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1.
Dry reforming of methane (CH 4) with carbon dioxide (CO 2) is an attractive technology for producing value-added syngas and mitigating greenhouse gas emission. However, this process usually requires high energy input due to the intrinsic inertness of CH 4 and CO 2. Besides, the widely investigated solid Ni-based catalysts typically suffer from coking and sintering issues, leading to degradation in catalytic performance. Liquid alloys and molten salts are emerging as promising catalytic materials for CH 4 dry reforming. In this work, we combine electrolysis with thermocatalysis for CH 4 dry reforming in a naturally stratifying liquid alloy-salt system, which achieves effective and stable catalytic performance under relatively mild operation conditions. The conversions of CH 4 and CO 2 reach 37% and 95%, respectively, in a bubble column reactor comprising Ni–Bi alloy and LiNaCO 3 during constant current electrolysis at 1.5 A and 900 °C. The selectivities of H 2 and CO were maintained at 85% and 92%, respectively. Ab initio molecular dynamics simulation shows that the oxides of both Ni and Bi promote the C–H bond dissociation. Therefore, the electrochemical process combine electrolysis with thermocatalysis in the liquid alloy-salt system represents a promising approach to achieving effective and stable CH 4 dry reforming. 相似文献
2.
The CH 4 chlorination over Y zeolites was investigated to produce CH 3Cl in a high yield. Three different catalytic systems based on Y zeolite were tested for enhancement of CH 4 conversion and CH 3Cl selectivity: (i) HY zeolites in H +-form having various Si/Al ratios, (ii) Pt/HY zeolites supporting Pt metal nanoparticles, (iii) Pt/NaY zeolites in Na +-form supporting Pt metal nanoparticles. The reaction was carried out using the gas mixture of CH 4 and Cl 2 with the respective flow rates of 15 and 10 mL min −1 at 300–350 °C using a fixed-bed reactor under a continuous gas flow condition (gas hourly space velocity = 3000 mL g −1 h −1). Above the reaction temperature of 300 °C, the CH 4 chlorination is spontaneous even in the absence of catalyst, achieving 23.6% of CH 4 conversion with 73.4% of CH 3Cl selectivity. Under sufficient supplement of thermal energy, Cl 2 molecules can be dissociated to two chlorine radicals, which triggered the C-H bond activation of CH 4 molecule and thereby various chlorinated methane products (i.e., CH 3Cl, CH 2Cl 2, CHCl 3, CCl 4) could be produced. When the catalysts were used under the same reaction condition, enhancement in the CH 4 conversion was observed. The Pt-free HY zeolite series with varied Si/Al ratios gave around 27% of CH 4 conversion, but there was a slight decrease in CH 3Cl selectivity with about 64%. Despite the difference in acidity of HY zeolites having different Si/Al ratios, no prominent effect of the Si/Al ratios on the catalytic performance was observed. This suggests that the catalytic contribution of HY zeolites under the present reaction condition is not strong enough to overcome the spontaneous CH 4 chlorination. When the Pt/HY zeolite catalysts were used, the CH 4 conversion reached further up to 30% but the CH 3Cl selectivity decreased to 60%. Such an enhancement of CH 4 conversion could be attributed to the strong catalytic activity of HY and Pt/HY zeolite catalysts. However, both catalysts induced the radical cleavage of Cl 2 more favorably, which ultimately decreased the CH 3Cl selectivity. Such trade-off relationship between CH 4 conversion and CH 3Cl selectivity can be slightly broken by using Pt/NaY zeolite catalyst that is known to possess Frustrated Lewis Pairs (FLP) that are very useful for ionic cleavage of H 2 to H + and H −. Similarly, in the present work, Pt/NaY(FLP) catalysts enhanced the CH 4 conversion while keeping the CH 3Cl selectivity as compared to the Pt/HY zeolite catalysts. 相似文献
3.
The methane oxidation activities of Pt−NiO and Co−NiO bimetallic catalysts have been investigated as part of a larger research
program on the autothermal reforming of methane (combined methane oxidation and steam reforming) in a fluidized bed reactor.
Experiments at atmospheric pressure and 783–1023 K for both catalysts showed that the reaction was more selective towards
H 2 production at CH 4∶O 2 ratios greater than unity. Light-off temperature increased with decreasing CH 4∶O 2 ratios, but increase in gas velocity (beyond minimum fluidization) increased the light-off temperature. Co−NiO was as promising
as the more expensive Pt−NiO catalyst for the oxidation. 相似文献
4.
Dissociative chemisorption of methane over ruthenium, cobalt, platinum and their bimetallic counterparts supported by alumina
and NaY was investigated under a wide range of temperatures. The extent of hydrogen loss from methane was monitored by deuterium
uptake of the surface CH x species formed from methane during the course of methane chemisorption. The presence of a high average number of deuterium
in the desorbing methane suggested a widespread dissociation of methane. The initial distribution of the deuterated products
generally decreased in the sequence CD 4>CHD 3>CH 2D 2. The amount of chemisorbed methane during methane chemisorption increases with temperature and it follows the sequence of
reducibility of the supported metals and particle size which, in turn, depends on the support and the alloy formed. CH x (x=1) species prevailed on alumina supported catalysts, while on NaY supported metals, CH 2 species are dominant when small metal particles are stabilized inside the supercage.
Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday 相似文献
5.
Natural gas resources, stimulate the method of catalytic methane decomposition. Hydrogen is a superb energy carrier and integral component of the present energy systems, while carbon nanotubes exhibit remarkable chemical and physical properties. The reaction was run at 700 °C in a fixed bed reactor. Catalyst calcination and reduction were done at 500 °C. MgO, TiO 2 and Al 2O 3 supported catalysts were prepared using a co‐precipitation method. Catalysts of different iron loadings were characterized with BET, TGA, XRD, H 2‐TPR and TEM. The catalyst characterization revealed the formation of multi‐walled nanotubes. Alternatively, time on stream tests of supported catalyst at 700 °C revealed the relative profiles of methane conversions increased as the %Fe loading was increased. Higher %Fe loadings decreased surface area of the catalyst. Iron catalyst supported with Al 2O 3 exhibited somewhat higher catalytic activity compared with MgO and TiO 2 supported catalysts when above 35% Fe loading was used. CH 4 conversion of 69% was obtained utilizing 60% Fe/Al 2O 3 catalyst. Alternatively, Fe/MgO catalysts gave the highest initial conversions when iron loading below 30% was employed. Indeed, catalysts with 15% Fe/MgO gave 63% conversion and good stability for 1 h time on stream. Inappropriateness of Fe/TiO 2 catalysts in the catalytic methane decomposition was observed. 相似文献
6.
In this review, we summarize the recent development of nanostructured perovskite oxide catalysts for methane combustion, and shed some light on the rational design of high efficient nanostructured perovskite catalysts via lattice oxygen activation, lattice oxygen mobility and materials morphology engineering. 相似文献
7.
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
8.
Manganese oxide catalysts modified by Mg, Ca, Sr and Ba additives were studied for methane deep oxidation. The Ba promoted sample is the most effective one for this reaction among all the catalysts. The catalysts were examined by BET, XRD and H 2-TPR techniques. It is speculated that the formation of some more active oxygen species and the formation of basic sites from the addition of alkaline earth metal oxides are responsible for the improvement of the inherent CH 4 oxidation activity of the modified catalysts. 相似文献
9.
In this study, alumina-supported NiMo catalysts were carburized to obtain alumina-supported nickel–molybdenum carbides as potential catalysts for dry reforming of methane. The typical carbide was compared with a low carburized material (in 5% H 2/CH 4) and a reduced NiMo catalyst. It was shown that the passivated alumina-supported NiMo catalysts by carbon lead to higher reactivity, selectivity, and stability for dry methane reforming reaction. 相似文献
10.
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
11.
Nickel–aluminium and magnesium–aluminium hydrotalcites were prepared by co-precipitation and subsequently submitted to calcination. The mixed oxides obtained from the thermal decomposition of the synthesized materials were characterized by XRD, H 2-TPR, N 2 sorption and elemental analysis and subsequently tested in the reaction of methane dry reforming (DRM) in the presence of excess of methane (CH 4/CO 2/Ar = 2/1/7). DMR in the presence of the nickel-containing hydrotalcite-derived material showed CH 4 and CO 2 conversions of ca. 50% at 550 °C. The high values of the H 2/CO molar ratio indicate that at 550 °C methane decomposition was strongly influencing the DRM process. The sample reduced at 900 °C showed better catalytic performance than the sample activated at 550 °C. The catalytic performance in isothermal conditions from 550 °C to 750 °C was also determined. 相似文献
12.
Dry reforming of methane (CH 4) with carbon dioxide (CO 2) catalysts produces synthesis gas at atmospheric pressure. Synthesis gas is important feed stock to chemical and petrochemical industries to produce chemicals such as methanol and ammonia. It is also a source of hydrogen that is potential to fuel cells. Reforming reactions have also environmental benefit as CO 2 and CH 4, which are classified as green house gases, that cause global warming, are consumed. Reforming with CO 2 is attractive method since it can be employed in areas where water is not available. Considerable efforts have been made to obtain catalysts for dry reforming to achieve both high activity and good stability. In this review, we will take an over view of the dry reforming process and concentrate on the various catalysts used in the process, in general and Ni/Al 2O 3 catalytic system in particular and report the available data in the literature and the present state of the art for this process. 相似文献
13.
A series of metal catalysts was used for methane conversion to higher hydrocarbons and hydrogen in a dielectric barrier discharge. The main goal of this study is to identify the metal catalyst components which can influence the reactions in room‐temperature plasma conditions. The catalysts supported by γ‐Al 2O 3 and zeolite (ZSM 5x) were prepared by the incipient wetness method with solutions containing the metal ions of the second component. Among the catalysts tested, only Pt and Fe catalysts showed a unique result of catalytic reaction in a reactor bed packed with glass beads. 相似文献
14.
