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1.
The mechanism of the HCN formation from ammonia and methane over Pt black was investigated using a temporal analysis of products (TAPs) reactor system. At 1173 K the hydrogen cyanide production rate depends on the order of introducing the reactants. HCN is formed rapidly on the methane pulse just after introducing ammonia. However, a slow formation of HCN is observed on the ammonia pulse that follows a methane pulse. Moreover the form of the HCN response resembles closely that of the nitrogen and hydrogen also released during the ammonia pulse. Thus, the rate-determining step for the formation of HCN is the decomposition rate of ammonia. A reaction sequence based on elementary steps is proposed for the HCN synthesis. The formation of HCN after pulsing H2 points to a pool of surface intermediate species that are hydrogenated to HCN. 相似文献
2.
合成氨催化技术与工艺进展 总被引:6,自引:0,他引:6
Fe1-xO催化剂体系的发明,使合成氨催化剂的活性有了飞跃性进步。采用Fe1-xO基A301催化剂可实现低压合成氨工艺,其合成回路吨氨能耗可降低1.30GJ。钌催化剂的发明则有可能成为真正突破经历了近一个世纪的铁催化剂。以钌催化剂为基础的KAAP工艺开发成功,每吨氨的生产成本可降低2.2~6.6美元,节能1.20GJ。由于钌的稀有和昂贵,在可以预见的时间内,钌催化剂不可能立即取代铁催化剂。采用超临界技术有可能实现非平衡限制氮加氢技术的设想。 相似文献
3.
Hydrothermal synthesis by using urea hydrolysis at 1.0-3.0 MPa and 120-130 ‡C was employed to prepare Mn-substituted hexaaluminate
catalysts for methane combustion. The results from DTA-MS demonstrated that CO3- and Off anions co-exist in the hydrothermal reaction. XRD reveals that the components of carbonates and hydroxides in the
hydrothermal reaction are more favorable than those in the (NH4)2CO3 co-precipitation for the formation of the Mn-substituted hexaaluminate phase. After calcination at 1,200 ‡C for 2 h, LaMnAl11O19 is the major phase of the catalyst prepared by the hydrothermal synthesis method while LaAlO3 is the major one of the catalysts prepared by NH4OH and (NH4)2CO3 co-precipitation. The catalyst prepared by hydrothermal synthesis has higher activity than that prepared by NH4OH and (NH4)2CO3 co-precipitation. The major reason is that more Mn2+ ions have incorporated into the hexaaluminate lattice. The effect of drying methods on the formation of hexaaluminate phase
was also discussed. 相似文献
4.
丙烯酸是一种重要的化工中间体和聚合物单体,需求量巨大。我国丰富的煤炭资源和可再生生物质资源为煤基和生物质基丙烯酸合成路线提供坚实的物质保障。本文将综述这两条主要路线,具体包括以煤基化工原料CO、低碳醇(甲醇和乙醇)、甲醛、乙酸、乙烯等为原料的丙烯酸合成路线;以生物质基平台化合物甘油、3-羟基丙酸、乳酸、富马酸、黏糠酸等为原料的丙烯酸合成路线;并对这些路线进行了比较,为路线的选择提供参考。重点关注了这些过程中的催化问题:反应所需的活性位、副反应分析、催化剂的类型与特点以及催化性能与失活机理,为未来实用煤基和生物质基丙烯酸生产用高效稳定廉价催化剂的设计开发提供理论参考。 相似文献
5.
Zhenyu Zhang J. Douglas Way Colin A. Wolden 《American Institute of Chemical Engineers》2021,67(8):e17259
Production of ammonia using hydrogen derived from renewable electricity instead of hydrocarbon reforming would dramatically reduce the carbon footprint of this commodity chemical. Novel technologies such as catalytic membrane reactors (CMRs) may potentially be more compatible with distributed ammonia production than the conventional Haber–Bosch process. A reactor model is developed based on integrating a standard industrial iron catalyst into a CMR equipped with an inorganic membrane that is selective to NH3 over N2/H2. CMR performance is studied as functions of wide ranges of membrane properties and operating conditions. Conversion and ammonia recovery are dictated principally by the ammonia permeance, and the benefits by using membranes become significant above 100 GPU = 3.4 × 10−8 mol m−2 s−1 Pa−1. To be effective, the CMR requires a minimum selectivity for ammonia of 10 over both nitrogen and hydrogen and purity scales with the effective selectivity. Increasing the pressure of operation significantly improves all metrics, and at P = 30 bar with a quality membrane, ammonia is almost completely recovered, enabling direct recycle of unreacted hydrogen and nitrogen without need for recompression. Temperature drives conversion and scales monotonically without thermodynamic limitations in a CMR. Alternatively, the temperature may be reduced as low as 300°C while achieving conversion levels surpassing equilibrium limits at T = 400°C in a conventional reactor. 相似文献
6.
