共查询到20条相似文献,搜索用时 31 毫秒
1.
Na-Mn-W/SiO 2 catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH 4 conversion of 15.1% with a C 2+ selectivity of 71.8% was obtained under 750 oC, 1.0×10 5h -1 GHSV, CH 4/O 2 ratio of 8 and 1.0 MPa. Moreover, 17.3% CH 4 conversion with 51.6% C 2 selectivity and 23.6% C 3-C 4 selectivity was obtained under 750 oC, 2.0×10 5h -1 GHSV, CH 4/O 2 ratio of 8 and 1.0 MPa. 相似文献
2.
The effect of the HF modification of ferrospheres separated from fly ash after the combustion of brown coal on their chemical, phase compositions and catalytic properties in the oxidative coupling of methane was studied. The modification led to a change in the phase composition in comparison with that of the initial ferrospheres: a CaF2 phase appeared, the hematite phase content increased, and the ferrospinel content decreased. The yield of C2 hydrocarbons at 750°C increased by a factor of 1.5–2.0, and the fraction of ethylene in them increased to 30 or 65% at 750 or 850°C, respectively. It was assumed that an increase in the efficiency of HF-modified ferrospheres in the formation of ethane and its dehydrogenation into ethylene was due to the formation of oxyfluoride-type active sites. The pyrohydrolysis of fluorine-containing catalyst components at 850°C due to interaction with water vapor in a reaction atmosphere led to the formation of systems active in deep oxidation; this manifested itself in a sharp decrease in selectivity for the formation of C2 hydrocarbons and an increase in selectivity for CO2. 相似文献
4.
The effect of the carrier on catalytic properties of ruthenium supported catalysts in partial oxidation of methane (POM) was
investigated. A variety of supports differed in texture and reducibility (Al 2O 3, SiO 2, TiO 2, Cr 2O 3, CeO 2 and Fe 2O 3) were used. The catalyst activity is governed by ruthenium phase formation (RuO 2 → Ru 0), and it depends on redox properties of the support as well as support-ruthenium phase interaction. The activity of Ru supported
catalysts decreases in the order Al 2O 3 ≈ SiO 2 > Cr 2O 3 > TiO 2 > CeO 2 > Fe 2O 3. No significant effects of the specific surface area and porosity of catalysts on the methane conversion and selectivity
of CO formation were found. The selectivity of CO 2 formation (total oxidation of CH 4) under conditions of POM (a ratio of CH 4/O 2 = 2) is associated with the contribution of reducible support oxides into the catalytic performance. 相似文献
5.
The effect of reaction mixture quenching on C 2 product formation in the methane coupling reaction on La 2O 3/CaO is disclosed. For reaction with the mixture (vol. %): 54.5 CH 4, 9.1 O 2 and 36.4 N 2 at 973 K, quenching of products results in a two-fold decrease in C 2 product yield. The results give evidence that in methane oxidative coupling methyl radical formation can occur in the gas phase to an extent comparable with that on the catalyst surface. The effect described must be taken into account in the case of an industrial application of methane oxidative coupling, too, because quenching is a regular procedure in the high temperature oxidative processes. 相似文献
6.
碱土元素氧化物是一类具有较好催化活性和选择性的甲烷氧化偶联(OCM)催化剂[1,2]。Filkova[3]等研究了不同的碱土金属氧化物促进的Nd2O3催化剂的OCM催化性能,发现在所有碱土金属氧化物-Nd2O3催化剂中,SrO-Nd2O3催化剂具有最高的生成C2烃的选择性,这可能因为SrO较强的碱性以及Sr 相似文献
7.
Oxovanadium(IV) immobilized on Fe 3O 4@S‐ABEN is reported as a highly efficient nanocatalyst for the oxidation of sulfides and oxidative coupling of thiols (using H 2O 2 as green oxidant), the products of which are obtained in high to excellent yields. The products can be separated by a simple extraction with organic solvent and the catalyst is highly efficient, especially in terms of selectivity of desired product. The catalytic system can be recycled and reused without significant loss of catalytic activity. 相似文献
8.
Photo-driven CH 4 conversion to multi-carbon products and H 2 is attractive but challenging, and the development of efficient catalytic systems is critical. Herein, we construct a solar-energy-driven redox cycle for combining CH 4 conversion and H 2 production using iron ions. A photo-driven iron-induced reaction system was developed, which is efficient at selective coupling of CH 4 as well as conversion of benzene and cyclohexane under mild conditions. For CH 4 conversion, 94 % C 2 selectivity and a C 2H 6 formation rate of 8.4 μmol h −1 is achieved. Mechanistic studies reveal that CH 4 coupling is induced by hydroxyl radical, which is generated by photo-driven intermolecular charge migration of an Fe 3+ complex. The delicate coordination structure of the [Fe(H 2O) 5OH] 2+ complex ensures selective C−H bond activation and C−C coupling of CH 4. The produced Fe 2+ can be used to reduce the potential for electrolytic H 2 production, and then turns back into Fe 3+, forming an energy-saving and sustainable recyclable system. 相似文献
9.
