Showing papers on "Chemical decomposition published in 1991"
TL;DR: In this paper, the present position of decomposition catalysts is mentioned and the catalytic performance of copper ion-exchanged zeolites and Ag-Co3O4 oxides is summarized based on the respective authors' results.
749 citations
TL;DR: Stability of the solid was optimal when produced from solutions in the pH range, 7–7.5, with severe aggregation being observed at high pH, and the observation that dextran 40 formulations showed poor stability toward aggregation demonstrates that an amorphous excipient system is not a sufficient condition for stability.
Abstract: Formulation often has a dramatic effect on degradation of proteins during the freeze-drying process as well as impacting on the "shelf-life" stability of the freeze-dried product. This research presents the results of a formulation optimization study of the "in-process" and shelf-life stability of freeze-dried human growth hormone (hGH). Chemical decomposition via methionine oxidation and deamidation of asparagine residues as well as irreversible aggregation were characterized by HPLC assay methodology. In-process degradation and stability of low moisture freeze-dried solids were studied at 25 and 40 degrees C in a nominal nitrogen headspace (approximately 0.5% O2). Formulation variables included pH, level of salts, and the nature of the lyoprotectant. Studies of the effect of shear on aggregation in solutions indicated that shear comparable to that experienced during filtration does not induce aggregation. Irreversible changes in hGH during the freeze-drying process were minimal, but chemical decomposition via methionine oxidation and asparagine deamidation and aggregation did occur on storage of the freeze-dried solid. Decomposition via methionine oxidation was significant. A combination of mannitol and glycine, where the glycine remains amorphous, provided the greatest protection against decomposition and aggregation. It is postulated that an excipient system that remains at least partially amorphous is necessary for stabilization. However, the observation that dextran 40 formulations showed poor stability toward aggregation demonstrates that an amorphous excipient system is not a sufficient condition for stability. Stability of the solid was optimal when produced from solutions in the pH range, 7-7.5, with severe aggregation being observed at high pH. The level of sodium phosphate buffer affected stability of the solid, although this relationship was complex. Freeze-drying in the presence of NaCl produced severe aggregation and precipitation during the freeze-drying process as well as acceleration of oxidation and/or deamidation.
306 citations
TL;DR: In this article, a gas phase reaction of isocyanic acid with nitric oxide in the presence of various amounts of O2, H2O, and CO was studied.
Abstract: The RAPRENOx process for NO reduction in combustion products involves reaction of nitric oxide with isocyanic acid. We have developed a mechanism for the gas-phase reaction of isocyanic acid with nitric oxide in the presence of various amounts of O2, H2O, and CO. Kinetics calculations using the mechanism are compared with the experimental data of Siebers and Caton, and the model reproduces all trends of these data. Sensitivity and rate-of-production analyses show that the reactions of HNCO with OH, O, and H play a major role in the NO-removal process and that NO removal occurs primarily by reaction of NO with NCO to form N2O, which subsequently reacts slowly to form N2. The overall reaction is critically dependent on production of radicals. When O2, H2O, and CO are present, the radicals are supplied by the moist-CO chain branching sequence. When any of these species is absent, radicals must be supplied by other reactions, principally the N2O decomposition reaction and the reaction of the NH2 radical with NO.
156 citations
145 citations
TL;DR: In this article, a decomposition of ozone was carried out on metal oxide catalysts and the activity of these catalysts increased roughly in the order of the increase in their surface area and in the amount of surface oxygen on them.
Abstract: Decomposition of ozone was carried out on metal oxide catalysts. The activity of the metal oxide catalysts increased roughly in the order of the increase in their surface area and in the amount of surface oxygen on them. Conductance change of these metal oxides on an introduction of ozone suggested that negatively charged oxygen species were formed on their surface. The Ag catalyst showed the highest activity, and the reactivity of the oxygen species produced on the surface of Ag catalyst toward carbon monoxide was much higher than that of the oxygen species on Co, Ni, Fe, and Mn oxides
141 citations
TL;DR: In this paper, the first intermediate formed in the molecular oxygen reaction is chemisorbed O2(a), e.g., a peroxy radical or a peroxide bridge.
103 citations
TL;DR: In this paper, the authors measured the thermal decomposition of hexanitrohexazaisowurtzitane (HNIW) by the isothermal weight loss (TGA) and absorbance changes in the FTIR spectrum at 1 atm.
97 citations
TL;DR: In this article, the decomposition of hydrogen peroxide in high purity water at temperatures ranging from 100 to 280°C in a laboratory test loop has been investigated, and a first-order decomposition kinetics has been observed in all cases, but decomposition rates vary widely, depending on the material used in the reaction chamber.