High catalytic activity for synthesis of aniline from phenol and ammonia found on gallium-containing MFI 总被引:1,自引:0,他引:1
Gallium-containing zeolitic materials, i.e., MFI-type gallosilicate and gallium-loaded ZSM-5 zeolite, exhibited quite high activity for vapor-phase reaction of phenol and ammonia into aniline. Co-presence of the extra-framework gallium species and the ion-exchange site ascribed to framework gallium or aluminum atom is considered to generate the high activity. 相似文献
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8.
天然气储量丰富,日益成为重要的清洁能源之一,而从其主要成分甲烷合成高附加值化合物更是研究前沿。由于甲烷结构稳定,CH键能很高,因而活化甲烷需要的条件非常苛刻。本文首先介绍了普通光催化氧化甲烷合成化合物的反应原理、研究进展、催化反应器和存在不足,然后综述了激光催化氧化甲烷合成化合物的反应原理、研究进展和催化反应器。指出激光光源具有提高光催化剂量子效率和缩短催化反应时间等诸多优势,接下来在深入研究激光催化反应机理的基础上,通过设计科学合理的激光反应体系,并遴选高效的光催化剂,有望显著提升包括甲烷氧化在内的激光催化反应性能,从而具有重要的学术意义和实践价值。今后的重点研究方向是通过激光催化氧化的方法使甲烷在温和的条件下活化,并合成高附加值化合物。 相似文献
9.
L. S. Marchenko S. I. Zhuk N. V. Kir'yakov M. D. Nersesyan E. H. Grigoryan 《Catalysis Today》1992,13(4):593-594
Oxidative dehydrodimerization of methane to C2 - hydrocarbons has been examined for complex oxide ceramics prepared by using method of self-propagating high-temperature synthesis (SHS) in a combustion mode. The novel catalysts containing rare-earth, alkali-earth metals and copper showed sufficiently high level of activity, C2 selectivity and stability in the presence of oxygen at temperature 700–800C, atmospheric pressure, the mole ratio CH4/O2= 5–8 and contact time 0.6–9.0 s. 相似文献
10.
Self-propagating high-temperature synthesis technology for preparation of porous permeable materials
V. I. Vereshchagin V. V. Evstigneev D. V. Kolesnikov V. I. Prolubnikov N. P. Tubalov 《Refractories and Industrial Ceramics》2005,46(6):416-418
The principles for development of porous permeable materials based on the self-propagating high-temperature synthesis are
discussed. A technology based on the use of industrial oxide wastes from the mechanical engineering industry is proposed.
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Translated from Novye Ogneupory, No. 12, pp. 40–43, December, 2005. 相似文献
11.
A wide variety of carbon materials (ordered mesoporous carbons, carbon blacks, activated carbon, carbon nanotubes, coke and graphite) have been investigated as catalysts for hydrogen production by methane decomposition, with the aims of identifying the carbon properties which control in a greater extension the catalytic activity and determine the nature of the active sites involved in the reaction.The catalytic activity of the different carbon materials was determined and compared using temperature-programmed experiments in a thermobalance. The initial activity was followed through the threshold temperature, defined as the temperature at which hydrogen production starts being detected, whereas the average reaction rate was also calculated and compared. The lowest threshold temperature was observed with ordered mesoporous carbons (CMK materials), followed by activated carbon and carbon blacks. On the other hand, at long reaction times activated carbon was quickly deactivated yielding a relatively low average reaction rate. The deactivation process seems to be greatly linked to the presence of micropores while the long-term activity is retained in those materials with ordered mesoporosity (CMKs) or formed by nanoparticles (carbon blacks), which make them more resistant to deactivation by the formation of carbonaceous deposits.Whereas no clear dependence is observed between the threshold temperature and the surface area neither with the presence of polar groups in the carbon catalysts, characterization of these materials by XPS shows that a direct relationship exists with the amount of defects present on the graphene layers. This fact strongly supports that these defects are the main active sites for methane decomposition over carbon catalysts. 相似文献
12.
The effects of promoters K, Ba, Sm on the resistance to carbon-methanation and catalytic activity of ruthenium supported on active carbon (Ru/AC) for ammonia synthesis have been studied by means of TG-DTG (thermalgravity-differential thermalgravity), temperature-programmed desorption, and activity test. Promoters Ba,K, and Sm increased the activity of Ru/AC catalysts for ammonia synthesis significantly. Much higher activity can be reached for Ru/AC catalyst with bi- or tri-promoters. Indeed, the triply promoted catalyst showed the highest activity, coupled to a surprisingly high resistance to methanation. The ability of resistance of promoter to methanation of Ru/AC catalyst is dependent on the adsorption intensity of hydrogen. The strong adsorption of hydrogen would enhance methanation and impact the adsorption of nitrogen, which results in the decrease of catalytic activity. 相似文献
13.
