Topic
Oxygen
About: Oxygen is a research topic. Over the lifetime, 48149 publications have been published within this topic receiving 1113788 citations. The topic is also known as: O & Oxygen.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, the authors reported the dehydration of glycerol over vanadium phosphate oxide (VPO) catalysts in a gas-phase fixed-bed reactor at temperatures from 250 to 350°C with O2/glycerol ratios of 0 −13.6.
194 citations
TL;DR: The surface nitrogen species were identified by X-ray photoelectron spectroscopy as pyridinic, pyrrolic or others as discussed by the authors, and it was found that the formation of surface oxygen complexes by the C-O[sub 2] reaction is essential for the carbon-nitric oxide reaction.
Abstract: The carbon-nitric oxide (NO) reaction plays an important role in many processes where the reduction of NO is attempted. In all cases, there is a certain amount of oxygen that significantly increases the rate of C-NO reaction. The objects of this study are to clarify the role of oxygen gas and to elucidate the reaction mechanism by analyzing the surface species. It was found that the formation of surface oxygen complexes by the C-O[sub 2] reaction is essential for the C-NO reaction. In addition to oxygen complexes, a considerable amount of nitrogen was also trapped in the carbon matrix during reaction. In the initial stage of the reaction, the concentration of nitrogen-containing product gas was much lower than expected from the NO consumption. The surface nitrogen species were identified by X-ray photoelectron spectroscopy as pyridinic, pyrrolic or others. These are rather stable in an inert atmosphere even at 950 C, but they can easily be removed at 600 C in the NO- or O[sub 2]-containing reaction atmosphere.
194 citations
TL;DR: In this article, the same authors performed a similar study on single-crystal silicon and showed that the oxidation of both and Si followed parabolic growth kinetics with activation energies of about 115 kcal/mol and about 30 kcal/min, respectively.
Abstract: Oxidation studies of CVD were performed in dry oxygen, oxygen‐argon, and oxygen‐nitrogen‐argon gas mixtures of various oxygen and nitrogen partial pressures at a total pressure of 1 atm at 1100°–1400°C. Parallel oxidation studies of single‐crystal silicon were also conducted for direct comparison. It was observed that the oxidation of both and Si followed parabolic growth kinetics with activation energies of about 115 kcal/mol and about 30 kcal/mol, respectively. The formation of a single layer of and evolution of could not account for the much lower parabolic rate constants and much higher activation energy for than for Si during the oxidation. Detailed characterization of the oxidation scales using ellipsometry, step‐by‐step etching, SIMS, and XPS techniques indicated that a duplex oxidation scale consisting of and was formed when was oxidized. The intermediate scale was identified as a single‐phase material, not a physical mixture of and . The low oxidation rate and high activation energy for during the oxidation were attributed to the formation of and low oxygen diffusivity in this structurally dense phase.
193 citations
01 Jan 2011
TL;DR: The mechanism of oxo-active site formation in Cu-ZSM-5 is defined and the formation of an O(2)-precursor of this reactive site with an associated absorption band at 29,000 cm(-1) is reported.
Abstract: The reactive oxidizing species in the selective oxidation of methane to methanol in oxygen activated Cu-ZSM-5 was recently defined to be a bent mono(μ-oxo)dicopper(II) species, [Cu(2)O](2+). In this communication we report the formation of an O(2)-precursor of this reactive site with an associated absorption band at 29,000 cm(-1). Laser excitation into this absorption feature yields a resonance Raman (rR) spectrum characterized by (18)O(2) isotope sensitive and insensitive vibrations, νO-O and νCu-Cu, at 736 (Δ(18)O(2) = 41 cm(-1)) and 269 cm(-1), respectively. These define the precursor to be a μ-(η(2):η(2)) peroxo dicopper(II) species, [Cu(2)(O(2))](2+). rR experiments in combination with UV-vis absorption data show that this [Cu(2)(O(2))](2+) species transforms directly into the [Cu(2)O](2+) reactive site. Spectator Cu(+) sites in the zeolite ion-exchange sites provide the two electrons required to break the peroxo bond in the precursor. O(2)-TPD experiments with (18)O(2) show the incorporation of the second (18)O atom into the zeolite lattice in the transformation of [Cu(2)(O(2))](2+) into [Cu(2)O](2+). This study defines the mechanism of oxo-active site formation in Cu-ZSM-5.
193 citations
TL;DR: Silicon dioxide films were grown using an atmospheric-pressure plasma jet that was produced by flowing oxygen and helium between two coaxial metal electrodes that were driven by 13.56 MHz radio frequency power as discussed by the authors.
Abstract: Silicon dioxide films were grown using an atmospheric-pressure plasma jet that was produced by flowing oxygen and helium between two coaxial metal electrodes that were driven by 13.56 MHz radio frequency power. The plasma exiting from between the electrodes was mixed with tetraethoxysilane (TEOS), and directed onto a silicon substrate held at 115-350 °C. Silicon dioxide films were deposited at rates ranging from 20±2 to 300±25 nm min-1. The deposition rate increased with decreasing temperature and increasing TEOS pressure, oxygen pressure and RF power. For the latter two variables, the rate increased as follows: Rd∝P0.3O2(RF)1.4. Films grown at 115 °C were porous and contained adsorbed hydroxyl groups, whereas films grown at 350 °C were smooth, dense and free of impurities. These results suggest that the mechanism in the atmospheric pressure plasma is the same as that in low-pressure plasmas.
193 citations