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1.
The ammoxidation of propane to acrylonitrile was investigated over various multicomponent mixed oxidecatalysts. Bi 3GaMo 2 oxide, Bi 0.85V 0.55Mo 0.45 oxide and Bi 2TiMo oxide showed a good selectivity to acrylonitrile. The catalytic performance was strongly dependent on the components constituting the oxides due to the concentration of defects, the nature of the component and the mixed oxide phases. The effect of support type on the catalytic performance of Bi 0.85V 0.55Mo 0.45 oxide showed that selectivity to acrylonitrile decreased in the order silica > alumina > magnesia. The catalytic performance of Bio 0.85V 0.55Mo 0.45 oxide was improved by the addition of a small amount of a component such as magnesium, calcium and tellurium. The catalytic performance of Bi 3GaMo 2, oxide catalyst, however, decreased significantly with the addition of a smallamount of alkali metal (Li, Na, K, Cs). 相似文献
2.
ME-doped γ-Bi 4V 2O 11 (BIMEVOX) oxides are highly oxide ion conducting materials and this property may be profitably used in selective oxidation of hydrocarbons. The catalytic properties of BICUVOX and BICOVOX when shaped as dense membranes displayed in catalytic dense membrane reactor are examined in the oxidation of propene and of propane. Mirror-polished BICUVOX and BICOVOX membranes studied previously were poorly active for propene oxidation because of a small number of active sites but showed an excellent stability and reproducibility (lasting more than 1 month) during which products of mild oxidation (acrolein, hexadiene) and CO were formed. Membranes with depolished surfaces exhibit high conversions of propene (up to 60 mol%), and also of propane (up to 20 mol%) but – contrary to mirror-polished membranes – a complex transient behaviour is observed during which syngas production occurs. The membrane polarisation followed by in situ solid electrolyte potentiometry shows that the oxygen reservoir is far higher than expected on the reaction side which is separated (by the membrane) from the oxidising side where (diluted) oxygen is reduced to O 2− specie. The influence of oxygen partial pressure on the catalytic performance suggests that the electronic conductivity of the material is limiting the oxygen flux through the membrane, and thus is determining the catalytic properties and transient behaviours of depolished membranes. 相似文献
3.
以硅烷化凹凸棒黏土为载体,满孔浸渍法制备了负载型杂多酸盐催化剂,采用X射线衍射、比表面积测定、傅里叶变换红外光谱等手段对催化剂进行了表征。分别考察了双氧水用量、杂多酸盐负载量及循环使用次数等因素对环己烷氧化反应的影响。结果表明,负载型杂多酸盐CoH 7P 2Mo 15V 3O 62能显著提高环己烷氧化能力;催化剂回收烘干后可直接重复利用,催化活性没有明显降低。在优化条件下,环己烷转化率达到35.28%,目标产物环己醇和环己酮的总收率达到12.48%。实验表明,负载型杂多酸盐CoH 7P 2Mo 15V 3O 62是一种具有应用前景的催化剂,便于与产物分离,且对设备和环境污染小。 相似文献
4.
An automated robotic method using a solution at pH=2 containing four precursor salts dissolved has been developed and validated for high-throughput preparation of Mo, Nb, Sb and V mixed metal oxide solids, which are known to be selective for propane oxidation to acrylic (AA) and acetic (AcA) acids. Spherical shaped silica beads of exceptionally narrow size distribution were synthesised using oil drop technique from a Brace™ instrument. Automated impregnation of the beads by the previous solution has been developed and validated. Catalytic studies were performed using a conventional micro-reactor system with an Ultra-Fast™ GC analysis (<2 min against >30 min). After calcination of the samples under either N 2 or air at 873 K, a mixture of phases was obtained, such as VSbO 4, Mo xM 1−xO 2.8 (M=V and/or Nb), Sb 4(2)Mo 10O 31, and other minor phases, such as MoO 3 if activated in air. Mixed oxide samples calcined under N 2 gave better catalytic activity and selectivity to AA/AcA compared to those calcined under air. Measures of catalytic performance of 16 supposedly identical materials fell within a ±5% range of the median values, showing that our experimental set-up is relevant to combinatorial studies. By preparing 15 samples of different chemical composition, optimum catalytic performance was found to correspond to Mo 0.55 Nb 0.09 Sb 0.18V 0.18 mixed oxide calcined at 773 K under N 2, containing a mixture of phases, in particular Mo xM 1−xO 2.8 and Sb 2Mo 10O 31, similarly to the M1 and M2 phases observed for MoNbTeV mixed oxide catalysts. 相似文献
5.
