Influence of calcination and lithium promotion on the surface properties of oxide supports

Thermal treatment and the addition of lithium influence the surface area of the oxides SiO₂, Al₂O₃ and MgO. A calcination temperature 1073 K causes a significant decrease of the surface area of SiO₂ and Al₂O₃; the same is not observed in case of MgO. Systems Li/MgO and Li/SiO₂ are characterized by a much smaller specific surface area than pure oxides thermally treated at the same temperature.     

钙钛矿型氧化物催化剂SrTiO3的甲烷氧化偶联反应性能的研究

碱土元素氧化物是一类具有较好催化活性和选择性的甲烷氧化偶联(OCM)催化剂[1,2]。Filkova[3]等研究了不同的碱土金属氧化物促进的Nd2O3催化剂的OCM催化性能,发现在所有碱土金属氧化物-Nd2O3催化剂中,SrO-Nd2O3催化剂具有最高的生成C2烃的选择性,这可能因为SrO较强的碱性以及Sr     

Oxygen permeation and oxidative coupling of methane in membrane reactor: A new facile synthesis method for selective perovskite catalyst

A dense membrane of La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF) perovskite was prepared by a new chelating agent, ethylene diamine N,N,N′,N′-tetra N-acetyl diamine (EDTNAD). As a potent ligand, EDTNAD provided a facile one-step method to form complexes of the four metal ions, simultaneously. The oxygen permeation flux through the pure perovskite LSCF dense membrane was measured over temperature range of 1073–1223 K, thickness of 0.7–1.0 mm and oxygen partial pressure of 0.1–1.0 bar. Oxidative coupling of methane (OCM) reaction using LSCF disk in the atmospheric membrane reactor and over the temperature range of 1073–1173 K showed a C₂ selectivity of 100% and C₂ yield of 5.01% at 1153 K. Furthermore, OCM reaction data of the membrane reactor were discussed and compared with those of the fixed bed using the same perovskite powder as the catalyst.     

Modeling the oxidative coupling of methane： Heterogeneous chemistry coupled with 3D flow field simulation

The oxidative coupling of methane (OCM) over titanate perovskite catalyst has been developed by three-dimensional numerical simulations of flow field coupled with heat transfer as well as heterogeneous kinetic model. The reaction was assumed to take place both in the gas phase and on the catalytic surface. Kinetic rate constants were experimentally obtained using a ten step kinetic model. The simulation results agree quite well with the data of OCM experiments, which were used to investigate the effect of temperature on the selectivity and conversion obtained in the methane oxidative coupling process. The conversion of methane linearly increased with temperature and the selectivity of C2 was practically constant in the temperature range of 973–1073 K. The study shows that CFD tools make it possible to implement the heterogeneous kinetic model even for high exothermic reaction such as OCM.     

钠助剂对Fe/SiO_2催化剂结构及其催化甲烷氧化偶联反应性能的影响(英文)

以二氧化硅担载铁氧化物（１ｗｔ％ Ｆｅ／ＳｉＯ２）为探针,结合ＸＲＤ、ＸＡＮＥＳ以及ＥＸＡＦＳ分析结果首次从表面配位几何的观点讨论了钠助剂对Ｆｅ／ＳｉＯ２催化剂结构及其甲烷氧化偶联反应性能所产生的影响。ＸＲＤ分析表明,Ｆｅ／ＳｉＯ２经８００℃焙烧后仍保持无定形特征,添加钠助剂并经８００℃焙烧后,Ｎ２Ｆｅ／ＳｉＯ２已转化为α－方石英结构。Ｆｅ／ＳｉＯ２的ＥＸＡＦＳ拟合结果显示,铁中心被５个近邻氧环绕,平均Ｆｅ－Ｏ键长为０．１９４ｎｍ。与Ｆｅ／ＳｉＯ２相比,Ｎａ－Ｆｅ／ＳｉＯ２的径向结构函数谱中最强峰的相对强度提高了１／４,表明形成了一个更加密集的Ｆｅ－Ｏ壳层。拟合结果表明围绕中心铁原子０．１８９ｎｍ处平均有４．１个氧近邻。Ｆｅ－Ｋ边ＸＡＮＥＳ谱表明钠的参与使催化剂的活性组分由配位不饱和的八面体位逐渐向四配位四面体位迁移。甲烷氧化偶联反应结果显示,添加钠助剂后甲烷转化率有所下降,但是Ｃ２烃的选择性提高了近４２个百分点,ＣＯｘ的选择性则明显下降。说明钠的引入使催化剂的表面结构发生变化,所形成的多数四面体／少数八面体混合结构有效地抑制了甲烷的深度氧化,乙烯乙烷的选择性明显提高。     

