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.     

A New Way to Obtain Mo/HZSM-5 Catalyst with High Activity and Selectivity for Methane Dehydro-aromatization 一种制备高活性和高稳定性甲烷无氧芳构化Mo/HZSM-5的新方法

 采用气相化学沉积法对HZSM-5分子筛的外表面进行选择性修饰,然后将它作为载体制备Mo/HZSM-5 催化剂,并应用于甲烷无氧脱氢芳构化反应. 改性的催化剂比未改性的催化剂表现出更好的甲烷转化活性、芳烃选择性和稳定性,明显地抑制了积碳的生成. 利用核磁氢谱对催化剂进行了表征. 在未经改性的Mo/HZSM-5催化剂表面,平均每个晶胞中含有1.12个B酸中心, 而在改性后的催化剂表面,平均每个晶胞中只有0.61个B酸位. 说明在甲烷无氧芳构化反应中,少量的B酸中心即可达到反应要求,过多的酸性位只会导致更多积碳物种的生成,从而加快催化剂失活速度,降低其稳定性.     

Mo/HZSM-5催化剂载体对甲烷无氧芳构化反应的影响

着重研究了挤条成型的纳米Mo/HZSM-5催化剂在甲烷无氧芳构化反应中的催化性能.结果表明,Al2O3载体的加入减少了催化剂的B酸量,对甲烷无氧芳构化反应不利,导致甲烷转化率降低,并且催化剂积碳严重.通过适量添加SiO2载体,减少Al2O3载体的量,可以使催化剂的B酸量提高,从而可提高甲烷转化率,并且可降低催化剂的积碳量.     

预处理条件对Mo/HZSM-5和Mo-Zn/HZSM-5甲烷芳构化性能的影响

甲烷无氧芳构化 ,具有选择性高、技术简单及产物易分离等特点 ,已引起人们的广泛关注 [1,2 ] .Mo/HZSM- 5是芳构化的良好催化剂 ,为了探讨预处理条件对反应的影响 ,我们对不同预处理条件下的 Mo/HZSM- 5及 Zn改性的 Mo/HZSM- 5催化剂上的甲烷无氧芳构化反应进行了研究 ,并以热重法对催化剂的稳定性进行了表征 .1实验部分1 .1原料和试剂钼酸铵 ( A.R.级 ) ,乙酸锌 ( A.R.级 ) ,铵型ZSM- 5分子筛 (硅铝比为 5 0～ 70 ) .1 .2催化剂制备铵型 ZSM- 5分子筛于 81 3K、空气气氛下焙烧3h,即成 HZSM- 5分子筛 .以一定浓度的钼酸铵溶液…     

分子筛的酸处理对Mo/HZSM-5催化甲烷无氧芳构化反应性能的影响

 采用HNO3溶液对HZSM-5分子筛进行预处理,并以处理后的分子筛为载体制备了Mo/HZSM-5 催化剂. 结果表明,改性的Mo/HZSM-5催化剂在甲烷无氧脱氢芳构化反应中表现出很好的稳定性,显著地抑制了积炭物种在催化剂表面的形成. SEM,XRD和1H MAS NMR等表征结果表明,酸处理在一定程度上降低了HZSM-5分子筛的结晶度,使部分Al物种脱离骨架结构,迁移到骨架外形成新的表面Al羟基,从而使HZSM-5分子筛上B酸中心的数目明显减少. 未经改性的Mo/HZSM-5催化剂表面,平均每个晶胞中有1.12个B酸位,而改性的Mo/HZSM-5催化剂表面,平均每个晶胞中仅有0.88个B酸位. 这表明过多的酸性位存留在催化剂上会引起积炭的生成,降低催化剂的稳定性.     

N掺杂Mo/HZSM-5催化剂制备及对甲烷无氧芳构化催化性能影响

采用三聚氰胺作为N源,N掺杂改性HZSM-5沸石分子筛后负载Mo活性金属组分,制备了一种用于甲烷无氧芳构化反应(MDA)的催化剂。采用XPS、N_2吸附-脱附、XRD、H2-TPR、TEM和NH3-TPD对催化剂性质和Mo金属组分状态进行了分析表征,并考察了催化剂的甲烷无氧芳构化反应催化性能。结果表明,HZSM-5经过N掺杂改性后,会在分子筛表面生成一层含氮基团,有序调控了分子筛的酸性位点;同时会诱导Mo金属组分在催化剂表面更好的锚定落位。此方法制备的Mo/HZSM-5-CN催化剂能有效提高MDA反应的甲烷转化率和芳烃选择性,减缓了积炭的生成,展现出更优良的催化性能。     

CH_4在Mo/HZSM-5及其改性催化剂上的无氧芳构化(英文)

