共查询到20条相似文献,搜索用时 15 毫秒
1.
The role of framework oxygen atoms in N 2O decomposition [N 2O(g)→N 2(g) and 1/2O 2(g)] over Fe‐ferrierite is investigated employing a combined experimental (N 218O decomposition in batch experiments followed by mass spectroscopy measurements) and theoretical (density functional theory calculations) approach. The occurrence of the isotope exchange indicates that framework oxygen atoms are involved in the N 2O decomposition catalyzed by Fe‐ferrierite. Our study, using an Fe‐ferrierite sample with iron exclusively present as Fe II cations accommodated in the cationic sites, shows that the mobility of framework oxygen atoms in the temperature range: 553 to 593 K is limited to the four framework oxygen atoms of the two AlO 4? tetrahedra forming cationic sites that accomodate Fe II. They exchange with the Fe extra‐framework 18O atom originating from the decomposed N 218O. We found, using DFT calculations, that O 2 molecules facilitate the oxygen exchange. However, the corresponding calculated energy barrier of 87 kcal mol ?1 is still very high and it is higher than the assumed experimental value based on the occurrence of the sluggish oxygen exchange at 553 K. 相似文献
2.
The decomposition of N 2O is strongly promoted by NO over steam-activated FeZSM-5. The promoting effect of NO is catalytic, and in addition to NO 2, 2 is formed much more extensively at lower temperatures than in the absence of NO. The promotion effect only requires low NO concentrations in the feed, with no significant improvements at molar NO/N 2O feed ratios higher than 0.25. No inhibition by NO was identified even at a molar NO/N 2O feed ratio of 10, suggesting different sites for NO adsorption and oxygen deposition by N 2O. The latter sites seem to be remote from each other. Transient experiments using in situ FT-IR/MS and Multitrack over FeZSM-5 further elucidate the mechanism of NO promotion. The release of oxygen from the catalyst surface during direct N 2O decomposition is a rate-determining step due to the slow oxygen recombination, which is favored by high reaction temperatures. NO addition promotes this oxygen desorption, acting as an oxygen transfer agent, probably via NO 2 species. Adsorbed NO may facilitate the migration of atomic oxygen to enhance their recombination. Less than 0.9% of Fe seems to participate in this promotion. A model is proposed to explain the phenomena observed in NO-assisted N 2O decomposition, including NO 2 decomposition. 相似文献
3.
Selective reduction of nitric oxide (NO) by ethene in the presence of excess oxygen was investigated using a silver supported
on TiO 2 (Ag/TiO 2) catalyst. Ag/TiO 2 showed high catalytic activity for the reduction of NO to N 2 and N 2O. The activity for the reduction of NO to N 2 and N 2O was enhanced with an increase up to 3 wt.% Ag loading level. On increasing the concentration of ethene, the catalytic activity
for the reduction of NO to N 2 and N 2O was enhanced. The reduction of NO over Ag/TiO 2 catalyst never proceeds without coexistent oxygen. 相似文献
4.
The behavior of lattice oxygen species of the ferroelectric material during methane oxidation was investigated using a nonthermal plasma reactor packed with BaTiO
3
pellets. Lattice oxygen species in BaTiO
3
play an important role in the formation of N
2
O and the oxidation of CH
4
. The oxidation products such as CO and CO
2
were formed from independent reaction pathways. Lattice oxygen species were able to preferentially oxidize the carbon species deposited on the pellet surface into CO. Also, N
2
O and NO
x
were independently formed in the N
2– O
2
reaction, suggesting that different oxygen species give N
2
O and NO
x. N
2
O was produced by the oxidation of molecular nitrogen with lattice oxygen species. 相似文献
5.
The adsorption of N 2O on finely divided ZnO at room temperature shows two principal infrared absorption bands at 2237 cm −1 (strong) and 1255 cm −1 (weak), corresponding to the reversible adsorption of an N 2O surface species. The N 2O is postulated to be coordinated to Zn 2+ cations by the oxygen atom. Water pre-treatment of the ZnO surface gives only weak bands from adsorbed N 2O, indicating that the latter's adsorption site is taken up by adsorbed water. Spectroscopic experiments on ‘reduced’ surfaces of ZnO at 200°C show that limited reaction of N 2O with the surface has occurred, presumably through decomposition to nitrogen and adsorbed oxygen. New adsorptions on the ZnO surface itself, and a reduced amount of reversibly adsorbed N 2O, implied a reduction in pressure of the adsorbate. Such effects were not observed appreciably over ‘oxidised’ ZnO. 相似文献
6.
Different surface sites of solid catalysts are usually quantified by dedicated chemisorption techniques from the adsorption capacity of probe molecules, assuming they specifically react with unique sites. In case of methanol synthesis catalysts, the Cu surface area is one of the crucial parameters in catalyst design and was for over 25 years commonly determined using diluted N 2O. To disentangle the influence of the catalyst components, different model catalysts were prepared and characterized using N 2O, temperature programmed desorption of H 2, and kinetic experiments. The presence of ZnO dramatically influences the N 2O measurements. This effect can be explained by the presence of oxygen defect sites that are generated at the Cu‐ZnO interface and can be used to easily quantify the intensity of Cu‐Zn interaction. N 2O in fact probes the Cu surface plus the oxygen vacancies, whereas the exposed Cu surface area can be accurately determined by H 2. 相似文献
7.
The reactivity of phosphenium dication [(Ph 3P) 2C‐P‐N iPr 2] 2+, 1 2+ , towards pyridine N‐oxide (O‐py) has been investigated. The resulting oxophosphonium dication [(Ph 3P) 2C(N iPr 2)P(O)(O‐py)] 2+, 2 2+ , was surprisingly stabilized by a less nucleophilic O‐py ligand instead of pyridine (py). This compound was then identified as an analogue of the elusive Criegee intermediate as it underwent oxygen insertion into the P?C bond through a mechanism usually observed for Baeyer–Villiger oxidations. This oxygen insertion appears to be the first example of a Baeyer–Villiger oxidation involving O‐py. 相似文献
8.
The reaction of precursors containing both nitrogen and oxygen atoms with Ni II under 500 °C can generate a N/O mixing coordinated Ni‐N 3O single‐atom catalyst (SAC) in which the oxygen atom can be gradually removed under high temperature due to the weaker Ni?O interaction, resulting in a vacancy‐defect Ni‐N 3‐V SAC at Ni site under 800 °C. For the reaction of Ni II with the precursor simply containing nitrogen atoms, only a no‐vacancy‐defect Ni‐N 4 SAC was obtained. Experimental and DFT calculations reveal that the presence of a vacancy‐defect in Ni‐N 3‐V SAC can dramatically boost the electrocatalytic activity for CO 2 reduction, with extremely high CO 2 reduction current density of 65 mA cm ?2 and high Faradaic efficiency over 90 % at ?0.9 V vs. RHE, as well as a record high turnover frequency of 1.35×10 5 h ?1, much higher than those of Ni‐N 4 SAC, and being one of the best reported electrocatalysts for CO 2‐to‐CO conversion to date. 相似文献
9.
The application of nitrous oxide as an alternative oxidant provides new opportunities for selective oxidation of olefins. Here, we studied for the first time the thermal oxidation of isobutene with N 2O in the liquid phase. The study revealed that the oxidation proceeds via 1,3-dipolar cycloaddition of N 2O to the CC bond by two routes forming unstable 4,5-dihydro-[1,2,3]-oxadiazole intermediates. The main route (the contribution of 91%) includes the addition of the N 2O oxygen to the second carbon atom in olefin. In this case, the oxadiazole decomposes with the CC bond cleavage yielding acetone, methylene (:CH 2), and N 2. The methylene then readily reacts with isobutene and benzene (solvent). The minor route involves the addition of the N 2O oxygen to the first carbon atom and the oxadiazole decomposition with a hydrogen shift leading to isobutanal and N 2.The main distinctive feature of the studied reaction is the formation of methylene in high yield. 相似文献
10.
Plasma polymerizations (under 13.5-MHz radiofrequency inductively coupled glow discharge) of some organic compounds are investigated by their properties (elemental analysis, surface energy, and infrared spectra) and their relations to the concentrations of free radicals in the polymers as detected by electron spin resonance (ESR) spectroscopy. Monomers that have been investigated are hexamethyldisiloxane, tetrafluoroethylene, acetylene, acetylene/N 2, acetylene/H 2O, acetylene/N 2/H 2O, allene, allene/N 2, allene/H 2O, allene/N 2/H 2O, ethylene, ethylene/N 2, ethylene oxide, propylamine, allylamine, propionitrile, and acrylonitrile. Plasma-polymerized polymers generally contain oxygen, even if the starting monomers do not contain oxygen. This oxygen incorporation is related to the free-radical concentration in the polymer. Molecular nitrogen copolymerizes with other organic monomers such as acetylene, allene, and ethylene, and their properties are very similar to those of plasma-polymerized polymers from nitrogen-containing compounds such as amines and nitriles. The addition of water to the monomer mixture reduces in a dramatic manner the concentration of free radicals in the polymer and consequently the oxygen-incorporation after the polymer is exposed to air. The concentrations of free radicals (by ESR) are directly correlated to the change of the properties of plasma-polymerized polymers with time of exposure to the atmosphere. These changes are primarily the introduction of carbonyl (and possibly hydroxyl) groups. The addition of water to the plasma introduces these groups during the polymerization. 相似文献
11.
The aim of this study is to explore the potential of utilizing carbon-doped fullerene-like boron-nitride nanocages (B11N12C and B12N11C) as an efficient metal-free catalyst for the oxidation of SO2 to SO3 molecule in the presence of N2O. The oxidation of SO2 over B11N12C includes two steps. First, the N2O molecule is decomposed into an activated oxygen atom (O*) and N2 molecule, and then the SO2 molecule is oxidized by the O* species. In the case of B12N11C and B12N12, however, the reaction starts with the coadsorption of SO2 and N2O molecules, followed by the decomposition of N2O and the formation of SO3 and N2 species. According to our results, B11N12C exhibits larger catalytic activity for the SO2 oxidation compared with B12N11C and B12N12 clusters. The estimated activation energy for the SO2 + O* → SO3 reaction catalyzed over the B11N12C surface is 5.8 kcal/mol, which is comparable with those reported about noble-metal catalysts. The results of this study can be useful for developing metal-free catalysts based on C-doped BN nanostructures. 相似文献
12.
Commercial silicon powders are nitrided at constant temperatures (1453 K; 1513 K; 1633 K; 1693 K). The X-ray diffraction results show that small amounts of Si 3N 4 and Si 2N 2O are formed as the nitridation products in the samples. Fibroid and short columnar Si 3N 4 are detected in the samples. The formation mechanisms of Si 3N 4 and Si 2N 2O are analyzed. During the initial stage of silicon powder nitridation, Si on the outside of sample captures slight amount of O 2 in N 2 atmosphere, forming a thin film of SiO 2 on the surface which seals the residual silicon inside. And the oxygen partial pressure between the SiO 2 film and free silicon is decreasing gradually, so passive oxidation transforms to active oxidation and metastable SiO(g) is produced. When the SiO(g) partial pressure is high enough, the SiO 2 film will crack, and N 2 is infiltrated into the central section of the sample through cracks, generating Si 2N 2O and short columnar Si 3N 4 in situ. At the same time, metastable SiO(g) reacts with N 2 and form fibroid Si 3N 4. In the regions where the oxygen partial pressure is high, Si 3N 4 is oxidized into Si 2N 2O. 相似文献
13.
Summary Multipulse experiments reveal qualitative and quantitative, time-resolved information about the interaction of N 2O with ZSM-5 type zeolites under conditions of catalytic applications, like the mechanism of N 2O decomposition, amount and reactivity of an atomic surface oxygen species. 相似文献
14.
The AC high-voltage discharge-induced decomposition chemistry of trace levels of hydrogen cyanide in helium has been studied. In the absence of oxygen only low levels of molecular nitrogen were evolved. With oxygen added, the principal products were CO, CO 2, and N 2. No significant concentrations of NO or N 2O were observed. The response of a commercial NO x analyzer to HCN and C 2N 2, in the NO x mode, was determined to be linear through three decades in concentration. The oxidation chemistry of HCN and C 2N 2 in the stainless steel converter of the analyzer was studied as a function of the amount of added oxygen.NRL/NRC Postdoctoral Fellow (1983–1985). 相似文献
15.
用溶胶凝胶法制备了一组Ni xCo 1-xCoAlO 4尖晶石型复合氧化物,并采用表面润湿浸渍K 2CO 3溶液进行了K掺杂改性,用于有氧气氛下的N 2O催化分解反应.采用N 2物理吸附、X-射线衍射(XRD)、扫描电镜(SEM)、H 2-程序升温还原(H 2-TPR)等技术对催化剂进行了表征,考察了催化剂组成、母液pH值、K负载量等制备参数对其催化活性的影响.结果表明,母液pH值为3、K/(Ni+Co)物质的量比为0.1的K/Ni 0.15Co 0.85CoAlO 4催化剂具有较高的N 2O分解活性,450 ℃ N 2O可完全分解.助剂K的加入弱化了催化剂表面金属氧键,提高了催化剂的还原性、催化活性和抗水性. 相似文献
16.
The rate constant for the reaction of ground-state oxygen atoms with methanol has been determined between 297 and 544 K by a phase-shift technique using mercury photosensitized decomposition of N 2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 10 12 exp[(?2267 ± 111)/ T]cm 3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third-body efficiency of CH 3OH relative to N 2O for the reaction O + NO + M → NO 2 + M (M = CH 3OH) was determined to be 3.1 at 298 K. 相似文献
17.
以十六烷基三甲基溴化胺(CTAB)为模板剂,通过调变CTAB浓度水热合成了氧化钴前驱体,焙烧制得棒状形貌的Co 3O 4,在其表面浸渍K 2CO 3溶液制得K改性的Co 3O 4催化剂,用于N 2O分解。用X射线衍射(XRD)、N 2物理吸附(BET)、扫描电镜(SEM)、X射线光电子能谱(XPS)、H 2程序升温还原(H 2-TPR)和O 2程序升温脱附(O 2-TPD)等技术对催化剂进行了表征,考察了CTAB/钴及尿素/钴物质的量比等制备参数对Co 3O 4催化分解N 2O活性的影响。结果表明,CTAB浓度为0.05 mol/L、CTAB/钴离子物质的量比为1、尿素/钴离子物质的量比为4时,所制备的Co 3O 4催化剂具有较高的N 2O分解活性,而K改性可以进一步提升其催化性能。K改性的Co 3O 4在有氧有水气氛中400℃下进行N 2O分解反应,50 h后N 2O转化率仍保持在91%以上。 相似文献
18.
The oxidation of alcohols with N 2O as the hydrogen acceptor was achieved with low catalyst loadings of a rhodium complex that features a cooperative bis(olefin)amido ligand under mild conditions. Two different methods enable the formation of either the corresponding carboxylic acid or the ester. N 2 and water are the only by‐products. Mechanistic studies supported by DFT calculations suggest that the oxygen atom of N 2O is transferred to the metal center by insertion into the Rh?H bond of a rhodium amino hydride species, generating a rhodium hydroxy complex as a key intermediate. 相似文献
19.
The reactions of N 2O with NO and OH radicals have been studied using ab initio molecular orbital theory. The energetics and molecular parameters, calculated by the modified Gaussian-2 method (G2M), have been used to compute the reaction rate constants on the basis of the TST and RRKM theories. The reaction N 2O + NO → N 2 + NO 2 (1) was found to proceed by direct oxygen abstraction and to have a barrier of 47 kcal/mol. The theoretical rate constant, k1 = 8.74 × 10 −19 × T 2.23 exp (−23,292/T) cm 3 molecule −1 s −1, is in close agreement with earlier estimates. The reaction of N 2O with OH at low temperatures and atmospheric pressure is slow and dominated by association, resulting in the HONNO intermediate. The calculated rate constant for 300 K ≤ T ≤ 500 K is lower by a few orders than the upper limits previously reported in the literature. At temperatures higher than 1000 K, the N 2O + OH reaction is dominated by the N 2 + O 2H channel, while the HNO + NO channel is slower by 2–3 orders of magnitude. The calculated rate constants at the temperature range of 1000–5000 K for N 2O + OH → N 2 + O 2H (2A) and N 2O + OH → HNO + NO (2B) are fitted by the following expressions: in units of cm 3 molecule −1s −1. Both N 2O + NO and N 2O + OH reactions are confirmed to enhance, albeit inefficiently, the N 2O decomposition by reducing its activation energy. © 1996 John Wiley & Sons, Inc. 相似文献
20.
Ab initio MO calculations predict the preferred site of protonation of N 2O to be at the oxygen atom, and yield a structure of N 2OH + and protonation energies in excellent accord with experiment. 相似文献
|