Now showing 1 - 5 of 5
  • Publication
    Beneficial and problematic interactions between NOx trapping materials and carbonaceous particulate matter
    The presence of a NOx trapping BaO component with a Pt active phase does not per-se promote carbon combustion. However when coupled with trap regeneration, promotion of soot combustion is seen. Operating NOx trapping materials promote combustion due to the periodic localised increases in [NO2](g) generated during the regeneration rather than due to a co-generated exotherm. However, it has been noted that the presence of soot prevents NOx traps from employing their full trapping capacity.
      405Scopus© Citations 27
  • Publication
    The role of Bronstead acidity in poisoning the SCR-urea reaction over FeZSM-5 catalysts
    (Elsevier, 2005-11) ;
    Two series of FeZSM-5 catalysts prepared from Na+ and NH4+ ZSM-5 precursors are studied in the selective reduction of NOx using NH3 and urea as reducing agents. All Fe-containing catalysts are active for NOx reduction in the SCR-NH3 reaction with ex-NH4+ catalysts being more active than ex-Na+ materials and the activity depending (to a minor extent within each series of catalysts) upon [Fe]. Catalysts with Bronstead acid sites also show a small transient deNO(x) activity at low temperatures. All catalysts are less active for the SCR-urea reaction but the ex-Na+ catalysts retain far more deNO(x) activity than the ex-NH4+ materials. NH3 TPD shows that strongly binding Bronstead acid sites are present on the ex-NH4+ materials and H+-treated parent zeolites while Urea TPD shows that the mode of decomposition of urea differs as a function of initial zeolite counter-ion. Urea TPSR shows that the reaction between adsorbed urea and gaseous NO/O-2 is related to [Fe]. It is proposed that the decreased activity of the ex-NH4(+) catalysts in the SCR-urea reaction is due to a less favourable mode of decomposition over these catalysts. Furthermore it is suggested that the Bronstead acidity plays some part in this less favoured decomposition.
      319Scopus© Citations 33
  • Publication
    A combination of NOx trapping materials and Urea-SCR catalysts for use in the removal of NOx from mobile diesel engines
    (Elsevier, 2007-01) ;
    Preliminary studies on a series of nanocomposite BaO–Fe ZSM-5 materials have been carried out to determine the feasibility of combining NOx trapping and SCR-NH3 reactions to develop a system that might be applicable to reducing NOx emissions from diesel-powered vehicles. The materials are analysed for SCR-NH3 and SCR-urea reactivity, their NOx trapping and NH3 trapping capacities are probed using temperature programmed desorption (TPD) and the activities of the catalysts for promoting the NH3 ads + NO/O2 → N2 and NOx ads + NH3 → N2 reactions are studied using temperature programmed surface reaction (TPSR).
      828Scopus© Citations 27
  • Publication
    The influence of SO2-/4 on the catalytic combustion of soot using O-2 and NO/O-2 mixtures over Na-promoted Al2O3 catalysts
    Na/Al2O3 catalysts are tested in the soot oxidation reaction using O-2 and NO/O-2 as oxidising agents. The activity of the catalysts . varies with oxidising agent and the presence of surface SO42-.. NO(g) increases conversion of soot to COx-. Surface SO42- has no effect on activity for the C-(s) + O-2 reaction but decreases activity in the Carbon + NO/O-2 oxidation. This is interpreted in terms of SO42- blocking NO adsorption sites, thus poisoning the 4 NO + O-2 --> NO2 reaction, which is essential for the NOx promoted oxidation.
      452Scopus© Citations 14
  • Publication
    The combustion of carbon particulates using NO/O2 mixtures : The influence of SO42− and NOx trapping materials
    (Elsevier, 2006-05-30) ;
    The activity of several catalysts are studied in the soot combustion reaction using air and NO/air as oxidising agents. Over Al2O3-supported catalysts NO(g) is a promoter for the combustion reaction with the extent of promotion depending on the Na loading. Over these catalysts SO42− poisons this promotion by preventing NO oxidation through a site blocking mechanism. SiO2 is unable to adsorb NO or catalyse its oxidation and over SiO2-supported Na catalysts NO(g) inhibits the combustion reaction. This is ascribed to a competition between NO and O2. Over Fe-ZSM-5 catalysts the presence of a NOx trapping component does not increase the combustion of soot in the presence of NO(g) and it is proposed that this previously reported effect is only seen under continuous NOx trap operation as NO2 is periodically released during regeneration and thus available for soot combustion. Experiments during which the [NO](g) is varied show that CO, rather than an adsorbed carbonyl-like intermediate, is formed upon reaction between NO2 (the proposed oxygen carrier) and soot.
      349Scopus© Citations 9