甲烷在Li-Ln-MgO氧化物上催化氧化偶联

近年来,对天然气的综合利用已逐渐为人们所重视。甲烷氧化偶联制乙烯、乙烷这一新课题受到催化工作者愈来愈多的关注^[1~5]。本工作初步探讨了Li-Ln-MgO三元氧化物催化剂对甲烷氧化偶联反应的催化性能。添加稀土元素可使C₂的选择性、单收明显提高。本催化剂体系制备简单、原料便宜,值得进一步开发研究。     

甲烷部分氧化制合成气Ni/MgO和Ni-MgO/MgO催化剂的研究

甲烷氧化偶联制乙烷、乙烯以及甲烷选择氧化制甲醇、甲醛等反应 ,因其转化率和收率低 ,故短期内无法实现工业化 .目前 ,工业上应用甲烷蒸汽转化制合成气 ,进而合成氨等化工产品 .甲烷蒸汽转化制的合成气 ,其 H2 /CO≥ 3,不适用于甲醇合成和 F- T合成 .而甲烷部分氧化制的合成气 ,其H2 /CO≤ 2 ,因而最适合用于甲醇合成和 F- T合成 ,故近 1 0年来倍受科学家的关注[1 ,2 ] .在 CH4部分氧化制合成气中 ,钌、铑、钯、铂等贵金属催化剂的活性高、选择性好、稳定性好[1 ] ,但价格昂贵 (负载量以 1 2 %～ 4 0 %为佳 ) ,因而难以实现商品化 .N…     

在Li-Nd-Zn-Mg氧化物上甲烷氧化偶联

天然气资源丰富,其中主要成分为甲烷.以甲烷为原料开发化工产品一直引起人们的重视.1982年Keller首先提出甲烷氧化偶联制乙烯、乙烷的催化过程,为开拓廉价乙烯原料路线提供了新的可能途径,从而引起各国催化工作者的重视.近年来,此催化过程的乙烯及乙烷的收率(y_(02))已提高到10—30%之间.各国都在努力开发活性高及选择性好的催化剂,促使此催化过程工业化。本文研究了Li-Nd-Zn-Mg氧化物甲烷氧化偶联催化剂,对反应条件进行了初步考察,乙烯及乙烷的收率y_(02)达到30.8%。     

4-溴-5-甲基靛红的Baeyer-Villiger氧化反应

Baeyer-Viliger反应是由酮制备酯的重要方法^[1].氧化剂通常有两类:(1)有机过酸;(2)过硫酸钾/硫酸(Caro酸).由于靛红结构特殊,我们分别以单过邻苯二甲酸^[2]和过硫酸钾/硫酸^[3]为氧化剂氧化4-溴-5-甲基靛红(1).     

表面偶联甲基自由基实现低温高效甲烷氧化偶联

天然气作为一种低碳清洁能源,其储量大,价格低,被认为是最有前途的石油替代资源之一.而以天然气的主要成分——甲烷为原料来生产高价值化学品被认为是石化工业中实现天然气取代石油为原料新化工路线的技术基础,具有极为可观的社会经济价值.目前甲烷的化学利用主要采用间接转化法,即先从甲烷制合成气,再由合成气制备各种化工原料和油品.但该路线流程复杂,能耗大,生产成本高及投资大,具有明显的局限性,这促使着人们不断探索能量效率更高的甲烷直接转化技术.甲烷氧化偶联(OCM)是最重要的甲烷直接转化技术之一.自1982首次报道以来,人们开发了1000多种OCM催化剂,涉及元素超过68种,但C₂烃类(乙烷和乙烯)的收率普遍低于30%,尚未实现工业化.传统研究认为,OCM反应遵循“多相-均相”催化反应机理,甲烷在催化剂表面活化产生甲基自由基后,在气相中进行偶联生成乙烷和乙烯等产物.由于高温下甲基自由基很容易脱附到气相,传统的OCM催化剂一般只在甲基自由基的产生这一步发挥作用.而随后在气相中发生的甲基自由基均相反应并不受催化剂控制,在热力学驱动下,会倾向于深度氧化生成CO2等副产物,因此OCM反应中C₂的收率上限为25%–28%.理论上来说,只有当催化剂能够在甲基自由基偶联这一步发挥作用时,C₂物种的收率才可能打破上限,但目前尚未有催化剂实现甲基自由基可控表面偶联.本文提出并证实5wt%Na₂WO₄/SiO₂(5NaWSi)具有催化甲基自由基表面偶联的能力.在低温下,5NaWSi本身对于OCM没有催化活性,但是它的加入能够显著提高La₂O₃催化剂的C₂选择性,进而提高C₂收率,使其在570℃的低温下即可达到10.9%的C₂收率.在La₂O₃和5NaWSi之间加入一层甲基自由基淬灭剂——石英砂,这种提升作用随即消失,表明甲基自由基在5NaWSi上的表面偶联可能是C₂选择性和收率提升的主要原因.本文进一步采用同步辐射光电离质谱技术原位检测了反应过程中的自由基中间体,结果发现,La₂O₃表面产生的甲基自由基确实可以在5NaWSi表面进行偶联,进而提高C₂的选择性和收率.通过对5NaWSi的组成和结构进行分析,发现5NaWSi中的Na₂WO₄纳米团簇可能是甲基自由基偶联的活性位点,该位点不仅具有很强的甲基自由基吸附能力,为甲基自由基表面偶联提供机会,同时不会深度氧化C₂物种,有效地提高了C₂选择性.以此为基础建立理论模型,我们通过DFT计算对甲基自由基在5NaWSi表面的偶联机制进行了研究.结果表明,5NaWSi对甲基自由基具有很强的吸附能力,而吸附后的甲基自由基更倾向于偶联生成C₂产物,而不是β-H消除生成HCHO等副产物,表明5NaWSi确实是很好的甲基自由基表面偶联催化剂.甲基自由基表面偶联的证实为OCM催化剂的开发开辟了新方向.从双功能催化剂设计的角度出发,将OCM反应分解成甲烷活化和甲基自由基偶联这两个部分,并分别针对这两个部分来筛选和优化催化剂,将有望突破C₂收率上限,进而推进OCM的工业化进程.     

