Silver-catalysed Oxidation Research Articles

Kinetics of Silver-Catalysed Oxidation of Formamide by Potassium Peroxydisulphate

Kinetics of Silver-Catalysed Oxidation of Formamide by Potassium Peroxydisulphate

Structural Inhibition of Silver Surface Oxidation

Surface structure and oxidation are key to silver-based heterogeneous catalysis. Prevention of surface reconstruction may favor electrophilic oxygen, which is believed to be the active species in silver-catalyzed oxidation. To determine whether terrace width or step geometry enables control of oxidation and concomitant reconstruction, we investigated oxidation of the topmost layer of a curved Ag(111) crystal. This crystal contains a range of terrace widths having either A- or B-type step geometries. Atomic oxygen was used to facilitate oxidation, temperature-programmed desorption quantified the extent of oxygen adsorption, and scanning tunneling microscopy characterized the formation of reconstructed areas. While A-type steps prove to have little influence, B-type steps hinder reconstruction. We attribute the difference to geometric-dependent growth mechanisms of silver oxide surface reconstructions.

Portable solid sensor supported in nylon for silver ion determination: testing its liberation as biocide.

This paper reports the fabrication and utility of a new solid sensor, which allows the quantitation of silver ions acting as catalyst at the low micromolar level. The optical sensor was prepared by incorporating both reagents, pyrogallol red (PGR) and 1,10-phenanthroline (Phen), in a nylon membrane. The effect of parameters in determining silver-catalyzed oxidation of PGR by persulfate in the presence of Phen as an activator was studied and optimized for achieving suitable sensitivity. Semiquantitative analysis can be performed by visual inspection of the color of the sensor by comparing it with standard responses and quantitative analysis can be carried out by its diffuse reflectance (DR) measurement or by a digital image-processing tool (GIMP) using a smartphone. The sensor exhibited a linear relationship toward Ag(I) concentrations ranging from 0.4 to 10μM or 1-25μM and limits of detection of 0.1μM or 0.3μM for incubation times of 50 and 30min, respectively. The relative standard deviation achieved for several batches of sensors was around 2%. The analysis of water samples from tap and refrigerating circuits containing solid biocides, which leach silver ions, prove that this portable and sustainable sensor is successfully operational in real situations. Graphical abstract.

Mechanistic insights into the selective oxidation of 5-(hydroxymethyl)furfural over silver-based catalysts

Silver-catalyzed oxidation of 5-(hydroxymethyl)furfural (HMF) to 5-hydroxymethyl-2-furancarboxylic acid (HFCA) was investigated using in situ X-ray absorption spectroscopy under reaction conditions over Ag/ZrO2 and Ag/TiO2 catalysts.

Silver-Catalyzed Oxidation of Atropine Drug by Cerium(IV) in Aqueous Perchlorate Solutions: A Kinetics and Mechanistic Approach

The kinetics of oxidation of atropine drug (ATR) by cerium(IV) in aqueous perchlorate solutions in the presence of silver(I) catalyst has been studied spectrophotometrically at a constant ionic strength and temperature. The reaction showed first order dependence with respect to each [Ce(IV)] and [Ag(I)], and less than unit order kinetics with respect to [ATR]. The reaction exhibited negative fractional-first order kinetics with respect to [H+]. Increasing ionic strength and dielectric constant of the medium increased the reaction rate. In the present work, the kinetically active species of cerium(IV) was found to be Ce(OH)3+. Addition of Ce(III) product had no significant effect on the oxidation rate. The oxidation products of atropine were identified by spectral and chemical analyses as tropine, benzaldehyde, methanol and carbon dioxide. A plausible mechanistic scheme for the catalyzed oxidation was proposed. The activation parameters of the second order rate constant were calculated and the rate law associated with the reaction mechanism was derived.

Phenoxazine dyes in zeolite L, synthesis and properties

The preparation and characterisation of brightly luminescent dye-zeolite L host–guest microcrystals and of nitro, amino, N-acetyl, and N-alkyl phenoxazine dyes is reported. The synthesis of 3-ethylamino-7-ethyliminophenoxazinium nitrate ( 9) is based on five steps including simple and highly efficient silver-catalysed oxidation at room temperature, which can also be used to synthesise oxonine ( 6). 6 and 9 are inserted in about 1.5 μm long zeolite L crystals by means of ion exchange. The former from an aqueous suspension and the latter from 1-butanol by applying a selective ionophore. The orientation of the electronic transition dipole moment of 9 inside of the linear channels of zeolite L, as observed by fluorescence microscopy, is compared with that of four other selected dye-zeolite L microcrystals.

