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1.
Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO 2 + CO). However, addition of LiCl drastically improved the yield of C 2 compounds (C 2H 6 + C 2H 4). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH 4. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH 4 to C 2H 4 through C 2H 6 (2CH 4 → C 2H 6 → C 2H 4). The study on the oxidation of C 2H 6 over the LiCl/NiO showed that the oxidative dehydrogenation of C 2H 6 to C 2H 4 occurs very selectively, which is the main reason why partial oxidation of CH 4 over LiCl/NiO gives C 2H 4 quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH 4. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni (2+δ)+ or Ni 3+). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH 4---CD 4 exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide. 相似文献
2.
Several hexaaluminate-related materials were prepared via hydrolysis of alkoxide and powder mixing method for high temperature combustion of CH 4 and C 3H 8, in order to investigate the effect of the concentration of the fuels, O 2 and H 2O on NO x emission and combustion characteristics. Among the hexaaluminate catalysts, Sr 0.8La 0.2MnAl 11O 19− prepared by the alkoxide method exhibited the highest activity for methane combustion and low NO x emission capability. NO x emission at 1500 °C was increased linearly with O 2 concentration, whereas water vapor addition decreased NO x emission in CH 4 combustion over the Sr 0.8La 0.2MnAl 11O 19− catalyst. In the catalytic combustion of C 3H 8 over the Sr 0.8La 0.2MnAl 11O 19− catalyst, the amount of NO x emitted was raised in the temperature range between 1000 and 1500 °C when the C 3H 8 concentration increased from 1 to 2 vol.%. It was found that NO x emission in this temperature range was reduced effectively by adding water vapor. 相似文献
3.
为研究C 2H 6/C 3H 8对甲烷爆炸极限参数及动力学特性的影响,采用标准的可燃气体爆炸极限测定装置测定了不同配比的C 2H 6/C 3H 8混合气体对甲烷爆炸极限的影响规律,同时得出了氮气惰化条件下甲烷爆炸临界参数的变化规律。此外,利用Chemkin软件模拟了C 2H 6/C 3H 8混合气体对甲烷爆炸过程中中间产物浓度的影响情况,并进行了敏感性分析。结果表明,C 2H 6/C 3H 8的存在降低了甲烷的爆炸上下限,增大了甲烷的爆炸危险度;在氮气惰化过程中甲烷的爆炸上限下降,爆炸下限上升,最终爆炸上下限重合,重合点处甲烷浓度和氮气临界浓度均随C 2H 6/C 3H 8的添加而逐渐减小;此外,C 2H 6/C 3H 8混合气体使甲烷爆炸过程中CO和·H的生成量逐渐增大,而CO 2、·O和·OH的生成量则有下降趋势,通过对爆炸过程中甲烷体积的敏感性分析,发现C 2H 6/C 3H 8的存在在某种程度上促进了甲烷爆炸。对比不同配比的C 2H 6/C 3H 8混合气体,发现C 3H 8含量越高,其对甲烷爆炸过程中相关参数的影响越大,这可为工矿企业的安全生产提供一定的理论依据。 相似文献
4.
The selective reduction of NO x over H-mordenite (H-m) was studied using CH 3OH as reducing agent. Results are compared with those obtained with other conventional reducing agents (ethylene and methane), with gas-phase reactions, and with other metal-exchanged mordenites (Cu-mordenite (Cu-m) and Co-mordenite (Co-m)). H-m was found to be an effective catalyst for the SCR of NO x with CH 3OH. When different reducing agents were compared over H-m, CH 3OH > C 2H 4 > CH 4 was the order according to the maximum NO conversion obtained using 1% of oxygen in the feed. Instead, if selectivity is considered, the order results CH 4 > CH 3OH > C 2H 4. In reaction experiments, two distinct zones defined by two maxima with NO to N 2 conversion are obtained at two different temperatures. A correlation exists between the said zones and the CO : CO 2 ratio. At low temperatures, CO prevails whereas at high temperatures CO 2 prevails. These results indicate that there exist different reaction intermediates. Evidence from reaction experiments, FTIR results, and transient experiments suggest that the reaction mechanism involves formaldehyde and dimethyl ether (DME) as intermediates in the 200–500°C temperature range. The surface interaction between CH 3OH (or its decomposition products) and NO is negligible if compared with NO 2, indicating that the oxidation of NO to NO 2 on acid sites is a fundamental path in this system. Different from other non-oxygenated reductants (methane and ethylene), a gas-phase NO x initiation effect on hydrocarbon combustion was not observed. 相似文献
5.