Abstract: Decomposition of hydrogen peroxide in high-purity water has been measured at temperatures ranging 100 to 280°C in a laboratory test loop. A first-order decomposition kinetics has been observed in all cases, but the decomposition rates were found to vary widely, depending on the material used in the reaction chamber. In a 4 mm ID stainless steel tubing, the decomposition rate constant is determined to be k = 2 × 105 exp(−14800/RT). This decomposition rate is approximately 100 times faster than that observed in a Teflon tubing.
The variation of decomposition rate in different reaction chambers is attributed to the heterogeneous catalytic effects. There is no evidence of reaction between H2 and H2O2 in the highpurity water at temperatures up to 280°C.
96 citations
89 citations
TL;DR: In this article, a vibrational spectra was used to study the adsorption and decomposition of formic acid and formaldehyde on the Rh(111) surface, and it was shown that the addition of 14 monolayer of oxygen atoms to the clean surface shifted the formate decomposition temperature to 330 K. This formate intermediate was formed, fingerprinted by its strong O-C-O vibrational modes.
86 citations
28 Sep 1991
TL;DR: In this paper, the performance of surface discharge induced plasma chemical processing with a cylindrical ceramic-based reactor for chlorofluorocarbon gases was measured in atmospheric air, pure oxygen gas, or pure nitrogen gas.
Abstract: The decomposition performance of surface discharge induced plasma chemical processing (SPCP) with a cylindrical ceramic-based reactor for chlorofluorocarbon gases was measured in atmospheric air, pure oxygen gas, or pure nitrogen gas. In the case of decomposition test for 1000 p.p.m. CFC-22 in air, a maximum decomposition rate of about 90% was recorded. In the case of the decomposition test for 100 p.p.m. CFC-113, more than 99% fluorocarbon could be removed. The decomposition mechanism of fluorocarbon is not yet known exactly but is assumed to be due to the effect of the surface discharge plasma near the discharge electrode. The decomposition rate for fluorocarbon in nitrogen gas was the largest among three gases (air, nitrogen, and oxygen), indicating the strong activity of the nitrogen radicals. A large ceramic reactor was also tested, and the decomposition performance was found to be proportional to the real electric power consumption under best conditions. The reaction products after the SPCP are not yet identified, but phosgene and its derivatives have not yet been found. >
TL;DR: In this paper, the decomposition of methanol on Pt(110) is examined by TPD and EELS, and it is found that on the (1×1) reconstruction of Pt (110), the methanoil adsorbs molecularly at 100 K. When the layer is heated to 140 K, the C-O bond breaks to yield water and a mixture of CH xad species.
Abstract: Recently there has been some controversy whether C-O bond scission occurs during methanol decomposition on the (111) faces of platinum and palladium. Here, the decomposition of methanol on Pt(110) is examined by TPD and EELS. It is found that, on the (1×1) reconstruction of Pt(110), the methanol adsorbs molecularly at 100 K. When the layer is heated to 140 K, the C-O bond breaks to yield water and a mixture of CH xad species. The CH xad species then further react to form CH 4 , H ad , C ad ) and some as yet unidentified higher hydrocarbons
TL;DR: In this article, the authors found that the enhanced decomposition was proportional to both the acoustic pressure and the square root of the acoustic intensity, and that the analysis was also applicable to the solvolysis of 2-chloro methylpropane, a volatile substrate.
TL;DR: The decomposition of methanol on (2 × 1)Pt(110) terraces was examined using TPD and EELS in this paper, and it was shown that steps can decrease the rate of a simple decomposition reaction.
TL;DR: In this paper, the authors find the most effective catalyst of stoichiomagnetic ferrospinels for the decomposition of H2O2, their effectiveness is dependent on the composition of the catalyst.
Abstract: Some ferrospinels act as catalysts for the decomposition of H2O2, their effectiveness is dependent on the composition of the catalyst. This study is to find the most effective catalyst of stoichiom...
TL;DR: In this paper, the formation of vanadium oxide overlayers by the adsorption-decomposition of VO(OC 2 H 5 ) 3 vapor on high-surface area SiO 2 was studied by IR (infrared) spectroscopy, TPD (temperature-programmed decomposition), and the stoichiometry of the surface reactions.
Abstract: Elementary processes of the formation of vanadium oxide overlayers by the adsorption-decomposition of VO(OC 2 H 5 ) 3 vapor on high-surface area SiO 2 were studied by IR (infrared) spectroscopy, TPD (temperature-programmed decomposition), and the stoichiometry of the surface reactions. In this study the adsorption-decomposition process will be called a CVD (chemical vapor deposition) cycle. The structure of the vanadium oxide prepared by repeated CVD cycles was characterized by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy)
TL;DR: In this paper, the power rate law dα dt = A(1 − α) n exp (− E a RT ) was solved nonisothermally and linearized with n = 2.