Cobalt was supported on ZrO2, La-doped ZrO2 and La2O3 through atomic layer epitaxy (ALE) and wet impregnation. The rate data obtained at 770 K is compared with literature information about cobalt inserted in other matrixes. The ALE technique using ZrO2 and La-doped ZrO2 yielded the best cobalt-containing catalysts. Bulk and surface characterization techniques provided key clues to understand the origin of the large difference in catalytic activity reported for cobalt-containing formulations. 相似文献
14.
Toshiki Tsubota Masaki Morita Sunao Kamimura Teruhisa Ohno 《Journal of Porous Materials》2016,23(2):349-355
Unconventional pretreatment, that is, delignification and the addition of guanidine phosphate, was performed for the synthesis of activated carbon having a high specific surface area from bamboo by physical activation. The values of the specific surface area, total pore volume, and average pore size depended on the amount of added guanidine phosphate and the CO2 activation time. The amount of the added guanidine phosphate under the optimum conditions for the highest specific surface area was much lower than that of the phosphorous acid chemical activator under conventional conditions. The N2 adsorption isotherms of all the samples were type I, which means that micropores were dominant. The pore sizes of the samples in this study were similar to that of the physically-activated carbon. Therefore, the activation process was presumed to be essentially not chemical, but physical. The relation between the yield and the specific surface area improved with the addition of guanidine phosphate. The reason for the improvement may be the change in the reactivity of the carbon material generated during the heating process. The maximum specific surface area was ca. 2000 m2 g?1, which is a high value for a physically-activated carbon. 相似文献
15.
T.P. Caremans C.E.A. Kirschhock P. Verlooy J.S. Paul P.A. Jacobs J.A. Martens 《Microporous and mesoporous materials》2006,90(1-3):62-68
In the hydrothermal synthesis of microporous and mesoporous materials a large number of parameters including chemical composition of the mixture, reagent sources, organic templates, temperature, and time play a role. The high-throughput experimental approach facilitates screening of this multi-parameter space for conditions favoring formation of desired zeolite phases and ordered mesoporous materials. A critical issue in the development of a high-throughput system for hydrothermal synthesis is the avoidance of cross-contamination between the individual synthesis volumes. Further important issues are automation of reactant dosing, product filtration, calcination and identification. In this work, a prototype multi-clave was designed with three 5 mL synthesis vials for operation at temperatures up to 200 °C under autogenous pressure. The multi-clave is equipped with a sample tray for filtration, washing and drying of all of the synthesis products at the same time. This multi-filter also serves as the sample holder for X-ray diffraction characterization. The innovation resides in the multi-clave concept and the integration of the entire process from synthesis over product workup to XRD characterization without necessitating individual sample transfer. The performance of the prototype was evaluated with the synthesis of the mesoporous–microporous hybrid material zeotile-2, and of clathrasils. 相似文献
16.
S.P. Elangovan Katsuki Inoue Toshiyuki Yokoi Tatsuya Okubo Akio Kojima Masaru Ogura 《Catalysis Today》2008,131(1-4):367-371
Catalytic transformation of 1-adamantanol has been carried out over nano-porous materials with pore sizes ranging from 0.55 to 6 nm and acidic sites ranging from 0.07 to 4 mmol/g. Zeolites viz., H-USY, H-beta, H-mordenite, H-L and H-ZSM-5, and sulfonic-acid functionalized mesoporous silica viz., MCM-41, SBA-15 and SBA-16, were employed for the reaction. Shape selectivity in a confined micropore plays a role with the combination of medium strength acid sites toward formation of desirable 2-derivatives, which comprises a maximum amount of 2-adamantanone. 相似文献
17.
氨磺酸催化合成马来酸二丁酯的研究 总被引:4,自引:0,他引:4
研究了以氨磺酸为催化剂,马来酸和正丁醇为原料合成马来酸二丁酯,并考察了影响反应的因素。结果表明,醇酸物质的量比为3:1,催化剂用量为0.5g(马来酸为0.05mol的情况下),带水剂甲苯为5mL,反应时间为1.5h是量适宜的反应条件,醇化率达96.8%。 相似文献
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20.
Tomoyuki Inui Kotaro Ichino Isao Matsuoka Tatsuya Takeguchi Shinji Iwamoto Shu-Bin Pu Sei-ichi Nishimoto 《Korean Journal of Chemical Engineering》1997,14(6):441-444
Development in highly active catalysts for the reforming of methane with CO2 and partial oxidation of methane was conducted to produce hydrogen and carbon monoxide with high reaction rates. An Ni-based
four-components catalyst, Ni-Ce2O3-Pt-Rh, supported on an alumina wash-coated ceramic fiber in a plate shape was suitable for the objective reaction. By combining
the catalytic combustion of ethane or propane, methane conversion was markedly enhanced, and a high space-time yield of syngas,
25,000 mol/l·h was obtained at a catalyst temperature of 700 ‡C or furnace temperature of 500 ‡C. The extraordinary high space-time yield
of syngas was also confirmed even under the very rapid flow rate conditions as a contact time of 3 m-sec by using a monolithic
shape of catalyst bed without back pressure. 相似文献