Showing papers on "Reducing agent published in 1999"

Catalytic NOx reduction by carbon supporting metals

Abstract: Catalytic NOx reduction by carbon supporting transition metals (Fe, Co, Ni, Cu) and potassium has been studied. The effect of oxygen on the catalytic properties of the metals has been analyzed. Temperature-programmed reactions and isothermal reactions have been conducted in a fixed bed flow reactor. Temperature-programmed reduction in hydrogen, XRD and XPS have been used to characterize the catalysts. All the metals studied catalyze the NOx reduction by carbon in the presence of oxygen, but also the O2–carbon reaction. Metal catalytic activity is the result of two factors, the tendency of the metal to be oxidized by NO and the easiness of the resulting oxide to be reduced by carbon. Among the metals studied, nickel exhibits the highest selectivity for NOx reduction. The results of this study strengthen the possible benefit of the lack of a gaseous reducing agent (such as ammonia or hydrocarbons) since the reduction of NOx is performed by the carbon support itself.

Oxidation of ochratoxin A by an Fe-porphyrin system: model for enzymatic activation and DNA cleavage.

Abstract: Ochratoxin A (OTA, 1) is a fungal toxin that facilitates single-strand DNA cleavage, DNA adduction, and lipid peroxidation when metabolically activated. To model the enzymatic activation of OTA, we have employed the water-soluble iron(III) meso-tetrakis(4-sulfonatophenyl)porphyrin (FeTPPS) oxidation system. In its presence, OTA has been found to facilitate single-strand cleavage of supercoiled plasmid DNA through production of reactive oxygen species (ROS) (i.e., the hydroxyl radical, HO(*)). The reaction of OTA with the FeTPPS oxidation system also generated three hydroxylated products (chlorine atom still attached), which was taken as evidence for production of the known hydroxylated metabolites (2-4) of OTA. This result suggested that the FeTPPS system served as a reasonable model for the enzymatic activation of OTA. When the reaction of OTA with FeTPPS was carried out in the presence of excess hydrogen peroxide (H(2)O(2)) and sodium ascorbate, a hydroquinone species (OTHQ, 5) was detected in which an OH group has replaced the chlorine atom of OTA. The production of OTHQ (5) was dependent on the presence of the reducing agent, sodium ascorbate, which suggested that the oxidation catalyst furnished the quinone derivative OTQ (6) that was subsequently reduced to OTHQ (5) by ascorbate. Utilizing a synthetic sample of OTHQ (5), the hydroquinone was found to undergo autoxidation with a t(1/2) of 11.1 h at pH 7.4, and to possess a pK(a) value of 8.03 for the phenolic oxygen ortho to the carbonyl groups. Our findings imply that the hydroquinone (OTHQ) and quinone (OTQ) metabolites of OTA have the ability to cause alkylation/redox damage and have allowed us to propose a viable pathway for oxidative damage by OTA.

Redox behaviour and catalytic properties of Ce0.5Zr0.5O2-supported palladium catalysts

Abstract: Ce 0.5 Zr 0.5 O 2 -supported palladium catalysts were prepared and used for CO and methane oxidation. The redox behaviour of these catalysts was investigated by using H 2 -TPR and CO-TPR. The shape and temperature of TPR peaks depend on the nature of reducing agent. Two peaks (α 1 and γ) were observed when H 2 was used as reducing agent for the fresh catalyst, while three peaks (α′, β′ and γ′) were observed when CO was used as a reducing agent. The addition of a noble metal effectively promotes the reduction of Ce 0.5 Zr 0.5 O 2 support, which is attributed to hydrogen spillover. After re-oxidation treatments, the PdO reduction process splits into two peaks (α 1 and α 2 ). On the basis of the catalytic activity and CO-TPR results, the activity of CO oxidation is related to the finely dispersed PdO, while the activity of methane oxidation is related to the large PdO particles.