The influence of the incorporation of Ca 2+ into MgV 2O 6, Mg 2V 2O 7 and Mg 3V 2O 8 on the catalytic activities for the oxidative dehydrogenation of propane and the mobility of lattice oxygen in those catalysts has been investigated. On Mg 2V 2O 7 and Mg 3V 2O 8 incorporated with Ca 2+, the selectivity to propylene evidently increased with increasing the content of Ca 2+ in those catalysts. A decrease of the conversion of propane was observed on Ca 2+-added Mg 2V 2O 7 with increasing Ca 2+-content; while on Ca 2+-added Mg 3V 2O 8, no dependence on the Ca 2+-content was observed. The incorporation of Ca 2+ was rather insensitive to both the selectivity and the conversion on Ca 2+-added MgV 2O 6. In order to examine the mobility of lattice oxygen in those catalysts, those catalysts were employed for the oxidative dehydrogenation in the absence of oxygen for 2.25 h, followed by the addition of gaseous oxygen into the feedstream. After the addition of gaseous oxygen under the present conditions, oxygen in the effluent was detected at 9, 3.5 and 2 min with Mg 2V 2O 7 incorporated with Ca 2+ at these Ca/(Mg + Ca) ratios: 0, 0.05 and 0.1. The times were 1.4, 2 and 4 min with Mg 3V 2O 8 incorporated with Ca 2+ as Mg 2V 2O 7. However, no oxygen was detected with MgV 2O 6 incorporated with Ca 2+ even 15 min after the addition of the gaseous oxygen. The present results reveal that the mobility of the lattice oxygen in those catalysts is strongly influenced by the amount of Ca 2+ incorporated, resulting in significant effects on the activities for the oxidative dehydrogenation of propane. 51V MAS NMR was also employed for the observation of redox behaviors of vanadium species in those catalysts during the reaction. 相似文献
6.
Acrolein is synthesized in a tubular membrane reactor with a porous membrane acting as oxygen distributor at 450–550 °C with the catalyst Ag 0.01Bi 0.85V 0.54Mo 0.45O 4 by direct partial oxidation of propane. The reaction in the membrane reactor is compared with the reaction in the classical co-feed reactor. If the oxygen is dosed through the porous reactor wall to the tube side of the reactor, higher acrolein yields and selectivities are obtained. The catalyst is located inside the tube, where the propane streams through. For the simulation – based on a kinetic model – the membrane reactor was partitioned into 14 separate sections through which the oxygen supply takes place. In accordance with the experiment the simulations show that the acrolein selectivities will increase if the oxygen is dosed through the reactor wall acting as membrane oxygen distributor. 相似文献
7.
Dehydrogenation of propane is studied in a high temperature packed bed catalytic membrane reactor with a hydrogen-selective silica membrane. The silica membrane is prepared by a two-step sol–gel process. The removal of hydrogen in the membrane reactor results in higher propane conversion and higher propene yields in comparison to an equivalent fixed-bed reactor. Unfortunately, as a result of the H 2 removal coking is favoured in the membrane reactor. Therefore, the higher propene yields are found only for the first 100–120 min time on stream. However, the lower selectivity of the membrane reactor due to coking is compensated to some extend by a reduced hydrogenolysis. Two commercial dehydrogenation catalysts of different activity were tested in the membrane reactor: Cr 2O 3/Al 2O 3 and Pt–Sn/Al 2O 3. The two catalysts show a different activity, coking, and regeneration behaviour in the membrane-supported propane dehydrogenation. 相似文献
8.