Mo掺杂CeO2催化剂上甲烷的无氧偶联:表面和气相过程(英文)

甲烷无氧偶联是一种很有前景的甲烷转化利用的增值途径.由于高温条件下催化剂表面反应与气相自由基反应共存且均对产物分布具有重要影响,因而很难深入理解该反应的机理.本文采用火焰喷雾热解方法制备了一系列具有高度分散Mo位点的Mo掺杂的CeO₂样品,并用于催化甲烷无氧偶联反应.结果表明,在气相产物中,附加值较高的C₂烃产物(乙烷和乙烯)的选择性可达98%.反应过程中催化剂中高度分散的Mo-oxo物种被还原并转化为Mo(oxy-)碳化物物种,它是甲烷活化的活性位点.通过改变反应器内气相部分(即无催化剂部分)的体积,研究了气相反应对于产物分布的贡献.乙烷是甲烷无氧偶联的初级产物,部分乙烯和大部分苯是通过气相化学形成的.综上,本文为甲烷无氧偶联高效催化剂的设计提供了参考,并明确了减少反应器中自由体积以限制二次气相反应的重要性.     

La2O3/BaCO3上甲烷氧化偶联反应动力学与历程

以8％La_2O_3/BaCO_3为催化剂,用无梯度反应器,在720～800℃温度范围内,通过改变甲烷与氧分压进行了一系列的甲烷氧化偶联反应动力学测量,确定了该反应的反应历程。乙烷和大部分CO_x(主要是CO_2)是甲烷氧化的一次产物。乙烯是乙烷串行反应的产物。用幂式动力学方程拟合动力学试验数据,估算了各步反应速度方程的动力学参数。还用脉冲反应技术与过渡应答技术证明了参与活化甲烷的是催化剂表面上的可逆吸附氧。     

磷钼酸盐作为反应控制相转移催化剂催化氧化醇

以磷钼酸盐[C₇H₇N(CH₃)₃]₃{PO₄[MoO(O₂)₂]₄}为反应控制相转移催化剂, 用过氧化氢水溶液为氧化剂, 在液相选择性氧化醇制备醛的反应中, 发现该催化剂具有良好的催化活性. 在H₂O₂与醇的物质的量比为0.75的条件下, 产物中未检测到任何副产物, 基于H₂O₂的醇转化率最高达到95.2%. 反应结束时, 催化剂以沉淀的形式析出, 回收率不低于78%. 以苯甲醇的氧化为探针反应, 详细考察催化剂的反荷阳离子和溶剂种类对反应控制相转移现象和催化活性的影响. 结果表明, 选择 [C₇H₇N(CH₃)₃]^＋作为反荷阳离子和乙腈为溶剂, 体系出现了反应控制相转移催化的特征. 催化剂循环使用三次, 在保持较高回收率的同时其催化活性无明显降低, 说明该催化剂具有良好的稳定性.     

不饱和格氏试剂与不饱和酯的共轭加成 Ⅳ.乙烯四羧酸四乙酯与烯烃基溴化镁的加成作用

邢其毅等^[1]研究了烷基、芳基格氏试剂对乙烯四羧酸四乙酯的加成,发现这类反应为1,4-加成^[2~6].     