DNA cleavage by hydroxy-salicylidene-ethylendiamine-iron complexes

Abstract: Bis(hydroxy)salen.Fe complexes were designed as self-activated chemical nucleases. The presence of a hy-droxyl group on the two salicylidene moieties serve to form a hydroquinone system cooperating with the iron redox system to facilitate spontaneous formation of free radicals. We compared the DNA binding and cleaving properties of the ortho -, meta- and para -(bishydroxy) salen.Fe complexes with that of the corresponding chelate lacking the hydroxyl groups. DNA melting temperature studies indicated that the para complex exhibits the highest affinity for DNA. In addition, this para compound was considerably more potent at cleaving supercoiled plasmid DNA than the regio-isomeric ortho - and meta -hydroxy-salen.Fe complexes, even in the absence of a reducing agent, such as dithiothreitol used to activate the metal complex. The DNA cleaving activity of the para isomer is both time and concentration dependent and the complexed iron atom is absolutely essential for the sequence uniform cleavage of DNA. From a mechanistic point of view, electron spin resonance measurements suggest that DNA contributes positively to the activation of the semi-quinone system and the production of ligand radical species responsible for subsequent strand scission in the absence of a reducing agent. The para -hydroxy-salen.Fe complex has been used for detecting sequence-specific drug-DNA interactions. Specific binding of Hoechst 33258 to AT sequences and chromomycin to GC sequences were shown. The para -bis(hydroxy)salen.Fe derivative complements the tool box of footprinting reagents which can be utilised to produce efficient cleavage of DNA.

Mechanism of the Chemical Deposition of Nickel on Silicon Wafers in Aqueous Solution

Abstract: The deposition of metallic nickel on n-Si(100) wafers was performed without external potential control in aqueous NiSO 4 solutions of different compositions at pH 8.0. Without giving any catalyzation treatment, the deposition of nickel on hydrogen-terminated Si(100) was confirmed in a conventional electroless plating bath containing NaH 2 PO 2 as the reducing agent, sodium citrate as the complexing agent, and (NH 4 ) 2 SO 4 as the buffering agent. The deposition of nickel was found to take place also in a bath without the reducing agent, and even in a simple solution consisting of NiSO 4 and (NH 4 ) 2 SO 4 . By using a transmission electron microscope equipped with an energy dispersive X-ray spectrometer, the cross sections of the films deposited from these solutions were examined, which revealed formation of silicon oxide between the Ni deposit and Si substrate. Based on these results, the mechanism of the entire process of electroless Ni deposition on Si is discussed.

Determination of active palladium species in ZSM-5 zeolite for selective reduction of nitric oxide with methane

Abstract: The active site in ZSM-5 zeolite-supported palladium, which shows the catalytic activity for NO reduction with methane as a reducing agent, has been investigated qualitatively and quantitatively by means of NO chemisorption and NaCl titration, comparing with PdO supported on silica. Palladium species in 0.4 wt.% Pd loaded H-ZSM-5 can adsorb NO equimolarly after calcination at 773 K, and almost all the NO was desorbed at around 673 K, while the palladium species on PdO/SiO2 hardly adsorbed NO. The palladium species in Pd(0.4)/H-ZSM-5 are ion-exchangeable with Na+ in NaCl solution, indicating that they exist in a cationic state of an isolated Pd2+. This method for quantitative analysis of the isolated Pd2+ cations is named as ‘NaCl titration’. The amount of the isolated Pd2+ cationic species increased with increasing palladium content on Pd/H-ZSM-5, and PdO co-existed above 1 wt.%. The amount of the isolated Pd2+ cation was unchanged after the reaction of NO2–CH4, NO2–CH4–O2, or CH4–O2 at 673 K, while the adsorbed amount of NO per the Pd2+ as determined by NO-TPD decreased after the NO2–CH4–O2 reaction. It was found by NaCl titration that the catalytic activity of Pd/H-ZSM-5 for NO2–CH4–O2 reaction increased with increasing amount of the isolated Pd2+ cationic species up to 0.7 wt.%, while the increase in the amount of PdO led to decrease in selectivity towards NO2 reduction. The palladium species that are active and selective for NO reduction with CH4 will be proposed.

Aerobic hydrocarbon oxidation catalyzed by the vanadomolybdophosphate polyoxometalate, H5PV2Mo10O40, supported on mesoporous MCM-41

Abstract: The impregnation of H5PV2Mo10O40 polyoxometalate onto MCM‐41 and amino‐modified MCM‐41 materials provided mesoporous active catalysts with large surface areas for aerobic hydrocarbon oxidation using isobutyraldehyde as a reducing agent. The results of the oxidation of alkenes and alkanes gave product selectivities similar to those observed in the corresponding homogeneous reaction although catalytic activity was somewhat reduced. Under appropriate experimental conditions there was no leaching and the solid catalyst could be recovered and reused without loss in activity.

Method for producing chemically bonded phosphate ceramics and for stabilizing contaminants encapsulated therein utilizing reducing agents

Abstract: Known phosphate ceramic formulations are improved and the ability to produce iron-based phosphate ceramic systems is enabled by the addition of an oxidizing or reducing step during the acid-base reactions that form the phosphate ceramic products. The additives allow control of the rate of the acid-base reactions and concomitant heat generation. In an alternate embodiment, waste containing metal anions are stabilized in phosphate ceramic products by the addition of a reducing agent to the phosphate ceramic mixture. The reduced metal ions are more stable and/or reactive with the phosphate ions, resulting in the formation of insoluble metal species within the phosphate ceramic matrix, such that the resulting chemically bonded phosphate ceramic product has greater leach resistance.

Reductive decomposition of nitrate ion to nitrogen in water on a unique hollandite photocatalyst

Abstract: Photocatalysis of a hollandite compound K x Ga x Sn 8− x O 16 ( x = ca. 1.8) was examined for the reduction of nitrate ion with a reducing agent of methanol in water under UV irradiation. Hollandites have a characteristic one-dimensional tunnel structure. The hollandite powder, which was prepared by the sol–gel method and unloaded with any additives like metals, was used as the photocatalyst and its photocatalytic reaction was analyzed quantitatively by using ion chromatography and on-line mass spectrometry, and its reaction mechanism was analyzed by in-situ FT-IR. The hollandite photocatalyst showed a significant activity for the formation of N 2 from NO 3 − . The nitrate was reduced to N 2 and NO 2 − , while the reducing agent methanol was partly oxidized to change to formic acid. The conversion of NO 3 − was proportional to the yields of N 2 , NO 2 − , and HCOO − . The present photocatalyzed decomposition of NO 3 − to N 2 would be a useful photocatalysis for the environmental protection of water.

Asymmetric Reduction of Prochiral Cyclic Imines to Alkaloid Derivatives by Novel Asymmetric Reducing Reagent in THF or under Solid-State Conditions

Abstract: Asymmetric reductions of prochiral cyclic imines were studied using chiral nonracemic sodium acyloxy borohydride 2. The chiral nonracemic reducing agent 2 has been easily prepared by the reaction o...

Engineering aspects of preparation of nanocrystalline particles in microemulsions

Abstract: Engineering aspects of the preparation of palladium nanoparticles in non-ionic w/o-microemulsions are examined. In order to achieve reproducible synthesis conditions a semi-batch reactor with a standardized design is used. Influences of the stirring rate and of different ways of concentration control on the product properties are observed. For reproducible synthesis it is important to establish appropriate and defined preparation conditions. Monodisperse palladium particles of around 5 nm size are obtained by adding the microemulsion containing the palladium salt at a constant feed rate to the precharged microemulsion containing the reducing agent. A quantitative kinetic model is proposed to describe particle formation in microemulsions. Unknown parameters of the model have been estimated by independent examinations or can be achieved by fitting to the experimental data.

