水蒸汽对Mn-Na2WO4/SiO2催化剂上乙烷氧化脱氢的影响

在Ｍｎ－Ｎａ２ＷＯ４／ＳｉＯ２催化剂上,考察了水蒸汽对惭烷氧化掊氢制乙烯反应伯影响。结果表明加入适量水蒸汽对提高乙烯选择性有利。在催化剂装量１０ｍＬ,Ｖ（Ｃ２Ｈ６）：Ｖ（Ｏ２）：Ｖ（Ｈ２Ｏ）＝１：０．６５：３．８,ＧＨＳＶ＝１６００ｈ＾－１,７４０℃时,乙烯收率仍可以稳定在５２％以上,过多加入水蒸汽将使催化剂活性很快下降,反应后的催化剂经ＸＲＤ及ＸＰＳ表征表明,不仅单层Ｎａ２ＷＯ４有流失,而且载体     

甲烷氧化偶联Na-W-Mn/SiO2催化剂的喇曼光谱

By calcinating commercial silica gel at 1500℃or adding Na2C2O4 and then calcinating at 850℃,α-cristobalite was formed. On the basis of the vibration spectroscopy of silica support, Na-W-Mn/SiO2 catalyst was characterized by Raman spectroscopy. The results show that the structure of support and the interaction among metal components have significant effect on the dispersion and the structure of metal sites, and the tetrahedrally coordinated [WO4] formed on α-cristobalite surface is the most possible site of methane activation with high C2 selectivity.     

对甲烷氧化偶联W—Mn／SiO2催化剂Na2WO4的流失及其影响的考察

用ＸＲＤ,ＦＴ－ＩＲ,ＥＳＲ,Ｈ２－ＴＰＲ和ＴＯＰ等方法,对Ｎａ２ＷＯ４Ｍｎ２Ｏ３／ＳｉＯ２催化剂和其经水煮处理的一系列样品进行一表征。实验发现该催化剂中的结晶态ＮａＷＯ４易于流失,单层分布的Ｎａ２ＷＯ４在苛刻的处理条件下也有可能流失。     

水蒸汽对Mn-Na2WO4/SiO2催化剂上乙烷氧化脱氢的影响

水蒸汽对Mn-Na2WO4/SiO2催化剂上乙烷氧化脱氢的影响     

2%Mn2O3-5%Na2WO4/SiO2催化剂上的甲烷氧化偶联反应动力学

在Ｍｎ２Ｏ３－Ｎａ２ＷＯ４／ＳｉＯ２催化剂上的甲烷氧化偶联反应可用Ｒｉｄｅａｌ－ｒｅｄｏｘ机理描述,它包括均相及多相两个步骤。甲基自由基的生成是一个多相过程,Ｃ２烃的生成是一个均相过程。催化剂的活性同氧化速率和ＣＨ４与表面氧种的反应速率有关,Ｃ２烃的选择性与甲基自由基氧化速率常数和甲基自由基偶联速率常数的比值有关,这些常数均可从实验中求得。     

甲烷氧化偶联Na-W-Mn/SiO2催化剂的喇曼光谱

Ｎａ Ｗ Ｍｎ／ＳｉＯ２ 是甲烷氧化偶联反应的最好催化剂之一．该体系不仅具有良好的活化甲烷能力和Ｃ２ 烃选择性,且具有较好的稳定性并适合于加压反应 ［１ -３］．对于该催化剂,我们用不同的表征手段做了大量的研究,对各组分的作用及甲烷的活化机理都有了较深入的认识．我们也曾用Ｒａｍａｎ光谱对该体系进行过研究［４,５］,但由于焙烧过程中载体结构及伴随的振动光谱变化,使谱峰的解析出现错误,将载体结构变化出现的新峰归属成了钨氧四面体的畸变．最近我们在确认载体振动光谱及其变化的基础上又对该体系进行了细致的研究,确…     

甲烷氧化偶联W-Mn/SiO2催化剂上O2-脉冲频率效应(PFE)的研究

采用频率脉冲反应方法,以Mn-Na2WO4/S iO2催化剂上甲烷氧化偶联为探针反应,通过实时、原位的四极质谱检测手段,研究氧物种对甲烷C-H键选择性活化的微观历程.首次发现了Mn-Na2WO4/S iO2催化剂上O2-脉冲频率效应,即脉冲反应产物量随氧脉冲注入频率的增加而增加.研究结果表明,在反应条件下,Mn-Na2WO4/S iO2催化剂上有两种活化甲烷的氧物种同时存在,它们活化甲烷的方式不同。     

OXIDATIVE COUPLING OF METHANE OVER Mn_2O_3-Na_2WO_4/SiO_2 CATALYST Ⅰ.CHARACTERIZATION OF ACTIVE SITES ON THE CATALYST

EPR and Raman spectroscopy have been used to characterize the catalyst. F-centers with EPR parameter of g=2. 0046 form when gas phase oxygen is admitted onto the catalyst reduced with methane at 800℃- Molecular oxygen plays an induced role in the electron transfer from W4 to the oxygen ion vacancy which is produced by methane reduction. Raman spectra give the further evidence for the production of lattice oxygen from molecular oxygen.     