The vapor-phase selective oxidation of propylene (H 2CCHCH 3) to acrolein (H 2CCHCHO) was investigated over supported V 2O 5/Nb 2O 5 catalysts. The catalysts were synthesized by incipient wetness impregnation of V-isopropoxide/isopropanol solutions and calcination at 450 °C. The catalytic active vanadia component was shown by in situ Raman spectroscopy to be 100% dispersed as surface VO x species on the Nb 2O 5 support in the sub-monolayer region (<8.4 V/nm 2). Surface allyl species (H 2CCHCH 2*) were observed with in situ FT-IR to be the most abundant reaction intermediates. The acrolein formation kinetics and selectivity were strongly dependent on the surface VO x coverage. Two surface VO x sites were found to participate in the selective oxidation of propylene to acrolein. The reaction kinetics followed a Langmuir–Hinshelwood mechanism with first-order in propylene and half-order in O 2 partial pressures. C 3H 6-TPSR spectroscopy studies also revealed that the lattice oxygen from the catalyst was not capable of selectively oxidizing propylene to acrolein and that the presence of gas phase molecular O 2 was critical for maintaining the surface VO x species in the fully oxidized state. The catalytic active site for this selective oxidation reaction involves the bridging VONb support bond. 相似文献
9.
The catalytic behaviour of multiphasic catalysts based on -bismuth pyrostannate, Bi 2Sn 2O 7, was investigated in the selective oxidation of isobutene into methacrolein. When -Bi 2Sn 2O 7 is mixed with MoO 3, strong cooperation effects on the yield and selectivity in methacrolein occur. However, XRD analyses performed on samples after test revealed the formation of a low quantity of -bismuth molybdate, -Bi 2Mo 3O 12, when the reaction temperature exceeded 673 K. Additional experiments were therefore carried out on the “Bi–Sn–Mo–O” catalysts in order to shed light on the role of Bi 2Mo 3O 12 in the synergetic effects observed in the Bi 2Sn 2O 7–MoO 3 system. The experimental results are discussed in terms of several hypotheses. First, the intrinsic activity of Bi 2Mo 3 O 12 is probably the simplest explanation for the synergetic effects, although experiments have shown that this phase present in a low quantity is only poorly active. Second, catalytic tests made on Bi 2Sn 2O 7–Bi 2Mo 3O 12 mechanical mixtures have evidenced a cooperation between these two ternary oxides, particularly when Bi 2Sn 2O 7 was the major component of the mixture. Consequently, it is likely that a synergy between Bi 2Sn 2O 7 and the in situ generated Bi 2Mo 3O 12 might play a role in the synergy observed in the Bi 2Sn 2O 7–MoO 3 association. Third, as bismuth pyrostannate was previously shown to behave as an oxygen donor phase with respect to WO 3, a remote control mechanism could therefore occur between Bi 2Sn 2O 7 and MoO 3, independently from the formation of -Bi 2Mo 3O 12. 相似文献
10.
以人工合成的3种不同层板组成的层状双羟基金属氢氧化物MgAl-CO 3-LDHs、CoAl-CO 3-LDHs和NiCr-CO 3-LDHs为载体,以偏钒酸钠NaVO 3为柱撑剂和钒前体,采用离子交换法制备了钒柱撑的催化剂样品(MgAlVO、CoAlVO和NiCrVO),通过XRD、FTIR、XPS和Raman等手段表征了样品的物相、钒物种的存在形态以及钒的价态,以丙烷氧化脱氢制丙烯为模型反应,表征了所制备的催化剂样品的催化性能,着重探讨了LDHs载体的层板组成以及钒的含量对催化剂样品中的钒氧物种存在形态及其丙烷氧化脱氢催化性能的影响。结果表明:以20%理论含量的钒柱撑MgAl-CO 3-LDHs所制备的催化剂样品20%MgAlVO对丙烷氧化脱氢反应的催化性能较好,当反应温度为560℃时,丙烯收率可以达到11.3%,Raman光谱显示该催化剂样品中的钒以Mg 3V 2O 8和α-Mg 2V 2O 7两种形式共存,且晶格氧O 2-和吸附氧O -所占的比例较为均衡,有利于获得较好的丙烷氧化脱氢催化性能,而在同样条件下制备的催化剂样品20%CoAlVO和20%NiCrVO中的钒物种只观察到分别以Co 3V 2O 8和Ni 3V 2O 8存在的正钒酸盐,前者对丙烯的收率不到8%,后者甚至完全得不到丙烯。 相似文献
11.