OXIDATIVE COUPLING OF METHANE IN A CIRCULAR FIXED BED REACTOR WITH 30 mL MgO/BaCO_3 CATALYST

在甲烷氧化偶联反应中，采用了一种薄层环形固定床反应器，这种反应器有利于反应热的转移。在环形固定床反应器中进行的ＭｇＯ／ＢａＣＯ３催化剂稳定性试验结果表明，催化剂在５００ｈ试验中一直保持较高的活性。在ＣＨ４：Ｏ２：Ｈ２Ｏ＝５：１：２．３，ＣＨ４的ＧＨＳＶ为５７００ｈ－１的条件下，得到甲烷转化率为２６％，Ｃ２烃收率为１７．３％，Ｃ２选择性为６７．５％；水蒸汽作为稀释气引入反应中，可分散和带走催化剂床层过多的反应热，减小床层温差。ＸＲＤ结果表明，反应后的催化剂与新鲜催化剂的结构基本一致，催化剂具有稳定催化活性的原因，应归属于其结构的稳定性和具有一定的抗水蒸汽性能。     

Particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen:Construction and performance for oxidative coupling of methane

A novel particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen is constructed comprising of the upper-layer 5wt%Na2WO4-2wt%Mn/SiO2 particle catalyst and the under-layer 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3 /FeCrAl metal-based monolithic catalyst as well as a side tube in the interspaces of two layers for supplementing O2.The reaction performance of oxidative coupling of methane(OCM) in the dual-bed reactor system is evaluated.The effects of the reaction parameters such as feed CH 4 /O 2 ratio,reaction temperature and side tube feed O2 flowrate on the catalytic performance are investigated.The results indicate that the suggested mode of dual-bed reactor exhibits an excellent performance for OCM.CH4 conversion of 33.2%,C2H4 selectivity of 46.5% and C2 yield of 22.5% could be obtained,which have been increased by 6.4%,4.1% and 5.5%,respectively,as compared with 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst in a single-bed reactor and increased by 10.7%,31.9% and 17.7%,respectively,as compared with 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3 /FeCrAl metal-based monolithic catalyst in a single-bed reactor.The effective promotion of OCM performance in the reactor would supply a valuable reference for the industrialization of OCM process.     

铒激光脉冲消融泌尿结石和胆结石比较研究

利用光学弱相干显微成像系统对脉冲激光消融硬生物组织后形成的凹坑二维和三维形貌进行了扫描,分析了Erbium∶YAG激光脉冲消融生物硬组织特性.结果表明：相同激光参量条件下,消融胆结石比消融泌尿结石具有更高的消融效率|消融胆结石或消融泌尿结石时,脉冲能量越大,消融效率越高|消融效率提高主要体现在凹坑表面直径更宽、高度更深、体积更大|光学弱相干显微成像技术比光学弱相干光层析成像技术测量准确度提高约一个量级,更适合于测量脉冲激光消融生物硬组织后形成的凹坑形貌.     

Kinetic simulation of oxidative coupling of methane over perovskite catalyst by genetic algorithm： Mechanistic aspects

The reaction kinetics of oxidative coupling of methane catalyzed by perovskite was studied in a fixed bed flow reactor. At atmospheric pressure, the reactions were carried out at 725, 750 and 775 ℃, inlet methane to oxygen ratios of 2 to 4.5 and gas hourly space velocity (GHSV) of 100 min-1. Correlation of the kinetic data has been performed with the proposed mechanisms. The selected equations have been regressed with experimental data accompanied by genetic algorithm (GA) in order to obtain optimized parameters. After investigation the Langmuir-Hinshelwood mechanism was selected as the best mechanism, and Arrhenius and adsorption parameters of this model were obtained by linear regression. In this research the Marquardt algorithm was also used and its results were compared with those of genetic algorithm. It should be noted that the Marquardt algorithm is sensitive to the selection of initial values and there is possibility to trap in a local minimum.     

Fluctuating Storage of the Active Phase in a Mn-Na2WO4/SiO2 Catalyst for the Oxidative Coupling of Methane

Structural dynamics of a Mn-Na₂WO₄/SiO₂ catalyst were detected directly under reaction conditions during the oxidative coupling of methane via in situ XRD and operando Raman spectroscopy. A new concept of fluctuating storage and release of an active phase in heterogeneous catalysis is proposed that involves the transient generation of active sodium oxide species via a reversible reaction of Na₂WO₄ with Mn₇SiO₁₂. The process is enabled by phase transitions and melting at the high reaction temperatures that are typically applied.