Catalytic Oxidation Of Ammonia Research Articles

Reactivity and catalytic activity of layered YBa2Cu3O7-δ (123) type defect perovskites

The chemical modifications of structure, reactivity and catalytic properties of layered triple perovskite oxides, related to the YBa2Cu3O7-δ (123) system, have been briefly reviewed. These oxides form a versatile family of materials with wide-ranging chemical and physical properties. The multiple sites available for chemical doping, and the ability to reversibly intercalate oxygen at the defect sites have rendered these oxides important model systems in the area of oxide catalysis. An attempt has been made to comprehend the hitherto known catalytic reactions and correlate them to various factors like structure, oxygen diffusional limitations, different geometries adopted by various substituents, oxidative non-stoichiometry and activation energy for oxygen desorption. In particular, results on the enhanced catalytic activity of cobalt-substituted 123 oxide systems towards the selective catalytic oxidation of ammonia to nitric oxide and carbon monoxide to carbon dioxide are presented.

ChemInform Abstract: The Catalytic Oxidation of Ammonia in a Ceramic Electrochemical Reactor, Using Metal Oxide Electrodes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Catalytic Oxidation of Ammonia in a Ceramic Electrochemical Reactor, Using Metal Oxide Electrodes

The oxidation of ammonia to nitric oxide can be realized in a ceramic electrochemical reactor. Electrochemical control of the catalytically active electrode allows for an increased selectivity to the products of interest. This work examines the effect of metal oxide electrodes as catalysts for the above reaction. When Co 3O 4 was used, for example, control of the material could be realized and a more active catalytic species could be produced. Co 3+ was postulated to be a very active species for the reaction and as such its stabilization by an applied potential allowed for an increased selectivity to nitric oxide.

Design and fabrication of an automated thermal desorption gas-solid reaction system: Oxidation of ammonia and methanol over YBa2Cu3O7−δ(123) oxide systems

A fully automated, versatile Temperature Programmed Desorption (TDP), Temperature Programmed Reaction (TPR) and Evolved Gas Analysis (EGA) system has been designed and fabricated. The system consists of a micro-reactor which can be evacuated to 10−6 torr and can be heated from 30 to 750°C at a rate of 5 to 30°C per minute. The gas evolved from the reactor is analysed by a quadrupole mass spectrometer (1–300 amu). Data on each of the mass scans and the temperature at a given time are acquired by a PC/AT system to generate thermograms. The functioning of the system is exemplified by the temperature programmed desorption (TPD) of oxygen from YBa2Cu3−xCoxO7 ± δ, catalytic ammonia oxidation to NO over YBa2Cu3O7−δ and anaerobic oxidation of methanol to CO2, CO and H2O over YBa2Cu3O7−δ (Y123) and PrBa2Cu3O7−δ (Pr123) systems.

Molybdena on silica catalysts: selective catalytic oxidation of ammonia to nitrogen over MoO 3 on siO 2 catalysts

MoO 3 on SiO 2 catalysts are suitable for the selective oxidation of ammonia into nitrogen (N 2) and water. The catalysts were prepared by homogeneous deposition precipitation using electrochemically reduced precursors. The experiments were carried out at atmospheric pressure and at temperatures ranging from 200 to 400 °C. Nitrogen and water yields of up to 100% at temperatures over 375 °C were obtained when ammonia and excess oxygen in helium were passed over a MoO 3 on SiO 2 catalyst. Catalysts containing less than 15 wt.% MoO 3 gave rise to no conversion of ammonia. The presence of small amounts of lead in the catalyst appeared to influence the conversion of NH 3 in a positive way. However, the presence of nitric oxide in the feed did not influence either the conversion of ammonia or the selectivity to nitrogen. The nitric oxide concentration remained constant during the conversion of ammonia. The results indicate that species reducible by hydrogen at 540 °C are related to the activity of the catalysts.

CARS Spectroscopy of Ammonia in the Laboratory and a Commercial Scale Ammonia Oxidation Plant

CARS spectra of NH3 have been obtained from a commercial catalytic ammonia oxidation plant operating at ∼10 atmospheres (absolute) and 250°C. A purpose-designed ruggedized CARS spectrometer—incorporating a novel dye laser, remote control, and fiber optic signal transfer—is described. A new and simple technique for CARS concentration analysis using polarized beams gave a precision of 5.9% for NH3 from single-shot spectra under laboratory conditions. Unfortunately, severe beam steering problems were encountered in the full-scale plant; this prevented a quantitative analysis of the spectra obtained. The origins of this problem together with suggestions for overcoming or reducing its effect are given.

