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1.
The high-temperature complete oxidation of methane over metallic monolith-supported zeolite catalysts containing isolated Mn, Co, and Pd ions was studied. The reaction involves heterogeneous and heterogeneous-homogeneous catalytic processes. The ratio between these processes depends on the temperature, feed rate, and the amount of catalyst charged in the reactor. In the heterogeneous catalytic process, the activity of the catalysts supported on the Fe—Cr—Al monolithic alloy decreases in the series Pd > Mn > Co > Fe—Cr—Al monolith and the reaction rate uniformly increases with increasing contact time. In the heterogeneous-homogeneous process, the reaction rate drastically increases and a 100% conversion of methane to CO2 can be achieved by minor variations of the contact time. In this case, methane oxidation depends not only on the catalyst chemical composition but also on its external surface area and the reaction volume. 相似文献
2.
The catalytic activity of Pd/Co3O4 toward methane oxidation has been examined in this study as a function of Pd loading, reaction temperature, space velocity
and methane concentration in the reaction gas mixture. The bare oxide is quite active achieving a 100% methane conversion
at 480°C under the reaction conditions used. The catalyst with the highest Pd loading tested of 10 wt.% yields the best activity
curve, but the 5 wt.% Pd/Co3O4 catalyst performs nearly as well. Complete conversion for this catalyst is attained at 300°C and the activity remains stable
over a 90-min test period. 相似文献
3.
Effects of carrier and Mn loading on supported manganese oxide catalysts for catalytic combustion of methane
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Supported manganese oxide catalysts were prepared by incipient wetness impregnation method for methane catalytic combustion, and effects of the support (Al2O3, SiO2 and TiO2) and Mn loading were investigated. These catalysts were characterized with N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Methane conversion varied in a large range depending on supports or Mn loading. Al2O3 supported 15% Mn catalyst exhibited better activity toward methane catalytic oxidation. The manganese state and oxygen species played an important role in the catalytic performance, 相似文献
4.
Bernard Béguin Edouard Garbowski Stefan Dietrich Peter Michel Primet 《Reaction Kinetics and Catalysis Letters》1996,59(2):253-262
Monometallic and bimetallic catalysts based on palladium and copper deposited on a spinel carrier have been investigated in the catalytic combustion of methane. Great differences were found in catalytic activity, according to the sequence Pd/MgAl2O4>CuO–Pd/MgAl2O4>Pd–CuO/MgAl2O4>CuO/MgAl2O4. They were explained by changes in surface composition of the catalysts. In the case of bimetallic catalysts the metallic surface is preferentially enriched in copper, which acts as a diluting agent for the Pd atom ensembles. As a consequence, the adsorption of reactants is limited and the catalysts so obtained behave like copper slightly doped with palladium. 相似文献
5.
考察了具有相同金属分散度的Pt/NaY、Pt/HNaY、 Pt/HY、Pt/NaBeta和Pt/HBeta催化剂中沸石载体的酸性对在低温下(≤250 ℃)甲烷两步等温转化反应以及由甲烷解离吸附产生的表面碳物种分布的影响。由甲烷等温两步转化生成的C2+烃类产物的总量随着载体酸性的增加而明显增加;C2~C6产物的分布也发生了变化。由表面碳物种的程序升温加氢结果表明,在各种催化剂上碳物种的形式是相似的,其总量和具有活性的Cα物种的量均因载体酸性增加而增加,反应性也增大。这种因沸石载体酸性变化而引起的载体效应是由金属和载体的相互作用造成负载在酸性载体上铂粒子的贫电子性而引起,即由金属粒子电子性质的变化而引起的催化性质的变化。 相似文献
6.
Effect of Cu promoter on Ni-based SBA-15 catalysts for partial oxidation of methane to syngas 总被引:1,自引:0,他引:1
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A series of Ni/SBA-15 catalysts with 5wt% to 15wt% Ni content as well as a series of 12.5%Ni/Cu/SBA-15 catalysts with 1% to 10% copper
content were prepared by the impregnation method. The catalytic performance for partial oxidation of methane was investigated in a continuous
flow microreactor under atmospheric pressure. The textural and chemical properties of the catalysts were characterized by XRD, TEM, BET
and H2-TPR techniques. The results indicated that the catalysts modified with Cu promoter showed better performance than those without
modification. For the 12.5%Ni/2.5%/Cu/SBA-15 catalyst, at 850 ◦C the conversion of CH4 reached 97.9% and the selectivity of CO and
H2 reached 98.0% and 96.0%, respectively. In XRD patterns of the Ni/Cu/SBA-15 catalyst with 7.5 to 10% Cu contents there were CuO
characteristic peaks beside NiO characteristic peaks. The mesoporous structure of SBA-15 was retained in all of the catalysts. TPR analysis
of the catalysts revealed that a strong interaction between Ni, Cu promoter and SBA-15 support may be existed. This interaction enhanced
significantly the redox properties of the catalysts resulting in the higher catalytic activity. 相似文献
7.
