Experimental investigation of fluidized-bed reactor performance for oxidative coupling of methane

Performance of the oxidative coupling of methane in fluidized-bed reactor was experimentally investigated using Mn-Na2WO4/SiO2,La2O3/CaO and La2O3-SrO/CaO catalysts.These catalysts were found to be stable,especially Mn-Na2WO4/SiO2 catalyst.The effect of sodium content of this catalyst was analyzed and the challenge of catalyst agglomeration was addressed using proper catalyst composition of 2%Mn2.2%Na2WO4/SiO2.For other two catalysts,the effect of Lanthanum-Strontium content was analyzed and 10%La2O 3-20%SrO/CaO catalyst was found to provide higher ethylene yield than La2O3/CaO catalyst.Furthermore,the effect of operating parameters such as temperature and methane to oxygen ratio were also reviewed.The highest ethylene and ethane (C2) yield was achieved with the lowest methane to oxygen ratio around 2.40.5% selectivity to ethylene and ethane and 41% methane conversion were achieved over La2O3-SrO/CaO catalyst while over Mn-Na2WO4 /SiO2 catalyst,40% and 48% were recorded,respectively.Moreover,the consecutive effects of nitrogen dilution,ethylene to ethane production ratio and other performance indicators on the down-stream process units were qualitatively discussed and Mn-Na2WO4/SiO2 catalyst showed a better performance in the reactor and process scale analysis.     

A DFT Study on the Adsorption of CO_2 Molecules on CaO(001) Surface at Different Coverages

The CO_2 adsorption on CaO(001) surface at different coverages from 1/9 monolayer(ML) to 1 ML has been investigated using density functional theory calculations. With the analysis of the most stable adsorption structures at different coverages, the mechanism of CaO(001)surface carbonating into CaCO_3 has been explored. At low coverages(≤1/3 ML), CO_2 molecule prefers sitting in parallel pattern on the CaO(001) surface, while the structure of the CaO(001)surface remains unchanged. At medium coverage(4/9 ～ 2/3 ML), the repulsive interactions between oxygen atoms of CO_2 become stronger, and the calcium carbonation structure appears on the CaO(001) surface. At high coverage( ≥ 7/9 ML), the structure of the CaO(001) surface is deeply damaged, and a few CO_2 molecules have penetrated into the surface and bound to the O atom of the second layer(sub-surface), eventually forming the layered structure of CaCO_3.Additionally, herein has discussed the simulation of HREELS and thermodynamical stability of these structures at different coverages.     

Rare Earth Complex Initiated Ring-Opening Polymerization of 2,2-Dimethyltrimethylene Carbonate

Aliphatic polycarbonate is a series of useful biodegradable materials attracting more interests recently. Poly(2,2-dimethyltrimethylene carbonate) (polyDTC) has been studied for a long time. Polymerization of DTC can be catalyzed by alkyl metals1, trifluoromethanesulfonic acid and its esters2, alcohol/methylaluminum diphenolate system3 and etc. Herein tris(2,6-di-tert-butyl-4-methylphenoxo) lanthanides (Ln(OAr)3, Ln=La, Nd) are firstly applied to initiate the polymerization of DTC. Ln(O…     

First-principles Study on the Properties of CaO(100) Surface Adsorbing Carbon Dioxide

The increasing carbon dioxide emissions have a huge impact on the global environment. Carbonation reaction of CaO is regarded as a potential method to capture carbon dioxide. The density functional theory calculations have been performed to investigate the adsorption of CO_2 on CaO(100) surface. This paper systematically studied the adsorption of CO_2 at different adsorption sites on CaO(100) surface and the influence of adsorption angle on adsorption energy. Based on the studying of adsorption sites, adsorption energy and electronic structure of the CO_2/CaO(100) systems, chemical adsorption mainly happens when CO_2 molecules are absorbed on the CaO(100) surfaces, but physical adsorption may also happen. The research found that CO_2 molecules reacted with surface O atom through C, forming monodentate surface carbonate species and tridentate carbonate. Among them, low-coordinated monodentate ligands have a higher stability than tridentate ligands due to the shorter C–OS bond length of monodentate ligands.     