运用微型固定床反应器装置,研究了Mo/HZSM-5催化剂的Mo载量、金属助剂改性、载体模数对甲烷无氧芳构化反应性能的影响。结果表明,Ni/Mo摩尔比为0.1的Mo-Ni/HZSM-5(SiO2/Al2O3=25)催化性能最好,其稳定性较好,芳烃收率最高可达15.74%;此时甲烷转化率60.24%,芳烃选择性26.13%。     

甲烷在Mo/HZRP-1催化剂上无氧脱氢芳构化反应 Ⅰ.Mo/HZRP-1催化剂的催化性能和积炭行为

用高硅含磷五员环沸石分子筛(商品代号HZRP-1)作为载体,制备了Mo/HZRP-1催化剂.与Mo/HZSM-5相比,Mo/HZRP-1对甲烷无氧脱氢芳构化反应也表现出较好的催化性能.实验过程中,在反应气中添加N2作为内标物,给出包括甲烷在Mo/HZRP-1上的结焦量、转化率及各产物选择性在内的总碳物料平衡计算结果.考察了不同Mo担载量对催化剂性能和积炭行为的影响;重点考察了不同温度焙烧后20%Mo/HZRP-1催化剂的性能和积炭行为.在反应的初始阶段,6%Mo/HZRP-1表现出很高的活性:反应进行30 min时,甲烷转化率为11%,芳烃选择性达81%,而催化剂的结焦选择性仅为12%.BET,NH3-TPD和催化反应等表征结果表明:Mo物种的数量和状态,分子筛的酸强度和酸量以及分子筛的孔道结构是决定甲烷无氧脱氢芳构化反应性能和积炭行为的关键因素.     

甲烷无氧芳构化反应催化剂Mo/HZSM-5的H2-TPR研究

 采用H2-TPR技术研究了不同方法制备的Mo/HZSM-5催化剂,并借助 1H MAS NMR等表征手段对Mo/HZSM-5催化剂还原过程中可能出现的6个TPR谱峰进行了详细归属,首次指认了分布于分子筛孔道内并与B酸性位相互作用的Mo物种的还原峰. 此外,还考察了各种Mo基催化剂在甲烷无氧芳构化反应中的催化性能. 结果表明,与B酸中心相互作用的Mo物种比其他形式的Mo物种具有更好的活性和稳定性.     

硅烷化处理对Mo/HZSM-5催化剂上甲烷脱氢芳构化活性的影响

 结合催化剂的活性评价及固体高分辨核磁共振谱、X射线光电子能谱和X射线荧光光谱和热重等技术,考察了硅烷化处理对Mo/HZSM-5催化剂上甲烷脱氢芳构化活性的影响. 结果表明,采用大分子有机硅烷对HZSM-5分子筛进行硅烷化处理,除去了分子筛外表面的酸性位,并使分子筛本身发生了脱铝. 硅烷化处理使Mo/HZSM-5催化剂在进行甲烷脱氢芳构化反应时催化剂上总的积碳量明显减少,从而提高了催化剂的活性.     

非那雄胺合成工艺改进

非那雄胺能抑制5α-还原酶的活性,明显降低二氢睾酮水平,是一种治疗良性前列腺增生的有效药品。该合成工艺以甾烯酮酸为原料,将其与氯化亚砜反应,无须分离即与叔丁胺反应得17β-酰胺化合物,再氧化开环,环合,氢化,脱氢合成了非那雄胺。经元素分析、IR、1HNMR、13CNMR、MS分析表征了其结构。该法无须使用昂贵的2,2-二吡啶二硫化物和剧毒药品苯亚硒酸酐,且以乙酸铵代替氨气,降低了对设备的要求和腐蚀,更适用于工业生产。     

Dichroism of absorption and polarization of phosphorescence of molecules of the closed form of nitrobenzospirothiopyran

The spectral-polarization characteristics of absorption and phosphorescence of molecules of the initial form of nitro-substituted indolinospirobenzothiopyran were studied in oriented polyethylene films and in solutions with different polarity. An oscillator model of the electron transitions responsible for the formation of absorption and luminescence spectra was suggested. It was established that the principal differences in the spectral and photophysical properties of the compound studied and its oxygen-containing analog are associated with the fact that the electronegativity of the S atom is lower than that of the O atom. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1143–1146, June, 1997.     

Synthesis of phenolic components of Grains of Paradise

Two vanilloids, (5E)-8-(4-hydroxy-3-methoxyphenyl)oct-5-en-4-one (1) and 4-[3-hydroxydecyl]-2-methoxyphenol (2), isolated from the dried seeds of Grains of Paradise (Aframomum melegueta), were synthesized; the latter compound was made as the S-enantiomer and the material derived from the seeds was found to be a 1:1.7 mixture of the R and S isomers. The synthetic route used should allow the preparation of analogs having extended alkyl chains and consequently different lipophilicity, and 3, a homolog of 2, was also prepared.     

Acid hydrolysis of carboxymethylcellulose of low degree of substitution

Cotton cellulose was swollen in a sodium hydroxide solution and carboxymethylated by a two-bath method for different periods of time for each process. The kinetics of acid hydrolysis and the crystallinity of the swollen and carboxymethylated samples were measured. The proportion of broken bonds, rate constants for hydrolysis, and permeability of cellulose to hydrolyzing agents were calculated. The susceptibility of glycosidic linkages to acid hydrolysis was improved by carboxymethylation more than by swelling in alkali. The increased accessibility of carboxymethylcellulose to acid was regarded as a consequence of increased intra-and intercrystalline swelling and of the glycosidic bonds' weakness caused by the electron-attracting carboxymethyl group on the C-6 position.     

Study of hydration of two cements of different strengths

Main hydration products of two cement pastes, i.e. CSH-gel, portlandite (P) (and specific surface S) were studied by static heating, and by SEM, TEM and XRD, as a function of cement strength (C-33 and C-43) hydration time (th) and subsequent hydration in water vapour.Total change in mass on hydration and air drying, M_o, increased with strength of cement paste and with hydration time. Content of water escaping at 110 to 220°C, defined as water bound with low energy, mainly interlayer and hydrate water, was independent on cement strength but its content increased with (th). Content of chemically bound (zeolitic) water in CSH-gel, escaping at 220-400°C, was slightly dependent on strength and increased with (th). It was possibly derived from the dehydroxylation of CSH-gel and AFm phase. Portlandite water, escaping at 400-500°C, was independent on cement strength and was higher on longer hydration. Large P crystals were formed in the weaker cement paste C-33. Smaller crystals were formed in C-43 but they increased with (th). Carbonate formated on contact with air (calcite, vaterite and aragonite), decomposed in cement at 600-700^oC. It was high in pastes C-33(1 month) and C-43(1 month), i.e. 5.7 and 3.3%, respectively; it was less than 1% after 6 hydration months (low sensitivity to carbonation) in agreement with the XRD study showing carbonates in the air dry paste (1month), and its absence on prolonged hydration (6 months) and on acetone treatment. Water vapour treatment of (6 months) pastes or wetting-drying increased this sensitivity.Nanosized P-crystals, detected by TEM, could contribute to the cement strength; carbonate was observed on the rims of gel clusters.This revised version was published online in November 2005 with corrections to the Cover Date.     

Estimation of Kinetic Parameters of Thermal Oxidation of Ilmenite

The aim of the presented work was the investigation of thermal oxidation of ilmenite in static air atmosphere. The investigations were carried out by use of a derivatograph (MOM, Hungary). The changes of crystallographic structure of investigated samples were identified by X-ray diffractometry on Philips PW-1710 diffractometer. In temperature above 500°C appears structure of hematite Fe₂O₃. On the basis of the thermogravimetric measurements, the contracting area and contracting volume models were found as the best fitting experimental data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanism of action of base-catalyzed oxygenation of phenol derivatives

Cyclopropyl derivative of 2,6-di-tert-butylphenol is synthesized as a probe to investigate the mechanism of base-catalyzed autooxidation of phenol derivatives. Our study indicates that one electron reduction of molecular oxygen from phenolate gives phenoxyl radical 3, a key intermediate of autooxidation. The coupling of phenoxyl radical and superoxide radical gives peroxylate anion 4 and produces the final epoxy alcohol adduct 6.     

氯氧化镁生成热的研究

用氧化镁氯化镁水溶液制备了8水合氯氧化镁[nMg(OH)2·MgCl2·8H2O], 并测定了其在盐酸中的溶解热, 实验结果表明, 氯氧化镁溶解热与n值呈线性关系, 根据溶解热求出5Mg(OH)2·MgCl2·8H2O和3Mg(OH)2·MgCl2·8H2O的生成热分别为-7727.1和5888.1kJ·mol^1^-。     

化学计量中不确定度评定研究进展

测量不确定度是表征合理地赋予被测量之值的分散性的参数。本文针对化学计量不确定度评定基础模型仅适用于线性模型、概率分布为正态分布或缩放位移t分布等局限,介绍了近年来不确定度评定的研究热点:蒙特卡罗方法(Monte Carlo Method,MCM),不确定度评定的来源、评定概念、评估方法及其发展过程,扩大了测量不确定度评定与表示的适用范围。