A novel catalyst based on copper-silver was developed to solve the contradiction between the high conversion temperature of Cu-based catalyst and low N 2 selectivity of Ag-based catalyst during selective oxidation of ammonium gas. The Cu-Ag-based catalyst (Cu 5 wt.%-Ag 5 wt.%/Al 2O 3) displayed a relatively low complete conversion temperature (<320 °C) with a high N 2 selectivity (>95%). Increasing loading of Cu and Ag decreases N 2 selectivity. The low N 2 selectivity of Ag-based catalyst is possibly related to the formation of Ag 2O crystals. Improvement of N 2 selectivity of Ag-based catalyst was obtained by doping Cu to decrease crystallized Ag 2O phase. The temperature programmed reaction (TPR) data show that N 2O is the main byproduct of oxidation of ammonia at temperature lower than 200 °C. Two bands of nitrate species at 1541 and 1302 cm −1 were observed on Ag 10 wt.%/Al 2O 3 at the temperature higher than 250 °C, which indicates the formation of NO x during the selective catalytic oxidation of ammonia. No nitrate species was observed on Cu 10 wt.%/Al 2O 3 and Cu 5 wt.%-Ag 5 wt.%/Al 2O 3, while only one nitrate species (1543 cm −1) existed on Cu 10 wt.%-Ag 10 wt.%/Al 2O 3. We proposed that mixing Ag with Cu inhibited the formation of NO x during the selective catalytic oxidation of ammonia over Cu-Ag/Al 2O 3. 相似文献
12.
Syntheses of Mo–V–Sb–Nb–O bulk materials, which are candidate catalyst systems for the selective oxidation of propane to acrolein and acrylic acid, were made using soluble precursor materials. The products were characterized by X-ray powder diffraction and Raman spectroscopic studies. The objectives of this work were to explore the utility of liquid phase automated synthesis for the preparation of bulk mixed metal oxides, and the identification of the oxide phases present in the system. This is the first published study of the phase composition for these materials. After calcination of these bulk oxides under flowing nitrogen at 600°C, and using stoichiometric ratios of Mo–V–Sb–Nb (1:1:0.4:0.4) and Mo–V–Sb–Nb (3.3:1:0.4:0.4) it was demonstrated that a mixture of phases were obtained for the syntheses. X-ray powder diffraction studies distinguished SbVO 4, Mo 6V 9O 40, MoO 3, and a niobium-stabilized defect phase of a vanadium-rich molybdate, Mo 0.61–0.77V 0.31–0.19Nb 0.08–0.04O x, as the major phases present. Complementary data were provided by the Raman spectroscopic studies, which illustrated the heterogeneity of the phases present in the mixture. Raman also indicated bands attributable to the presence of phases containing terminal M=O bonds as well as M–O–M polycrystalline phases. Previous studies on this system have identified SbVO 4 and niobium-stabilized vanadium molybdate species as the active phases necessary for the selective oxidation of alkanes. 相似文献
13.
