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1.
In the present study, the adsorption behaviour of methanol (CH3OH) and ethanol (C2H5OH) molecules over heterofullerene C59B surface is studied by density functional theory calculations. This heterofullerene is obtained from C60 by substituting a carbon atom with a boron atom and relaxing self-consistently the structure to the local minimum. The adsorption of CH3OH and C2H5OH on the C59B is exothermic and the relaxed geometries are stable. The CH3OH and C2H5OH adsorption can also induce a change in the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gap of the nanocage. The dehydrogenation pathways of CH3OH and C2H5OH via O–H and C–H bonds scission are also examined. The results indicate that O–H bond scission is the most favourable pathway on the C59B surface. 相似文献
2.
The methanol decomposition and oxidation on a Pd(111) single crystal have been investigated in situ using ambient-pressure X-ray photoelectron spectroscopy (XPS) and mass-spectrometry (MS) in the temperature range of 300–600 K. It was found that even in the oxygen presence the methanol decomposition on palladium proceeds through two competitive routes: fast dehydrogenation to CO and H2, and slow decomposition of methanol via the C–O bond scission. The rate of the second route is significant even in the millibar pressure range, which leads to a blocking of the palladium surface by carbon and to a prevention of the further methanol conversion. As a result, no gas phase products of methanol decomposition were detected by mass-spectrometry at 0.1 mbar CH3OH in the whole temperature range. The methanol C–O bond scission produces CHx species, which fast dehydrogenate to atomic carbon even at room temperature and further partially dissolve in the palladium bulk at 400 K with the formation of the PdCx phase. According to in situ XPS data, the PdCx phase forms even in the oxygen excess. The application of an in situ XPS–MS technique unambiguously shows a good correlation between a decrease in the surface concentration of all carbon-containing species and the rate of methanol conversion. Since these carbon species have a high reactivity towards oxygen, heating of Pd(111) above 450 K in a methanol–oxygen mixture yields CO, CO2, and water. The product distribution indicates that the main route of methanol conversion is the dehydrogenation of methanol to CO and hydrogen. However, under the experimental conditions used, hydrogen is completely oxidized to water, while CO is partially oxidized to CO2. No palladium oxide was detected by XPS in these conditions. 相似文献
3.
The adsorption and activation of methyl acetate (CH3COOCH3), one of the simplest carboxylic esters, on Pd(111) have been studied using self-consistent periodic density functional theory calculations. Methyl acetate adsorbs weakly through the carbonyl oxygen. Its activation occurs via dehydrogenation, instead of direct C–O bond dissociation, on clean Pd(111): It is much more difficult to dissociate the C–O bonds (Ea ≈ 2.0 eV for the carbonyl and acetate–methyl bonds; Ea = 1.0 eV for the acetyl–methoxy bond) than to dissociate the C–H bonds to produce enolate (CH2COOCH3; Ea = 0.74 eV) or methylene acetate (CH3COOCH2; Ea = 0.82 eV). The barriers for C–H and C–O bond dissociation are directly calculated for enolate and methylene acetate, and estimated for further dehydrogenated derivatives (CH3COOCH, CH2COOCH2, and CHCOOCH3) based on the Brønsted–Evans–Polanyi linear energy relations formed by the calculated steps. The enolate pathway leads to successive dehydrogenation to CCOOCH3, whereas methylene acetate readily dissociates to yield acetyl. The selectivity for dissociating the acyl–alkoxy C–O bond, which is desired for alcohol formation, is therefore fundamentally limited by the facility of dehydrogenation under vacuum/low-pressure conditions on Pd(111). 相似文献
4.
The thermal evolution of acetylene and ethylene and their deuterated counterparts on a palladium (111) surface has been studied by high-resolution electron energy loss spectroscopy in the temperature range 150–500 K. Analysis of the vibrational spectra indicates that chemisorbed acetylene evolves at 300 K in the presence of surface hydrogen to mainly ethylidyne, CCH3, and a small amount of residual acetylene. Spectra obtained with and without preadsorbed hydrogen provide evidence for a 〉C CH2 intermediate in the reaction. Chemisorbed ethylene also evolves to ethylidyne after heating from 150 to 300 K but much of the ethylene desorbs. The high temperature (400–500 K) behavior of C2H2 and C2H4 involves formation of a CH species. Although a small amount of the CH species may be formed from the dehydrogenation of ethylidyne, it is found that carbon-carbon bond scission of acetylene near 400 K is the dominant mechanism in CH formation. 相似文献
5.