A dual-bed catalytic system is proposed for the direct conversion of methane to liquid hydrocarbons. In this system, methane is converted in the first stage to oxidative coupling of methane (OCM) products by selective catalytic oxidation with oxygen over La-supported MgO catalyst. The second bed, comprising of the HZSM-5 zeolite catalyst, is used for the oligomerization of OCM light hydrocarbon products to liquid hydrocarbons. The effects of temperature (650-800℃), methane to oxygen ratio (4 10), and SiO2/Al2O3 ratio of the HZSM-5 zeolite catalyst on the process are studied. At higher reaction temperatures, there is considerable dealumination of HZSM-5, and thus its catalytic performance is reduced. The acidity of HZSM-5 in the second bed is responsible for the oligomerization reaction that leads to the formation of liquid hydrocarbons. The activities of the oligomerization sites were unequivocally affected by the SiO2/Al2O3 ratio. The relation between the acidity and the activity of HZSM-5 is studied by means of TPD-NH:j techniques. The rise in oxygen concentration is not beneficial for the C5 selectivity, where the combustion reaction of intermediate hydrocarbon products that leads to the formation of carbon oxide (CO CO2) products is more dominant than the oligomerization reaction. The dual-bed catalytie system is highly potential for directly converting methane to liquid fuels. 相似文献
10.
The catalytic partial oxidation of methane was studied over single channels of monolith catalysts Pt/PrCeZrO/α-Al 2O 3 and Pt/GdCeZrO/α-Al 2O 3 using the temporal analysis of products (TAP) and kinetic transients. Effects of catalyst composition, oxidation state, time offset between O 2 and CH 4 pulses on activity, selectivity and dynamics of product formation were elucidated. Realization of the direct pyrolysis-CH 4 partial oxidation route was reliably established. This route is favored by optimum lattice/surface oxygen mobility and reactivity controlled by the dopant type (Gd, Pr) and oxidation state of the complex cerium/zirconium oxide. 相似文献
11.
Methane is an abundant and cheap feedstock to produce valuable chemicals. The catalytic reaction of methane conversion generally requires the participation of multiple molecules (such as two or three CH 4 molecules, O 2, CO 2, etc.). Such complex process includes the cleavage of original chemical bonds, formation of new chemical bonds, and desorption of products. The gas phase study provides a unique arena to gain molecular-level insights into the detailed mechanisms of bond-breaking and bond-forming involved in complicated catalytic reactions. In this Review, we introduce the methane conversion catalyzed by gas phase ions containing metals and three topics will be discussed: (1) the direct coupling of methane molecules, (2) the conversion of CH 4 with O 2, O 3 and N 2O, and (3) the conversion of CH 4 with CO 2 and H 2O. The obtained mechanistic aspects may provide new clues for rational design of better-performing catalysts for conversion of methane to value-added products. 相似文献
12.
Partial oxidation of methane(POM) co-fed with CO 2 to syngas in a novel catalytic BaCo 0.6Fe 0.2Ta 0.2O 3-δ oxygen permeable membrane reactor was successfully reported.Adding CO 2 to the partial oxidation of methane reaction not only alters the ratio of CO/H 2,but also increases the oxygen permeation flux and CH 4 conversion.Around 96%CH 4 conversion with more than 93%CO 2 conversion and 100%CO selectivity is achieved,which shows an excellent reaction performance.A steady oxygen permeation flux of 15 mL/(cm 2 min) is obtained during the 100-h operation,which shows good stability as well. 相似文献
13.
Direct conversion of methane to value‐added chemicals with high selectivity under mild conditions remains a great challenge in catalysis. Now, single chromium atoms supported on titanium dioxide nanoparticles are reported as an efficient heterogeneous catalyst for direct methane oxidation to C1 oxygenated products with H 2O 2 as oxidant under mild conditions. The highest yield for C1 oxygenated products can be reached as 57.9 mol mol Cr?1 with selectivity of around 93 % at 50 °C for 20 h, which is significantly higher than those of most reported catalysts. The superior catalytic performance can be attributed to the synergistic effect between single Cr atoms and TiO 2 support. Combining catalytic kinetics, electron paramagnetic resonance, and control experiment results, the methane conversion mechanism was proposed as a methyl radical pathway to form CH 3OH and CH 3OOH first, and then the generated CH 3OH is further oxidized to HOCH 2OOH and HCOOH. 相似文献
14.
Porous Vycor membrane tubes were used in shell-and-tube type membrane reactors to study the effect on the oxidative coupling of methane of metering the oxygen into the catalyst bed. Experimental studies showed that under conditions of complete oxygen conversion, Vycor membrane reactors packed with Sm 2O 3 catalyst exhibited enhanced hydrocarbon (C 2) selectivity. C 2 yields were comparable to those of the conventional co-feed packed bed reactors operated under the same conditions. The higher C 2 selectivity in the membrane reactors indicated that, for methane coupling, regulating the supply of oxygen along the length of the packed bed may be beneficial to C 2 formation. 相似文献
15.