The tetraammine copper(II) complex in zeolite Y. A Raman spectroscopic study

This preliminary report indicates that, by careful manipulation of metal-zeolite complexes, it is possible to obtain bonding information by spontaneous Raman spectroscopy. The copper-amine was chosen for study because of the extensive EPR and electronic spectroscopic information on these complexes in zeolites. Also, these complexes are active intermediates in the catalytic oxidation of ammonia. It is important to point out that IR spectroscopy of these systems is not very valuable in the low-frequency region, where metal-ligand virations are expected. 17 references, 2 figures.

Free radical formation in the catalytic oxidation of ammonia over a polycrystalline platinum surface at high temperatures

Etude de 800 a 1400 K. On n'a pu deceler que les especes NH et OH. On propose un mecanisme atome/radical pour l'oxydation de NH 3

ChemInform Abstract: Catalytic Oxidation of Ammonia. Part 4. Low Temperature Oxidation on a Nickel Oxide Catalyst Supported on Alumina.

Chemischer InformationsdienstVolume 14, Issue 36 Preparative Organic Chemistry ChemInform Abstract: Catalytic Oxidation of Ammonia. Part 4. Low Temperature Oxidation on a Nickel Oxide Catalyst Supported on Alumina. M. M. GIRGIS, M. M. GIRGISSearch for more papers by this authorD. P. LAZAR, D. P. LAZARSearch for more papers by this authorE. I. SEGAL, E. I. SEGALSearch for more papers by this author M. M. GIRGIS, M. M. GIRGISSearch for more papers by this authorD. P. LAZAR, D. P. LAZARSearch for more papers by this authorE. I. SEGAL, E. I. SEGALSearch for more papers by this author First published: September 6, 1983 https://doi.org/10.1002/chin.198336142AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue36September 6, 1983 RelatedInformation

Non-isothermal kinetic study of catalytic ammonia oxidation

Non-isothermal kinetic study of catalytic ammonia oxidation

Optimization of Catalytic Oxidation of Ammonia over a Platinum Gauze Pad

Optimization of Catalytic Oxidation of Ammonia over a Platinum Gauze Pad

Modeling of Catalytic Oxidation of Ammonia over a Platinum Gauze Pad

Modeling of Catalytic Oxidation of Ammonia over a Platinum Gauze Pad

Initial activation of platinum-rhodium gauzes for the catalytic oxidation of ammonia

Studies have been made of the activation of platinum-rhodium gauze catalysts for the oxidation of ammonia, using optical microscopy, electron probe microanalysis (EPMA), and electron spectroscopy to characterize the surfaces. The initial washing procedure is found to remove calcium and to reduce carbon residues on the surface, as a result of which the catalyst is active at lower temperatures. Subsequent activation in a hydrogen flame or in oxygen causes surface rearrangements and results in rhodium enrichment at the surface: this latter trend is partially reversed in the early stages of the oxidation of ammonia. Water vapor is found to deactivate the activated gauze.

Energy dissipation and selectivity in the catalytic oxidation of ammonia

A qualitative interpretation of selectivity changes in ammonia oxidation, based on considerations of energy dissipation processes is presented.

Oscillatory phenomena during ammonia oxidation in the presence of a PtRh catalyst

The paper describes oscillatory phenomena observed during ammonia oxidation on a PtRh catalyst in a single pellet reactor. The phenomena consist in periodical changes of the catalyst temperature and a periodical initiation of the reaction in the gas phase. They are interpreted via coupling of the catalytic dissociation and homogeneous oxidation of ammonia.

X-ray photoelectron spectroscopy and electron microscopy of PtRh gauzes used for catalytic oxidation of ammonia

Scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and sputtering techniques are used to study platinum-rhodium gauzes working in industrial burners for ammonia oxidation. Electron microscopy shows that during the combustion, two distinct crystalline systems develop, namely, small rhodium-rich crystals and large platinum-rich geometric crystals with well-developed facets. Chemical analysis of the surface by XPS associated with ion sputtering shows that the catalyst deactivation may be caused by the segregation of rhodium at the surface, resulting from the volatilization of platinum oxide at high temperature after the oxidation of Rh and Pt. The small rhodium-rich crystals are identified as Rh 2O 3 and the oxidation ratio ( Rh 2O 3 Rh + Rh 2O 3 ) varies with the location of the gauzes in the catalytic pack: it is 0.2 at the head of the reactor and reaches up to 0.8 in the tail.

