150 points for methanol dehydration were obtained at the temperature of 240~270^oC, the GHSV of 25,000~120,000 (mL/g_cat./h) and under atmospheric pressure. The data were fitted into six plausible equations. The kinetic equation derived from the molecular adsorption of methanol on two sites fit the kinetic data best, however, that from the dissociative adsorption of methanol could not be safely ruled out. The activation energy of 114.7 kJ/mol for methanol dehydration on γ-Al₂O₃ was obtained from the kinetic analysis.     

A facile synthetic route for the preparation of the Au/Mox/Al2O3 catalysts towards CO oxidation

Summary A new facile single-step synthetic route is reported for the preparation of Au/MO_x/Al₂O₃ catalysts. The preparation method has the merit of facility but leads to not only the simultaneous load of both gold source and MO_x precursor on Al₂O₃ support, but also the formation of Au/MO_x/Al₂O₃ with high gold loading ratio, high dispersion and high activity for CO oxidation.     

Catalytic carbon monoxide oxidation over CuO/CeO2 composite catalysts

Summary CeO₂ nanoparticles were prepared by thermal decomposition of cerous nitrate and then used as supports for CuO/CeO₂ catalysts prepared via the impregnation method. The samples were characterized by XRD, HRTEM, H₂-TPR and XPS. The catalytic properties of the catalysts for low-temperature CO oxidation were studied by using a microreactor-GC system.     

Rh2(OAc)4 catalyzed formation of fluorine-containing polysubstituted furans from diazocompounds and aromatic alkynes

A new building block strategy for the synthesis of fluorine-containing 1,2,4-trisubstituted furan was reported. The 1,2,4-trisubstituted furan was constructed through [3+2] cycloaddition reaction of fluoroacetyl-containing diazocompound and aromatic alkyne, catalyzed by Rh₂(OAc)₄.     

Surface of Ru/Fe2O3 catalysts used in water-gas shift reaction studied by auger electron spectrometry

Summary Carbon deposits on the surface ofRu/Fe₂O₃ catalysts used in the water-gas shift reaction have been investigated by Auger Electron Spectrometry. A correlation has been found between the thickness of the carbon deposit and the catalytic activity in WGSR. The carbon deposit covers the metallic active centers and blocks their contact with reagents. The dotting of the iron oxide support with sodium has been found to reduce the amount of carbon deposit. .