Synthesis and Structure of a La(Ⅲ) Complex of 1,10-Phenanthroline-2,9-dicarboxylate:a Three-dimensional Network via Hydrogen Bonding Interactions

A new La(Ⅲ) complex, {[La(L)(NO3)(H2O)3]·H2O}n (L = 1,10-phenanthroline- 2,9-dicarboxylate), has been synthesized and structurally determined by X-ray diffraction analysis. The complex crystallizes in the monoclinic system, space group P21/c with a = 7.7358(17), b = 8.1664(18), c = 28.271(6) , β = 95.184(4)°, V = 1778.6(7)3, Z = 4, C14H14LaN3O11, Mr = 539.19, Dc = 2.014 g/cm3, μ = 2.471 mm–1, F(000) = 1056, the final R = 0.0350 and wR = 0.0659. In this complex, each metal center adopts a ten-coordination geometry formed by two N atoms from a ligand L and eight O atoms from three H2O molecules, a nitrate ion and carboxylates of two ligands. Each ligand adopts a N2,O3-pentdentate coordination mode using two N and two O atoms chelating a La(III), and using another O atom of carboxylate to bridge another La(III) center resulting in a 1D helical chain molecule. Intermolecular strong O–H···O and weak C–H···O hydrogen bonds extend the 1D chain structure into a 3D supramolecular architecture.     

Structural Determination of a New La(Ⅲ) Coordination Polymer with Pseudo-merohedral Twinning Structure

Hydrothermal reaction of benzene-1,2,4,5-tetracarboxylic(Btec) dianhydride with La2O3 lead to a new organometallic compound, [La2(betc)(Hbtec)(H2O)3][HCONH(CH3)2](I). Single-crystal X-ray diffraction analysis reveals that it crystallizes in monoclinic space group P21/n that mimics orthorhombic space group Pnma(viz. pseudo-merohedral twinning structure) with a = 7.6002(16), b = 18.954(4), c = 18.213(4) ?, β = 90.121(3)o, V = 2623.5(9) ?3, Z = 4, Mr = 907.21, Dc = 2.297 g/cm3, F(000) = 1752, μ(Mo Kα) = 3.32 mm-1, R = 0.0575 and w R = 0.0956. The structure of I features a 3-D framework constructed by La(III) cations, btec4- ligands, Hbtec3-ligands and coordinated water molecule. All of the La(III) cations are 10-coordinated by O atoms into 1-D infinite chains, which are further interconnected by C atoms of btec ligands to form a 3-D framework.     

Influence of alkali metal doping on surface properties and catalytic activity/selectivity of CaO catalysts in oxidative coupling of methane

Surface properties （viz. surface area, basicity/base strength distribution, and crystal phases） of alkali metal doped CaO （alkali metal/Ca= 0.1 and 0.4） catalysts and their catalytic activity/selectivity in oxidative coupling of methane （OCM） to higher hydrocarbons at different reaction conditions （viz. temperature, 700 and 750 ℃; CH4/O2 ratio, 4.0 and 8.0 and space velocity, 5140-20550 cm^3 ·g^-1·h^-1） have been investigated. The influence of catalyst calcination temperature on the activity/selectivity has also been investigated. The surface properties （viz. surface area, basicity/base strength distribution） and catalytic activity/selectivity of the alkali metal doped CaO catalysts are strongly influenced by the alkali metal promoter and its concentration in the alkali metal doped CaO catalysts. An addition of alkali metal promoter to CaO results in a large decrease in the surface area but a large increase in the surface basicity （strong basic sites） and the C2＋ selectivity and yield of the catalysts in the OCM process. The activity and selectivity are strongly influenced by the catalyst calcination temperature. No direct relationship between surface basicity and catalytic activity/selectivity has been observed. Among the alkali metal doped CaO catalysts, Na-CaO （Na/Ca = 0.1, before calcination） catalyst （calcined at 750 ℃）, showed best performance （C2＋ selectivity of 68.8% with 24.7% methane conversion）, whereas the poorest performance was shown by the Rb-CaO catalyst in the OCM process.     

Synthesis of Mg5(CO3)4(OH)2·4H2O with Flower-like Microstructure and Its Catalytic Activity for Transesterification of Dimethyl Carbonate with Phenol

A novel flower-like hydrated magnesium carbonate hydroxide,Mg_5(CO_3)_4(OH)_2·4H_2O,with micro-structure composed of individual thin nano-sheets was synthesized using a facile solution route without the use of template or organic surfactant.Reaction time has an important effect on the final morphology of the product.The micro-structure and morphology of Mg_5(CO_3)_4(OH)_2·4H_2O were characterized by means of X-ray diffractometry(XRD),field-emission scanning electron microscopy(FE-SEM).Brunauer-Emmett-Teller(BET)surface areas of the samples were also measured.The probable formation mechanism of flower-like micro-structure was discussed.It was found that Mg_5(CO_3)_4(OH)_2·4H_2O with flower-like micro-structure was a novel and efficient catalyst for the synthesis of diphenyl carbonate(DPC)by transesterification of dimethyl carbonate(DMC)with phenol.     

