Reaction In Presence Research Articles

Role of added chloride ions in alteration of reaction pathway in the oxidation of cyclic ketones by dichloroisocyanuric acid—A kinetic study

Effect of added chloride ions on kinetics and pathway of reaction between cyclic ketones (five to eight membered rings) and dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Formation of aliphatic dicarboxylic acids as the end products demonstrates the ring cleavage oxidation. Positive effect of acid and negative effect of dielectric constant on the reaction rate reveals a interaction between positive ion (oxidant in the form of H2OCl+) and dipolar substrate molecule. Zero and first orders by oxidant in absence and presence of added chloride ions illustrates the participation of substrate as enolic form of ketone and protonated ketone, respectively, in the rate determining steps. The observed order of reactivity of cyclic ketones (cyclohexanone > cyclooctanone > cyclopentanone > cycloheptanone) was explained on the bases of ring strain, change of hybridization and conformational considerations. The envisaged plausible mechanism based on order of reactants in presence and absence of added chloride ions was substantiated by the order of Arrhenius parameters.

High Rate Capability of SiOC Ceramic Aerogels with Tailored Porosity as Anode Materials for Li-ion Batteries

Porous carbon-rich SiOC ceramic aerogels have been synthesized from a linear polysiloxane cross-linked with divinylbenzene (DVB) via hydrosilylation reaction in presence of a Pt catalyst and acetone as a solvent. The obtained wet gels are aged in solvent followed by drying under supercritical conditions using liquid carbon dioxide. The resulting pre-ceramic aerogels are subjected to pyrolysis at 1000°C under controlled argon atmosphere to form the desired SiOC aerogel. The synthesized SiOC ceramics contain 43wt% of free carbon, which is segregated within amorphous SiOC matrix. The high BET surface area up to 230m2g−1 of preceramic aerogels is only slightly diminished to 180m2g−1 after pyrolysis at 1000°C. The electrochemical characterization reveals a high specific capacity of more than 600mAhg−1 at a charging rate of C (360mAg−1) along with a good cycling stability. At a rate of 10C (3600mAg−1) the specific capacities as high as 200mAhg−1 are recovered. The excellent properties of the materials are discussed with respect to their structural features. The porous nature of the carbon rich ceramics allows for fast ionic transport and helps to accommodate the structural changes which in turn allow a stable performance during repeated lithiation/delithiation.

Highly photo-catalytically active hierarchical 3D porous/urchin nanostructured Co3O4 coating synthesized by Pulsed Laser Deposition

A porous coating assembled with hierarchical 3D Co3O4 urchin-like particles was synthesized by Pulsed Laser Deposition (PLD) and thermal oxidation. Laser ablation of CoB powder, used as the target material, in oxygen atmosphere formed core–shell particles on the coating surface with mainly a metallic Co core and a mixture of Co, B and O accommodating the shell. The thermal oxidation of these core–shell particles in air at 600°C induces the morphological transformation to urchin-like particles consisting of nanowires (NWs) (diameter: 30–60nm and length 1–3μm) grown radially from the core surface. The extrusion marks on the surface of NWs indicate that the stress induced growth process is caused by difference in the thermal expansion coefficient. XRD, Raman, EXAFS and HRTEM analysis confirmed that the NWs are polycrystalline consisting of pure Co3O4 phase. A wet-chemistry hydrothermal procedure was also employed to synthesize nanostructured urchin-like particles which are hollow and the structure is held together by the radially oriented nanorods (diameter: 40–150nm). During photocatalysis, urchin-like particles synthesized by PLD displayed significantly higher (∼5 times) degradation rates when compared to chemical urchins for degradation of methylene blue dye via a photo-Fenton reaction in presence of H2O2 and visible light. This is mainly attributed to poor stability of the nanorods in the chemical urchin structure. Features such as high surface area, enhanced stability against agglomeration, polycrystalline nature of the NWs, porous surface and superior adhesion, are responsible for the enhanced photocatalytic activity of Co3O4 urchin-like particles assembled in a porous coating synthesized by PLD and thermal oxidation. Reusability tests also demonstrate the robust nature of the catalyst coating.

Polymer Nanocomposite Hydrogels with Improved Metal Adsorption Capacity and Swelling Behavior: Influence of Spirulina Immobilization onto Montmorillonite Clay

Polacrylamide nanocomposite hydrogels were prepared by in situ free radical polymerization reaction in presence of Spirulina microalgae, which is immobilized in montmorillonite clay (Sp-MMT). The nanocomposite hydrogel having 1 wt.% Sp-MMT clay was found to have desired exfoliated structure, maximum swelling and improved thermal stability. It also showed maximum metal adsorption capacity, which is about 312% higher than that of neat PAAm hydrogel at the highest metal concentration. The presence of Spirulina's porous network structure where all potential binding sites are under receptive position was found to be responsible for the dramatic increase in the metal adsorption and swelling behavior.

