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Abstract

In this work, the mechanism and kinetics of the preferential CO oxidation over 0.5 wt. % Au/Al2O3 catalyst was investigated. For CO oxidation, the reaction was found to follow a two-step Eley–Rideal-type mechanism, in which the formation and decomposition of the reaction intermediate took place at the gold-support interface. For the PROX case, on the other hand, Langmuir–Hinshelwood-type mechanisms seem to be also significant.

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The effect of the distribution of CeO2–ZrO2 on Ni/MgAl2O4 catalyst on the catalytic performance during the combined steam and carbon dioxide reforming of CH4 (CSCR) was investigated on two different catalysts prepared using a sequential impregnation and co-precipitation of Ni and CeO2–ZrO2 components. The CeO2–ZrO2 plays an important role in the CO2 conversion by enhancing a facile activation of CO2 with an adjacent contact with nickel crystallites. The CSCR catalysts prepared by the co-precipitation of nickel and CeO2–ZrO2 on MgAl2O4 support shows a catalytic activity superior to the catalyst prepared by sequential impregnation of nickel on the MgAl2O4 support with CeO2–ZrO2 due to the homogeneous distribution of CeO2–ZrO2 with the formation of small nickel crystallites and a large amount of active sites for CO2 adsorption.

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Abstract

Gold catalysts supported on ceria doped with FeOx were studied. The mixed supports were synthesized by two methods: co-precipitation (CP) or mechanochemical activation (MA). Depending on the preparation method, the structure of the mixed supports was different: using CP, only a Fe-modified ceria phase exists, while supplementary to ceria, a second hematite phase presents in the case of MA preparation. The reduction behavior of the gold catalysts and the initial supports was commented on the basis of hydrogen consumption and kinetic parameters of the individual reduction process. Their assignment was proposed using also the data of Mössbauer measurements. It was established that the existing separate Fe-containing phase could participate in a redox process at relatively low temperatures (LTs) and it could be promising for improvement of the catalytic performance of the mechanochemically prepared gold catalyst.

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Gold catalysts supported on ceria doped with different metal oxides (Fe, Mn, Co and Sn) were synthesized using two techniques: CP and mechanochemical activation. The catalytic activity in complete benzene oxidation (CBO) was studied. The samples were characterized by means of XRD and high resolution transmission electron microscopy, and non-significant differences in the average size and the distribution of gold particles were observed. This means that the main reason for the different catalytic behavior in CBO has to be searched in the composition and structure of the supports. In spite of the higher hydrogen consumption (e.g., higher oxygen mobility) estimated by means of TPR, the gold catalysts on ceria doped with transition metal oxides generally are less active than gold/ceria catalyst. This observation could be explained taking into consideration that the key factor for the high oxidation activity is not the oxygen supplying but the activation of the very stable benzene molecule. The higher catalytic activity in comparison with that of the gold/ceria catalyst was observed only using a mixed ceria–CoOx support mechanochemically prepared. Very high and stable catalytic activity in CBO was obtained over this sample.

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The electrical conductivity and the catalytic activity of SnO2 loaded TiO2 (anatase) particles were investigated in operando conditions. SnO2 depositions over commercial TiO2 samples (Sigma Aldrich and Rhone Poulenc) were obtained by the impregnation method. The samples were characterized by XRD, SEM/EDX and BET–N2 adsorption techniques. The AC electrical conductivity of the samples were measured between 25 and 400 °C under various atmospheres. The effect of the reactant mixture on the electrical conductivity and the catalytic performances of the samples were tested in propene oxidation. The results showed that the conductivity of SnO2/TiO2 samples depends strongly on the surface area of TiO2 support. The reducing effect of propene is more evident for higher surface area catalysts, these one showing also higher activity. On the other hand, the SnO2 deposition results in an increase of catalytic performances.

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Abstract

This article focuses on the catalytic behavior of MO–Sm2O3 (M = Zn, Mg, Ca, Sr) mixed oxides. The obtained results could be interpreted in terms of solid acid–base catalysis. The mixed oxides were prepared starting from the tartarate complexes of the constituent metals. The concentration as well as the evolution of surface carbonate species with the nature of MO and reaction temperature were analyzed by XRD and TPD methods. The amount of surface basic sites responsible for the formation of C2 + was determined by measuring the amount of evolved CO2 in the 300–800 °C temperature range. The catalytic behavior of the investigated mixed oxides was expressed in terms of methane yield to C2 + and the concentration of CO2 in reaction mixture. The conclusion is that C2 + is formed on the basic sites whereas the acidic sites are responsible for nonselective oxidation of methane to CO2.

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Abstract

Preparation of a Fe-mordenite catalysts was carried out by impregnation using Fe(acac)3 precursor in order to have iron oxide species deposited at the surface of the zeolite. The selective presence of iron oxide species was determined and ascertained by temperature programmed reduction (TPR). In the selective catalytic reduction of NO by ammonia, no difference of conversion between the catalysts was observed indicating that well dispersed iron oxide species are active species for this reaction. Nevertheless, the obtained activity remains lower than catalysts containing iron cationic species at the exchange sites.

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Efficient catalysts for the nitration of benzene are prepared by surface capping of Ag nanoparticles using glycerol and urea with their subsequent loading over anatase titania. Herein glucose was used as an environmentally benign reducing agent for the silver ions. The catalyst was characterized and its catalytic activity was evaluated in the low temperature preparation of nitrobenzene. Ag nanoparticle loading gives rise to improved performance when compared to bare anatase titania. The influence of stabilizers and the percentage metal loading of Ag on the catalytic activity was investigated. The increased reactivity of titania seen after Ag nanoparticle loading may be due to the presence of highly dispersed nano sized surface capped Ag. Among the two capping agents studied, glycerol provides maximum efficiency for a short reaction time. These new generation catalysts appear to be an efficient alternative for the conventional use of environmentally hazardous sulfuric acid catalyst. The side reactions are found to be minimal over the present catalytic systems which lead to excellent nitrobenzene selectivity.

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Abstract

Titanium (IV) precursors anchored to alkyl substituted polyhedral oligomeric silsesquioxane (POSS) trisilanol and disilanol were prepared and characterized. These catalysts, formulated as [Ti-POSS(OOO)OPri, 1] and [Ti-(POSS(OO))2, 2], were found to be active in the polymerization of ethylene at high temperatures in combination with ethylaluminum sesquichloride (Et3Al2Cl3) as a co-catalyst. The polyethylene products so obtained are linear, crystalline and display narrow dispersities. The effect of various reaction parameters on the catalyst performance is described.

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Abstract

Second generation (2G) biofuels are produced from non-edible lignocellulosic biomass providing sustainable alternatives for fossil fuels. The OH reaction rate constant has been determined for the 2G biofuel ethyl levulinate (CH3C(O)CH2CH2C(O)OCH2CH3, ELA) () for the first time. The direct reaction kinetic technique of pulsed laser photolysis (PLP) coupled with resonance fluorescence (RF) detection of OH radicals has been used to determine the rate constant value of k 1 = (3.43 ± 0.36) × 10−12 cm3 molecule−1 s−1 (298 K), where the error given designates 2σ accuracy. Implications for atmospheric chemistry have been discussed.

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