v. CRUPI A. FARAONE D. MAJOLINO P. MIGLIARDO V. VENUTI V. VILLARI 《Molecular physics》2013,111(18):1525-1533
A study has been made of vibrational properties in ethylene glycol (EG; H(OCH2CH2)OH) and EG monomethyl ether (EGmE; CH3(OCH2CH2)OH) in solution together with poly(ethylene oxide) (PEO; H(OCH2CH2)n,OH) at different concentrations, performed by Fourier transform infrared absorbance (FT-IR) spectroscopy. The results ae compared with previous viscometry and photon correlation spectroscopy (PCS) studies, using EG dimethyl ether (EGdE; CH3(OCH2CH2)OCH3) as solvent as well. These homologous systems differ from each other in the number of OH end groups, in particular two for EG, one for EgmE and zero for EGdE. Combining analysis of the vibrational and transport properties of EG, EGmE and EGdE in solution with PEO over a wide range of concentration made it possible to check the quality (good theta or poor) of these three different solvents and the role played by the hydrogen bond in the various solute-solvent interaction mechanisms, resulting in the well known de Gennes scaling law. 相似文献
6.
Using the density functional theory, the initial dehydrogenation of methanol on NixMy (M?=?Ni, Co, Fe, Mn, Cr, x?+?y?=?4, y?=?1, 2) clusters is investigated. Two adsorption and dehydrogenation mechanisms of methanol are studied: one proceeds along the C–H scission and another begins with the breaking of the O-H bond. The adsorption sites of methanol on the Ni or M sites of the NixMy clusters are considered. The adsorption of methanol on Ni4 cluster is stronger than those on bimetallic clusters, while the initial dehydrogenation barriers on NixMy clusters are lower than that on Ni4 cluster. The comparable energy barriers of two pathways (O–H or C–H dissociation) on Ni-based clusters indicate that these two paths are quite competitive. In addition, the Ni2M2 clusters show superior activation performance compared with the Ni3M clusters, especially for Ni2Mn2 and Ni2Cr2 clusters. The effects of alloyed metal on the catalytic activity of Ni for methanol initial dehydrogenation, including the adsorption energy, O–H or C–H bond scission barrier and frontier molecular orbital levels, are discussed. It can be concluded that the addition of Co, Fe, Mn and Cr to Ni catalyst is able to enhance the activity of the methanol dehydrogenation reaction. 相似文献
7.
Clay M. Horiuchi 《Surface science》2010,604(2):98-1297
The adsorption and thermal chemistry of γ-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts of CO2 are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO2, and H2. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism. 相似文献
8.
Wing-Cheung Tam C.E. Brion 《Journal of Electron Spectroscopy and Related Phenomena》1974,3(4):263-279
Electron impact energy loss spectra at impact energies of 100 eV and 50 eV and a scattering angle of 2 degrees are presented for alkyl derivatives of H2O and related compounds. Spectra of H2O, CH3OH, CH3OCH3, ethylene oxide, CH3CH2OH, (CH3)2CHOH, (CH3)3C C2H5OC2H5 and tetrahydrofuran are tentatively assigned using derived term values and ionization potentials from photoelectron spectrosc Substituent effects on Rydberg orbital energies are discussed using Taft σ* values. 相似文献
9.
Benni Du 《Molecular physics》2020,118(2)
Kinetics and mechanism of the gas-phase reaction of CH3C(O)OCH(CH3)CH2OCH3 (MPA) with OH radicals in the presence of O2 and NO have been investigated theoretically by performing a high and reliable level of theory, viz., CCSD(T)/6-311?+?G(d,p)//BH&HLYP/6-311++G(d,p)?+?0.9335×ZPE. The calculations predict that the H-abstraction from the ?CH2?O? position of MPA is the most facile channel, which leads to the formation of the corresponding alkoxy radicals CH3C(O)OCH(CH3)C(O ?)HOCH3 under atmospheric conditions. This activated radicals CH3C(O)OCH(CH3)C(O ?)HOCH3 will undergo further rearrangement, fragmentation and oxidative reactions and predominantly leads to the formation of various products (methyl formate HC(O)OCH3 and acetic anhydride CH3C(O)OC(O)CH3). In the presence of water, acetic anhydride can convert into acetic acid CH3C(O)OH via the hydrolysis reaction. The calculated total rate constants over the temperature range 263–372?K are used to derive a negative activation energy (Ea= ?5.88 kJ/mol) and an pre-exponential factor (A?=?1.78×10?12 cm3 molecule?1 s?1). The obtained Arrhenius parameters presented here are in strong agreement with the experimental values. Moreover, the temperature dependence of the total rate constant over a temperature range of 263?1000?K can be described by k?=?5.60 × 10?14×(T/298?K)3.4×exp(1725.7?K/T) cm3 molecule?1 s?1. 相似文献
10.
Yeny A. Tobón Rosana M. Romano Evamarie Hey‐Hawkins Roland Boese Carlos O. Della Védova 《Journal of Physical Organic Chemistry》2009,22(9):815-822
Potassium isopropyl xanthate, (CH3)2CHOC(S)SK, reacts with methyl chloroformiate ClC(O)OCH3 to yield (methoxycarbonyl) (2‐propoxythiocarbonyl) sulfide, (CH3)2CHOC(S)SC(O)OCH3. This novel xanthogen formate was characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry and IR and Raman spectroscopy. The structure of a single crystal of (CH3)2CHOC(S)SC(O)OCH3 was determined by X‐ray diffraction analysis at 173 K. The conformational properties have been studied by liquid IR and Raman spectroscopy, matrix isolation spectroscopy together with photochemical studies and quantum chemical calculations (HF and B3LYP methods with the 6‐31+G* basis set). The analysis of the IR spectrum of liquid (CH3)2CHOC(S)SC(O)OCH3 suggests the presence of two conformers in equilibrium at room temperature. However, in the photochemical matrix study, an equilibrium of three conformers was detected. These forms were further characterized by theoretical calculations. Different photolysis products, such as CH3OC(O)SCH(CH3)2, OCS, CO, CO2 and CS2, were identified by matrix spectroscopy. The IR absorptions of CH3OC(O)SCH(CH3)2, for which literature data are scarce, were analysed in the light of the results of appropriate theoretical calculations. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
11.
An oxyethylene chain (–CH2–CH2–O–) grafted polymer (P(MMA–MAh)–PEGME) was synthesized by reacting poly(ethylene glycol) monomethyl ether (PEGME) with the copolymer of poly(methyl metacrylate–maleic anhydride) (P(MMA–MAh)) and endcapping the residual carboxylic acid with methanol. Rectorite modified with dodecyl benzyl dimethyl ammonium chloride (OREC) was used as a filler additive to modify gel polymer electrolytes (GPE) that consisted of P(MMA–MAh)–PEGME used as polymer matrix, propylene carbonate (PC) as plasticizer and LiClO4 as lithium ion producer. Characterization of interaction of the polar group of C=O or C–O–C in PC and grafted polymer with Li+ and OH group on OREC surface has been thoroughly examined using Fourier transform infrared (FTIR), respectively. The quantitative analysis of FTIR shows that the absorptivity coefficients (a) of polymer/LiClO4, PC/LiClO4, PC/OREC and polymer/OREC are 0.705, 0.113, 0.430 and 0.500, respectively, which means that the Li+ or OH bonded polar group of C=O and C–O–C is more sensitive than free C=O and C–O–C in FTIR spectra. The limited values of bonded C=O and C–O–C equivalent fraction of polymer/LiClO4, PC/LiClO4, PC/OREC and polymer/OREC are 33%, 94%, 60% and 22%, respectively, which implies that the interaction within the components is reversible and the intensity of interaction is ordered as PC/LiClO4, PC/OREC, polymer/OREC and polymer/LiClO4. 相似文献
12.
We applied density functional theory (DFT) calculations to study ethylidyne (CCH3) adsorption and decomposition to C and H over flat and stepped Pd surfaces. Our calculations show that ethylidyne is the most stable molecule among all the possible dehydrogenation or decomposition residues of ethylene. We discuss various possible reaction pathways for ethylidyne decomposition and point out that the most probable one is via ethynyl (CCH) species suggested also by experimental observations. Our calculations indicate that the presence of steps modify the potential energy surface by increasing the binding of most of the species, and also lowering the activation barrier for several reactions. Furthermore we show that the energetics related to dehydrogenation of ethylene and its derivatives manifest a Brønsted–Evans–Polanyi type of behavior. 相似文献
13.
Rongping Deng 《Surface science》2004,573(2):310-319
Methylidyne (CH) was prepared on Pt(1 1 1) by three methods: thermal decomposition of diiodomethane (CH2I2), ethylene decomposition at temperatures above 450 K, and surface carbon hydrogenation. Methylidyne and its precursors are characterized by reflection absorption infrared spectroscopy (RAIRS). The C-I bond of diiodomethane breaks upon adsorption to produce methylene (CH2), which decomposes to methylidyne at temperatures above 130 K. Above 200 K, methylidyne is the only hydrocarbon species observed with RAIRS, although reaction channels for the formation of methane (CH4) and ethylene (C2H4) are indicated by temperature programmed desorption (TPD). As is well known from numerous previous studies, ethylene decomposes to ethylidyne (CCH3) upon exposure to Pt(1 1 1) at 410 K. Upon annealing to 450 K, ethylidyne dissociates through two reaction pathways, dehydrogenation to ethynyl (CCH) and C-C bond scission to methylidyne. Ethylene dehydrogenation on the surface at 750 K and under low ethylene exposures produces surface carbon that can be hydrogenated to methylidyne with C-H and C-D stretch frequencies of 2956 and 2206 cm−1, respectively. Hydrogen co-adsorption on the surface causes these frequencies to shift to higher values. Methylidyne is stable on Pt(1 1 1) to temperatures up to 500 K. 相似文献
14.
《Surface science》1986,171(1):111-134
The mechanism of ethanol decomposition on the Ni(111) surface has been investigated between 155 and 500 K. The sequence of bond scission steps which occur as ethanol undergoes dissociative reactions on this surface has been deduced using deuterium and 13C isotopic labels. Bond activation occurs in the order (1) OH, (2) CH2 (methylene CH), (3) CC, (4) CH3 (methyl CH). The products observed are CH3CHO(g), CH4(g), CO(g), H2(g) and surface carbon, C(a). The latter species exhibits a carbidic AES lineshape in the temperature range 450 to 670 K, at which temperature it dissolves into the Ni bulk. Acetaldehyde, CH3CHO, and methane, CH4, desorb with the same threshold temperature (260–265 K), and the formation of both of these products is controlled by scission of the methylene CH bond (CH2 group). The CH3 group is cleaved from the intermediate surface CH3CHO species to form CH3(ads). H2 exhibits a broad, doublet desorption peak from 300 to 450 K. The carbonoxygen bond in ethanol remains intact and CO ultimately desorbs in a single desorption limited process (Tp = 430 K). A small fraction of CO(a) species undergo exchange with the carbidic surface carbon in a minor process observed above 440 K. 相似文献
15.
The reaction mechanisms of methylhydrazine (CH3NHNH2) with O(3P) and O(1D) atoms have been explored theoretically at the MPW1K/6-311+G(d,p), MP2/6-311+G(d,p), MCG3-MPWPW91 (single-point), and CCSD(T)/cc-pVTZ (single-point) levels. The triplet potential energy surface for the reaction of CH3NHNH2 with O(3P) includes seven stable isomers and eight transition states. When the O(3P) atom approaches CH3NHNH2, the heavy atoms, namely N and C atoms, are the favourable combining points. O(3P) atom attacking the middle-N atom in CH3NHNH2 results in the formation of an energy-rich isomer (CH3NHONH2) followed by migration of O(3P) atom from middle-N atom to middle-H atom leading to the product P6 (CH3NNH2+OH), which is one of the most favourable routes. The estimated major product CH3NNH2 is consistent with the experimental measurements. Reaction of O(1D) + CH3NHNH2 presents different features as compared with O(3P) + CH3NHNH2. O(1D) atom will first insert into C–H2, N1–H4, and N2–H5 bonds barrierlessly to form the three adducts, respectively. There are two most favourable paths for O(1D) + CH3NHNH2. One is that the C–N bond cleavage accompanied by a concerted H shift from O atom to N atom (mid-N) leads to the product PI (CH2O + NH2NH2), and the other is that the N–N bond rupture along with a concerted H shift from O to N (end-N) forms PIV (CH3NH2 + HNO). The similarities and discrepancies between two reactions are discussed. 相似文献
16.
The general features of two series of sol-gel derived materials, designatedurethanesils (Ut), have been investigated by infrared and Raman spectroscopies with the goal of elucidating the chemical environment of
the Eu3+ cations.
The host frameworks of the two families of ormolytes studied have been represented by m-Ut(350) and d-Ut(300), where m stands
for mono, d stands for di, 350 and 300 are the average molecular weights of the organic precursors (poly(ethylene glycol)
methyl ether, PEGME, and poly(ethylene glycol), PEG, respectively).
The hybrid matrix of the mono-xerogels is composed by a siliceous backbone bonded by means of urethane linkages (-NHC (=O)O-)
to pendant methyl end capped oligopolymer chains with approximately 7 oxyethylene units, whereas that of the di-xerogels is
based on a siliceous network grafted through urethane groups to both ends of poly(oxyethylene) segments containing about 6
(OCH2CH2) repeat units.