Conversion of CH 4, C 2H 6, C 3H 8, benzene and their binary mixtures over H-NaZSM-5 catalyst in the presence of N 2O was studied. It was found that under experimental conditions methane alkylates benzene to give toluene and xylenes. Acidity of the catalyst had no effect on the reactivity of active oxygen formed from N 2O towards methane and benzene, but affected their secondary transformation. Acidic samples favored the reaction of aromatic ring methylation with methane whereas deep oxidation of CH 4 prevailed on NaHZSM-5. Based on the relative reactivities and 13C label distribution in the products of 13CH 4+C 6H 6+N 2O feed conversion, the scheme of hydrocarbon transformation was proposed. 相似文献
6.
Selective catalytic reduction of NO x by C 3H 6 in the presence of H 2 over Ag/Al 2O 3 was investigated using in situ DRIFTS and GC–MS measurements. The addition of H 2 promoted the partial oxidation of C 3H 6 to enolic species, the formation of –NCO and the reactions of enolic species and –NCO with NO x on Ag/Al 2O 3 surface at low temperatures. Based on the results, we proposed reaction mechanism to explain the promotional effect of H 2 on the SCR of NO x by C 3H 6 over Ag/Al 2O 3 catalyst. 相似文献
7.
The effect of different reducing agents (H 2, CO, C 3H 6 and C 3H 8) on the reduction of stored NO x over PM/BaO/Al 2O 3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO 2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H 2 and CO have a relatively high NO x reduction efficiency compared to C 3H 6 and especially C 3H 8 that does not show any NO x reduction ability except at 350 °C over Pd/BaO/Al 2O 3. The type of precious metals affects the NO x storage-reduction properties, where the Pd/BaO/Al 2O 3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al 2O 3 catalyst shows a high reduction ability but a relatively low NO x storage capacity. 相似文献
8.
It has been shown that it is possible to decrease fuel-NO x produced from NH 3 using catalytic combustion of a synthetic gasified biomass at fuel-lean conditions. In a certain temperature regime where the conversion of fuel components, such as CO, H 2 and CH 4, is low and conversion of NH 3 is high, it is suggested that the formed NO x is reduced by the remaining fuel components, mainly hydrocarbons. With oxide catalysts only ca. 10% of the NH 3 was converted to NO x, the rest to N 2. It has also been shown that the ignition sequence of CO, H 2 and CH 4 varied for different catalysts and different experimental conditions, and that methane coupling and methanation reactions occurred before ignition of CH 4. 相似文献
9.
Experimental proofs of a free radical mechanism in methane oxidative coupling, with homolytic rupture of the C---H bond are given. High concentrations of free radical sites are produced by mechanical milling of SiO 2. A study of C 1---C 3alkanes interaction with these sites allows to simulate the, processes of alkanes oxidation and oxidative dehydrogenation. The reactivity of ethane and propane is higher than that of methane in accordance with the Polanyi-Semenov rule. Oxidative dehydrogenation of ethane is studied on Cd-containing zeolites. CH 4, C 2H 6 and C 3H 8 oxidative dehydrogenation by O 2 or CO 2 is studied on a MNO/SiO 2 catalyst. The initiation of radical reactions of hydrocarbons on Cl-containing catalysts proceeds via chlorine atoms generation. 相似文献
10.
A dense membrane tube made of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3−δ (BSCF) was prepared by plastic extrusion from BSCF oxide synthesized by the complexing EDTA-citrate method. The membrane tube was used in a catalytic membrane reactor for oxidative coupling of methane (OCM) to C 2 without an additional catalyst. At high methane concentration (93%), about 62% C 2 selectivity was obtained, which is higher than that achieved in a conventional reactor using the BSCF as a catalyst. The dependence of the OCM reaction on temperature and methane concentration indicates that the C 2 selectivity in the BSCF membrane reactor is limited by high ion recombination rates. If an active OCM catalyst (La-Sr/CaO) was packed in the membrane tube, C 2 selectivity and CH 4 conversion increased compared to the blank run. The highest C 2 yield in the BSCF membrane reactor in presence of the La-Sr/CaO catalyst was about 15%, similar to that in a packed-bed reactor with the same catalyst under the same conditions. However, the ratio of C 2H 4/C 2H 6 in the membrane reactor was much higher than that in the packed-bed reactor, which is an advantage of the membrane reactor. 相似文献
11.