OXIDATIVE COUPLING OF METHANE OVER Mn_2O_3-Na_2WO_4/SiO_2 CATALYST IN THE ABSENCE OF DILUTE GAS

The oxidative coupling of methane over Mn2O3-Na2WO4/SiO2 catalyst has been investigated in the absence of dilute gas. 16.4% of C2 yield and 80.4% of the selectivity to C2 hydrocarbons were obtained at CH4/O2 = 8.5/1.5. The effect of flow rate on the selectivity to C2 hydrocarbons and CH4 conversion was different under the reaction condition of different ratio of CH4 to oxygen. The flow rate had a more remarkable effect on the selectivity at the lower ratio of methane to oxygen. The addition of steam into the reaction gas can increase C2 yield to some extent, but that of HC1 decrease the selectivity to C2 hydrocarbons.     

Oxidative coupling of methane over BaCl2-TiO2-SnO2 catalyst

The performance of BaCl2-TiO2-SnO2 composite catalysts in oxidative coupling of methane reaction has been investigated. A series of BaCl2-TiO2, BaCl2-SnO2, TiO2-SnO2, and BaCl2-TiO2-SnO2 catalysts were prepared, and characterized by BET, XRD, XPS, CO2-TPD and H2-TPR, respectively. The synergistic effect among BaCl2, SnO2 and TiO2 compositions enhances the catalytic performance. The best C2 selectivity and ethylene yield are obtained on the catalyst with the equal molar amount of the three compositions (BaCl2 : TiO2 : SnO2 molar ratio of 1 : 1 : 1). The optimal reaction conditions are as follows: 800°C, 44 mL·min-1 for methane, 22 mL·min-1 for oxygen and a space velocity of 5000 mL·h-1 g-1, and the C2H4 yield over the catalyst is 20.1% with the CH4 conversion of 43.8% and C2 selectivity of 53.3%.     

KINETIC STUDY OF THE OXIDATIVE COUPLING OF METHANE OVER La_2O_3/BaSO_4 CATALYST

IntroductionOxidativccouplingofmethanc(0CM)hasbccnthcsubjcctofmuchintcrcstrcccntl}Man}'mctaloxides,alkali-mctaI-promotcdmctaloxidcs-mixcdmcta1oxidcsandchlorinc-prom0tedmCtuloxidcshavcbecnf0undtobcactivcfor0CMHot` cvcr.thcrcisatprcscntnoclearagreemcntaboutthcmcchanismofthecouplingrcaction.T`omodclsll1.thcthdeal-rcdoxandthcLangmuir-Hinshtt-oodmcchanisms.havcbccndcvcIopcdtodcscr1bc0CMreation-thecsscntialdiffercnccbctt\"ccnthctt\"omodclsisthatthclattcrinvolvcsadsorbedmothancasarcactionintcrmcd…     

METHANE OXIDATIVE COUPLING ON ThO_2/CaF_2CATALYST

The oxidative coupling of methane(OCM)over ThO_2/CaF_2 catalystwas investigated.The catalyst was found to be active and selective for OCMreaction.At 1153 K,the C_2~ yield was 19.9% with 61.7% C_2~ selectivityand 32.1% CH_4 conversion.XRD results indicated that F~-(?)O~(2-)exchangehappened between ThO_2 and CaF_2 phases.XPS and Raman results suggestedthat the active oxygen species were generated and suitable for OCM reactionover the catalyst.     

Reaction Chemistry of W—Mn／SiO2 Catalyst for the Oxidative Coupling of Methane

Reaction chemistry of the OCM reaction on W-Mn/SiO2 catalyst has been reviewed in this account.Initial activity and selectivity,stability in a long-term reaction,reaction at elevated pressures and a modelling test in a stainless-steel fluidized-bed reactor show that W-Mn/SiO2 has promising performance for the development of an OCM process that directly produces ethylene from natural gas.A study on surface catalytic reaction kinetics and used cataly st structure characterization revealed a possible reason why C2 and COx selectivity changed during the long-term reaction.Further improvement of the catalyst composition and preparation metbod should be a future direction of study on OCM reaction over W-Mn/SiO2 catalyst.     

甲烷在SrO－La_2O_3／CaO催化剂上的氧化偶联──IV．热点温度效应和反应气中添加CO_2的影响

研究了甲烷在ＬＣ和ＳＬＣ催化剂体系上氧化偶联反应过程的热效应现象和反应气中添加ＣＯ２对催化剂反应行为的影响．在不使用稀释气的情况下，当反应温度由８７３升至９２３Ｋ时，反应活性存在一个突变点．这主要是由ＣＨ４燃烧反应放出大量热使催化剂床层的局部温度很高，形成一个局部过热区，因此引发甲烷氧化偶联．此即所谓热点温度效应，它严重影响催化剂活性评价结果的可靠性和重复性．在反应气中添加ＣＯ２对ＬＣ几乎无影响；由于ＳＬＣ中各组分与ＣＯ２作用生成碳酸盐，使催化剂表面氧浓度显著减少，导致催化剂的反应活性大大降低和严重失活．