The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H2)–CH3 and trans (staggered) configuration of the O= C (H)– O – C (H2)– C H3 dihedral angles. We observed the following ethyl formate pyrolysis products: CH3CH2OH, CH3CHO, C2H6, C2H4, HC(O)OH, CH2O, CO2, and CO, with HC(O)OH and C2H4 pyrolyzing further, forming CO + H2O and C2H2 + H2. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH3CH2O + CHO and CH3CH2 + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures. 相似文献
The methods of temperature-programmed reaction/desorption (TPR/TPD) are used to study azomethane (CH3N=NCH3) decomposition and the reactions of the products of its pyrolysis (CH
3*
radicals and N2) on the polycrystalline molybdenum surface. A TPR spectrum of adsorbed azomethane decomposition shows mainly N2, H2, and unreacted azomethane. Upon preliminary adsorption of azomethane pyrolysis products on a catalyst sample, a TPR spectrum
shows N2, H2, and CH4 in comparable amounts. The difference in the composition of desorption products found for these two types of experiments
shows that, in the decomposition of adsorbed azomethane, surface methyl moieties are not formed. The rate constants were calculated
for the dissociation of adsorbed CH3, CH2, and CH, recombination of hydrogen atoms with each other and with CH3 and CH2, and the recombinative desorption of nitrogen atoms.
Deceased. 相似文献
The carbon deposits forming upon the suboxidative pyrolysis of methane on resistive FeCrAl catalysts heated with electric current were studied. The suboxidative pyrolysis of methane was carried out in a flow reactor at the ratio CH4: O2 = 15: 1 in a catalyst-coil temperature range of 600–1200°C; a cold reaction mixture (~20°C) was supplied. The morphology and structure of the carbon deposits and changes in the composition and structure of the catalyst were characterized by scanning electron microscopy, transmission electron microscopy with EDX analysis, Raman spectroscopy, and X-ray diffraction analysis. Various forms of carbon deposits, including branched nanotubes, and metal carbides formed by catalyst constituents were detected. It was found that the carbon deposits on the catalyst surface were morphologically different from the deposits on quartz reactor walls. The reasons for these differences were considered. 相似文献
The chemical kinetic effects of RF plasma on the pyrolysis and oxidation of methane were studied experimentally and computationally in a laminar flow reactor at 100 Torr and 373 K with and without oxygen addition into He/CH4 mixtures. The formation of excited species as well as intermediate species and products in the RF plasma reactor was measured with optical emission spectrometer and Gas Chromatography and the data were used to validate the kinetic model. The kinetic analysis was performed to understand the key reaction pathways. The experimental results showed that H2, C2 and C3 hydrocarbon formation was the major pathways for plasma assisted pyrolysis of methane. In contrast, with oxygen addition, C2 and C3 formation dramatically decreased, and syngas (H2 and CO) became the major products. The above results revealed oxygen addition significantly modified the chemistry of plasma assisted fuel pyrolysis in a RF discharge. Moreover, an increase of E/n was found to be more beneficial for the formation of higher hydrocarbons while a small amount of oxygen was presented in a He/CH4 mixture. A reaction path flux analysis showed that in a RF plasma, the formation of active species such as CH3, CH2, CH, H, O and O (1D) via the electron impact dissociation reactions played a critical role in the subsequent processes of radical chain propagating and products formation. The results showed that the electronically excitation, ionization, and dissociation processes as well as the products formation were selective and strongly dependent on the reduced electric field. 相似文献
Homogeneous pyrolysis of 1,4-dimethoxynaphthalene was studied. The yield and group composition of liquid products and the component compositions of the gaseous products and hydrocarbons were determined; the asphaltenes and neutral oxygen-containing compounds were characterized. The kinetic parameters were determined, and possible mechanisms suggested, for decomposition of 1,4-dimethoxynaphthalene with the formation of CH4, H2, CO, and CO2. 相似文献
This study aims to experimentally characterize the carbonaceous and nitrogenous species, from the flash pyrolysis of millet stalks and polyethylene plastic bags, using the device of the tubular kiln, coupled to two gas analyzers: Analyzer Fourier Transform Infrared (FTIR) and an analyzer Infrared Non-Dispersive (IRND). Gaseous products analyzed are: CH4, C2H2, C2H4, C3H8, C6H6, CO, CO2, NO2, NO, N2O, HCN and NH3. Whatever the temperature of thermal degradation, the pyrolysis shows us that in terms of mass:
•For the millet stalks, the gaseous compounds are formed mainly CO and CO2 to the carbonaceous species, HCN and NH3, for the nitrogenous species analyzed;
•As regards the polyethylene bags, hydrocarbons for carbonaceous species and HCN, NH3 and NO2 for the nitrogenous species, are most abundant.
In addition, the results suppose that in our experimental conditions, the hydrocarbon which is involved primarily in the formation of CO is ethylene C2H4. At the end of this characterization, we determined the rate of carbon and nitrogen found in the volatile gas. With millet stalks we have about 45% of volatile carbon and 15% of the nitrogen of fuel that are found in gaseous products. The results obtained with the plastic bags give 68% carbon and 15% nitrogen found in the nitrogenous species analyzed. 相似文献
Si7C16H36 (1) can be separated from the pyrolysis products of Si(CH3)4 by columnchromatography. Its structure is shown to consist of two 1,3,5,7-tetrasilaadamantane skeletons which are connected through the C-atoms 2 and 4 and the Si-atom 3, by analysis of the 100 and 220 MHz PMR spectra in connection with double resonance. Except for the framework bonds carbon atoms are saturated by hydrogen, silicon atoms by CH3 groups. (1) is a very stable compound (m.p. 225°C without decomposition). 相似文献
A detailed reaction mechanism is developed and used to model experimental data on the pyrolysis of CHF3 and the non-oxidative gas-phase reaction of CHF3 with CH4 in an alumina tube reactor at temperatures between 873 and 1173 K and at atmospheric pressure. It was found that CHF3 can be converted into C2F4 during pyrolysis and CH2CF2 via reaction with CH4. Other products generated include C3F6, CH2F2, C2H3F, C2HF3, C2H6, C2H2 and CHF2CHF2. The rate of CHF3 decomposition can be expressed as 5.2×1013 [s−1] e−295[kJ mol−1]/RT. During the pyrolysis of CHF3 and in the reaction of CHF3 with CH4, the initial steps in the reaction involve the decomposition of CHF3 and subsequent formation of CF2 difluorocarbene radical and HF. It is proposed that CH4 is activated by a series of chain reactions, initiated by H radicals. The NIST HFC and GRI-Mech mechanisms, with minor modifications, are able to obtain satisfactory agreement between modelling results and experimental data. With these modelling analyses, the reactions leading to the formation of major and minor products are fully elucidated. 相似文献
The number of products and the H2/CH4 ratio obtained from the flow pyrolyses of (CH3)3GeH and (CH3)3SiH were very different. The (CH3)3GeH decomposition is consistent with the following mechanism:
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The pyrolysis of (CH3)3SiH was found to be much more complex, presumably due to the formation of silicon-carbon double bonded intermediates and the (CH3)2Si(H)CH2 radical. We also present data which supports the presence of a H atom chain sequence during this pyrolysis. 相似文献
The kinetics of the acetaldehyde pyrolysis have been studied at temperatures from 450° to 525°C, at an acetaldehyde pressure of 176 torr and at 0 to 40 torr of added nitric oxide. The following products were identified and their rates of formation measured: CH4, H2, CO, CO2, C2H4, C2H6, H2O, C3H6, C2H5CHO, CH3COCH3, CH3COOCH?CH2, N2, N2O, HCN, CH3NCO, and C2H5NCO. Acetaldehyde vapor was found to react with nitric oxide slowly in the dark at room temperature, the products being H2O, CH3COOCH3, CO, CO2, N2, NO2, HCN, CH3NO2, and CH3ONO2. The rates of formation of N2 and C2H5NCO depend on how long the CH3CHO-NO mixture is kept at room temperature before pyrolysis; the rates of formation of the other products depend only slightly on the mixing period. The pyrolysis of “clean” CH3CHO–NO mixtures (i.e., the results extrapolated to zero mixing time, which are independent of products formed in the cold reaction) are interpreted as follows: (1) There are two chain carriers, CH3 and CH2CHO, their concentrations being interdependent and influenced by NO in different ways: the CH3 radical is both generated and removed by reactions directly involving NO, whereas CH2CHO is generated only indirectly from CH3 but is also removed by direct reaction with NO. (2) An important mode of initiation by NO is its addition to the carbonyl group with the formation of which is converted into ; this splits off OH with the formation of CH3NCO or CH3 + OCN. (3) Important modes of termination are The steady-state equations derived from the mechanism are shown to give a good fit to the experimental rate versus [NO] curves and, in particular, explain why there is enhancement of rate by NO at higher CH3CHO pressures and, at lower CH3CHO pressures, inhibition at low [NO] followed by enhancement at higher [NO]. The cold reaction is explained in terms of chain-propagating and chain-branching steps resulting from the addition of several NO molecules to CH3CHO and the CH3CO radical. In the “unclean” reaction it is found that the rates of N2 and C2N5NCO formation are increased by CH3NO2, CH3ONO, and CH3ONO2 formed during the cold reaction. A mechanism is proposed, involving the participation of α-nitrosoethyl nitrite, CH3CH(NO)ONO. It is suggested that there are two modes of behavior in pyrolyses in the presence of NO: (1) In the paraffins, ethers, and ketones, the effects are attributed to the addition of NO to a radical with the formation of an oxime-like compound. (2) In the aldehydes and alkenes, where there is a hydrogen atom attached to a double-bonded carbon atom, the behavior is explained in terms of addition of NO to the double bond followed by the formation of an oxime-like species. 相似文献
Highly efficient epoxidation of alkenes with H2O2 catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes (MWCNTs) modified with 1,2-diaminobenzene is reported. The prepared catalyst, [W(CO)6@DAB-MWCNT], was characterized by elemental analysis, scanning electron microscopy, FT-IR, and diffuse reflectance UV-Vis spectroscopic methods. The prepared catalyst was applied as an efficient catalyst for green epoxidation of alkenes with hydrogen peroxide in CH3CN. This heterogeneous metal carbonyl catalyst showed high stability and reusability in epoxidation without loss of its catalytic activity. 相似文献
A kinetic model presented for the selective reduction of NO with CH4 over an In-Fe2O3/HZSM-5 catalyst by considering the process as a combination of two simultaneous reactions: NO+O2+CH4 (reaction 1) and O2+CH4 (reaction 2). Linear regression calculation was employed to find the kinetic parameters. It was found that although the activation energies of the two reactions were almost identical, the reaction rate constants were dramatically different, namely, k1k2, indicating that the NO+O2+CH4 reaction was more preferable to take place on the In-Fe2O3/HZSM-5 catalyst as compared with the O2+CH4 reaction. 相似文献
A novel plasma-catalyst converter (NPCC) was engineered in applying the carbon capture utilization technology for the destruction of carbon dioxide (CO2), which is a cause of global warming and is generated from the combustion of fossil fuels. The NPCC has an orifice-type baffle to improve an amount of gas feed with the higher CO2 destruction for a stationary point sources application . To examine its ability for the CO2 destruction, the performance analysis was conducted on the effects of methane additive, nozzle injection velocity, total gas feed, and catalyst type. The product gas from the NPCC was combustible components like CO, H2, CH4, THCs. The CO2 destruction and the CH4 conversion at a 1.29 CH4/CO2 ratio were 37 and 47 %, respectively, and the energy decomposition efficiency was 0.0036 L/min W. The nickel oxide catalyst among other catalysts showed the most effectiveness for the CO2 destruction and CH4 conversion at a lower temperature. The carbon-black produced without the catalytic bed has carbon nanoparticles with diverse shapes, such as spherical carbon particles and carbon nanotubes; and its high conductivity and specific surface area were suitable for special electronic materials, fuel cells, and nanocomponents. 相似文献
In this work, graphite encapsulated Fe nanoparticles and thin carbon nanotubes (CNTs) supported on the pristine CNTs, respectively, were synthesized using plasma enhanced chemical vapor deposition via efficiently controlling the flow rate of discharging CH4 and H2 gas. The properties of the obtained hybrid materials were characterized with superconducting quantum interference and field emission measurements. The results showed that the encapsulated Fe nanoparticles had diameters ranging from 1 to 30 nm, and this hybrid nanocomposite exhibited a ferromagnetic behavior at room temperature. Thin CNTs with an average diameter of 6 nm were attached to the surface of the prepared CNTs, which exhibited a lower turn-on field and higher emission current density than the pristine CNTs. The Fe nanoparticles either encapsulated with graphite or used as catalyst for thin CNTs growth were all originated from the pyrolysis of ferrocene. 相似文献
Slow pyrolysis experiments of China fir (Cunninghamia lanceolata) wood were performed in a vertical tubular furnace at various heating rates. The raw material was pretreated by impregnation with phosphoric acid solutions of various concentrations for given times. The evolution of the gaseous products CO, CO2, H2 and CH4 was analyzed online by using gas spectrometry to investigate the effect of phosphoric acid on the pyrolytic gaseous products of biomass. The addition of phosphoric acid was shown to significantly reduce the pyrolysis temperature necessary for the production of CO, CO2 and H2 gases, and the pyrolysis variables exerted an influence on the amount of the gases released. Moreover, phosphoric acid appreciably depressed the CO, CO2 and CH4 production, and promoted H2, especially when a higher heating rate was employed. This suggested that phosphoric acid catalyzed both the primary thermal decomposition of biopolymers and the secondary reactions that took place among the pyrolytic vapor products. 相似文献
The thermal decomposition of ethylbenzene has been investigated behind reflected shock waves over the temperature and pressure ranges of 1350–2080 K and 0.25–0.5 atm using a 1.6% C8H10 ? Ne mixture. Major products of the pyrolysis are C7H8, C7H7, C6H6, C4H2, C2H4, C2H2, and CH4; C8H8 appears throughout the temperature range as a minor product. Comparison of the product profiles obtained by time-of-flight mass spectrometry and the results of model calculations strongly supports the initiation step of β C? C bond homolysis for C8H10 dissociation. A 51 kinetic step reaction mechanism with 24 species was formulated to model the temperature and time dependence of the major products observed in our experiments. 相似文献
In the present paper, the catalytic dehydrogenation of C2H6 to C2H4 under non-oxidative conditions was investigated in a fixed-bed micro-reactor under ambient pressure at 823 - 923 K. The 6Cr/g-Al2O3 catalyst was found to be the best catalyst among the g-Al2O3, SiO2, MCM41, MgO and Si-2 supported chromium oxide catalysts. The features of the 6Cr/g-Al2O3 catalyst for the reaction could be listed as follows: (1) At 823 - 923 K, the C2H4 selectivity of 92.5-78.6% at a C2H6 conversion of 9.5-29.8% could be obtained. (2) The catalyst had the good regeneration performance, i.e., could be regenerated by air repeatedly. (3) The main products were C2H4, CH4, H2 and coke. No carbon oxides were identified. 相似文献