Reaction mechanism and kinetic study of the•OHinitiated tropospheric oxidation of 3-methyl-2-buten-1-ol: A quantum chemical investigation

In this article a theoretical study of mechanism and kinetics of the OH -initiated oxidation reaction of 3-methyl-2-buten-1-ol (MBO-321) is presented. This degradation mechanism of MBO-321 consists of H -abstraction reaction and OH -addition to olefinic bond. In addition, probable product analysis alongwith the mechanism for secondary reactions in presence of O2and NO has been investigated. Energetics have been studied at the CCSD(T)/6-311++g(d,p)//MP2 = full/6-31+G(d) level of theory. Thermochemical analysis has been done using CBS-QB3 method starting from the geometry obtained in the MP2 method. All the H -abstraction reactions pass through positive energy barrier except H4 -abstraction channel. OH -addition to the double bond takes place via formation of the pre-reactive complex as these reaction channel pass through negative activation barrier. OH -addition is the predominant reaction pathway for the overall oxidation process. Using TST theory at 1 atm pressure and in the temperature range of 200 K–400 K, the calculated rate constant and lifetime of OH -addition is [Formula: see text] molecule-1s-1and 1.88 h, which is consistent with the previous experimental data, [Formula: see text] molecule-1s-1and 1.9 h respectively (Imamura et al., Rate coefficients for the gas phase reactions of OH radical with methylbutenols at 298 K, Int J Chem Kinet36:379–385, 2004).

Inhibitory Effects of Quercetin and Kaempferol as two Propolis Derived Flavonoids on Tyrosinase Enzyme

inhibitors. Materials and Methods: In this work, the effects of quercetin and kaempferol as propolis-derived compounds on activity of mushroom tyrosinase (MT) were studied. These flavonoids showed inhibitory activity on catecholase and cresolase reactions in presence of caffeic acid and p-comaric acid, respectively. The inhibition mode of quercetin and kaempferol were competitive towards both catecholase and cresolase activities of the enzyme. Results: The inhibition constants (Ki) were determined as 0.072 and 0.112 mM for catecholase activity, and 0.016 and 0.06 mM for cresolase activity, respectively. Conclusions: In general, quercetin and kaempferol can be used as good candidates in melanogenesis inhibition. Moreover they should be considered as good blockers of enzyme activity in hyper pigmentation and clinical application.

Supported Pt nanoparticles for the hydrogen mitigation application

Accidents at TMI, USA and the recent one at Fukushima, JAPAN has emphasized the need for mitigation of hydrogen generated in nuclear reactor containment during accidental conditions. Passive Autocatalytic Recombiner (PAR) is one of the best solutions to deal with such situations during loss of coolant accidents. A novel breed of catalysts based on cordierite supported Pt nanoparticles has been prepared by chemical reduction route for mitigating the hydrogen generated during such accidents. These catalysts have been characterized for their phase purity, surface composition, surface area, particle size, morphology and elemental loading of the noble metal. The supported noble metal particles are found to be of 7 nm–11 nm dimensions, depending on the extent of noble metal loading. The catalytic activity of these catalysts has been evaluated in presence and absence of various prospective contaminants like carbon monoxide, carbon dioxide, methane, humidity, and condensed water in a laboratory scale reactor. Developed catalysts have been found to be catalytically active for H2–O2 recombination reaction in presence of 100% relative humidity and 2000 ppm of carbon monoxide.

Correlation Between Theoretical Data and Experimental Propierties of Selective PtAg Core-Shell Nanoparticles for Oxygen Reduction Reaction

In previous reports PtAg core-shell catalyst has showed selective properties for the oxygen reduction reaction in presence of glucose 0.1 M as interference in basic media. This characteristic has allowed the operation of microfluidic fuel cell with only one feeding stream mixing fuel and oxidant. In this work Molecular dynamics (MD) and Density functional theory (DFT) were used to explain the nanoparticle stability and conductive properties. Also is reported the analysis by XRD, XPS and STEM characterization, and electrochemical tests for oxygen reduction reaction in absence and presence of glucose, and testing in a microfluidic fuel cell. The structural simulation agrees with the experimental data showing the core-shell formation from an alloy nanoparticle by heating. Also, the electronic properties of the PtAg core-shell nanoparticles are very similar to the Pt nanoparticles.

