Applied Catalysis B, Environmental (v.36, #3)
On the selectively catalytic reduction of NO x with methane over Ag-ZSM-5 catalysts by Chuan Shi; Mojie Cheng; Zhenping Qu; Xuefeng Yang; Xinhe Bao (173-182).
The catalytic performance of silver-modified ZSM-5 catalysts in the selectively catalytic reduction (SCR) of NO x with methane was investigated. NO was selectively reduced by CH4 to N2 in the presence of excess O2, and the catalytic activity depended on both the activation of CH4 and the adsorption properties of NO x . Silver incorporated in ZSM-5 zeolite activated CH4 at low temperatures and lowered the “light-off” temperature for the CH4-SCR of NO x . Temperature-programmed (TP) spectroscopy studies depicted that surface nitrosyl species directly decomposed to N2 in the absence of O2. CH4 could not effectively reduce surface nitrosyl species, but might facilitate the direct decomposition of NO through the removal of surface oxygen. Surface nitrates were formed in NO and O2 coexisting system and could be effectively reduced by CH4 to nitrogen. The priority of surface nitrates to O2 in the reaction with CH4 clearly demonstrated that CH4 selectively and preferentially reduced the surface nitrate species to N2 in the excess of oxygen.
Keywords: Ag-ZSM-5; NO x ; Methane; TPR;
Metal grids with high-porous surface as structured catalysts: preparation, characterization and activity in propane total oxidation by I. Yuranov; N. Dunand; L. Kiwi-Minsker; A. Renken (183-191).
Metal nickel and copper grids are shown to be suitable supports for structured combustion catalysts. The increase of specific surface area (SSA) of metal grids was achieved due to the porous outer layer with the structure of Raney metal developed on the wire surface. Transition metals (Co, Cu, Mn, Cr) oxides were deposited as active components on the pre-oxidized support and tested in total propane oxidation. Cobalt oxide demonstrated the highest activity. Reductive pre-treatment in the flow of hydrogen resulted in a more active catalyst than the activation in oxygen atmosphere. This effect was assigned to the partial reduction of Co3O4 until metallic Co, which was detected by XPS on the catalyst surface. Deactivation of the pre-reduced Co-oxide catalyst was observed during propane combustion in excess of oxygen and was ascribed to the oxidation of partially reduced active phase. After 4 h on stream, the catalyst reached his steady-state and showed stable activity without further deactivation. The catalytic activity expressed in the terms of propane conversion was observed to depend on the propane/oxygen ratio.
Keywords: Catalytic combustion; Total propane oxidation; Metal oxide catalysts; Metal grids; Structured catalytic bed; Raney metals;
Reactivity of ceria, Gd- and Nb-doped ceria to methane by E Ramı́rez-Cabrera; A Atkinson; D Chadwick (193-206).
The reactivity of methane with ceria, and ceria doped with either 10 cation% Gd, 1.4 cation% Nb, 5 cation% Nb has been investigated using temperature-programmed reaction (TPRx) and isothermal reaction at 900 °C in 5% methane in argon. The influence of the calcination atmosphere on the Nb-doped ceria has also been studied. All the cerias showed activity for conversion of methane to hydrogen and carbon monoxide with only small amounts of carbon deposition. Methane conversion is controlled by surface reaction with an activation energy of 165±10 kJ mol−1. Gd doping was found to have a relatively minor effect on the reaction rate, but reaction with Nb-doped ceria was significantly slower. XPS results suggested that this is due to segregation of Nb to the ceria surface on the samples calcined in air, however, the XPS results were more complex for the samples calcined in N2/H2 mixture. Nb-doped ceria was capable of oxidising carbon deposits at lower temperatures than ceria or Gd-doped ceria.
Keywords: Cerium oxide; Carbon deposition; Carbon oxidation; Gadolinium oxide; Niobium oxide; Methane reforming;
Investigation of the promotional effect of V2O5 on the SCR reaction and its mechanism on hybrid catalyst with V2O5 and TiO2-SO4 2− catalysts by Seong Moon Jung; Paul Grange (207-215).
Hybrid V2O5 and TiO2-SO4 2− catalysts used in selective catalytic reduction (SCR) reaction of NO with NH3 have been studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), SCR, temperature-programmed reaction (TPR), and NH3-temperature-programmed desorption (TPD). Single phase or bi-phasic catalyst disposed in non-adjacent layers in a reactor show an improved activity and an expansion of the reaction temperature window, as compared with the sum of the individual activity of the pure phase. In the presence of V2O5 on hybrid catalysts, DRIFTS shows that the NH2 and nitrate species appear at a lower temperature than in pure TiO2-SO4 2− catalyst. The improved reactivity of NH3 in NH3-TPD by NO and TPR is also closely related to the enhanced formation of NH2 species. As a result, the high reactivity in hybrid catalysts can be explained by the promotional effect of V2O5 leading to the high rate of formation of NH2 and nitrate species at lower temperature.
Keywords: DRIFTS; SCR; NH3-TPD; V2O5; Promotional effect; Mechanism; Sulfate;
The catalytic activity of CuSO4/ZrO2 for the selective catalytic reduction of NO x with NH3 in the presence of excess O2 by Daniela Pietrogiacomi; Diana Sannino; Alessandro Magliano; Paolo Ciambelli; Simonetta Tuti; Valerio Indovina (217-230).
Sulphated ZrO2 catalysts were prepared by (i) impregnation of ZrO2 with aqueous solutions of (NH4)2SO4, Na2SO4, or CuSO4, or (ii) sulphation of CuO x /ZrO2 via gas-phase (2770 ppm SO2 and 1%O2, in He). Samples were characterised by means of electron spin resonance (ESR), X-ray diffraction (XRD), diffuse reflectance (DRS), Fourier transformed infrared (FT-IR) (using CO, NO and NH3 as probes), and TPD of NH3. The selective catalytic reduction (SCR) of NO with NH3 in the presence of excess O2, and the NH3 oxidation with O2 were studied in a flow apparatus fed by reactant mixtures of various composition (NO:NH3:O2=0–700:700:36,000 ppm, in He).Characterisation and catalysis results indicated that impregnation with CuSO4 or sulphation via gas-phase yielded nearly identical catalysts. Covalent sulphates of various nuclearity formed on both sulphated ZrO2 and copper-containing sulphated ZrO2. Sulphated ZrO2 catalysts were only slightly more active than unsulphated ZrO2. As the CuSO4-content in the CuSO4/ZrO2 catalysts increased, (i) the (polynuclear)/(mononuclear) sulphate ratio, (ii) the concentration and strength of Lewis acid sites, (iii) the concentration of Brönsted acid sites, and (iv) the SCR activity increased in parallel. In the temperature region 473–600 K, a range at which CuSO4/ZrO2 yielded nearly 100% SCR selectivity, NO molecules converted to N2 per second per Cu-site were nearly independent of the Cu-content, up to 2.3 nm−2 of CuSO4 molecules.CuSO4/ZrO2 were much more selective than the relevant unsulphated CuO x /ZrO2. The higher selectivity of CuSO4/ZrO2 depended on their lower activity in the NH3 oxidation reaction.
Keywords: NO abatement; Sulphated ZrO2; Supported copper oxide;
A preliminary study on iron species as heterogeneous catalysts for the degradation of linear alkylbenzene sulphonic acids by H2O2 by Angela Cuzzola; Maristella Bernini; Piero Salvadori (231-237).
Different eco-sustainable methods based on the activation of H2O2 promoted by iron species in homogeneous and heterogeneous phase, in the presence and absence of solar irradiation was compared in order to evaluate their effectiveness in the wastewater treatment. Commercial linear alkylbenzene sulphonic acids (LAS) have been chosen as model compound, being a pollutant largely used in different fields. Supported iron species were identified as new promising class of photo-activable and recyclable catalysts.
Keywords: Surfactant degradation; Iron oxides; Hydrogen peroxide; Catalysis; Photocatalysis;
Catalytic combustion of trichloroethylene over TiO2-SiO2 supported catalysts by M. Kułażyński; J.G. van Ommen; J. Trawczyński; J. Walendziewski (239-247).
Combustion of trichloroethylene (TCE) on Cr2O3, V2O5, Pt or Pd catalysts supported on TiO2-SiO2 as a carrier has been investigated. It was found that oxide catalysts are very active but their activity quickly diminishes due to loss of the active component, especially at higher reaction temperatures and/or at high concentrations of TCE in the feed. Addition of water to the feed results in slower deactivation. The noble metal-based catalysts have a lower activity than the oxidic ones, but they are stable during the test and can be used under more severe conditions: higher temperature and high concentration of chlorine. Pt/SiO2-TiO2 is mildly and reversibly poisoned during the reaction. TiO2-SiO2 appears to be a stable and resistant support of catalysts for TCE combustion.
Keywords: Trichloroethylene (TCE); Combustion; Catalysts;