This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO 2 with C 2H 4 as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C 2H 4/SO 2, and pretreatment are all important factors affecting catalyst activity. Fe 2O 3/γ-Al 2O 3 was found to be the most active catalyst among six γ-Al 2O 3-supported metal oxide catalysts tested. With Fe 2O 3 as the active species, of the supports tested, CeO 2 is the most suitable one. Using this Fe 2O 3/CeO 2 catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C 2H 4/SO 2 is 1:1, and the catalyst presulfidized by H 2+H 2S exhibits a higher performance than those pretreated with H 2 or He. Although the feed concentrations of C 2H 4:SO 2 being 3000:3000 ppm provide a higher conversion of SO 2, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C 2H 4 temperature-programmed desorption (C 2H 4-TPD) and SO 2-TPD desorption patterns illustrate that Fe 2O 3/CeO 2 can adsorb and desorb C 2H 4 and SO 2 more easily than can Fe 2O 3/γ-Al 2O 3. Moreover, the SO 2-TPD patterns further show that Fe 2O 3/γ-Al 2O 3 is more seriously inhibited by SO 2. These findings may properly explain why Fe 2O 3/CeO 2 has a higher activity for the reduction of SO 2. 相似文献
12.
The decomposition of different hydrocarbons (CH 4, C 2H 6, C 2H 4, C 2H 2, C 3H 8, and C 3H 6) over Ni (5 wt.%)/SiO 2 catalysts was carried out. The initial rates of decomposition of the hydrocarbons, the kinetic curves of the decomposition and the kinetic curves of the hydrogenation of deposited carbon into methane depended on the types of hydrocarbons. In addition, the catalytic life of the Ni/SiO 2 catalyst was also dependent on the types of hydrocarbons, i.e. the life was longer according to the order, alkanes>alkenesacetylene. The carbons deposited on the catalyst were characterized by SEM and Raman spectroscopy. The appearances of the deposited carbons were different among alkanes, alkenes, and acetylene, i.e. a zigzag fiber structure from methane, and a rolled fiber structure from alkenes and acetylene. From Raman spectra of the deposited carbons, it was found that the degree of graphitization of deposited carbon was higher in the order, alkanes>alkenes>acetylene. These results suggest that the mechanism of decomposition of hydrocarbons and the growth mechanism of carbon fibers on the catalyst were different among alkanes, alkenes and acetylene. 相似文献
13.
The composition and structure of the product of mixture CH 4+CD 4 oxidative coupling over natural manganese mineral catalyst at 3% and 25% methane conversion in redox mode at 850°C have been determined by IR-Absorption- Reflection spectroscopy technique. At low methane conversion there were ethanes: H 3OCH 3, H 3OCD 3, D 3CCD 3 and ethylenes: H 2CCH 2, H 2CCD 2, D 2CCD 2 only The data obtained showed that the reaction proceeds by gas-phase CH 3, CD 3 radicals coupling and ethane is the primary C 2-product and ethylene is produced by gas-phase conversion of ethane. 相似文献
14.
Catalytic hydrodehalogenation of CBrF 3 with methane was studied over NiZSM-5 and HZSM-5 in tubular reactor between 573 and 873 K and at ambient pressure. It was found that the incorporation of nickel into HZSM-5 significantly enhanced the activity of the zeolite. A variety of products were formed during reaction, including CH 3Br, CHF 3, CH 2Br 2, C 2F 6, C 2H 4, C 2H 2, C 2H 2F 2, CHBrF 2, CH 2BrF, and C 2H 3Br. XRD analysis showed that these two zeolite catalysts did not suffer any loss in their crystallinity during use. Deactivation of both NiZSM-5 and HZSM-5 may, in part, be due to poisoning of the zeolite by halogens. Coking is another cause of the deactivation of HZSM-5, but appears to play a minor role in NiZSM-5 deactivation. A series of methylated silicone oils was detected during reaction over NiZSM-5. 相似文献
15.
A disk-type Sm 0.4Ba 0.6Co 0.2Fe 0.8O 3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H 2). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH 4 diluted with Ar. While CH 4 conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH 4 conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH 4 compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH 4 was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H 2 was fed. It is implied that the oxidation of CO and H 2 with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO 2 and H 2O react with CH 4 by reforming reactions to form syngas. 相似文献
16.
