Now showing 1 - 10 of 32
  • 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).
    Scopus© Citations 27  814
  • Publication
    The use of alkaline earth oxides as pH modifiers for selective glycerol oxidation over supported Au catalysts
    The activity and selectivity of an Au/TiO2 catalyst in a reaction mixture which has had its pH adjusted by the addition of NaOH (aq) is compared to that of the same catalyst in reaction mixtures whose pH was adjusted using suspensions of BaO and CaO. It was found that the suspensions acted as effective bases and reactions in their presence showed similar conversions to those where NaOH(aq) was used. The selectivities of the reactions were different in each case. In all cases dihydroxyacetone, glyceric acid, glycolic acid and formic acid was produced but more glyceric acid was produced when alkaline earth oxide suspensions were used (at the expense of glycolic and formic acid) than when NaOH(aq) was used. Given glycolic and formic acids are produced from oxidation of glyceric acid, it seems that glyceric acid is somewhat stabilized against further oxidation in the presence of the group II oxides. One explanation for this is the formation of glyceric acid hemicalcium salts (and analogous Ba2+ species) in solution.
    Scopus© Citations 13  575
  • Publication
    Suzuki coupling activity of an aqueous phase Pd nanoparticle dispersion and a carbon nanotube/Pd nanoparticle composite
    An aqueous phase dispersion of Pd nanoparticles stabilised by 4-dimethylaminopyridine (DMAP) promotes model Suzuki coupling reactions. The dispersion contains Pd nanoparticles of 3.4 ± 0.5 nm and a Pd(II) species (Pd(DMAP)4(OH)2) which forms following aerobic oxidation of the nanoparticles. The activity of the nanoparticle dispersion in promoting the Suzuki reactions is directly proportional to the size of the halogen on the substrate (as is usual for these coupling reactions) and also to the age of the nanoparticle dispersion. The Pd(DMAP)4(OH)2 complex can be isolated from the dispersion and is found to be very active in promoting the reactions. Its formation following aerobic oxidation of the nanoparticles is proposed as the reason for the improved activity of the dispersion with age. The nanoparticles present in the dispersion can, through displacement of the stabilising ligand, be immobilised onto functionalised multi-walled carbon nanotubes (MWCNTs) and the composite formed is an active and recyclable catalyst. The MWCNT/Pd-DMAP NP composite acts as a reservoir of dissolved Pd species, which function as homogeneous catalysts under reaction conditions.
    Scopus© Citations 51  551
  • Publication
    Visible Light-Driven Gas-Phase Artificial Photosynthesis Reactions over Ruthenium Metal Nanoparticles Modified with Anatase TiO2
    Ruthenium metal nanoparticles with a narrow size distribution have been synthesised via a solvothermal method. The solids were characterised using a range of analytical techniques (XRD, TEM, TPD, and XPS) and tested in the CO2+H2O reaction under simulated solar radiation, showing photocatalytic activity towards the production of CH4 and CO. The photocatalysis was promoted through a plasmonic excitation of the Ru. The addition of Ti to the preparation resulted in the formation of anatase TiO2. Notwithstanding the fact that the energy of the light used during the photocatalysis was insufficient to excite TiO2, its presence affects the catalysts’ optical and chemical properties and the product (CH4/CO) ratios, favouring the evolution of CO over that of CH4 (suggesting exciton transfer to TiO2 from plasmonically excited Ru).
    Scopus© Citations 3  476
  • Publication
    Different dispersions of group II catalysts over SBA 15 and MCM-41: Effects on transesterification reactivity
    Activities of CaO catalysts on SBA-15 and MCM-41 have been compared in transesterification and SBA-15 supported samples invariably more active than those on MCM-41. Increased activity is not due to diffusional effects (as measured using substrates of differing size) but rather to increased dispersion of CaO on SBA-15 (as measured using NOx TPD). The effect, i.e. increased reactivity of SBA-15 supported catalysts being related to increased dispersion, is also noted in supported BaO catalysts while supported MgCO3 catalysts show little variation in dispersion (or in reactivity) as a function of the support used.
    Scopus© Citations 9  319
  • Publication
    The effect of support and copper precursor on the activity of supported CuO catalysts in the Selective Catalytic Reduction of NOx.
    (Kluwer Academic Publishers-Plenum Publishers, 2002-04)
    A series of Cu catalysts were studied as a function of support (Al2O3, TiO2 and SiO2) and Cu precursor (ex-SO4 and ex-NO3) for activity in the SCR-NH3 reaction. The catalysts were characterized using NOx TPD and SEM/EDAX analysis and the effects of residual sulphur interpreted in terms of site-blocking and NH3 activation mechanisms.
    Scopus© Citations 15  353
  • 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.
      335Scopus© Citations 9
  • Publication
    Attempts at an in-situ Raman study of Ceria / Zirconia catalysts in PM combustion
    CexZr1−xO2 catalysts with various Ce/Zr contents were studied using Raman spectroscopy under different gaseous atmospheres, at different temperatures and in the presence of a model soot. Catalysts with high concentrations of Zr fluoresced at elevated temperatures making analysis of their spectra impossible. This effect became even more pronounced at higher temperatures. CeO2 and solid solutions with relatively low concentrations of Zr showed a red shift and a decrease in intensity of the characteristic F2g peak at high temperatures under different atmospheres. The magnitude of the latter effect was higher under reducing atmospheres. These changes are reversible upon cooling, showing that they relate to a lattice expansion effect rather than any major chemical change to the material. In the presence of the model soot the Raman spectra of all materials was much decreased due to the absorption of the incident and scattered radiation by the soot particles. The presence of soot does not change the relative intensities or positions of the peaks in the spectra of the solid solutions. Evidence is shown for the production of a Ce3+–CO species following interaction between the soot and the surface at high temperature in an inert atmosphere.
      718Scopus© Citations 19
  • Publication
    The Preparation of Group II Oxide Catalysts Through Acetate Calcination: The Influence of a Support on the Nature of the Final Catalyst.
    The preparation of supported and unsupported group II oxide catalysts through oxidation of analogous group II acetates (Mg, Ca and Ba) in the presence and absence of a mesoporous silica material (SBA-15) was analysed using TGA. In the absence of the mesoporous support the acetates oxidised at different temperatures with a stability trend whereby Mg
      372Scopus© Citations 2
  • Publication
    Tethering of bi-nuclear complexes to SBA-15 and their application in CO2 hydrogenation
    Two bimetallic cryptates (containing Cu and Co), which have previously been shown to react with and activate atmospheric CO2, have been tethered to modified mesoporous SiO2 and their activities in promoting the CO2 + H2 reaction has been analysed. The cryptates have been tethered to –C3H6Cl modified SBA-15 through a condensation reaction between surface alkyl chlorides and 2° amines of the ligands releasing HCl and forming a 3° amine. The materials have been characterised using BET, TGA, FTIR and elemental analysis and their activity in promoting the CO2 + H2 reaction has been tested under batch reactor conditions. Co ions appear to selectively populate the medal sites of the tethered ligands while Cu ions appear to deposit on the surface as Cu(BF4)2 salts. The composite materials generate CO and CH4 from the CO2 + H2 mixtures. Co-containing catalysts are more effective than the Cu analogues in promoting the reaction.
      437Scopus© Citations 8