Both classes of materials have been doped with europium triflate (Eu(CF3SO3)3). The doped samples have been identified by m-Ut(350)nEu(CF3SO3)3 and d-Ut(300)nEu(CF3SO3), where n is the molar ratio of (OCH2CH2) repeat units per Eu3+ ion. Materials with n ranging from ∞ to 5 have been analyzed. The spectral data obtained provide evidence that the cations
begin to coordinate to the ether oxygen atoms of the oligopolymer chains at n=40 in the mono-urethanesils and at n=10 in the
di-urethanesils. In mono-urethanesils samples with n>40 and in di-urethanesils materials with n>10, the Eu3+ coordinate exclusively to the carbonyl oxygen atoms of the urethane linkages.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
17.
用X射线电子能谱(XPS)、热脱附谱(TDS)和紫外光电子能谱(UPS)方法研究了乙烯(C2 sub>H4)在Ru(1010)表面的吸附,在低温下(200K以下)乙稀(C2H4)可以在Ru(1010)表面上以分子状态稳定吸附,在200K以上乙烯(C2H 4)则发生了脱氢分解反应.TDS结果表明乙烯(C2H4)分 解后的主要产物为乙炔(C<
关键词:
乙烯
钌(1010)表面
吸附与分解 相似文献
18.
ZnO with various morphologies have been prepared by a simple microwave-assisted solvothermal method in a short period of time.
In this synthetic method, Zn(CH3COO)2⋅2H2O is used as the reactant, a mixture of water and ethylene glycol is used as solvents, and no other additives are used. The
morphology of the prepared samples can be controlled by changing the mixing ratio of ethylene glycol to water. The photocatalytic
activities of the prepared samples are also investigated. 相似文献
19.
The production of hydrogen via steam reforming of ethanol (SRE) is favourable for the use of hydrogen as an alternative fuel. Co–Mo6S8 possesses high activity and stability for SRE to sustainably produce hydrogen. The competition among reaction pathways related to C–H, O–H, C–C, C–O cleavage and H2 formation was studied. The adsorption and reaction of related intermediates in the ESR reaction pathway are described. The results indicated that the most feasible route for the decomposition of ethanol catalysed by Co–Mo6S8 is CH3CH2OH*→CH3CH2O*→CH3CHO*→CH2CHO*→CHCHO*→CHCO*→CH*+CO*. The CH* can be decomposed into C*+H*, and CO* can be oxidised via the redox mechanism of the water gas shift (WGS) reaction. Thus the final products are CO2 and H2. The present result may help people to design an SRE catalyst, which has the ability to break C–C to form CO and H2, then CO react with H2O in the WGS reaction generating CO2 and H2. 相似文献
20.
Anjani Gunturu Rubik Asatryan Joseph W. Bozzelli 《Journal of Physical Organic Chemistry》2011,24(5):366-377
Sulfur–Oxygen containing hydrocarbons are formed in oxidation of sulfides and thiols in the atmosphere, on aerosols and in combustion processes. Understanding their thermochemical properties is important to evaluate their formation and transformation paths. Structures, thermochemical properties, bond energies, and internal rotor potentials of methyl sulfinic acid CH3S(?O)OH, its methyl ester CH3S(?O)OCH3 and radicals corresponding to loss of a hydrogen atom have been studied. Gas phase standard enthalpies of formation and bond energies were calculated using B3LYP/6‐311G (2d, p) individual and CBS‐QB3 composite methods employing work reactions to further improve accuracy of the ${\Delta} _{{\bf f}} H_{{\bf 298}}^{{\bf o}} $ . Molecular structures, vibration frequencies, and internal rotor potentials were calculated. Enthalpies of the parent molecules CH3S(?O)OH and CH3S(?O)OCH3 are evaluated as ?77.4 and ?72.7 kcal mol?1 at the CBS? QB3 level; Enthalpies of radicals C?H2? S(?O)? OH, CH3? S?(?O)2, C?H2? S(?O)? OCH3 and CH3? S(?O)? OC?H2 (CBS‐QB3) are ?25.7, ?52.3, ?22.8, and ?26.8 kcal mol?1, respectively. The CH3C(?O)O—H bond dissociation energy is of 77.1 kcal mol?1. Two of the intermediate radicals are unstable and rapidly dissociate. The CH3S(?O)? O. radical obtained from the parent CH3? S(?O)? OH dissociates into methyl radical (${\bf CH}_{{\bf 3}}^{{\bf .}} $ ) plus SO2 with endothermicity (ΔHrxn) of only 16.2 kcal mol?1. The CH3? S(?O)? OC?H2 radical dissociates into CH3? S?=O and CH2=O with little or no barrier and an exothermicity of ?19.9 kcal mol?1. DFT and the Complete Basis Set‐QB3 enthalpy values are in close agreement; this accord is attributed to use of isodesmic work reactions for the analysis and suggests this combination of B3LYP/work reaction approach is acceptable for larger molecules. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献