采用超声辅助等体积浸渍法制备了K改性Mo掺杂SBA-16催化剂x K/Mo-SBA-16,评价其对乙烷选择氧化反应的催化性能,并利用XRD、TEM、N_2吸附-脱附、UV-Vis、UV-Raman和FT-IR等对催化剂物化性质进行表征,同时考察反应温度和K含量等因素对催化剂性能的影响。结果表明,K的添加提高了产物中醛类选择性。在V(C_2H_6)∶V(O_2)=3∶1和反应温度550℃条件下,0. 1K/5. 0Mo-SBA-16催化剂上乙醛选择性为17. 1%,总醛(包括乙醛和丙烯醛)产率7. 4%。碱金属K的添加改变了催化剂中活性组分的结构和分散度,孤立和高分散的MoO_4四面体逐渐转变为低聚扭曲的MoO_x四面体,可能形成了K_2Mo_2O_7新相。 相似文献
14.
Nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) was synthesized by a templating method using mesostructured cellular foam silica (MCF-S) and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MCF-C was then modified to have a positive charge, and thus, to provide a site for the immobilization of [PMo 10V 2O 40] 5−. By taking advantage of the overall negative charge of [PMo 10V 2O 40] 5−, H 5PMo 10V 2O 40 (PMo 10V 2) catalyst was chemically immobilized on the N-MCF-C support as a charge-matching component. Characterization results showed that the PMo 10V 2 catalyst was finely dispersed on the N-MCF-C support via strong chemical interaction, and that the pore structure of N-MCF-C was still maintained even after the immobilization of PMo 10V 2. In the vapor-phase oxidation of benzyl alcohol, the PMo 10V 2/N-MCF-C catalyst showed a higher conversion and a higher oxidation activity (formation of benzaldehyde) than the unsupported PMo 10V 2 and PMo 10V 2/MCF-S catalysts. 相似文献
15.
采用碳酸盐共沉淀法和高温烧结工艺将一定量的Mo 6+掺杂到Li 1.20Mn 0.54Ni 0.13Co 0.13O 2正极材料中。利用XRD、SEM、EDS和恒流测试仪研究Mo 6+掺杂对Li 1.20Mn 0.54Ni 0.13Co 0.13O 2正极材料的晶体结构、微观形貌和电化学性能的影响。结果显示,Li 1.20Mn 0.52Ni 0.13Co 0.13Mo 0.02O 2表现出更低的阳离子混排和优异的电化学性能。经过Mo 6+掺杂后的正极,由于Li +高速的迁移速率,使得首次不可逆容量损失降低,并展现出更好的高倍率性能和优异的循环稳定性。在0.5C倍率下循环100周后,Li 1.20Mn 0.52Ni 0.13Co 0.13Mo 0.02O 2的容量保持率达到92.2%,远远大于Li 1.20Mn 0.54Ni 0.13Co 0.13O 2的87.5%。另外,当放电倍率增大到5C时,Li 1.20Mn 0.54Ni 0.13Co 0.13O 2的放电比容量要比Li 1.20Mn 0.52Ni 0.13Co 0.13Mo 0.02O 2低21.0 mA·h/g。因此,采用Mo 6+掺杂改性Li 1.20Mn 0.54Ni 0.13Co 0.13O 2正极材料,可以有效提高锂电池的循环保持率和高倍率放电性能。 相似文献
16.
以浸渍法制备VMo/γ-Al 2O 3和VMoMg/γ-Al 2O 3催化剂,考察其催化丙烷氧化脱氢制丙烯的反应活性,采用XRD、UV-Vis DRS和In suit IR对催化剂进行表征。结果表明,V负载质量分数为3%、Mo负载质量分数为7%时的3V7Mo/γ-Al 2O 3催化剂表现出较好的催化性能;添加Mg后催化剂的催化性能有所改善,反应温度500 ℃时,丙烷转化率为18.19%,丙烯选择性74.76%。丙烷和丙烯在3V7Mo/γ-Al 2O 3和3V 7Mo 4Mg/γ-Al 2O 3催化剂上吸附后,C—H键的H与催化剂活性中心的晶格氧发生作用形成H—O键,且3V 7Mo 4Mg/γ-Al 2O 3催化剂上出现C—O键的温度比3V 7Mo/γ-Al 2O 3催化剂高,表明加入Mg有利于提高丙烯选择性。 相似文献
17.