FeOx-SiO2 catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeOx-SiO2 with an iron content of 0.5 wt% at 898 K. This 0.5 wt% FeOx-SiO2 catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeOx/SiO2 prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H2-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeOx-SiO2 by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeOx-SiO2 catalyst (P/Fe = 0.5) at 898 K. Raman spectroscopic measurements indicated the formation of FePO4 nanoclusters in this catalyst, which were more selective toward formaldehyde formation. 相似文献
8.
采用H2 TPR、TEM及活性评价等手段,考察了还原方式(等温和程序升温还原)及还原温度对不同温度(550℃和950℃)焙烧制备的镍基催化剂结构和甲烷部分氧化反应性能的影响。结果表明,与程序升温还原方式相比,等温还原的催化剂中镍物种的还原度较低、Ni晶粒度较小。还原方式对550℃焙烧制备的催化剂(POM-1)的甲烷部分氧化反应性能影响不明显,但等温还原的催化剂反应过程中床层温度较低。随着等温还原温度的提高,POM-1催化剂的镍还原度有所降低,而950℃焙烧制备的催化剂(POM-5)还原度略有增加,且具有较小的镍晶粒。随着等温还原温度的提高,POM-1催化剂反应性能无明显差异,但床层热点温度提高;POM-5催化剂反应性能随还原温度的提高而提高,且床层温度呈现降低趋势。通过分析发现,催化剂床层温度与催化剂镍晶粒大小密切相关,较小的镍晶粒利于床层热点温度的降低,这与较大镍晶粒利于甲烷完全氧化反应有关。 相似文献
9.
Catalytic combustion of methane was carried out using platinum catalysts supported on low-and high-surface area alumina (denoted
respectively as LSA and HSA) and platinum supported on silica. Methane conversion was the highest for platinum supported on
LSA alumina, smaller for Pt/HSA alumina and the smallest for Pt/silica. However, the 3 wt.% Pt/HSA catalyst was found to show
the highest selectivity. 相似文献
10.
Investigation of performances of commercial diesel oxidation catalysts for CO,C3H6, and NO oxidation
Hande GÜNE Deniz ANLI YILDIZ Hüseyin Barkn
ZENER Gkhan HSAR Selmi Erim BOZBA Can ERKEY 《Turkish Journal of Chemistry》2021,45(3):673
Four commercial monolithic diesel oxidation catalysts (DOCs) with two different platinum group metal (PGM) loadings and Pt:Pd ratios of 1:0, 2:1, 3:1 (w/w) were investigated systematically for CO, C3H6, and NO oxidation, CO-C3H6 co-oxidation, and CO-C3H6-NO oxidation reactions via transient activity measurements in a simulated diesel engine exhaust environment. As PGM loading increased, light-off curves shifted to lower temperatures for individual and co-oxidation reactions of CO and C3H6. CO and C3H6 were observed to inhibit theoxidation of themselves and each other. Addition of Pd to Pt was found to enhance CO and C3H6 oxidation performance of the catalysts while the presence and amount of Pd was found to increase the extent of self-inhibition of NO oxidation. NO inhibited CO and C3H6 oxidation reactions while NO oxidation performance was enhanced in the presence of CO and C3H6 probably due to the occurrence of reduced Pt and Pd sites during CO and C3H6 oxidations. The optimum Pt:Pd ratio for individual and co-oxidations of CO, C3H6, and NO was found to be Pt:Pd = 3:1 (w/w) in the range of experimental conditions investigated in this study. 相似文献
11.