TL;DR: In vitro enzymatic degradation of non-porous films of segmented poly(ether urethane) (Pellethane 2363-80AE) was investigated, and trypsin has the ability to induce degradation in PEU, the soft segment being most affected, particularly the CH2-O bond of the ether linkages.
Abstract: In vitro enzymatic degradation of non-porous films of segmented poly(ether urethane) (Pellethane 2363-80AE) was investigated by incubating the biomaterial in concentrated trypsin solutions for 5 months at room temperature. Chemical degradation of films was monitored by surface analysis techniques such as Fourier transform infrared spectroscopy-attenuated total reflectance and electron spectroscopy for chemical analysis. This latter technique proved to be much superior in detecting chemical changes. Extraction of films with methanol and characterization of the extracts by gel permeation chromatography revealed the presence of low-molecular-weight polymers. Results have shown that trypsin has the ability to induce degradation in PEU, the soft segment being most affected, particularly the CH2-O bond of the ether linkages.
TL;DR: In this paper, a one-box, time-dependent model was used to simulate the evolution of the isotopic composition of the O2 and O3 and the comparison of thermal and photolysis experiments indicates that the initial decomposition step is most likely responsible for the observed isotopic fractionations.
Abstract: Experimental and theoretical studies of O3 decomposition are reported which resolve kinetic mechanisms for isotopic fractionations in O-O2-O3 chemistry. The thermal gas phase decomposition of O3 at high temperatures (90°C, 110°C) produces isotopically heavy O2 with respect to precursor O3 with a non-mass-dependent fractionation pattern (δ17O ≠ 0.5δ18O). At 90°C, a noticeable component of heterogeneous decomposition is present, but is insignificant at 110°C. The product O2 from O3 photolysis by visible (532 nm) and UV light is depleted in the heavy isotopes, opposite from thermal decomposition. These well controlled experiments permit a quantitative kinetic analysis. A one-box, time-dependent model was used to simulate the evolution of the isotopic composition of the O2 and O3. The comparison of thermal and photolysis experiments indicates that the initial decomposition step is most likely responsible for the observed isotopic fractionations. Based upon detailed kinetic model calculations, the roles of isotope exchange reactions, initial O3 isotopic distribution, and various branching ratios of isotopic reactions involved in the isotopic fractionation have been examined. The possible importance of these conclusions for understanding stratospheric isotopically heavy O3, and possible implications for non-mass-dependent isotopic fractionations and chemical kinetic theory are discussed.
TL;DR: In this paper, the decomposition of nitrous oxide was carried out at the initial pressures of 50 and 200 Torr (1 Torr = 133.3 Pa), and two regions of activity were observed based on the mechanism x x ⩽0.5.
TL;DR: In this article, the mechanisms and kinetic parameters of thermal decomposition of 3-Nitro-1,2,4-triazol-5-one (NTO) and M · nH2O (M Cu, m 2, n 4; M Pb, H3NCH2CH2NH2NH3, m 2,n 0, m ∆ 0, n ∆ 1) are obtained by TG, DSC,
TL;DR: In this article, a des temperatures comprises entre 1013 and 1133 K, a des pressions de 1,3 a 3,1 atm. and a des debits d'alimentation compris entre 2,8•10 −4 and 3,5•10−3 mol/s•cm 2.
Abstract: L'etude est realisee a des temperatures comprises entre 1013 et 1133 K, a des pressions de 1,3 a 3,1 atm. et a des debits d'alimentation compris entre 2,8•10 −4 et 3,5•10 −3 mol/s•cm 2 . On determine les parametres cinetiques et l'influence de la temperature sur ceux-ci. On presente et on discute l'influence de la temperature sur la desactivation irreversible du catalyseur
TL;DR: In this paper, the copper ion-exchanged ZSM-5 zeolite (Cu-Z) was found to be the most active catalyst for decomposition of NO.