Oberflächenveränderungen an Pt-Rh-netzen bei der katalytischen oxidation von ammoniak

E. Raub has indicated that the surface of metals and alloys pertaining to the platinum metals group show a new profile after annealing at high temperatures in an atmosphere under the influence of oxygen. Dunken gives a quantum-chemical model of the corrosive adsorption. This reformation of the surface is also observed on PtRh gauze wires which are used for the catalytic oxidation of ammonia with atmospheric oxygen, to nitric oxide and then to nitric acid. The extent of the surface alteration in gauze wires will largely depend on catalytic reactions.

Catalytic oxidation of ammonia: II. Relationship between catalytic properties of substances and surface oxygen bond energy. General regularities in catalytic oxidation of ammonia and organic substances

Catalytic activity and selectivity of oxides of cobalt, manganese, copper, iron, vanadium and molybdenum with respect to ammonia oxidation to N 2 and N 2O have been studied. The activity decreases in the above-mentioned sequence of oxides. The specific activity of metallic platinum is much higher than that of the most active oxide catalysts. Generally, the selectivity towards mild oxidation (the formation of N 2) increases with decreasing activity of oxides. On the basis of the reaction mechanism proposed in the previous paper (Part I) the relationship between surface oxygen bond energy, q s , and catalytic behavior of oxides has been deduced theoretically. Catalytic activity, r, is expected to pass through a maximum which corresponds to low values of q s . For the majority of catalysts the activity must decrease with increasing q s . At the same time the selectivity for the formation of N 2 must increase while the selectivity for N 2O must fall. The experimental data obtained confirm these conclusions. In accordance with the theory, for the high temperature oxidation of ammonia to NO the selectivity in NO decreases with increasing q s . The following rule has been stated: more oxygen-catalyst bonds are broken in the formation of the activated complex of a stage leading to a deep oxidation product than in the formation of a mild oxidation product. This gives rise to an increase in selectivity in mild oxidation with q s . The above rule has been shown to be rather general and also applicable to the oxidation of organic substances. Thus, the similarity between selective oxidation of ammonia and organic molecules has been found. Some general regularities concerning heterogeneous catalytic oxidation are formulated.

Catalytic oxidation of ammonia: I. Reaction kinetics and mechanism

The kinetics of ammonia oxidation over oxides of manganese, cobalt, copper, iron and vanadium have been studied. The proposed reaction mechanism involves oxygen adsorption (oxidation of the catalyst surface) and reduction of the surface with ammonia to form the reaction products. The latter step consists of several stages involving the intermediate formation of nitroxyl and imide species. The interaction of imide with nitroxyl leads to nitrogen while the reaction between two nitroxyls results in nitrous oxide. For this model rate equations have been deduced which describe the overall process and the parallel reactions of the formation of N 2 and N 2O. These equations are shown to be in accordance with the experimental data obtained. It has been found that the selectivity in mild oxidation (N 2 formation) decreases and the selectivity in deep oxidation (N 2O formation) grows with an increase in the surface coverage with oxygen θ. The values of θ increase with the ratio of partial pressures of O 2 to NH 3 ( P O 2 P NH 3 ) in the reaction mixture. The governing role of θ has been supported by experiments in which catalysts were reduced with ammonia in the absence of O 2 in the gas phase. The reaction mechanism involving the formation of N 2, N 2O and NO is also considered. The corresponding rate equations have been derived, and the expected dependence of specificity on the reaction mixture composition and temperature has been examined.

Interpretation of some aspects of catalytic oxidation of ammonia and propylene by semiconducting oxides in terms of volcano-shaped plots

It has been shown that the activity spectrum of oxides towards oxidation of ammonia, when plotted against the heats of atomisation per equivalent (i.e. values of the average bond energies) of oxides, gives volcano-shaped plots. The significance of these correlations has been interpreted in terms of Sabalier-Balandin ideas of heterogeneous catalysis. The mechanistic significance of these volcano correlations has also been discussed qualitatively.