Partial oxidation of ethane to syngas over nickel-based catalysts modified by alkali metal oxide and rare earth metal oxide

The catalytic activity, thermal stability and carbon deposition of various modified NiO/gamma-Al2O3 and unmodified NiO/gamma-Al2O3 catalysts were investigated with a flow reactor, XRD, TG and UVRRS analysis. The activity and selectivity of the NiO/gamma-Al2O3 catalyst showed little difference from those of the modified nickel-based catalysts. However, modification with alkali metal oxide (Li, Na, K) and rare earth metal oxide (La, Ce, Y, Sm) can improve the thermal stability of the NiO/gamma-Al2O3 and enhance its ability to suppress carbon deposition during the partial oxidation of ethane (POE). The carbon deposition contains graphite-like species that were detected by UVRRS. The nickel-based catalysts modified by alkali metal oxide and rare earth metal oxide have excellent catalytic activities (C2H6 conversion of similar to 100%, CO selectivity of similar to 94%, 7x 10(4) l/(kg h), 1123 K), good thermal stability and carbon-deposition resistance.

Catalytic oxidation of chlorobenzene on supported manganese oxide catalysts

Total oxidation of chlorinated aromatics on supported manganese oxide catalysts was investigated. The catalysts have been prepared by wet impregnation method and characterized by XRD and TPR. Among the catalysts with the supports of TiO(2), Al(2)O(3) and SiO(2), titania supported catalyst (MnO(x)/TiO(2)) gives the highest catalytic activity. MnO(x)/TiO(2) (Mn loading, 1.9 wt.%) shows the total oxidation of chlorobenzene at about 400 degreesC. The activity can be stable for over 82 h except for the first few hours. At lower Mn loadings for MnO(x)/TiO(2), only one reduction peak appears at about 400 degreesC due to the highly dispersed manganese oxide. With the increase of Mn loading, another reduction peak emerges at about 500 degreesC, which is close to the reduction peak of bulk Mn(2)O(3) at 520 degreesC. TPR of the used catalyst is totally different from that of the fresh one indicating that the chemical state of the active species is changed during the chlorobenzene oxidation. The characterization studies of MnO(x)/TiO(2) showed that the highly dispersed MnO(x) is the precursor of the active phase, which can be converted into the active phase, mainly oxychlorinated manganese (MnO(y)Cl(z)), under working conditions of chlorobenzene oxidation. (C) 2001 Elsevier Science B.V. All rights reserved.

The role of Sn in Pt-Sn/CeO2 catalysts for the complete oxidation of ethanol

The structural features and catalytic properties of Pt-Sn/CeO2 catalysts prepared by modified polyol method were extensively investigated for the complete oxidation of ethanol. CO chemisorption, TPR, DTA and XPS measurements identically indicated that the electronic configuration of Pt by Sn as well as the formation of PtSn alloy were the key factors in determining the nature of the active sites, A strong Pt/Sn atomic ratio dependence of catalytic perfortmances was observed. which was explained in terms of the change., in the Surface structure of metal phases and the electronic Pt-Sn interaction. (c) 2005 Elsevier B.V. All rights reserved.

Low-temperature oxidation of CO over Pd/CeO2-TiO2 catalysts with different pretreatments

A comprehensive study of the low-temperature oxidation of CO was conducted over Pd/TiO2, Pd/CeO2, and Pd/CeO2-TiO2 pretreated by a series of calcination and reduction processes. The catalysts were characterized by N-2 adsorption, XRD, H-2 chemisorption, and diffuse-reflectance infrared Fourier transform spectroscopy. The results indicated that Pd/CeO2-TiO2 has the highest activity among these catalysts, whether in the calcined state or in the reduced state. The activity of all of the catalysts can be improved significantly by the pre-reduction, and it seems that the reduction at low temperature (LTR. 150 degrees C) is more effective than that at high temperature (HTR, 500 degrees C), especially for Pd/CeO2 and Pd/TiO2. The catalysts with various supports and pretreatments are also different in the reaction mechanisms for CO oxidation at low temperature. Over Pd/TiO2, the reaction may proceed through a surface reaction between the weakly adsorbed CO and oxygen (Langmuir-Hinshelwood). For Ce-containing catalysts, however, an alteration of reaction mechanism with temperature and the involvement of the oxygen activation at different sites were observed, and the light-off profiles of the calcined Pd/CeO2 and Pd/CeOi-TiO2 show a distortion before CO conversion achieves 100%. At low temperature, CO oxidation proceeds mainly via the reaction between the adsorbed CO on Pd-0 sites and the lattice oxygen of surface CeO2 at the Pd-Ce interface, whereas at high temperature it proceeds via the reaction between the adsorbed CO and oxygen. The high activity of Pd/CeO2-TiO2 for the low-temperature CO oxidation was probably due to the enhancements of both CO activation, caused by the facilitated reduction of Pd2+ to Pd-0, and oxygen activation, through the improvement of the surface oxygen supply and the oxygen vacancies formation. The reduction pretreatment enhances metal-support interactions and oxygen vacancy formation and hence improves the activity of CO oxidation. (c) 2005 Elsevier Inc. All rights reserved.

Selective oxidations on recoverable catalysts assembled in emulsions

Catalysts assembled in emulsions are found to be potentially recoverable and efficient for a number of catalytic reactions. The catalysts composed of polyoxometalate anions and quaternary ammonium cations have been designed and synthesized according to the catalytic reactions and by optimizing the structures of cations and anions. The catalysts act essentially as surfactants, which are uniformly distributed in the interface of the emulsion droplets, and accordingly behave like homogeneous catalysts. The catalysts show remarkable selectivity and activity in the oxidation of sulfur-containing molecules to sulfones in diesel and the selective oxidation of alcohols to ketones, using H2O2 as oxidant. For an example, the catalyst demonstrated over 96% efficiency of H2O2 and similar to 100% selectivity to sulfones for the selective oxidation of sulfur-containing molecules in real diesel. Moreover, the catalysts can be separated and recycled by a simple demulsification and re-emulsification.