Abstract: Direct decomposition and selective reduction of nitrogen monoxide over copper ion-exchanged zeolite catalysts are proposed as new methods for removal of NO. The copper ion-exchanged ZSM-5 zeolite (Cu-Z) was the most active catalyst for decomposition of NO. The activity of Cu-Z zeolites increased with increase in the exchange level. The zeolites with copper ion-excange levels of 100% or more, which could be prepared by repeating ion exchange of the ZSM-5 zeolite using aqueous copper(II) acetate solution or addition of ammonia into the aqueous copper(II) nitrate solution, showed significantly high activity even in the presence of oxygen and at high GHSV region. It was clarified concerning Cu-Z, by using IR, ESR, phosphorescence, TPD, and CO adsorption measurements that (1) the Cu2+ ions exchanged into zeolite were reduced to Cu+ and/or Cu+-Cu+ through evacuation at elevated temperature, (2) after exposure to oxygen at 773K and subsequent evacuation, about 40% copper ions in zeolite existed as Cu+ ions, (3) the NO- species formed by adsorption of NO on Cu+ would be an intermediate in the NO decomposition, and (4) redox cycle of Cu+_??_Cu2+ in the zeolite is probably a key step to achieve the decomposition reaction. Selective reduction of NO by hydrocarbon in the presence of oxygen was first found by the authors and Cu-Z was remarkably effective for NO removal at temperatures as low as 523-673K. The activity for this selective reduction in NO+C3H6+O2 system was not poisoned very much by addition of SO2. The conversion into N2 was changed to 85% (773K) in the presence of SO2, from 100% in the absence of SO2, which is in contrast with the fact that the catalytic activity for direct decomposition NO was completely lost on adding the same amount of SO2. Furthermore, the reduction rate over Cu-Z at 573K was higher than those over H-zeolite and alumina catalysts at 723 and 773K, respectively, which have been reported to be active, after findings by the authors.
TL;DR: In this article, a series of model organic haliae compounds were decomposed by the technique of microwave catalysis and the results clearly established the primary free radical mechanisms of the decomposition by breaking selectively the C-X bond, leading to an organic fragment and a stable form of solid metal halides.
Abstract: A series of model organic haliae compounds were decomposed by the technique of microwave catalysis. The reactions were 100% efficient which were followed and characterized by gas chromatography, mass spectrometry, and direct electron spin resonance detection. The results clearly establish the primary free radical mechanisms of the decomposition by breaking selectively the C-X bond, leading to an organic fragment/radical and a stable form of solid metal halides. Many of the non-halogenated organic products are of economic and chemical value and can be recovered in the microwave processing.
TL;DR: In this paper, static secondary ion mass spectroscopy (SSIMS), temperature programmed desorption (TPD), and Auger electron spectrograph (AES) were used under ultrahigh vacuum conditions to study the decomposition of CH{sub 3}SH on Ni(100).
Abstract: Static secondary ion mass spectroscopy (SSIMS), temperature programmed desorption (TPD), and Auger electron spectroscopy (AES) were used under ultrahigh vacuum conditions to study the decomposition of CH{sub 3}SH on Ni(100). Only methane, hydrogen, and the parent molecule are observed in TPD. Complete decomposition to C(a), S(a) and desorbing H{sub 2} is the preferred reaction pathway for low exposures, while desorption of methane is observed at higher coverages. Preadsorbed hydrogen promoted methane desorption. Upon adsorption, and for low coverages, SSIMS evidence indicates S-H bond cleavage into CH{sub 3}S and surface hydrogen. S-H bond cleavage is inhibited for high coverages. The TP-SSIMS data are consistent with an activated C-S bond cleavage in CH{sub 3}S, with an activation energy of 8.81 kcal/mol and preexponential factor of 10{sup 6.5}s{sup {minus}1}. The low preexponential factor is taken as indicating a complex decomposition pathway. A mechanism consistent with the observed data is discussed.
TL;DR: In this article, it was shown that at low oxygen potentials, YBa2Cu3O7−x decomposes by chemical reactions involving reduction, and the initial decomposition products were found to be Y2BaCuO5 and a Ba•Cu oxide phase.
Abstract: At low oxygen potentials, YBa2Cu3O7−x decomposes by chemical reactions involving reduction. The results of this study show that the compound also decomposes at higher oxygen potentials. The initial decomposition products were found to be Y2BaCuO5 and a Ba‐Cu oxide phase. The Ba‐Cu phase was found to be a peroxide‐type and the decomposition can be described by a chemical reaction involving oxidation: 4(YBa2Cu3O7−x)+(1/2 − 3/2δ +2x)O2⇄2Y2BaCuO5+3Ba2Cu3O6−δ+CuO. At 800 °C the equilibrium pressure for this reaction is slightly <1 bar, and the enthalpy change is ∼80‐kJ/mol Y123. This result is not consistent with the conclusions drawn from some other studies of the stability of the superconducting Y‐Ba‐Cu‐O compounds, and the differences are discussed.
TL;DR: In this paper, a ruthenium-phosphine catalytic system was proposed to decompose Parafonnaldehyde into CO and H 2 with the same catalyst, which can be applied to hydrogenation and to hydrocarbonylation reactions.
TL;DR: In this article, the authors investigated the adsorption, desorption and decomposition of carbon monoxide on a Rh(210) surface using TPD and X-ray photoelectron spectroscopy.
TL;DR: In this paper, the authors report the isolation and characterization of the less stable (CH 2 =CH) 4 Te, (n-Bu)-4 Te, and (Me 3 SiCH 2 ) 4 Te compounds, as well as their decomposition pathways to give R 2 Te compounds.