A Study on Production of Carbon Nanotubes by CH_4 Decomposition over LaNiO_3,La_4Ni_3O_(10),La_3Ni_2O_7 and La_2NiO_4

IntroductionIn the present study, by employing the citric acid complex method1, we prepared a series of perovskite-type oxides, viz. LaNiO3, La4Ni3O10, La3Ni2O7 and La2NiO4 for the growth of CNTs. After H2 reduction, the catalysts turn into La2O3 and active component Ni0 of various sizes. By means of CH4 decomposition over the reduced catalysts, high quality CNTs with dissimilar diameters can be generated in mass amount. In this paper, we attempt to make a comparison on the structure…     

Synthesis and Crystal Structure of a New Lanthanum(III) 4-Cyanobenzoate Complex

A new dinuclear La(III) complex [La2(4-cba)4[H(4-cba)2]2(phen)2(H2O)4] (4-Hcba = 4-cyanobenzoic acid and phen = 1,10-phenanthroline) 1 has been synthesized by solvothermal reaction in an ethanol/water mixed solution at 100 ℃ and structurally characterized by single- crystal X-ray diffraction. Crystallographic data: C88H58La2N12O20, Mr = 1881.28, triclinic P1, a = 7.518(3), b = 17.033(6), c = 17.551(6), α = 115.333(4), β = 92.9910(10), γ = 99.366(5)°, V = 1985.3(12)3, Z = 1, Dc = 1.574 g/cm3, F(000) = 944 μ = 1.145 mm–1, the final R = 0.0281 and wR = 0.0686 for 6708 reflections with I > 2σ(I). In 1, two nine-coordinated La(III) ions are connected by two 4-cba ligands in a syn-syn bidentate coordination mode, and the other six 4-cba ligands terminate the La(III) ions, resulting in an isolated dinuclear structure. Two different types of intramolecular hydrogen bonds, asymmetrical O-H…O and symmetrical O…H…O, exist in the crystal. The title complex molecules are connected through hydrogen bonds and weak π-π stacking interactions to generate a 2-D layered network. The thermogravimetric analysis of 1 has also been discussed.     

甲烷氧化偶联反应催化剂碱性与反应性能的相关性

在催化剂甲烷氧化偶联反应性能研究的基础上，利用ＣＯ２－ＴＰＤ技术考察了不同的碱金属化合物－Ｌａ２Ｏ３／ＢａＣｏ３催化剂的表面碱性。结果表明，ＢａＣＯ３的协同作用，碱金属化合物的添加都增大了催化剂表面碱性的强度，也增加了碱性位的数量。     

STUDIES ON BaF_2 PROMOTED PRASEODYMIUM OXIDE CATALYSIS FOR THE OXIDATIVE COUPLING OF METHANE

IntroductionTheoxidativecouplingofmethane(OCM)toetheneandethaneisanattractivereactiontoconvertnaturalgasintovaluablechemicals.SincethepioneeringworkbyKellerandBhasin[1],OCMhasbecomeasubjectofworldwideintenseresearchinrecentyears.Almostallofelementsinthepe…     

La2O3/MgO催化剂上的甲烷氧化偶联

研究了甲烷在La_2O_3/MgO催化剂上的氧化偶联。发现制备过等对催化剂的行为有显著影响。比较了催化剂的反应性能和体相结构,表明在MgO上存在着三种La_2O_3的状态:高分散La_2O_3是最活泼的;La(OH)_3不太活泼;而呈六方晶相的La_2O_3晶粒活性最低。在催化剂中加入Na_2CO_3和K_2CO_3可以改进催化剂的活性和选择性。还考察了反应条件如温度和空速的影响。     

Ba—La2O3催化剂的表面碱性,活性氧种对甲烷氧化偶联的影响

利用ＣＯ２－ＴＰＤ技术考察了Ｂａ－Ｌａ２Ｏ３系催化剂的表面碱性，实验发现，催化剂表面仅有单一的强碱位或中碱位时，其催化性能均较差。只有表面的中碱位与强碱位以适当量共同存在的样品（６％Ｂａ－Ｌａ２Ｏ３），才能获得好的催化活性和Ｃ２选择性。此碱性特征可能有利于表面活性位的产生。同时利用ＸＲＤ和ＸＰＳ等技术分别对体相结构和表面氧物种进行了研究。结果表明，Ｂａ－Ｌａ２Ｏ３系催化剂表面存在Ｏ２＾２－离子，但     

原位FT-IR研究甲烷和氧与SrO-La_2O_3/CaO催化剂表面的相互作用和反应(英文)

