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- PublicationThe effect of support and copper precursor on the activity of supported CuO catalysts in the Selective Catalytic Reduction of NOx.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.
298Scopus© Citations 15 - PublicationNH3 and urea in the selective catalytic reduction of NOx over oxide-supported copper catalystsThe temperature-programmed activity of a series of oxide-supported (TiO2, Al2O3 and SiO2) Cu catalysts formed from two different Cu precursors (Cu(NO3)(2) and CuSO4) for the selective catalytic reduction of NOx using solutions of urea as a reductant have been determined. These activities are compared to those found using NH3 as a reducing agent over the same catalysts in the presence of H2O and it is found that catalysts that are active for the selective reduction of NOx with NH3 are inactive for its reduction using solutions of urea. Poisoning of the surface by H2Oads is not responsible for all of this decrease in activity and it is postulated that the urea is not hydrolysing to form NH3 over the catalysts but rather is oxidising to form N-2 or forming passivated layers of polymeric melamine complexes on the surface. The catalysts were characterised by temperature-programmed reduction while temperature-programmed desorption and oxidation of NH3 and temperature programmed decomposition of urea are used to characterise the interaction of both reductants with the various catalysts.
896Scopus© Citations 61 - PublicationThe influence of SO2-/4 on the catalytic combustion of soot using O-2 and NO/O-2 mixtures over Na-promoted Al2O3 catalystsNa/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.
314Scopus© Citations 14 - PublicationThe role of Bronstead acidity in poisoning the SCR-urea reaction over FeZSM-5 catalystsTwo 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.
224Scopus© Citations 31 - PublicationThe combustion of carbon particulates using NO/O2 mixtures : The influence of SO42− and NOx trapping materialsThe 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.
275Scopus© Citations 9 - PublicationA combination of NOx trapping materials and Urea-SCR catalysts for use in the removal of NOx from mobile diesel enginesPreliminary 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).
710Scopus© Citations 26 - PublicationBeneficial and problematic interactions between NOx trapping materials and carbonaceous particulate matterThe 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.
306Scopus© Citations 27 - PublicationPreparation 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.619Scopus© Citations 42 - PublicationSelective H-D exchange catalysed by aqueous phase and immobilised Pd nanoparticlesPd nanoparticles (with a mean diameter of 3.4 ± 0.5 nm) prepared through BH4− reduction of Na2PdCl4 can catalyse selective H–D exchange (through reaction with D2O) at the carbon α to the N atom of a pyridine ring. Oxidised Pd(II) complex species also present as dissolved species in the nanoparticle dispersion play no part in the exchange. We have studied the effects of several different variables on the rate of the selective H–D exchange activity for a model pyridine, i.e. 4-dimethylaminopyridine (DMAP). These variables include temperature, nanoparticle aging, nanoparticle re-reduction with H2 and nanoparticle immobilisation onto multi-walled carbon nanotubes (MWCNTs). We have also extended the study to related pyridine containing molecules.
376Scopus© Citations 14 - PublicationMain-chain organometallic polymers comprising redox-active iron(II) centers connected by ditopic N-heterocyclic carbenesMain-chain organometallic polymers were synthesized from bimetallic iron(II)complexes containing a ditopic N-heterocyclic carbene (NHC) ligand [(cp)(CO)LFe(NHC~NHC)Fe (cp)(CO)L]X2 (where NHC~NHC represents a bridging dicarbene ligand, L = I– or CO). Addition of a diimine ligand such as pyrazine or 4,4’-bipyridine interconnected these bimetallic complexes and gave the corresponding co-polymers containing iron centers that are alternately linked by a dicarbene and a diimine ligand. Diimine coordination was depending on the wingtip groups at the carbene ligands and was accomplished either by photolytic activation of a carbonyl ligand from the cationic [Fe(cp)(NHC)(CO)2]+ precursor (alkyl wingtips) or by AgBF4-mediated halide abstraction from the neutral complex [FeI(cp)(NHC)(CO)] (mesityl wingtips). Remarkably, the polymeric materials were substantially more stable than the related bimetallic model complexes. Electrochemical analyses indicated metal-metal interactions in the pyrazine-containing polymers, whereas in 4,4’-bipyridine-linked systems the metal centers were electronically decoupled.
646Scopus© Citations 70 - PublicationA simple and efficient method for the synthesis of Erlenmeyer azlactonesWe have recently developed a novel and efficient method for synthesising Erlenmeyer azlactones under mild and rapid conditions. The reaction is performed by reacting 2-phenyl-5-oxazolone with an aldehyde in dichloromethane using alumina as a catalyst. The materials react instantly at room temperature, negating the need for high temperatures and long reaction times. We have successfully used this method for both aliphatic, aromatic and heteroaromatic aldehydes, synthesising previously unmade Erlenmeyer azlactones in moderate to high yields.
2624Scopus© Citations 61 - PublicationOne-step diketopiperazine synthesis using phase transfer catalysisA simple and efficient one-step procedure is described for the synthesis of a number of symmetrical 1,4-disubstituted piperazine-2,5-diones under phase transfer conditions. The reactions are carried out at room temperature, starting from a suitable N-chloroacetamide in the presence of an aqueous solution of sodium hydroxide. Piperazine-2,5-diones were obtained with excellent selectivity in yields of up to 90%.
495Scopus© Citations 22 - PublicationBioorganometallic Chemistry: A Key To New Chemotherapy?6-Substituted fulvenes are interesting and easily accessible starting materials for the synthesis of novel substituted titanocenes via reductive dimerisation, carbolithiation or hydridolithiation reactions, which are followed by a transmetallation reaction with titanium tetrachloride in the latter two cases. Depending on the substitution pattern, these titanocenes prove to be bioorganometallic anticancer drugs, which have significant potential against advanced or metastatic renal-cell cancer. Patients bearing these stages of kidney cancer have a poor prognosis so far and therefore real progress in the area of metal-based anticancer drugs may come from this simple and effective synthetic approach.
67 - PublicationSuzuki coupling activity of an aqueous phase Pd nanoparticle dispersion and a carbon nanotube/Pd nanoparticle compositeAn 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.
441Scopus© Citations 49 - PublicationCarbenes in ActionNew reactions of N-heterocyclic carbenes and the stabilization of abnormal variations of these ligands provide exciting perspectives for organic synthesis and organometallic catalysis.
156Scopus© Citations 34 - PublicationNon-classical N-Heterocyclic carbene complexesThe expansion of the concept of N-heterocyclic carbenes as ligands for transition metals to mesoionic ligand systems has led to the discovery of a wide range of non-classical carbene-type ligands. These non-classical carbene-type ligands are characterised by a significantly lower heteroatom stabilisation of the (putative) free carbene, a situation that also affects the ligand donor properties and hence the reactivity of the coordinated metal centre. Based on the unique impact of non-classical carbene-type ligands, a number of attractive transition metal-catalysed processes have been disclosed in recent years, predominantly in the area of cross-coupling reactions, hydrogenations, and olefin metathesis
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5909Scopus© Citations 642 - Publication[Ru(bpy)3]2+ analogues containing a N-heterocyclic carbene ligandA synthetic procedure is described that provides access to [Ru(bpy)3]2+ analogues in which one bpy ligand is replaced by a C,N-bidentate coordinating carbene-benzimidazole ligand (bpy = 2,2’-bipyridine). These new complexes were prepared by first installing the chelating carbene ligand onto a Ru(cymene) platform and subsequent ligand substitution using bpy or terpy (terpy = 2:2’,6’:2’’-terpyridine). The carbene ligand significantly affects the optical properties of the complex and lowers the ruthenium(II) oxidation potential substantially. Such modifications may be advantageous for the development of new classes of photosensitizer materials.
865Scopus© Citations 48 - PublicationBeyond catalysis: N-heterocyclic carbene complexes as components for medicinal, luminescent, and functional materials applicationsThis tutorial review compiles the advances that have been achieved in using transition metal complexes containing N-heterocyclic carbene ligands as components for materials. Applications of metal carbene complexes in fields different from catalysis are remarkably scarce. During the last few years, promising results have been accomplished in particular by utilizing such complexes as antimicrobial and cytotoxic agents, as photoactive sites in luminescent materials, for self-assembly into liquid crystalline materials and metallasupramolecular structures, and as synthons for molecular switches and conducting polymeric materials. These initial achievements clearly underline the great potential of N-heterocyclic carbene complexes in various fields of materials science.
2207Scopus© Citations 618 - PublicationExcited state behaviour of substituted dipyridophenazine Cr(III) complexes in the presence of nucleic acids(RSC Publishing, 2010)
; ; ; ; The photophysics and photochemistry of [Cr(phen)2(dppz)]3+ and its 11,12-substituted derivatives [Cr(phen)2(X2dppz)]3+ {X = Me or F} have been studied in the presence of purine nucleotides or DNA using steady state and time-resolved absorption and luminescence spectroscopy. 5'-Adenosine monophosphate (5'-AMP) shows only a weak interaction with the excited states of each complex. By contrast they are efficiently quenched by 5'-guanosine monophosphate (5'-GMP), consistent with photo-induced electron transfer. Laser flash photolysis spectroscopy in the presence of 5'--GMP suggests that both forward and back electron-transfers are rapid. All complexes also display a strong affinity for DNA and evidence for both static and dynamic quenching mechanisms is provided.418Scopus© Citations 13