Silver-Catalyzed Oxidation of Ethylene to Ethylene Oxide in a Microreaction System

Ethylene oxide synthesis has been chosen as a benchmark case to evaluate the performance of a microreaction system in comparison to an existing industrial process. This reaction was selected becaus...

Chlorine promoters in selective ethylene epoxidation over Ag(111): A comparison with Ag(110)

Chlorine promoters are added in the silver-catalyzed oxidation of ethylene (C 2H 4 + 1 2 O 2 → C 2H 4O) in order to improve the selectivity for ethylene epoxide production. We have recently (Campbell, C. T., and Paffett, M. T., Appl. Surf. Sci. 19, 28, 1984; Campbell, C. T., and Koel, B. E., J. Catal. 92, 272, 1985) modeled the role of chlorine promoters in this reaction by depositing chlorine adatoms onto the Ag(110) surface in ultrahigh vacuum (UHV) and monitoring the resultant effects on the medium-pressure (~1 atm) kinetics of the epoxidation reaction. This was accomplished with an apparatus that allowed rapid (<20 s) transfer of the model catalyst between the UHV chamber for surface analysis (XPS, AES, LEED, AES) and a high-pressure microreactor for kinetics. That work led to a detailed picture of the role of chlorine promoters in this reaction. This present study is an extension of that work to include the Ag(111) surface, which behaves much differently than Ag(110) in dissociative oxygen adsorption [(a) Campbell, C. T., Surf. Sci. 157, 43, 1985; (b) Campbell, C. T., submitted for publication but nevertheless displays very similar catalytic behavior for this reaction (Campbell, C. T., J. Catal. 94, 436, 1985). The results indicate that the effects of chlorine addition are very similar on Ag(111) and (110). They can be explained with the same reaction mechanism involving adsorbed oxygen and ethylene. The steady-state atomic oxygen coverage (under catalytic reaction conditions) goes through a large maximum with chlorine coverage on Ag(111), not seen with Ag(110). This is due to the very low reactivity of atomic oxygen on Ag(111) in the presence of chlorine. Evidence is presented that suggests that the standard method of measuring the Ag surface area of supported catalysts via oxygen chemisorption is very unreliable.

Study of the silver-catalysed pyrogallol red-peroxodisulphate reaction with 1,10-phenanthroline as activator by a kinetic-spectrophotometric method

The kinetics of the uncatalysed and silver-catalysed oxidation of pyrogallol red (PGR) by peroxodisulphate in the presence of 1,10-phenanthroline (phen) as an activator were investigated. Rate equations for these reactions were derived from the kinetic dependences on hydrogen ion and reagent concentrations. The rate constants and the orders of reaction were also calculated. A kinetic model is proposed. The optimum conditions for silver(I) determination are as follows: pH 2.0 (in a sulphuric acid medium); S2O82–, 2 × 10–2 mol dm–3; phen, 8 × 10–3 mol dm–3; PGR, 3 × 10–5 mol dm–3; and temperature, 25 °C. Under these conditions and using the fixed time and initial rate methods, silver can be determined in the range 0.85–21.36 ng ml–1. The regions of analyte measurement are as follows: analyte not detected, 0.88 ng ml–1 of silver(I). The relative standard deviation of the method at a fixed time of 300 s was 3.9–1.4% for silver concentrations from 0.85 to 15.10 ng ml–1. The influence of 25 foreign species was investigated.

Catalytic titration of iodide, bromide and thiocyanate by use of the silver catalysed phloxin-persulphate reaction

A method for the catalytic titrimetric determination of iodide, bromide and thiocyanate is described, based on the inhibitory effect of these anions on the silver-catalysed oxidation of phloxin by persulphate in the presence of 2,2'-bipyridyl. The end-point is determined photometrically by measuring the absorbance at 537 nm. Amounts of iodide, bromide and thiocyanate in the 0.01-7.94, 0.11-4.73 and 0.12-3.59mg ranges, respectively, are titrated with a relative error of about 1%.

Kinetic Study of Silver-Catalysed Oxidation of α-Hydroxy Monocarboxylic Acids - dl-Atrolactic, Isobutyric, Mandelic and Benzilic Acid by Potassium Peroxydisulphate

Kinetic Study of Silver-Catalysed Oxidation of α-Hydroxy Monocarboxylic Acids - dl-Atrolactic, Isobutyric, Mandelic and Benzilic Acid by Potassium Peroxydisulphate

Kinetics of Silver-Catalysed Oxidation of Propionamide by Potassium Peroxydisulphate

Kinetics of Silver-Catalysed Oxidation of Propionamide by Potassium Peroxydisulphate

Kinetics of Silver-Catalysed Oxidation of Dimethyl-Formamide by Potassium Peroxydisulphate

Kinetics of Silver-Catalysed Oxidation of Dimethyl-Formamide by Potassium Peroxydisulphate