Preparation of aluminum hydride polymorphs, particularly stabilized α-alh3

Abstract: The present invention features methods for preparing stabilized α-AlH 3 and α′-AlH 3 , compositions containing these alane polymorphs, e.g., energetic compositions such as rocket propellants, and methods for using the novel polymorphs as chemical reducing agents, polymerization catalysts, and as a hydrogen source in fuel cells and batteries. The method produces stabilized alane by treating α-AlH 3 with an acidic solution that optionally contains a stabilizing agent such as an electron donor, an electron acceptor, or a compound which coordinates the Al 3+ ion.

Methods for forming amorphous ultra-high molecular weight polyalphaolefin drag reducing agents

Abstract: A composition including polyalphaolefins that function as drag reducing agents and a process for the preparation of polyalphaolefins that function as drag reducing agents are disclosed. The process includes contacting alpha olefin monomers with a catalyst system, which includes a catalyst and an activator (co-catalyst) in a reactant mixture. The catalyst is a transition metal catalyst, preferably titanium trichloride, and the co-catalyst may include an alkylaluminoxane, alone or in combination, with a dialkylaluminum halide or a halohydrocarbon. The polymerization of the alpha olefin monomers produces a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of at least 10 dL/g. The addition of the alkylaluminoxane during the polymerization process provides for a non-crystalline, ultra-high molecular weight polyalphaolefin and a more uniform molecular weight distribution of the resulting polyalphaolefin, thereby creating a drag reducing agent superior to known drag reducing agents. A process for forming a drag reducing agent comprising a non-crystalline, ultra-high molecular weight polyalphaolefin having an inherent viscosity of about at least 10 dL/g and a process for reducing drag in a conduit are also disclosed.

Exhaust gas emission control device for internal combustion engine

Abstract: PROBLEM TO BE SOLVED: To perform efficient regeneration of an NOX occlusion reduction catalyst regardless of an exhaust gas temperature. SOLUTION: An NOX occlusion reduction catalyst 7 is arranged in the exhaust passage 3 of an engine 1 and absorbs NOX contained in exhaust gas from an engine under lean air-fuel ratio operation. When an NOX occlusion amount of the catalyst 7 is increased, a liquid reducing agent (diesel oil) is injected in an exhaust passage on the upper stream side of the catalyst 7 through a reducing agent injection valve 91 and NOX is emitted from the catalyst 7 for reduction purification. An electronic control unit(ECU) 30 calculates the temperature of exhaust gas flowing in the catalyst 7 based on an engine running state and the more a calculated exhaust gas temperature is lower, the more an injection pressure of the reducing agent injection valve is increased and the grain size of injected reducing agent particles is decreased. By decreasing the grain size, the injected reducing agent particles are easily evaporated even at a low exhaust gas temperature. Since liquid reducing agent particles are prevented from reaching the catalyst 7, the reduction agent supplied to the catalyst 7 is effectively utilized.

Plasma Enhanced Selective Catalytic Reduction: Kinetics of NOx-Removal and Byproduct Formation

Abstract: The mechanisms of plasma enhanced selective catalytic reduction of NOx on a V2O5-WO3/TiO2-catalyst were investigated for temperatures between 100 °C and 200 °C by applying various analytical methods. In experiments with synthetic gas mixtures containing Ar instead of N2 as a carrier gas the formation of N2 as a main product and thus catalytic reduction of NOx in reactions with NH3 has been proven using mass spectroscopy. More detailed information on the reaction kinetics of NO-formation and removal induced by non-thermal plasmas has been obtained from experiments in gas mixtures containing isotopically marked 15NO. FTIR-absorption spectroscopy was applied to measure the concentrations of 14Nand 15N-containing molecules. Particles formed by the combined plasmaand catalytic treatment of Diesel exhaust with NH3 as reducing agent were analyzed by energy dispersive X-ray scattering. The spectra indicate, that mainly sulfur containing particles were formed. Formation of NH4NO3 plays a minor role. Non-thermal plasma treatment did not show a strong influence on catalytic removal of unburned hydrocarbons, but increased CO-emission was observed. In all experiments plasma induced conversion of NO to NO2 increased NOx-reduction rates.

Adhesive, bonding method and assembly of mounting substrate

Abstract: The present invention is characterized by comprising a two-pack adhesive of an A agent selected from components, an acrylic monomer, a peroxide, a reducing agent, an epoxy resin precursor and a curing agent and containing at least one or two of the acrylic monomer, the peroxide and the reducing agent, and a B agent containing all of the remaining components which are not selected in the A agent. The use of this adhesive makes it possible to stably obtain the bonding free from a thermal stress with the excellent heat resistance and the good reliability.

Oxidation of NH3 and NOx formation During the catalytic combustion of gasified biomasses fuels over Mn–hexaaluminate and alumina-supported Pd catalysts

Abstract: The reactivity of a BaMnAl11O19 and a PdO/Al2O3 catalyst in the combustion of NH3-containing gasified biomass-derived fuels is investigated. Both catalysts produce significant amounts of fuel–NOx from ammonia, and particularly NO. The NO formation increases with temperature and over the BaMnAl11O19 catalyst shows a maximum near 750°C: above this temperature the NO formation is strongly reduced and a corresponding increase in N2 concentration is observed. This phenomenon, that is enhanced by the presence of the fuel components, is not apparent over the PdO/Al2O3 catalyst. The observed reduction in the NO concentration is related to the occurrence of a selective non-catalytic reduction (SNCR) process involving ammonia as reducing agent and occurring in the first part of the catalyst bed where the simultaneous presence of oxygen, NO and ammonia is attained. These conditions are not achieved in the case of the PdO/Al2O3 catalyst due to the rapid NH3 oxidation. The NO-SNCR reduction process is enhanced by the presence of the biogas fuel components, that do not directly reduce NO but that enhance the reactivity of gaseous ammonia through complex effects on the radical pool in the gas-phase.

Comparison between ammonia and propene as the reducing agent in the selective catalytic reduction of NO under lean conditions over Pt black

Abstract: The catalytic activity of Pt black towards the reduction of NO under lean conditions is examined. Ammonia and propene are tested as reducing agents. A scrambling between nitrogens is observed in the formation of N2 and N2O for NH3. For C3H6, a reduction of NO to mainly N2O is found. A minor formation of N2 is only observed for high C3H6 concentrations. The role of NO2 as an intermediate in the reduction of NO is examined by using a feed gas mixture containing NO2, as well as by studying the catalytic activity of Pt black towards the NO-O2 and NO2-O2 reactions. No effect is observed in the maximum NOx conversion for C3H6 whereas for NH3 a decreased activity is found. The presented results are put in perspective of the reaction mechanisms proposed in the literature.

Mass spectrometry detection and reduction of disulfide adducts between reducing agents and recombinant proteins with highly reactive cysteines

Abstract: Recombinant proteins with highly reactive thiol groups can form disulfide adducts with reducing agents commonly used in protein purification, such as beta-mercaptoethanol and dithiothreitol. These adducts can interfere with protein-protein or protein-ligand interactions.This report describes the reduction of persistent disulfide adducts between the reducing agents glutathione or beta-mercaptoethanol and the recombinant protein Cyto-MelCAM, which were detected using matrix-assisted laser desorption and ionization (MALDI) mass spectrometry.These adducts were effectively reduced using the trialkylphosphine reducing agent tris(2-carboxyethyl) phosphine hydrochloride.