采用SrFe 0.6Cu 0.3Ti 0.1O 3-δ混合导体透氧膜组装成膜催化反应器,进行甲烷部分氧化制合成气反应,考察了反应温度、空速、催化剂粒径等条件的影响,并分析了反应气氛引起的透氧膜结构变化情况。结果表明,在膜反应器内,催化反应与透氧过程存在相互制约和相互促进的关系。在膜反应器内进行甲烷部分氧化反应后,透氧膜的两侧表面均发生蚀刻现象,结晶度显著降低,反应侧蚀刻现象较为严重,膜表面形成了疏松的多孔层,反应气氛使膜表面晶体结构发生了较大改变,Sr容易从钙钛矿结构中析出并与CO 2结合形成SrCO 3,Sr的析出导致组成不平衡,促进了钙钛矿结构分解及其他物相的产生。 相似文献
18.
The selective oxidation of isobutane to methacrylic acid (MAA) has been studied on Cs 1.6H 2.4P 1.7Mo 11V 1.1O 40 which is a heteropolycompound (HPC). The oxidation mechanism isobutane → isobutene → MAL → MAA has already been proposed previously with a rate determining step corresponding to the first step of the reaction, i.e., to dehydrogenation of isobutane leading to isobutene. Here we show that the HPC which is active in the oxidation of isobutane possesses, in the reduced state, anionic vacancies able to store reactive hydrogen species H * presenting the ability to diffuse through the solid. Such a result is of great importance since dehydrogenation requires the abstraction of hydrogen from the molecule which could be performed by a lacunar phase. Therefore, a mechanism of the dehydrogenation step is proposed, involving a heterolytic abstraction of a H − species from the alkane. 相似文献
19.
The catalytic oxidation of unsymmetrical dimethylhydrazine (UDMH) by air has been studied in a vibro-fluidized catalyst bed laboratory kinetic setup over catalysts Cu xMg 1−xCr 2O 4/γ-Al 2O 3, 32.9%Ir/γ-Al 2O 3 and β-Si 3N 4 in a temperature range 150–400 °C. The catalyst Cu xMg 1−xCr 2O 4/γ-Al 2O 3 was found to be optimal regarding high yields of CO 2 and low yields of NO x. A probable mechanism of UDMH heterogeneous catalytic oxidation is proposed. Catalyst Cu xMg 1−xCr 2O 4/γ-Al 2O 3 has been further used in the pilot plant specially designed for the destruction of UDMH. Results of testing the main fluidized bed catalytic reactor for UDMH oxidation and the reactor for selective catalytic reduction of NO x with NH 3 are presented. These results prove that the developed UDMH destruction technology is highly efficient and environmentally safe. 相似文献
20.
A fixed bed reactor (FBR) and a packed bed membrane reactor (PBMR) were compared with respect to their performance in the oxidative dehydrogenation of ethane over VO x/γ-Al 2O 3 catalyst. The experiments were carried out at high space velocities and under oxygen excess conditions. In the PBMR, the oxidant air was distributed from the shell side of the membrane. At similar overall feed configurations, the conversion of ethane was found to be higher in the PBMR. This effect was most pronounced at the highest space velocity. Mostly ethylene yield was higher in the PBMR than in the FBR. However, the yield of carbon oxides increased more. Thus, an improvement of olefin selectivity was not observed. There were even sets of experimental conditions, where the ethylene yield in the PBMR fell below the corresponding value for the FBR. In the PBMR under oxygen excess conditions, the consecutive oxidation of ethylene is more favoured than in the FBR. Two essential reasons for the observed differences in the reactor performances are discussed. At first, there are different local reactant concentrations. Secondly, there are essential differences in the residence time behaviour of the reactants in the FBR and PBMR. In order to exemplify the latter aspect additional experiments have been carried out using a cascade of three identical PBMRs. Varying the specific oxygen flow rates over the individual membrane segment walls different dosing profiles were implemented. The results obtained in this study emphasise the general potential, but also the limits of membrane reactors compared to the FBR. 相似文献
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