Reaction products in the silver-catalyzed oxidation of ethylene

The kinetics of the complete oxidation of ethylene oxide over a supported silver catalyst in the absence of dichloroethane was studied by the flow circulation method. The temperature range 100–300°C was investigated under steady-state conditions and at atmospheric pressure. The kinetic measurements showed that ethylene oxide oxidation starts at 190°C. Below this temperature, the ethene oxidation over a silver catalyst proceeds according to the parallel reaction scheme. At 300°C and an oxygen: ethylene oxide feed ratio of 1:2 catalytic decomposition of ethylene oxide to ethene and oxygen was observed. A sequential experimental design was applied for the determination of the parameters and the simultaneous discrimination of rival kinetic models. A kinetic model is proposed that describes the rate of uninhibited ethylene oxide oxidation in the temperature range 250–300°C. The model corresponds to a mechanism in which ethylene oxide and oxygen adsorption (dissociative and non-dissociative) are fast steps at equilibrium. The rate-limiting steps are ethylene oxide oxidation to formaldehyde and further to carbon dioxide and water with the participation of both atomic and molecular adsorbed oxygen. These steps are irreversible. The calculated kinetic constants offer the possibility of evaluating tentatively the rate constants of the irreversible steps and the equilibrium constants of the fast reversible steps.

Kinetics of Silver-Catalysed Oxidation of Ethylene Glycol by Peroxydisulphate Ion-Part I.

Kinetics of Silver-Catalysed Oxidation of Ethylene Glycol by Peroxydisulphate Ion-Part I.

The geometric factor in ethylene oxidation over gold-silver alloy catalysts

The gold-silver alloy system was chosen for a study of the effect of the geometric factor in the silver-catalyzed oxidation of ethylene because of the known promoting ability and inertness for oxygen chemisorption of metallic gold. Alloys with gold contents of 0, 5, 15, 30, 45, 60, and 80 atom % were prepared by a chemical reduction technique and examined for catalytic activity for ethylene oxidation in a microreactor assembly coupled to a gas chromatography unit. Dynamic adsorption measurements and lattice parameter measurements were also performed on the alloy samples. The results of these studies show that activity for overall ethylene oxidation over gold-silver alloys is dependent on lattice spacing, and that gold, at low concentrations, is a promoter for ethylene oxide formation, markedly improving ethylene oxide selectivity even though conversion falls off somewhat. Activation energy values indicate that the number of active sites decreases as gold concentration increases. Oxidation activity appears to be related to surface sites having fairly low adsorption energies for oxygen. Ethylene adsorption was found to be relatively unimportant.

Kinetics of Silver-catalysed Oxidation of Tl(l) by Persulphate

Kinetics of Silver-catalysed Oxidation of Tl(l) by Persulphate

Oxidation by persulphate. Part V. Silver-catalysed oxidation of secondary aliphatic amines and α-amino-acids

Silver-catalysed oxidation by cold aqueous persulphate, which converts primary aliphatic amines into aldehydes or ketones, gave poorer yields when applied to related secondary amines of the types (RCH2)2NH and (R1R2CH)2NH. α-Amino-acids were converted into aldehydes, but the yields were not better than with other inorganic oxidants.

Oxidation by persulphate. Part IV. Silver-catalysed oxidation of primary aliphatic amines

Oxidation of a primary aliphatic amine, RCH2·NH2, by aqueous persulphate under alkaline conditions and in the presence of a catalytic amount of silver nitrate, gave the aldimine, RCH:N·CH2R, which was subsequently hydrolysed to the aldehyde, RCHO, and the original amine, or was hydrogenated to the corresponding secondary amine, (RCH2)2NH. The yield of aldehyde varied from 15 to 95% among C3—C9 amines, and the conversion was favoured by branching in the alkyl chain or by the presence of an α-phenyl group. Under similar conditions, a primary amine of the type R1R2CH·NH2 was converted into the ketone, R1R2CO, without separation of the ketimine. Primary amines of the type R1R2R3C·NH2 were unchanged. Secondary reactions may complicate the oxidations.

THE ROLE OF REACTION PRODUCTS IN THE SILVER-CATALYZED OXIDATION OF ETHYLENE

Initial-rate studies of the kinetics of the silver-catalyzed oxidation of ethylene oxide and carbon dioxide in a flow system have been made. It was found that, using carefully purified reactants, the effect of added carbon dioxide was to suppress the formation of ethylene oxide only. The initial rate of the formation of ethylene oxide is given by the equation[Formula: see text]where r0 is the initial rate in the absence of CO2; m, n, and k are constants with m + n = 1.These results together with the results of oxygen exchange reactions between O18 and C2H4O16, CO216 and H2O16 are interpreted mechanistically.