用原位FT－IR研究了甲烷和氧与纯CaO,La_2O_3和SrO氧化物以及LC和SLC催化剂的相互作用和反应．当不存在气相氧时,引入的甲烷与表面晶格氧反应生成碳酸盐物种。在室温或高温下,在这些氧化物和催化剂上不能检测到CH_4或O_2的吸附物类。但是,当CH_4和O_2同时存在时,在La_2O_3和LC催化剂上能检测到1118cm~－1的新谱带、这一谱带可能来自于表面碳酸盐在高温下氧气氛中的分解,并可归属为物种。甲烷与这一活性氧物种反应生成C_2H_4。但对SLC催化剂,在高温下不能检测到物种,而甲烷和氧在高温下反应也能产生表面碳酸盐并在气相中形成乙烯,这就表明,气相氧对这些催化剂也起着关键作用,但是在LC和SLC催化剂上甲烷氧化偶联反应可能有本质上的差别。     

氧化镧催化剂上甲烷氧化偶联—不同制备方法的比较

本文研究了５种不同制法的Ｌａ＿２Ｏ＿３对甲烷氧化偶联的催化性能，其Ｃ＿２选择性和Ｃ＿２收率的相对顺序为：Ｌａ＿２Ｏ＿３（１）＞Ｌａ＿２Ｏ＿３（２）＞Ｌａ＿２Ｏ＿３（４）＞Ｌａ＿２Ｏ＿３（５）＞Ｌａ＿２Ｏ＿３（３）。并运用ＸＲＵ、ＸＰＳ、ＣＯ＿２－ＴＰＤ、ＮＨ＿３－ＴＰＤ和ＩＰＡ转化反应等技术分别对催化剂的体相结构和表面性质，表面酸碱性进行了测定。结果表明，由于制备方法的不同，导致了Ｌａ＿２Ｏ＿３晶体表面结构的差异，这是影响催化性能的主要原因。同时还发现，催化剂的活性和Ｃ＿２选择性与表面酸碱性存在着相依性，Ｌａ＿２Ｏ＿３表面的总碱位数与总酸位数的比值，与其催化性能有较好的直接对应关系。     

甲烷氧化偶联La－Me－O（Me＝Mg，Ca，Sr，Ba）系催化剂表面氧种的研究

利用ＣＯ_２－ＴＰＤ法考察了Ｌａ－Ｍｅ－Ｏ（Ｍｅ＝Ｍｇ，Ｃａ，Ｓｒ，Ｂａ）系催化剂的表面碱性，并用Ｏ_２－ＴＰＤ、ＣＨ_４－ＴＰＤ法对该体系的表面活性氧种进行了表征，并与催化性能相关联。结果表明，Ｌａ－Ｂａ－Ｏ催化剂由于表面强碱性中心数目多，产生活性氧种的数目也多，有利于甲烷的活化，因而具有最高的甲烷转化率和Ｃ_２烃选择性。脉冲反应表明，在无气相氧存在下，表面晶格氧参与了氧化偶联，而且是选择氧化的活性氧种。     

STUDY ON OXID TIVE COUPLING OF METHANE Ⅱ.CATALY TIC PERFORMANCE AND CHARACTERIZATION OF TiO_2-BASED CATALYSTS

The catalytic performance of Mn/TiO_2,La-Mn/TiO_2,Li-La-Mn/TiO_2 etc for the oxidetive coupling of methane(OCM)was investignted.Thecatalysta were cheracterised with X-ray diffraction(XRD)and X-rayphotoelectron spectroscopy(XPS).The results reveal that catalyst Li-La-Mn/TiO_2 exhibits high activity and C_2 selectivity;Ti in this catalyst exists asTi~( 4) state;Li can promote the formation of lanthanum tituate via theinteraction between La and TiO_2;the formed La_2Ti_2O_7 and La_4Ti_9O_(24) aredistributed in the inner surface layer and Mn exists in outer surface layer in lowvalence states.The high activity and C_2 selectivity of catalyst Li-La-Mn/TiO_2are intimately related to the valence states of Mn,Li,La and theirdistribution on the catulyst surface layer.     

锂在甲烷氧化偶联催化剂中的助催化作用

自Lunsford等首次报道在Li/MgO催化剂上的甲烷氧化偶联(OCM)以来,许多研究者相继报道了添加碱金属对该反应的影响,其中以Li的添加最受关注。Li在OCM反应中对提高C_2烃选择性的作用最为明显,因而弄清Li在这一反应中的作用十分必要。本文讨论了Li在几个有代表性的碱土(CaO)及稀土(La_2O_3)中的存在形式与生成C_2产物的关系。