向担载镍基催化剂NiMgAl中添加助剂(Co,Ir或Pt)制备了三种助剂促进型催化剂,通过氢气程序升温还原(H2-TPR),CO2/CH4程序升温表面反应(CO2/CH4-TPSR)和CO2程序升温脱附(CO2-TPD)等方法对催化剂进行表征.助剂对催化剂性能的影响通过甲烷干重整实验进行评价.添加少量的Pt或Ir助剂可以降低Ni活性组分的还原温度和提高反应性能.添加助剂的样品与原始NiMgAl催化剂相比能够降低反应的活化能,添加Co或Ir助剂的催化剂与NiMgAl催化剂相比活化能有了明显的降低.NiMgAl催化剂的活化能为51.8 kJ·mol-1,添加Pt助剂的NiPtMgAl催化剂活化能降至26.4 kJ·mol-1.NiMgAl催化剂中添加Pt助剂制备的催化剂具有较好的催化活性和较低的活化能.CH4-TPSR和CO2-TPSR结果表明添加Pt助剂可以在更低的温度下(与NiMgAl催化剂相比)提高CH4的活化能力,并在催化剂表面形成更多的碳物种.CO2-TPD结果显示,添加助剂的催化剂与NiMgAl样品相比在反应温度区间内增加了CO2的吸附/脱附量. 相似文献
15.
Dry reforming of methane (DRM) involves catalytic reaction of CO 2 and CH 4 to produce syngas. Although the process is environmentally beneficial, it has not been implemented on industrial level due to multiple challenges, particularly with regard to catalyst deactivation because of use of very high temperature. A majority of research has been carried out with catalysts based on nickel. However, recently many new varieties catalysts using noble metals, structured silica-foams, zeolites, etc. have been investigated for DRM. The present review paper deals with understanding the process of DRM, importance of catalysts, supports and promoters, various methods of synthesis of catalysts, design of catalyst, catalytic performance and ways to enhance it, constraining elements like poisoning of the catalyst, in addition to physicochemical properties of catalysts. Various properties of supports and promoters like reduction/oxidation potential, acidity/basicity, reducibility, oxygen storage capacity, etc. are responsible for catalyst activity and stability. It identifies critical gaps and provides future directions. 相似文献
16.
The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present
review mainly focuses on CDR to produce synthesis gas over Ni/MO x/Al 2O 3 (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La 2O 3, MgO, and CaO have been found. The addition of promoters to Al 2O 3-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent
on the loading amount of promoters. For example, the highest CH 4 and CO 2 conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La 2O 3/Al 2O 3 catalyst, the highest CH 4 conversion (96%) and CO 2 conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al 2O 3 catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH 4 conversion (91%) and CO 2 conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al 2O 3 catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH 4 conversion (89%) and CO 2 conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al
for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic
performance of Al 2O 3-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization
of metal oxide on Al 2O 3 and the basic property of metal oxide to prevent carbon formation. 相似文献
17.
Rhodium- and iron phosphate-based catalysts are by far the most promising catalysts for oxy-bromination of methane (OBM) reaction. However, most literature reported either Rh- or FePO 4-based catalysts, and the results were rarely studied in a uniform environmental condition. In this report, comparative study was conducted on silica- and silicon carbide-supported rhodium and iron phosphate catalysts with the main focuses on stability performance and coke deposition. The catalytic results demonstrated that the stability of both Rh- and FePO 4-based catalysts was greatly influenced by the supports used, and silicon carbide-supported catalysts showed much better anti-coking ability as compared with silica-supported ones. Temperature-programmed oxidation over the used catalysts further indicated that the coke formation mechanisms were completely different between silica-supported rhodium and iron phosphate catalysts. While cokes might be caused by condensation of CH 2Br 2 over supported iron phosphate, methane decomposition might be the reason for coke formation over silica-supported rhodium catalyst. These findings might pave the way for designing highly efficient and stable catalysts of the OBM reaction. 相似文献
18.
CO 2 reforming of methane is performed over zirconia-supported nickel catalysts. The catalysts show high activity toward CH 4 and CO 2 conversions. Over the high Ni loading catalyst, long-term performances without significant deactivations have been achieved
at 1023 K for 30 h and 1123 K for 20 h, respectively. The effects of reduction and calcination temperatures on the catalytic
activities are also examined. 相似文献
19.
Mesoporous silica was used in conjunction with the ammonia evaporation method to prepare highly dispersed Ni catalysts for the dry reforming of methane (DRM). The effect of Ni dispersion on the catalytic performance was investigated by applying different Ni loadings. The pore structure, morphology, Ni dispersion, catalytic activity for DRM as well as the coke resistance were investigated. During the reaction at a relatively low temperature of 600 °C, all the three catalysts exhibited high stability in CH4 and CO2 conversion and excellent coke resistance, in comparison to Ni/SiO2 catalyst prepared by the incipient wetness method. Among them, 10% Ni–SiO2 exhibited the best catalytic performance with the maximum steady conversions of 62% and 69% for CH4 and CO2 at 600 °C, which was beneficial from its optimal Ni content and the presence of highly-dispersed metal nanoparticles confined in the mesopores. 相似文献
20.
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
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