在助催剂存在下以BaCO3为载体的金属氧化物对甲烷氧化偶联反应的催化作用

甲烷通过氧化偶联反应合成乙烯和乙烷,是其开发利用的途径之一.自Keller等再次报道这一反应研究结果以来,各国研究者不断报道了各种具有研究价值的催化剂.Hinsen等提出PbO/γ-Al_2O_3是较好的催化剂;Driscoll等以N_2O为供氧物质,提出了Li~+-MgO;Moriyama等进而认为Na~+-MgO是更好的催化剂.同时,Sm_2O_3,LaAlO_3,     

Effects of Preparation Methods and Interaction between Support and Oxide for Oxidative Dehydrogenation of Ethane over NiO/ZrO2

The previous studies indicated that the unsupported and alumina supported nickel oxide catalysts are the attractive candidates for the oxidative dehydrogenation of ethane (ODE) reaction at lower reaction temperature^[1,2]. In the present study, NiO/ZrO₂ catalysts were prepared by the impregnation, complex of ammonia and coprecipitation, respectively, using the conventional incipient wetness technique. Over all samples used in this study, no NiO crystal structure was detected by XRD measurements carried out in parallel with the present work, which indicated the nickel oxide was highly dispersed on the support The blank testing indicated that the support ZrO₂ had very little activity below 600℃. Comparing with the unsupported nickel oxide, it was found that the activity of NiO/ZrO₂ catalysts prepared by the methods mentioned above decreased slightly and the selectivity for ethylene improved. With the increasing temperature, the ethane conversion increased and the selectivity for ethylene decreased However, the cracking of the ethane occurred at ca.450℃ on all samples prepared by different methods. The optimum catalytic behavior could be obtained on 5wt%NiO/ZrO₂ prepared by coprecipitation, with the ethane conversion of 26.2% and selectivity for ethylene of 51.8% at as low temperature as 350℃. The sample prepared by coprecipitation and calcined at 500℃ was calcined again at 600℃ for 5 h,the activity decreased obviously, which may be attributed to the existence of the interaction between nickel oxide and support taking into account for the high dispersion of NiO on ZiO₂.     

沸石载体结构对甲烷无氧芳构化性能的影响

考察了担载MoO₃的沸石催化剂上甲烷的无氧芳构化性能,并与沸石结构相关联.结果表明,孔径与苯分子动态直径相当的ZSM-5、ZSM-8、ZSM-11和β沸石等是甲烷无氧芳构化催化剂的良好载体,其中3%MoO₃/HZSM-11具有最高的甲烷芳构化活性和稳定性,973K下的转化率和苯选择性分别为8.0%和90.9%;6%MoO₃/HZSM-8与7%MoO₃/H-β芳构化性能相当.以HMCM-41和HSAPO-34为载体时芳构化活性很低,以HMOR、HX和HY为载体时仅有少量乙烯生成,而以HSAPO-5和HSAPO-11为载体时未检测到烃类生成.     

CATALYTIC CRACKING OF LIGHT ALKANES IN THE PRESENCE OF O_2 AND SELECTIVE CONTROL OF OLEFIN PRODUCTS

lntroductionThesmallolefinslikeethylene,propeneandbutenearethec0mmerciallydesirablepetrochemicalfeedstocksandarefoundincreasingusageinchemicalindustry.Theyareusuallyobtainedfromthepyrolysis0fpetroleumhydrocarb0nswithsteaInatveryhightemPeratUreandarealsoavailablefromFCCprocess.TheimProvedFCCcatalystforeIhancingtheolefinproducthasbeenreportedll].However,FCCisalrnostimPossiblefortheshortchainalkanefeedstockscutfrompetroleum0robtuinedfromrefinerygasornatUralgassincecrackingofhydrocarbonsbeco…     

Catalytic Pyrolysis of Methane

Methane decomposition over metal oxides/SiO₂ surface was investigated. At 1400 K obtained product distribution of this decomposition varied with metal oxide used. The effectiveness of these catalysts has been discussed in terms of activity and C₂ selectivity. ThO₂/SiO₂ was found to be the most effective catalyst for the catalytic decomposition of methane. Positive catalytic effect of ThO₂/SiO₂ on the pyrolysis has also been confirmed at 1073 K. At low reaction conversions, ethane and ethylene are found as major products. Yields of ethylene and other unsaturated products are sensitively inhibited by NO impurities in the methane. A reaction mechanism has been proposed to account observed experimental results.     