Effect of visible light on catalytic hydrolysis of p-nitrophenyl palmitate by the Pseudomonas cepacia lipase immobilized on sol-gel support.

This paper demonstrates Pseudomonas cepacia lipase catalyzed hydrolysis of p-nitrophenyl palmitate under irradiation of light with wavelengths of 250-750nm. The reaction follows Michaelis-Menten Kinetics and the light irradiation increases the overall rate of hydrolysis. Using Lineweaver-Burk plot K M and V max values for the reaction in presence of light are found to be 39.07 and 66.67mM/min/g, respectively; while for the same reaction under dark condition, the values are 7.08 and 10.21mM/min/g. The linear form of enzyme dependent rate of reaction confirms that no mass-transfer limitations are present and the reaction is a kinetically controlled enzymatic reaction.

State of the components of (K)(Ni)W/γ-Al2O3 catalysts as oxide precursors and after water-gas shift reaction in the presence of sulphur

A W/γ-Al2O3 system doped with K and/or Ni has been synthesized by consecutive incipient wetness impregnation. The state of the components was characterized by XRD, UV–vis–NIR, XPS, and EPR spectroscopy as well as by means of N2 physisorption. A variety of surface species was available after calcination, such as monotungstate (WO4) and polymeric monolayers (WO6)n with incorporated Ni2+ or K+ ions or more complex NiWO(Al) and KNiWO(Al). Presulphided samples were investigated in the water-gas shift (WGS) reaction in presence of sulphur in the feed. In case of H2S-free feed, catalyst deactivation readily occurred. W4+, W5+, and W6+ oxidation states as well as different sulphur-containing species like paramagnetic sulphur, sulphide sulphur, oxysulphides and sulphate sulphur were registered on the surface after catalytic activity tests with sulphur present in the feed. Both tungsten reducibility and sulphur stability to oxidation represent informative indices related to the catalytic properties of γ-Al2O3-supported tungsten system, doped with Ni and K, in the WGS reaction. The tricomponent KNiW system exhibited these features to a moderate extent thus leading to its highest catalytic performance that allowed attaining equilibrium values at high temperatures.

CO- and NO-Induced Disintegration and Redispersion of Three-Way Catalysts Rhodium, Palladium, and Platinum: An ab Initio Thermodynamics Study

Disintegration of supported nanoparticles (NPs) in the presence of reactants can lead to catalyst deactivation or be exploited to redisperse sintered catalysts. To better understand the stability of TiO2(110)-supported three-way catalysts Rh, Pd, and Pt NPs during NOx and CO reduction, we present an ab initio thermodynamics study of the feasibility for these NPs to disintegrate into adatom-reactant complexes across a large parameter space of temperatures, pressures, and sizes. The tendencies for disintegration and redispersion between supported Rh, Pd, and Pt NPs are established. Compared to both Pd and Pt, Rh NPs are found to be more susceptible to either NO- or CO-induced disintegration, due to the large and exothermic formation energy of the Rh adatom complexes. Moreover, NO is a more efficient reactant for particle redispersion than CO. These findings provide valuable insights for how to either prevent reactant-induced NP disintegration or facilitate reactant-induced redispersion of sintered catalysts.

Thermal cracking of free fatty acids in inert and light hydrocarbon gas atmospheres

The aim of this work was to study the pyrolytic conversion of free fatty acids to renewable hydrocarbons in the presence of short-chain alkane and alkene hydrocarbon gases. Oleic acid (cis-9-octadecanoic acid) was used as model for fatty acids produced from hydrolysis of lipids from animal and plant feedstock. Batch pyrolysis reactions were conducted at 410°C for 2h at an initial pressure between 130psi (896.3kPa) and 500psi (3447.4kPa) under constant agitation. Identification and quantification of the pyrolysates in the gas and liquid phase were carried out using gas chromatography and mass spectrometry. Under inert N2 atmosphere liquid product yields were between 74 and 81wt% of feed with lower pressure giving the highest product yields. Liquid product was composed mainly of alkanes and alkenes ranging in carbon number from 6 to 19 and fatty acids from carbon numbers 4 to 18. Pyrolysis reactions conducted in the presence of short-chain alkane gases did not appreciably influence the liquid product yield and the composition compared to the inert atmosphere. On the other hand, pyrolysis reaction in presence of short-chain alkene gases resulted in a marked increase in the liquid product yield, the production of branched alkanes and alkenes and increased fatty acid decarboxylation. This work demonstrates a novel approach to concurrently increase the liquid product yield in pyrolysis of free fatty acids and produce highly valuable branched hydrocarbons for fuel and solvent applications.

