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Cobalt-exchanged mordenites: preparation, characterization and catalytic activity for the abatement of NO with CH4 in the presence of excess O-2
No full textCo-exchanged mordenites: preparation, characterization and catalytic activity for the abatement of NO with CH4 in the presence of excess O2
No full textVIETRI, 20-23 SEPTEMBER 2003
Isolated Co2+ and [Co-O-Co](2+) species in Na-MOR exchanged with cobalt to various extents: An FTIR characterization by CO adsorption of oxidized and prereduced samples
No full textEffect of alkaline ions on the selectivity for SCR of NO with CH4: a comparison between Co-Na-MOR and Co-H-MOR catalysts
No full textFTIR of adsorbed species on Co-H-MOR and Co-Na-MOR under CH4 + NO + O2 stream: Catalytic activity and selectivity
No full textThe selective catalytic reduction (SCR) of NO with CH4 in the presence of excess O-2 was studied on Co-H-MOR and Co-Na-MOR prepared from H-MOR and Na-MOR, respectively, by cobalt ion-exchange and containing nearly the same Co percentage (66 and 61%) but very different H+ and Na+ amounts. Catalyst characterization was performed using NO as a probe at room temperature, and by means of in situ FTIR study at the reaction temperature (573-773 K) in the presence of flowing reactant mixtures of various compositions ([CH4] = 0 or 4000 ppm, [NO] = 0 or 4000 ppm, [O-2] = 0 or 20,000 ppm, balance He). In one selected case, the operando FTIR-GC methodology was used. The activity for SCR was nearly the same on the two catalysts, whereas the selectivity was higher on Co-H-MOR than on Co-Na-MOR. NO adsorption at room temperature did not show major differences in the type of cobalt species present on the two samples, being nearly all cobalt present as isolated Co2+ with two coordinative vacancies. The in situ FTIR characterization under reaction conditions identifies Co2+-mononitrosyls. We suggest that this mononitrosyl is a key species for the catalytic activity in the SCR reaction. Conversely, the in situ FTIR study under reaction conditions evidenced major differences between the surface nitrogen-oxo species (NOy, oxidation number of nitrogen >2) formed on the two samples, specifically NO+ on Co-H-MOR-66, and Co2+-monodentate nitrates on Co-Na-MOR-61. We suggest that Co2+-monodentate nitrate favors the CH4 combustion, accounting for the finding that the S-SCR selectivity of Co-Na-MOR-61 is lower than that of Co-H-MOR-66. (C) 2010 Elsevier B.V. All rights reserved
The dependence of catalytic activity for N2O decomposition on the exchange extent of cobalt or copper in Na-MOR, H-MOR and Na-MFI
No full textCatalytic decomposition of N2O was studied on Na-MOR, H-MOR, and Na-MFI samples exchanged to various extents with cobalt or copper. Co-MOR samples were characterized by FTIR and volumetric measurements of NO adsorption. The most abundant species on Co-MOR was Co2+(NO)(2). In agreement, the volumetric data yielded NO/Co = 1.8 +/- 0.2. On Co-MOR, N2O conversion progressively increased as the cobalt content increased. All samples yielded similar apparent activation energy, E-a = 75 +/- 5 kJ mol(-1). The reaction order was 0.9 +/- 0.1 for N2O, and 0.0 +/- 0.1 for O-2. For samples having a Co-exchange percentage up to 61%, the turnover frequency per total Co atom was independent of the cobalt content and was significantly lower for more extensively exchanged samples. On all Co-MOR samples, the turnover frequency per isolated Co atom was nearly constant, indicating isolated Co2+ as the active site. On Cu-MOR and Cu-MFI samples, N2O conversion markedly increased with the copper contet. Samples having a Cu-exchange percentage up to 62% yielded higher E-a. than more extensively exchanged samples (150 5 kJ mol-1 vs. 100 5 kJ mol-1). The reaction order was 0.5 +/- 0.1 for N2O, and 0.0 0.1 for O-2. We conclude that in Co-MOR and Co-MFI catalysts the active site for N2O decomposition is isolated Co2+, whereas in Cu-MOR and Cu-MFI isolated Cu2+ is nearly inactive. In extensively exchanged Cu-MOR and Cu-MFI, the active site for N2O decomposition is most probably Cu1+. A similar reaction mechanism for N2O decomposition operates over Co-zeolites and extensively exchanged Cu-zeolites. (C) 2009 Elsevier B.V. All rights reserved
CuOx/sulphated-ZrO2, in situ sulphated CuOx/ZrO2, and CuSO4/ZrO2 as catalysts for the abatement of NO with C3H6 in the presence of excess O2
No full textThe catalytic activity of CoOx/sulphated-ZrO2 for the NO abatement with C3H6 in the presence of O2: the dependence of activity and selectivity on the sulphate content
No full textCobalt sulphated-ZrO2 catalysts were prepared by impregnation of ZrO2 with aqueous solutions of CoSO4, or impregnation of sulphated-ZrO2 with toluene solutions of Co(acetylacetonate)(2). NO reduction with C3H6 in the presence of excess O-2 was studied in a flow apparatus fed by a reactant mixture of NO:C3H6:O-2 = 4000:2000:20,000 ppm in He.
Diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) results showed that the presence of sulphates prevented the formation Of Co3O4. XPS indicated the presence of Co(II) alone. Irrespective of the preparation method, Fourier transformed infrared (FTIR) showed that catalysts with the same sulphate content had the same covalent sulphates. As the sulphate content in the sample increased, FTIR with CO or NO showed that the Lewis acid-strength of Co(II) increased, whereas the reducibility and heterogeneity of Co(II) decreased.
Sulphated samples with a cobalt content higher than 2 atoms nm(-2) were far more active and selective than the corresponding unsulphated CoOx/ZrO2. The presence of sulphates had a weaker effect on the catalytic behaviour of samples with lower Co content (<2 atoms nm(-2)). We conclude that cobalt and sulphate co-operate in determining the catalytic activity and selectivity of cobalt sulphated-ZrO2 catalysts
Sulfated zirconia as catalysts for the n-butane isomerisation: The dependence of activity on the sulphate content and activation temperature
No full textInnsbruck (Austria), 31 August - 4 September 200
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