A gliding arc discharge (GRD) reactor was used to decompose ethanol into primarily H 2 and CO with small amounts of CH 4, C 2H 2, C 2H 4, and C 2H 6. The ethanol concentration, electrode gap, input voltage and Ar flow rate all affected the conversion of ethanol with results ranging from 40.7% to 58.0%. Interestingly, for all experimental conditions the S H2/S CO selectivity ratio was quite stable at around 1.03. The mechanism for the decomposition of ethanol is also described. 相似文献
17.
The pulse corona plasma has been used as an activation method for reaction of methane and carbon dioxide, the product was C 2 hydrocarbons and by-products were CO and H 2. Methane conversion and the yield of C 2 hydrocarbons were affected by the carbon dioxide concentration in the feed. The conversion of methane increased with increasing carbon dioxide concentration in the feed whereas the yield of C 2 hydrocarbons decreased. The synergism of La 2O 3/γ-Al 2O 3 and plasma gave methane conversion of 24.9% and C 2 hydrocarbons yield of 18.1% were obtained at the power input of plasma was 30 W. The distribution of C 2 hydrocarbons changed by using Pd-La 2O 3/γ-Al 2O 3 catalyst, the major C 2 product was ethylene. 相似文献
18.
In order to examine the importance of the further oxidation of the desired C 2 products in the oxidative coupling of methane, ethylene and ethane have been added to the feed (containing methane and oxygen) to a Li/MgO or Ca/Sm 2O 3 catalyst. The results of these measurements show that neither of these C 2 molecules is stable under these conditions with either of the catalysts. Additionally, the rates of the oxidation of ethane and of ethylene alone have been measured using a gradientless reactor for both catalysts as well as for a quartz bed. It was found that the Ca/Sm 2O 3 material had higher activities for the oxidation of C 2H 6 and C 2H 4 (and also of CH 4) than had the Li/MgO material. These higher activities result in a lower optimal reaction temperature for the oxidative coupling of methane and are (at least partially) responsible for the lower selectivity to C 2 products observed with the Ca/Sm 2O 3 catalyst compared to that with the Li/MgO catalyst. 相似文献
19.
Conversion of NO x with reducing agents H 2, CO and CH 4, with and without O 2, H 2O, and CO 2 were studied with catalysts based on MOR zeolite loaded with palladium and cerium. The catalysts reached high NO x to N 2 conversion with H 2 and CO (>90% conversion and N 2 selectivity) range under lean conditions. The formation of N 2O is absent in the presence of both H 2 and CO together with oxygen in the feed, which will be the case in lean engine exhaust. PdMOR shows synergic co-operation between H 2 and CO at 450–500 K. The positive effect of cerium is significant in the case of H 2 and CH 4 reducing agent but is less obvious with H 2/CO mixture and under lean conditions. Cerium lowers the reducibility of Pd species in the zeolite micropores. The catalysts showed excellent stability at temperatures up to 673 K in a feed with 2500 ppm CH 4, 500 ppm NO, 5% O 2, 10% H 2O (0–1% H 2), N 2 balance but deactivation is noticed at higher temperatures. Combining results of the present study with those of previous studies it shows that the PdMOR-based catalysts are good catalysts for NO x reduction with H 2, CO, hydrocarbons, alcohols and aldehydes under lean conditions at temperatures up to 673 K. 相似文献
20.
The performance of unpromoted and MO x-(M: alkali (earth), transition metal and cerium) promoted Au/Al 2O 3 catalysts have been studied for combustion of the saturated hydrocarbons methane and propane. As expected, higher temperatures are required to oxidize CH 4 (above 400 °C), compared with C 3H 8 (above 250 °C). The addition of various MO x to Au/Al 2O 3 improves the catalytic activity in both methane and propane oxidation. For methane oxidation, the most efficient promoters to enhance the catalytic performance of Au/Al 2O 3 are FeO x and MnO x. For C 3H 8 oxidation a direct relationship is found between the catalytic performance and the average size of the gold particles in the presence of alkali (earth) metal oxides. The effect of the gold particle size becomes less important for additives of the type of transition metal oxides and ceria. The results suggest that the role of the alkali (earth) metal oxides is related to the stabilization of the gold nanoparticles, whereas transition metal oxide and ceria additives may be involved in oxygen activation. 相似文献
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