Suppression of methane formation during Fisher-Tropsch synthesis using manganese-cobalt oxide supported on H-5A zeolite as a catalyst
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In Fischer-Tropsch synthesis reaction, methane formation is one of the side reactions which must be suppressed in order to get better catalytic selectivity for light olefins. In the present study, we have modified cobalt based Fischer-Tropsch catalyst and developed a process to minimize methane production, consequently to produce maximum yield of light olefins. Manganese-cobalt oxide supported on H-5A zeolite catalyst was synthesized using modified H-5A zeolite, to increase its surface acid sites. Increased acidity of zeolite plays a major part in the suppression of methane formation during the Fischer-Tropsch reaction. The modified zeolite results in the electronic modification of catalyst surface by creating new active catalytic sites. The results are compared with other supported catalysts along with unmodified zeolite. Appreciable reduction in methane formation is achieved on modified zeolite supported catalyst in comparison with unsupported catalyst. 相似文献
12.
Partial oxidation of methane and ethane to oxygenates over silica supported rhenium oxide 总被引:1,自引:0,他引:1
Silica supported rhenium oxide has been studied for partial oxidation of methane and ethane with oxygen. Loading of rhenium
oxide on silica remarkably increases the conversions of methane and ethane. The presence of rhenium oxide increases the selectivity
to useful oxygenates, particularly in ethane oxidation. The results suggest that rhenium oxide not only activates methane
or ethane but also enhances oxygen transfer to form oxygenates.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
Summary Carbonization of the surface of alumina-based catalysts has been studied with respect to the composition of the catalysts and conditions of the propionitrile ammonolysis. It was shown that the surface concentration of carbon increases with the increase in temperature and with time of the reaction and depends on the catalysts nature in the order: Al-Zr(5)-O < Al-Zr(40)-O < Al-O < Al-Mg-O. The surface concentration of the Brönsted acidic sites follows the same sequence. 相似文献
14.
Beata Michalkiewicz Joanna Sreńscek-Nazzal Piotr Tabero Barbara Grzmil Urszula Narkiewicz 《Chemical Papers》2008,62(1):106-113
The investigations of selective methane oxidation to formaldehyde over T-Nb2O5, the mixture of M-Nb2O5 and H-Nb2O5 as well as H-Nb2O5 were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as
the oxidizing agent. T-Nb2O5 samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h−1). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb2O5 displayed various formaldehyde and carbon dioxide yield. Using H-Nb2O5 and M-Nb2O5 phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared
to T-Nb2O5 (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of
formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb2O5 supported on SiO2.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
15.
The effects of CeO2 and CaO composite promoters on the properties of eggshell Ni/MgO-Al2O3 catalysts of 1.5 mm diameter for the partial oxidation of methane to syngas were investigated. The addition of 1wt.% promoters could enhance the catalytic performance of the Ni/MgO-Al2O3 catalyst, while further increasing the promoter content to 4wt.% results in the decrease of reactivity. The catalytic property is related to the oxidizability of surface nickel species. 相似文献
16.
利用共沉淀法制备了具有介孔结构的Ce0.5Zr0.5O2固溶体载体,然后浸渍不同质量分数(10%、20%、30%)的活性组分钴,制备了系列Co/Ce0.5Zr0.5O2催化剂。利用N2物理吸附(BET)、X射线粉末衍射(XRD)、H2-程序升温还原(H2-TPR)、扫描电子显微镜(SEM) 、透射电子显微镜(TEM) 、 程序升温氧化(TPO)和热重(TG)等手段对制备和反应后的催化剂进行了表征,研究了它们对甲烷部分氧化制合成气反应的催化性能。研究结果表明,铈锆固溶体负载的钴比较容易被还原,该系列催化剂具有较高的活性和对H2及CO的选择性,且随Co含量的增加,催化剂的活性和对H2和CO的选择性得到提高的同时,也增强了催化剂的抗积炭性能。 相似文献
17.
V. V. Lesnyak V. K. Yatsimirskii I. N. Gut O. Yu. Bondyreva 《Theoretical and Experimental Chemistry》2008,44(2):134-138
It has been shown that the phases HxMO3 and MO3−x (M = Mo, W), obtained by reduction of the oxides WO3 and MoO3 with hydrogen with supported Pt(Pd) (0.5 mass %), have higher catalytic activity in the deep oxidation of methane than the
catalysts Pt/Al2O3 and Pd/Al2O3 with the same amount of supported metal. At temperatures above 700 K the activity of these catalysts decreases in consequence
of the thermal decomposition of the phases HxMO3 and MO3−x and they become similar in activity with Pt(Pd)/Al2O3.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 126–129, March–April, 2008. 相似文献
18.
