Now showing 1 - 10 of 32
  • Publication
    SBA-15 Modified with Tethered Ionic Liquids Applied in the Esterification of Valeric Acid with Pentanol—Towards Cellulosic Biofuels
    Two catalysts are prepared by tethering ionic liquid cation components (1-(propyl-3-sulfonate)-3-(3-trimethoxysilylpropyl) imidazolium) with either chloride or sulphate anions, to the surface of a mesoporous SiO2 material through a condensation reaction. These are characterized using elemental analysis, TGA-MS, FTIR (and D-FTIR), TEM, physisorption and NH3 adsorption (TPD and FTIR), and applied in the valeric acid + pentanol esterification reaction to form the sustainable biodiesel Pentyl Valerate. The material containing the sulfate counter-ion was significantly more active than the chloride analogue.
  • 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.
      590Scopus© Citations 13
  • Publication
    The nature of surface deposits following valeric acid interactions with Al2O3-supported Alkaline Earth Oxide catalysts: Towards cellulosic biofuels
    Two Al2O3-supported alkaline earth metal oxide catalysts (MgO and BaO) were contacted with valeric acid at 250 °C. Each formed amounts of 5-nonanone (BaO more than MgO). A significant deposition of hydrocarbonaceous material onto the catalyst surface is noted. This adsorbed material is characterised using TGA and FTIR and relates to a carboxylate species.
      475Scopus© Citations 2
  • Publication
    Serendipity following attempts to prepare C-doped rutile TiO2
    Attempts to mimic the band gap narrowing seen in anatase TiO2 following C-doping of the lattice where the C arose from a melamine borate precursor were made in situations where the sol-gel mixture was directed towards rutile formation. The formed materials were characterised using XRD, BET, UV-Vis spectroscopy, XPS and TEM and their activities in promoting the photo-degradation of 4-chlorophenol were analysed. It was found that carbon was not doped into the lattice (in contrast to the situations where the sol-gel mixture was directed towards the precipitation of anatase TiO2). In spite of how common reports of the preparation of C-doped TiO2 using sol-gel processes have been, the presence of carbon dopant precursors in a crystallising sol does not necessarily result in the incorporation of C dopants within the final crystalline material, i.e. the nature of the condensing sol is also important. The presence of melamine borate did however increase the proportion of rutile in the final mixture (indeed in the presence of melamine borate the pure rutile phase was formed) and also resulted in materials with higher surface areas (as measured using BET). Furthermore, TEM has shown that rutile TiO2 condensed in the presence of melamine borate had a much more distinct rod-like shape than that condensed in its absence (the latter being more spherical in shape). These materials, notwithstanding the absence of any dopant effect, demonstrated enhanced photocatalytic activity when compared with analogous materials prepared in the absence of melamine borate and this effect is ascribed to both their relatively larger surface areas and their specific shape. Therefore, we have serendipitously come across a method for improving the performance of rutile photocatalysts while searching for a method to generate C-doped rutile TiO2.
      582Scopus© Citations 13
  • Publication
    Routes to visible light active C-doped TiO2 photocatalysts using carbon atoms from the Ti precursors
    In this work, different thermal treatments of titanium isopropoxide-derived photo-catalyst precursors, designed with the purpose of generating C-doped TiO2 photo-catalysts using carbon atoms present in the TiOx gel precursors as dopants, are presented. Specifically, these look at varying the standard calcination techniques using heat treatments in He (rather than calcination in air) and lower temperature calcinations (200 °C rather than 500 °C). The formed materials are characterised using N2 physisorption, XRD, UV Visible spectroscopy and XPS and their activities in promoting the oxidation of 4-chlorophenol under visible-light-only conditions were analysed. The nature of carbon remaining on the (or in the) material is discussed found to be both surface graphitic carbon and carbon present in anionic dopant positions. The different contributions of each type of carbon to the catalytic photo-activity under visible light are discussed.
      527Scopus© Citations 25
  • Publication
    Towards an understanding of the beneficial effect of mesoporous materials on dehydrogenation characteristics of NH3BH3
    Ammonia borane (AB) was loaded onto a range of mesoporous materials (MCM-41, SBA-15 and MCF) by wet impregnation from THF solutions and its thermal dehydrogenation studied using TGA/MS. The interactions between the AB and the surfaces were characterised using difference FTIR spectroscopy. The presence of mesoporous materials promotes lower temperature H2 release, and greater selectivity towards the formation of H2, i.e. decreased formation of gaseous boroncontaining side products. D-FTIR results confirm interactions between isolated silanol groups or surface Si-O-Si species and AB and this supports the proposal that a H-bonding interaction between the surface and deposited AB is important in promoting decomposition at lower temperature. AB interacting with silanol groups decomposes more readily than that coordinated to Si-O-Si. The effect on the temperature of H2 release is greater for materials of larger pore size (rather than materials of larger surface area), i.e. MCF>SBA-15>MCM-41. This suggests that access to the internal surface of the mesoporous material (where the majority of surface silanols are located) is important, and this in turn suggests that polymeric species, which may have restricted access to the internal surface of the different materials, form when AB is dissolved in THF. Decomposition of B-N-containing gaseous materials (to AB(g)) following their formation, on the silanol groups of the SiO2, is suggested as the reason for the increased selectivity of the reaction to H2 (and decreased release of unwanted side products) in the presence of mesoporous material.
      502Scopus© Citations 18
  • Publication
    Co-SBA-15 catalysts in the hydrolysis of NH3BH3 – Influences of Co precursors and catalyst pre-treatment
    H2 was released from ammonia borane (AB) through a hydrolysis reaction over several Co-SBA-15 catalysts. Each catalyst had an induction time prior to becoming active. The activation time related to the in-situ reduction of Co species to an active nano-particulate form and the length of this this induction time varied as a function of the Co-precursor used. The rate of the hydrolysis reaction over the reduced and active catalysts depended on the precursor. While the induction time was not noted in subsequent reactions over the reduced catalysts, the reactivity differences remained. A rationale for the differences based on the preparation steps is suggested
      306Scopus© Citations 8
  • 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.
      310Scopus© Citations 33
  • Publication
    Preparation and characterization of 4-dimethylaminopyridine-stabilized palladium nanoparticles
    (American Chemical Society, 2007-12-04) ; ;
    4-Dimethylaminopyridine (DMAP)-stabilized palladium nanoparticles with a mean diameter of 3.4 +/- 0.5 mn are prepared from the aqueous phase reduction of Na2PdCl4 using NaBH4 in the presence of DMAP. TEM and UV-vis spectroscopy characterization of the nanoparticle dispersion shows no obvious change in the nanoparticles several months after preparation. H-1 NMR spectroscopy of the nanoparticles shows that the nanoparticle dispersion also contains a boron/DMAP complex and two palladium/DMAP complexes. One of the palladium complexes crystallizes out of the dispersion and is identified as Pd(DMAP)(4)(OH)(2) by X-ray crystallography. Following extensive analysis, it is believed that the palladium/DMAP complexes are formed following the oxidation of the palladium nanoparticles. The prepared nanoparticle dispersion promotes selective hydrogen/deuterium (H/D) exchange on the carbon atoms alpha to the endocyclic nitrogen atom on the DMAP-stabilizing ligands through reaction with D2O. This activity is attributed to the presence of the nanoparticles rather than to the presence of the oxidized palladium/DMAP complexes.
      803Scopus© Citations 42
  • 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.
      344Scopus© Citations 9