Non-oxidative dehydro-oligomerization of methane to higher molecular weight hydrocarbons at low temperatures

The non-oxidative dehydro-oligomerization of methane to higher molecular weight hydrocarbons such as aroma tics and C2 hydrocarbons in a low temperature range of 773-973 K with Mo/HZSM-5,Mo-Zr/HZSM-5 and Mo-W/HZSM-5 catalysts is studied.The means for enhancing the activity and stability of the Mo-containing catalysts under the reaction conditions is reported.Quite a stable methane conversion rate of over 10% with a high selectivity to the higher hydrocarbons has been obtained at a temperature of 973 K.Pure methane conversions of about 5.2% and 2.0% have been obtained at 923 and 873 K,respectively.In addition,accompanied by the C2-C3 mixture,tht- methane reaction can be initiated even at a lower temperature and the conversion rate of methane is enhanced by the presence of tne initiator of C2-C3 hydrocarbons.Compared with methane oxidative coupling to ethylene,the novel way for methane transformation is significant and reasonable for its lower reaction temperatures and high selectivity to the desired prod     

Niobium phosphates as new highly selective catalysts for the oxidative dehydrogenation of ethane

Several niobium phosphate phases have been prepared, fully characterized and tested as catalysts for the selective oxidation of ethane to ethylene. Three distinct niobium phosphate catalysts were prepared, and each was comprised predominantly of a different bulk phase, namely Nb(2)P(4)O(15), NbOPO(4) and Nb(1.91)P(2.82)O(12). All of the niobium phosphate catalysts showed high selectivity towards ethylene, but the best catalyst was Nb(1.91)P(2.82)O(12), which was produced from the reduction of niobium oxide phosphate (NbOPO(4)) by hydrogen. It was particularly selective for ethylene, giving ca. 95% selectivity at 5% conversion, decreasing to ca. 90% at 15% conversion, and only produced low levels of carbon oxides. It was also determined that the only primary product from ethane oxidation over this catalyst was ethylene. Catalyst activity also increased with time-on-line, and this behaviour was ascribed to an increase of the concentration of the Nb(1.91)P(2.82)O(12) phase, as partially transformed NbOPO(4), formed during preparation, was converted to Nb(1.91)P(2.82)O(12) during use. Catalysts with predominant phases of Nb(2)P(4)O(15) and NbOPO(4) also showed appreciable activity and selectivities to ethylene with values around 75% and 85% respectively at 5% ethane conversion. The presence of phosphorous is required to achieve high ethylene selectivity, as orthorhombic and monoclinic Nb(2)O(5) catalysts showed similar activity, but displayed selectivities to ethylene that were <20% under the same reaction conditions. To the best of our knowledge, this is the first time that niobium phosphates have been shown to be highly selective catalysts for the oxidation of ethane to ethylene, and demonstrates that they are worthy candidates for further study.     

Oxidative dehydrogenation of ethane over sufated zirconia supported oxides catalysts

The oxidative dehydrogenation of ethane into ethylene has been investigated on metal oxide-based sulfated zirconia catalysts at temperatures of 400–600°C. It is found that the activity and selectivity toward ethylene depend on the nature of metal oxide and temperature and that Ni and V oxides supported on sulfated zirconia exhibited higher ethylene yields.     

MCl2-TiO2-SnO2 (M=Mg, Ca, Sr, Ba) 催化剂甲烷氧化偶联反应性能的研究

选用不同的碱土金属氯化物为原料,采用共研磨的方法制备出了具有不同表面碱性的MCl2-TiO2-SnO2(M=Mg,Ca,Sr,Ba)催化剂,并考察了催化剂的甲烷氧化偶联反应性能.通过N2吸脱附(BET)、X-射线衍射(XRD)、X-射线光电子能谱(XPS)和CO2程序升温脱附(CO2-TPD)等技术对催化剂进行了表征.结果表明,随碱土金属元素的不同,催化剂呈现出了强弱不同的碱性吸附位.催化剂表面的碱性对活化甲烷具有促进作用,同时也带来乙烯深度氧化副反应的发生.碱量越大的弱碱性吸附位对甲烷的活化越有利,而强碱性吸附位则能导致催化剂活性降低,甚至是催化剂失活.乙烯的选择性与催化剂表面晶格氧的相对浓度密切相关.表面晶格氧的相对浓度较高的催化剂,其乙烯选择性也较大.     

Oxidative processing of light alkanes: State-of-the-art and prospects

Recent literature data on partial oxidation of light alkanes into syngas and oxidative coupling of methane into C₂ hydrocarbons are reviewed. The problems of these processes (high cost of pure oxygen; safety; activity, selectivity and stability of catalysts; temperature regime; coke formation and other by-products; insufficient level of methane transformation into ethane and ethylene) are considered. Possible solutions of these problems and prospects of practical use of light alkanes processing are discussed.     

Oxidative dehydrogenation of ethane with carbon dioxide over sulfated zirconia supported metal oxides catalysts

Several metal oxides supported on sulfated zirconia catalysts were tested for the oxidative dehydrogenation of ethane into ethylene by carbon dioxide. It is found that the catalytic behavior of supported oxide catalysts differ depending on the nature of metal oxides. Chromium oxide-sulfated zirconia exhibits the highest ethane conversion and medium level of ethylene selectivity, producing 38% ethylene yield at 50% ethane conversion at 650°C.