Poly(pyrrole) films efficiently electrodeposited using new monomers derived from 3-bromopropyl-N-pyrrol and dihydroxyacetophenone—Electrocatalytic reduction ability towards bromocyclopentane

Three monomers 6-[3′-N-pyrrolpropoxy]-2-hydroxyacetophenone (1), 5-(3′-N-pyrrol propoxy)-2-hydroxyacetophenone (2) and 4-(3′-N-pyrrolpropoxy)-2-hydroxyacetophenone (3) were synthesized and their poly(pyrrole) films were electrodeposited on glassy carbon (GC) and Indium tin oxide (ITO) conductive electrodes by anodic oxidation in acetonitrile solutions containing n-Bu)4N+ClO4− (TBAP 0.1M). These films, currently called modified electrodes (noted ME), were obtained by the successive cycling at the appropriate potentials. These films contain chelating sites such as carbonyl group bearing the phenolic function which could play an important role in coordination chemistry. The electrodeposited poly(pyrrole) films on the ITO conductive glass electrodes offer some analytical advantages as the optical and electronic properties. Consequently, these new materials of electrodes were characterized by cyclic voltammetry while the morphology of these films was studied by FT-IR spectroscopy, scanning electron microscopy (SEM), dispersive energy X-ray spectroscopy and atomic force microscopy (AFM). The AFM studies show that the morphology of polypyrrole (PPy) films, electrodeposited on ITO surface, depends on the specific structure of the compound deriving from the monoalkylated dihydroxyacetophenone 1, 2 and 3. The coordination of copper was performed by electroreduction reaction in presence of ligand (3) and copper acetate salt. The resulting electrode material was tested towards the electrocatalytic activity in the reduction of bromocyclopentane.

First satellite detection of volcanic OClO after the eruption of Puyehue‐Cordón Caulle

AbstractVolcanoes release large amounts of halogen species such as HCl and HBr, which can be converted into reactive halogens by heterogeneous photochemical reactions that are currently not fully characterized. Here we report on the first satellite detection of volcanic chlorine dioxide (OClO). Measurements were performed using the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography instrument for the ash‐laden plume emitted after the 2011 eruption of Puyehue‐Cordón Caulle in Chile. We also identified volcanic BrO using the Ozone Monitoring Instrument, as well as enhanced HCl in data of the Microwave Limb Sounder instrument. These observations suggest that OClO was formed in the plume by the ClO + BrO reaction in presence of a large excess of ClO. The present satellite data set could help better understand reactive halogen chemistry in volcanic plumes and its impact on atmospheric composition.

A Comparative Study on the Textile Effluent Decolourization by Using Synthesized Nano Particle and Procured Nano Particle

Semiconductor photocatalysis often leads to partial or complete mineralization of organic pollutants. Upon irradiation with UV/visible light, semiconductors catalyze redox reactions in presence of air/O 2 and water. Here, the potential of a common semiconductor, ZnO, has been explored as an effective catalyst for the photodegradation of textile effluent. The effects of process parameters like, catalyst loading, initial dye concentration and pH on the extent of photo degradation have been investigated. It is difficult to give a general picture of the kinetics using these wastewaters but the process was found to be quite effective for the decolourization of textile waste water. In this work, a detailed investigation was done on photocatalytic degradation for selected textile effluent. The ZnO nano particle was synthesized by using fuel urea by solution combustion method. This nano particle was characterized by using X-ray diffraction (XRD), Scanning Electron Micrograph (SEM) and UV absorbance spectroscopy. The average size was found to be 41 nm. The band gap of the nano particle was found to be 3.2 eV and was tested for the photocatalytic degradation by varying parameters such as catalyst concentration, pH and dye concentration. Also, the efficiency of the synthesized nano particle was compared with the procured TiO 2 of size < 25 nm.