Aqueous solutions for obtaining noble metals by chemical reductive deposition

Abstract: An aqueous solution for obtaining a noble metal by chemical reduction containing at least one water-soluble compound or complex of a metal selected from the group consisting of gold, platinum, silver, and palladium as a source of the metal to be deposited, and at least one mercapto compound or sulfide compound or a salt thereof as a reducing agent. The reducing agent is typically mercaptoacetic acid, 2-mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, glucose cysteine, 1-thioglycerol, sodium mercaptopropanesulfonate, N-acetylmethionine, thiosalicylic acid, 2-thiazoline-2-thiol, 2,5-dimercapto-1,3,4-thiadiazole, 2-benzothiazolethiol, or 2-benzimidazolethiol. They may be used singly or in combination.

Method and system for purifying exhaust gases and exhaust gas purification catalyst for use therein and method for preparation thereof

Abstract: The emission of HC is greatly inhibited over a wide range from a low temperature to a high temperature by contacting an oxidation-reduction catalyst comprising an oxygen occluding and reducing agent and, carried thereon, at least one of Rh and Pd, with exhaust gases having been reduced with respect to HC. An oxidation-reduction catalyst comprising an oxygen occluding and reducing agent and, carried thereon, at least one of Rh and Pd exhibits a greatly improved activity for a gas having a low content of HC. And, a catalyst comprising ceria and Pd carried thereon produces a Pd in an oxidation state of more than two, which results in more improved oxidation activity of the catalyst. Further, the contact of an exhaust gas purification catalyst with exhaust gases which have been reduced in Nox content by means of an absorbent for Nox significantly improves the activity of the exhaust gas purification catalyst for purifying HC. In a low temperature region, the emission of Nox can be inhibited due to the adsorption of Nox, and in a low temperature region, HC and CO can be efficiently purified by the exhaust gas purification catalyst. The employment of a reduction catalyst of Nox occlusion type leads to more efficient purification of Nox.

Indium as a Reducing Agent: Deprotection of 4-Nitrobenzyl Ethers and Esters

Abstract: Indium in aqueous ethanolic ammonium chloride is an effective method for the deprotection of 4-nitrobenzyl ethers and esters.

Zeolite supported Pt catalysts for reduction of NO under oxygen excess: a comparison of C3H6, HNCO and NH3 as reducing agents

Abstract: The effect of the zeolite SiO2/Al2O3 ratio of ZSM-5 supported Pt catalysts on the reduction of NO under oxygen excess has been investigated. The activity and selectivity of three reducing agents were compared, i.e. C3H6, HNCO and NH3. The maximum NO reduction with both C3H6 and HNCO as the reducing agent was affected by the SiO2/Al2O3 ratio of the support. Although no effect was observed on the maximum NO reduction for NH3, the yields of Nz and N2O were affected. The results are put in perspective of reaction mechanisms proposed in the literature.

Application of Cryptand/Polystyrene Drift-Type Phase Transfer Catalysts for Reduction of Ketones

Abstract: A drift-type phase transfer catalyst, cryptand-22, adsorbed on poly(styrene/diviny benzene)-sulfonic resin was prepared and applied to catalyze the reduction of ketones, e.g., acetophenone, benzophenone and benzaldehyde with NaBH4 as a reducing agent. Before the reaction, cryptand-22 was adsorbed on the sulfonic resin with ion-pairing, resin-SO3− +NH-cryptand-22. The ion-pairs can be destroyed by adjusting the basicity of the reaction solution with NaOH and the cryptand can be released from the resin into the reaction solution as a homogeneous catalyst during the reaction period. After the reaction, the cryptand catalyst can be readsorbed on the resin by adjusting the acidity of the solution with HCl and can be readily recovered by filtration like a heterogeneous catalyst. The draft-type cryptand catalyst exhibited better catalytic ability than some common crown ethers, e.g., 15-crown-5, benzo-15-crown-5, 12-crown-4 and dibenzo-18-crown-6 for the reduction of acetophenone with NaBH4. Effects of solvents, pH of solutions, concentration of the catalyst, reducing agents and resin property on the reduction of ketones were investigated and discussed. The reaction mechanism of the cryptand catalyzed reduction was also studied.