The oxidative stream reforming of methane (OSRM) to syngas, involving coupling of exothermic partial oxidation of methane (POM) and endothermic steam reforming of methane (SRM) processes, was studied in a thin tubular Al 2O 3-doped SrCo 0.8Fe 0.2O 3−δ membrane reactor packed with a Ni/γ-Al 2O 3 catalyst. The influences of the temperature and feed concentration on the membrane reaction performances were investigated in detail. The methane and steam conversions increased with increasing the temperature and high conversions were obtained in 850–900 °C. Different from the POM reaction, in the OSRM reaction the temperature and H 2O/CH 4 profoundly influenced the CO selectivity, H 2/CO and heat of the reaction. The CO selectivity increased with increasing the temperature or decreasing the H 2O/CH 4 ratio in the feed owing to the water gas shift reaction (H 2O + CO → CO 2 + H 2). And the H 2 selectivity based on methane conversion was always 100% because the net steam conversion was greater than zero. The H 2/CO in product could be tuned from 1.9 to 2.8 by adjusting the reaction temperature or H 2O/CH 4. Depending on the temperature or H 2O/CH 4, furthermore, the OSRM process could be performed auto-thermally with idealized reaction condition. 相似文献
16.
One of the great challenges in the field of heterogeneous catalysis is the conversion of methane to more useful chemicals and fuels. A chemical of particular importance is ethene, which can be obtained by the oxidative coupling of methane. In this reaction CH 4 is first oxidatively converted into C 2H 6, and then into C 2H 4. The fundamental aspects of the problem involve both a heterogeneous component, which includes the activation of CH 4 on a metal oxide surface, and a homogeneous gas-phase component, which includes free-radical chemistry. Ethane is produced mainly by the coupling of the surface-generated CH radicals in the gas phase. The yield of C 2H 4 and C 2H 6 is limited by secondary reactions of CH radicals with the surface and by the further oxidation of C 2H 4, both on the catalyst surface and in the gas phase. Currently, the best catalysts provide 20% CH 4 conversion with 80% combined C 2H 4 and C 2H 6 selectivity in a single pass through the reactor. Less is known about the nature of the active centers than about the reaction mechanism; however, reactive oxygen ions are apparently required for the activation of CH 4 on certain catalysts. There is spectroscopic evidence for surface O ? or O ions. In addition to the oxidative coupling of CH 4, cross-coupling reactions, such as between methane and toluene to produce styrene, have been investigated. Many of the same catalysts are effective, and the cross-coupling reaction also appears to involve surface-generated radicals. Although a technological process has not been developed, extensive research has resulted in a reasonable understanding of the elementary reactions that occur during the oxidative coupling of methane. 相似文献
17.
Oxidative coupling of methane (OCM) is considered one of the most promising catalytic technologies to upgrade methane. However, C 2 products (C 2H 6/C 2H 4) from conventional methane conversion have not been produced commercially owing to competition from overoxidation and carbon accumulation at high temperatures. Herein, we report the codeposition of Pt nanoparticles and CuO x clusters on TiO 2 (PC-50) and use of the resulting photocatalyst for OCM in a flow reactor operated at room temperature under atmospheric pressure for the first time. The optimized Cu 0.1Pt 0.5/PC-50 sample showed a highest yield of C 2 product of 6.8 μmol h −1 at a space velocity of 2400 h −1, more than twice the sum of the activity of Pt/PC-50 (1.07 μmol h −1) and Cu/PC-50 (1.9 μmol h −1), it might also be the highest among photocatalytic methane conversions reported so far under atmospheric pressure. A high C 2 selectivity of 60 % is also comparable to that attainable by conventional high-temperature (>943 K) thermal catalysis. It is proposed that Pt functions as an electron acceptor to facilitate charge separation, while holes could transfer to CuO x to avoid deep dehydrogenation and the overoxidation of C 2 products. 相似文献
18.
The oxidative coupling of methane over (Bi 2O 3) 1-x(WO 3) x (x=0.2, 0.3, 0.4) oxygen ion conductive oxide catalysts irradiated by microwave has been studied. Compared with a conventional
heating mode, the temperature of the catalytic bed is much lower with microwave irradiation and there is a change in selectivity
favoring the production of C 2 products. 相似文献
19.
The dependences of the maximum selectivity and the limiting yield of C 2 hydrocarbons on the degree of methane conversion during its gas-phase oxidative coupling were calculated by means of kinetic simulation. The correlation between the results of the calculations and the rersults obtained in the experimental studies dealing with catalytic oxidative coupling of methane is discussed.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 568–570, March, 1995. 相似文献
20.
The catalytic activity of Ni/MgO catalysts was studied for the oxidative coupling of methane (OCM). The catalysts were characterized
using transmission electron microscope (TEM) and XRD. The increase in C2+ selectivity of Ni/MgO was attributed to the presence
of bulk dislocations and MgNiO 2 phase.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
|