Hydroisomerization of long-chain alkane over Pt/SAPO-11 catalysts synthesized from nonaqueous media

SAPO-11 molecular sieves were synthesized from nonaqueous media. The effects of Si and Al sources as well as solvents on the catalytic performance of SAPO-11 were investigated by the hydroisomerization reaction of n-dodecane. The samples were characterized by XRD, XRF, N-2-adsorption, SEM, NH3-TPD, IR-NH3 and Si-29 CP MAS NMR. The SAPO-11 samples synthesized with tetraethoxysilane as the Si source showed higher Si incorporation contents than the SAPO molecular sieves prepared with polymeric Si sources (fumed silica and Si colloidal gel). The reaction results showed that Pt/SAPO-11 catalysts synthesized from ethylene glycol and glycerol media with the monomeric Si and Al sources (tetraethoxysilane, aluminum isopropoxide) exhibited higher catalytic activities than those catalysts with the polymeric Si or Al (pseudo-boehmite) sources, due to the larger external surface area and higher acidity of the former ones. Especially, the catalyst synthesized in an ethylene glycol medium possessed the highest catalytic activity. Over this catalyst, 88% conversion of n-dodecane was achieved at a low temperature of 250 degrees C.

Characterization of metal-containing molecular sieves and their catalytic properties in the selective oxidation of cyclohexane

Three types of metal-containing molecular sieves with AFI, AEL and CHA structures (Me = Co, Mn, Cr and V) were synthesized hydrothermally and characterized by XRD, XRF, TG, TPR, NH3-TPD and FT-IR. It was revealed that metals were incorporated into the framework of molecular sieves and induced the presence of charge centers. Both cobalt and manganese in the framework of AIPO-5, AlPO-11 and SAPO-34 were not reducible before the structure collapse. The redox behaviours of these catalysts in cyclohexane oxidation at 403 K using O-2 as oxidant were examined. CoAPO-11 exhibited best activity and good selectivities for the monofunctional oxidation products (88.5%). Cyclohexanol was the major product over most catalysts, whereas for Cr-containing molecular sieves, high selectivity of cyclohexanone was observed. Investigation of reaction mechanism based on CoAPO-11 and CrAPO-5 catalysts indicated that the decomposition of cyclohexyl hydroperoxide (CHHP), the intermediate in cyclohexane oxidation, followed the pathway: cyclohexanone <-- CHHP --> cyclohexanol -->cyclohexanone. (C) 2004 Elsevier B.V. All rights reserved.

Production of isobutene from n-butane over Pd modified SAPOs and MeAPOs

Pd modified AlPO-11 and SAPO-5, 11, 34 were used in the direct transformation of n-butane to isobutene. The effect of acidity and porous structure on the supported Pd and the catalytic perfori-nance were discussed. For higher isobutene selectivity, some metals, such as Ti, Fe, Mg, Co and Mn, was incorporated into AlPO-11 framework and isobutene selectivity of 34.86% can be obtained over Pd/MnAPO-11. A combined catalyst system was used for a further improvement of the isobutene selectivity.

Skeletal isomerization of 1-hexene to isohexenes over zeolite catalysts

Several zeolite catalysts such as SAPO-11, ZSM-11, ZSM-12, etc. were selected to convert I-hexene to branched hexenes in this work. Pore size of the zeolite catalyst plays an important role on the yield and the distribution of branched isohexenes. And the zeolite catalysts with the pore size of 0.6nm are optimum to produce dimethylbutenes (DMB). SAPO-11 zeolite is a suitable skeletal isomerization catalyst, especially in the production of methyl pentenes. Under the following reaction conditions: WHSV=1.0 h(-1), H-2/hexene=8, T=250 degreesC, P=0.2 MPa, the yield of skeletal isohexenes remains above 80% at the prolonged time-on stream of 80 h, accompanying low C5-, C7+ products and low carbon deposition on the catalyst.

TMAOH-P_2O_5-Al_2O_3-SiO_2-H_2O-HF体系分子筛的合成研究

以H_3PO_4、水铝石和硅溶胶为原料,四甲基氢氧化铵(TMAOH)为模板剂,在HF参与下水热晶化出含磷P型沸石和SAPO-20分子筛,得到2种分子筛的生成相区,并用~(31)P和~(29)Si MASNMR方法研究了杂原子的取代方式。

磁等性自旋体系FT—NMR实验的乘积算符描述 Ⅲ.自旋拓扑滤波实验分析

在前文工作基础上指导了磁等性弱耦合体系多量子积算符(MQCPO)在哈密顿作用下演化的普适解析式,给出了一组多量子滤波实验分析中常用的MQCPO与对称化乘积算符(SAPO)的线关系式;用SAPO+MQCPO方法结合图论知识分析了某些自旋拓扑选择性滤波脉冲序列.结果表明,改进的密度算符理论适用于对称体系各种复杂滤波序列的分析,并具有运算简单、物理意义明确等优点.

自旋置换对称体系多脉冲及二维核磁共振实验的密度算符描述(Ⅱ)——多量子积算符方法

在对称化乘积算符(简称SAPO)方法基础上提出了多量子积算符(简称MQCPO)方法。改进的密度算符理论对I_nS(I=1/2,S=1/2;n为任意正整数)自旋体系多脉冲及二维核磁共振实验的描述普遍适用。MQCPO与SAPO从不同角度反映了自旋体系的对称性,故它们之间存在简单线性关系。文中给出I_n(I=1/2,n=2,3)自旋体系MQCPO的SAPO表示。MQCPO有利于自由演化过程的描述,而脉冲作用的描述则是SAPO为佳;利用MQCPO与SAPO的线性关系及SAPO笛卡儿分量的坐标轮换性质,“z”表象下脉冲作用的描述变得简单而直观。对异核谱剪辑及自旋拓扑滤波(spin topology filtration)等实验脉冲序列的分析,该方法是方便的。

New progress in R&D of lower olefin synthesis

This paper gives a brief review of R&D researches for light olefin synthesis directly and indirectly from synthesis gas in the Dalian Institute of Chemical Physics (DICP). The first pilot plant test was on methanol to olefin (MTO) reaction and was finished in 1993, which was based on ZSM-5-type catalyst and fixed bed reaction. In the meantime, a new indirect method designated as SDTO (syngas via dimethylether to olefin) was proposed. In this process, metal-acid bifunctional catalyst was applied for synthesis gas to dimethylether(DME) reaction, and modified SAPO-34 catalyst that was synthesized by a new low-cost method with optimal crystal size was used to convert DME to light olefin on a fluidized bed reactor. The pilot plant test on SDTO was performed and finished in 1995. Evaluation of the pilot plant data showed that 190-200 g of DME were yielded by single-pass for each standard cubic meter of synthesis gas. For the second reaction, 1.880 tons of DME or 2.615 tons of methanol produced 1 ton of light olefins, which constitutes of 0.533 ton of ethylene, 0.349 ton of propylene and 0.118 ton of butene. DICP also paid some attention on direct conversion of synthesis gas to light olefins. A semi-pilot plant test (catalyst 1.8 1) was finished in 1995 with a CO conversion > 70% and a C(2)(=)-C(4)(=) olefin selectivity 71-74% in 1000 h. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Coke formation during the methanol conversion to olefins in zeolites studied by UV Raman spectroscopy

Coke formation on/in ZSM-5, USY and SAPO-34 zeolites was investigated during the methanol conversion to olefins at temperatures from 298 to 773 K using ultraviolet (UV) Raman spectroscopy. The fluorescence interference that usually obscures the Raman spectra of zeolites in the conventional Raman spectroscopy, particularly for coked catalysts, can be successfully avoided in the UV Raman spectroscopy. Raman spectra are almost the same for adsorbed methanol on the three zeolites at room temperature. However, the Raman spectra of the surface species formed at elevated temperatures are quite different for the three zeolites. Coke species formed in/on SAPO-34 are mainly polyolefinic species, and in/on ZSM-5 are some aromatic species, but polyaromatic or substituted aromatic species are predominant in USY at high temperatures. Most of the coke species can be removed after a treatment with O-2 at 773 K, while some small amount of coke species always remains in these zeolites, particularly for USY. The main reason for the different behavior of coke formation in the three zeolites could be attributed to the different pore structures of the zeolites. (C) 2000 Elsevier Science B.V. All rights reserved.