近年来,过渡金属氮碳材料由于其廉价、高效与持久耐用的性质得到广泛研究,被视为钯基催化剂的良好替代品.除了可应用于电催化领域,过渡金属氮碳材料还可作为有机反应催化剂,并显示出良好的催化性能.金属卟啉化合物因其高效模拟自然酶的仿生催化功能而闻名,然而在均相催化体系中其难回收、易自我氧化失活的缺点大大阻碍了其实际应用.对金属卟啉进行热处理是提高其催化性能与稳定性的有效方法.此外,作为内部含有金属-氮配合键的含碳大环化合物,金属卟啉是一步合成金属氮碳材料的良好前驱体.本课题组已证明以金属钴卟啉作为前驱体制得的金属氮碳催化剂具有良好的催化乙苯氧化性能.在此基础上,本文采用含有不同过渡金属中心的四苯基金属卟啉(四苯基钴卟啉、四苯基铁卟啉和四苯基钴卟啉)为前驱体,通过无模板法热处理制备了过渡金属氮碳催化剂M-N-C (M=Co,Fe,Mn),考察不同过渡金属中心对催化剂性能的影响.所得催化剂采用N2吸附-脱附、热重(TG)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)、拉曼光谱(Raman)和X射线光电子能谱进行了表征.N2吸附-脱附结果表明,所得M-N-C材料具有不同的比表面积与孔道结构,其中Co-N-C催化剂比表面积最大.TG显示,不同金属卟啉的失重情况不同,四苯基钴卟啉失重最多,四苯基铁卟啉次之,四苯基锰卟啉失重最少.从TEM和Raman结果可见,所得不同金属氮碳材料具有不同的石墨化程度,其中Co-N-C材料具有明显的石墨化层状碳结构,石墨化程度最高,Fe-N-C材料次之,而Mn-N-C材料中的碳主要呈片状无定形状态,表明其石墨化程度最低.这可能是不同过渡金属中心在加热过程中对卟啉结构碳化过程催化效果不同所致,其中钴中心对卟啉结构碳化过程的催化效果最佳.另外,考察了该M-N-C催化剂在无溶剂条件下催化分子氧选择性氧化乙苯的性能.结果发现,不同金属中心的M-N-C催化剂表现出不同的催化性能.这可能归因于金属种类的不同、所得催化剂碳氮结构的差别以及金属中心与氮碳结构的协同效应.此外,这些M-N-C材料作为多相催化剂在以氧气为氧源的无溶剂选择性氧化乙苯反应中表现出良好的催化性能,且多次使用后没有明显的活性损失,具有良好的回收使用性能. 相似文献
19.
采用浸渍法制备了单一载体(Al2O3、ZrO2、CeO2)和ZrO2、CeO2改性的Al2O3复合载体的Ni催化剂,考察了在甲烷部分氧化制备合成气反应中的催化性能。通过N2-物理吸附、H2程序升温还原、X射线衍射、NH3程序升温脱附和程序升温氧化等技术对催化剂进行了表征。结果表明,在单一载体催化剂中,Ni/Al2O3具有较大的比表面积,其初始反应活性较高,但该催化剂表面易形成大量的积炭而快速失活。Ni/ZrO2和Ni/CeO2催化剂比表面积较小,活性金属Ni在其表面分散性差,催化剂具有较低的CH4转化率。而CeO2和ZrO2改性的Al2O3复合载体催化剂,具有较大的比表面积,反应活性明显高于单一载体催化剂。CeO2-Al2O3复合载体催化剂具有最高的反应活性和较好的反应稳定性。同时表明,含CeO2催化剂反应后表面积炭较少,CeO2的储放氧功能增强了催化剂对O2的活化,提高催化剂活性的同时,可以抑制积炭的生成。 相似文献
20.
Lee-Dong Hwang Hyoung-Sik Kim Byung-Hwan Kim Min Kang Jin-Won Park 《Reaction Kinetics and Catalysis Letters》2004,81(2):349-355
Alumina supported chromium oxide catalysts added potassium were prepared and tested for methylene chloride oxidation. They
were investigated by XRD, BET, XPS, chemisorption. Chromium oxide catalyst added potassium of 1 wt.% has a large beneficial
effect on activity.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献