Proton conductive membranes based on poly(styrene-co-allyl alcohol) Semi-IPN

The optimization of fuel cell materials, particularly polymer membranes, for PEMFC has driven the development of methods and alternatives to achieve systems with more adequate properties to this application. The sulfonation of poly (styrene-co-allyl alcohol) (PSAA), using sulfonating agent:styrene ratios of 2:1, 1:1, 1:2, 1:4, 1:6, 1:8 and 1:10, was previously performed to obtain proton conductive polymer membranes. Most of those membranes exhibited solubility in water with increasing temperature and showed conductivity of approximately 10-5 S cm-1. In order to optimize the PSAA properties, especially decreasing its solubility, semi-IPN (SIPN) membranes are proposed in the present study. These membranes were obtained from the diglycidyl ether of bisphenol A (DGEBA), curing reactions in presence of DDS (4,4-diaminodiphenyl sulfone) and PSAA. Different DGEBA/PSAA weight ratios were employed, varying the PSAA concentration between 9 and 50% and keeping the mass ratio of DGEBA:DDS as 1:1. The samples were characterized by FTIR and by electrochemical impedance spectroscopy. Unperturbed bands of PSAA were observed in the FTIR spectra of membranes, suggesting that chemical integrity of the polymer is maintained during the synthesis. In particular, bands involving C-C stretching (1450 cm-1), C=C (aromatic, ~ 3030 cm-1) and C-H (2818 and 2928 cm-1) were observed, unchanged after the synthesis. The disappearance or reduction of the intensity of the band at 916 cm-1, attributed to the DGEBA epoxy ring, is evidenced for all samples, indicating the epoxy ring opening and the DGEBA crosslinking. Conductivity of H3PO4 doped membranes increases with temperature, reaching 10-4 S cm-1.

Synthesis and Characterization of ethyl 4-(4-(benzyloxy) phenyl) -6-methyl-2-oxo-1,2,3,4- tetra hydro pyrimidine-5-carboxylate for Antioxidant and Radioprotective Activities

A novel pyrimidine derivative ethyl 4-(4-(benzyloxy)phenyl)-6-methyl-2-oxo-1,2,3,4- tetra hydro pyrimi- dine-5-carboxylate (4) was synthesized by Biginelli three component cyclocondensation reaction in presence of a catalyst SiCl4 in good yield and characterized by IR, 1 H NMR, 13 C NMR, LCMS and elemental analysis. The compound 4 was screened for in vitro antioxidant activity using DPPH radical, hydroxyl radical scavenging assay. The in vivo radioprotection property of compound 4 was determined by assaying on Drosophila melanogaster model system; inducing oxidative stress in flies at 3Gy electron beam irradiation. The flies treated with the compound prior to irradiation showed reduction in oxidative stress caused by ionizing e-beam radiation.

Evaluating tyrosinase (monophenolase) inhibitory activity from fragrant roots of Hemidesmus indicus for potent use in herbal products

Root organs of Hemidesmus indicus are traditionally known for multipurpose medicinal applications. Root extracts of H. indicus contained 2-hydroxy-4-methoxybenzaldehyde (MBALD) as principal fragrant phenolic compound. This methoxybenzaldehyde was shown to have inhibitory potential against diphenolase activity of the tyrosinase. The present work explored the effects of this MBALD (both in crude extracts and pure forms) on the monophenolase activity. The lag time of reaction and the activity of monophenolase were affected upon supplementation of methoxybenzaldehyde. The increase in lag time indicated an inhibition of monophenolase activity which subsequently led to the reduction in total tyrosinase activity. MBALD was shown to be more potent than vanillin in inhibiting monophenolase activity. Inhibition kinetic analysis confirmed the same observation, with a higher Km value (0.395mM) was determined for monophenolase reaction in presence of MBALD as compared to Km value of tyrosinase without any inhibition. As compared to pure MBALD, the crude root extract of H. indicus showed greater inhibition against monophenolase activity, which was also evidenced from the extension in lag time. This indicates its potential application in herbal products.

An inhibitory effect of self-assembled soft systems on Fenton driven degradation of xanthene dye Rhodamine B

Rhodamine B (RhB) is known to be a common organic pollutant despite having various technical applications. Treatment of effluents containing such compounds is important so as to minimize their effect on environment. Advanced Oxidation Processes (Fenton and Fenton like reactions) are such methods that can oxidize the contaminants powerfully and non-selectively. This work investigates the oxidation kinetics of dye RhB by hydroxyl radical (OH) generated via Fenton reaction in presence of surfactant assemblies of varying architectures using spectrophotometric, spectrofluorometic and tensiometric methods. The presence of surfactants viz. cationics, non-ionics and some binary mixtures in the pre-micellar and post micellar concentration ranges were found to inhibit the degradation of RhB to a varying degree. However, the reaction was totally inhibited in anionic surfactant. The experimental data was fitted to a pseudo first order kinetic model and the kinetic parameters obtained thereof were explained on the basis of the nature and type of interaction between the cationic form of RhB and the surfactants of varying architectures. The work has a critical significance in view of the fact that degradation studied in presence of surfactant assemblies is more representative than studied in aqueous solution because such conditions compare well with the conditions prevailing in the environment.

In Situ Imaging of Cu2O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer

Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of in situ microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst's chemical state and morphology are dynamically modified. The reduction of Cu2O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution in situ imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces.