Synthesis, Characterization and Catalytic Properties of TS-1 Monoliths

The point of zero charge (PZC) of common oxide catalyst supports such as alumina and silica can be altered by doping with anions such as Cl^-, which lower the ZPC, or cations such as Na⁺ or K⁺, which raise the PZC. In a prior work it was shown that such alterations did not influence the properties of either support toward the adsorption of either cationic amine or anionic chloride complexes of Pt(IV) [1]. This follow-up work explored the hypothesis that in the pH range of interest (low pH over cation-doped silica, high pH over anion-doped alumina) the dopant is dissolved and the surface behaves as pure.The PZCs of doped silica and alumina washed in acidic, neutral, and basic solutions was measured by the EpHL (equilibrium pH at high loading) technique. Repeated acid washes of K⁺-doped, PZC-raised silica quickly brought the PZC back to that of the pure oxide, and the same was observed for basic washed, PZC-lowered Cl^--doped alumina. Thus, ion doping of silica and alumina does not appear to create irreversible changes in the materials' PZC and cannot be used to influence adsorptive properties.     

含钨介孔SiO2的合成、表征及其催化性能

分别以廉价硅酸钠与正硅酸乙酯为硅源,通过复合模板剂制备了介孔二氧化硅,并利用吸附相反应技术合成了WO3/SiO2复合催化剂。用XRD,TEM等手段对其结构进行了表征,通过油酸的催化氧化反应考察了催化剂的催化性能。     

改性HZSM-5分子筛的表征及用其催化合成环十五内酯

采用浸渍法制备出了不同金属离子(Fe、Mo、Mo-Fe)改性的HZSM-5分子筛,用XRD,FTIR,NH3-TPD等检测方法考察了改性HZSM-5分子筛上Fe、Mo和Mo-Fe的体相状态和酸性;并将改性HZSM-5分子筛用于催化15-羟基十五烷酸甲酯合成环十五内酯。结果表明,Mo-Fe/HZSM-5分子筛的Mo-Fe引入到HZSM-5分子筛骨架中,分子筛的酸量和酸强度增加,15-羟基十五烷酸甲酯的最大转化率为58.85%,环十五内酯选择性为16.48%。     

Chemical,Physical, and Catalytic Properties of Large Pore Acidic Zeolites

Abstract

catalysts corminins acid zeolitea a m more active, more selective to gasoline production, aad more stable in thermal and hydrothermal environmcnu [1–3]. It was esdznaud in 1973 that the selecdvky characmrisdcs of zeolite cmcklag araiysts were respoasible for a savings of aver 200 million bvrals of cmda oil per year oa the North Amartcan coadaent [4]. Acftpttp aa be madoat; zta Since purzeolita catalysts a n be forrnrrktad whtch are many orden of magnitude more acde than the older amorphous catalysts. Typid relative actidties of some zeoffte catalysts Uons are presented in Table 1. Considerafforu other than intrinsic-vie, for example. heat and mass tzuufer Umi Molu and/or equipment design factors, may set limits on the maximum aczivly. Today rkrtudly all commerchl cracktnq aulysts conraia zeolites.     

Chemical, Physical, and Catalytic Properties of Large Pore Acidic Zeolites

catalysts corminins acid zeolitea a m more active, more selective to gasoline production, aad more stable in thermal and hydrothermal environmcnu [1-3]. It was esdznaud in 1973 that the selecdvky characmrisdcs of zeolite cmcklag araiysts were respoasible for a savings of aver 200 million bvrals of cmda oil per year oa the North Amartcan coadaent [4]. Acftpttp aa be madoat; zta Since purzeolita catalysts a n be forrnrrktad whtch are many orden of magnitude more acde than the older amorphous catalysts. Typid relative actidties of some zeoffte catalysts Uons are presented in Table 1. Considerafforu other than intrinsic-vie, for example. heat and mass tzuufer Umi Molu and/or equipment design factors, may set limits on the maximum aczivly. Today rkrtudly all commerchl cracktnq aulysts conraia zeolites.     

Synthesis, Characterization and Catalytic Properties of Mesoporous Cobalt Aluminophosphate Molecular Sieves

Isomorphously substituted cobalt(II) hexagonal mesoporous aluminophosphate (CoHMA) molecular sieves were synthesized hydrothermally and characterized by various analytical and spectroscopic techniques. It was deduced that cobalt ions exhibit a divalent oxidation state in tetrahedral coordination in mesoporous aluminophosphates. Further, unlike cobalt-containing microporous aluminophosphate molecular sieves, Co(II) ions remain in a tetrahedral geometry even after calcination. The catalytic activity of CoHMA was tested for the cyclohexane oxidation reaction under mild conditions. Remarkable substrate conversion and product (cyclohexanol) selectivity were obtained compared to several previously reported heterogeneous catalysts.     

Synthesis, Characterization, and Catalytic Properties of Chromium-Containing Hexagonal Mesoporous Aluminophosphate Molecular Sieves

Chromium-containing hexagonal mesoporous aluminophosphate molecular sieve materials were synthesized, characterized and evaluated for the oxidation of cyclohexane under mild conditions. The catalysts showed remarkable activity for the chosen reaction with very high substrate conversion and excellent product selectivity. In addition, recycling studies over the spent catalysts as well as studies on quenched solutions under the reaction conditions indicated no or very meager loss in activity; thus, the materials behaved truly as heterogeneous catalysts. This observation was well supported by ICP-AES analysis of the filtrates obtained from the washed catalysts where no leaching of active chromium species was detected. Furthermore, the reaction carried out using these filtrates confirmed the absence of active metal ions as it exhibited only a marginal activity.     

Pd-MCM-41介孔材料的合成、表征及催化性能研究

用微波辐射法合成了介孔分子筛MCM-41,采用浸渍法获得不同钯含量的Pd-MCM-41催化剂,用XRD、低温N2吸附-脱附、IR对MCM-41及组装体进行了表征;研究了Pd负载量、反应时间、反应温度等条件对葡萄糖氧化反应的影响,结果表明Pd-MCM-41能有效催化葡萄糖氧化反应。     

含钛介孔SiO2 催化剂的合成及其催化性能

分别以廉价硅酸钠与正硅酸乙酯为硅源,通过复合模板剂制备了介孔二氧化硅,并利用吸附相反应技术合成了TiO2/SiO2复合催化剂。用X射线衍射(XRD)、红外谱图分析(FT-IR)等手段对其结构进行了表征,通过苯酚的羟基化反应考察了催化剂的催化性能。     

纳米级ZSM-12分子筛的合成及表征

采用双季铵盐模板剂溴代1,4-二氮甲基哌啶基-丁烷,通过动态水热晶化法成功制备了纳米级ZSM-12分子筛。采用X射线衍射、扫描电镜、透射电镜、红外光谱分析及N2吸附-脱附技术等测试方法对所得颗粒进行了研究。所合成的颗粒呈长条形状,长约150 nm,宽约30 nm。所得的ZSM-12沸石结晶体结构完整,无明显骨架缺陷,富含微孔和介孔孔隙。介孔孔隙来源于ZSM-12纳米晶粒之间的堆积孔隙。在酸分布上,所得的HZSM-12分子筛的中强酸及B酸比例较多,使得该沸石在催化反应中具备优良的反应活性。     

Catalytic Synthesis of 2-Methyl Pyrazine Over Zn-Modified Zeolites

Cyclization of ethylene diamine and propylene glycol to 2-methyl pyrazine (2-MP) was investigated on Zn-modified zeolites, namely ZSM-5, Beta, and ferrierite catalysts, as a function of temperature, space velocity, and feed ratio. Zn-impregnated ZSM-5 was found to be the promising catalyst with 64% selectivity for 2-MP at 450 °C. ZnO-like species on Zn-impregnated ZSM-5, identified from XPS, enhance the selectivity to 2-MP. The difference in acidity, the nature of the Zn species, and its distribution on Zn-modified ZSM-5 catalysts obtained from FT-IR and XPS are in good agreement and they are correlated with catalytic activity.     

TUN, IMF and -SVR Zeolites; Synthesis, Properties and Acidity

The effect of synthesis conditions on the preparation and properties of three novel zeolites TUN, IMF, and -SVR was investigated and compared with MFI. X-ray powder diffraction, infrared spectroscopy, chemical analysis, sorption measurements, and scanning electron microscopy were employed to characterize the textural and chemical properties of these zeolites. FTIR spectroscopy in combination with pyridine as probe molecule was used to describe the type, concentration and acid strength of these zeolites. Zeolite -SVR was synthesized with Si/Al ratios higher than 100 in contrast with TUN and IMF having Si/Al ratios about 20–30, respectively. TUN, MFI and IMF zeolites exhibit similar concentrations of Brønsted and Lewis acid sites and also similar acid strength of Brønsted sites. In contrast, the presence of one vacancy/unit cell in the case of -SVR zeolite substantially changes its acidic properties. Generally, zeolites TUN and IMF exhibit similar acidic properties in terms of acid strength and Brønsted to Lewis acid site ratio like MFI and due to their slightly larger pores higher activities in catalytic reactions are expected.     

Synthesis, Characterization and Catalytic Properties of Vanadium Substituted Hexagonal Mesoporous Aluminophosphate Molecular Sieves

Vanadium substituted hexagonal mesoporous aluminophosphate (VHMA) molecular sieves were synthesized hydrothermally. Various physicochemical studies, viz., XRD, TEM, DRUV–VIS, EPR, N₂ sorption were used to find the location of vanadium ions in the VHMA matrix and to check the mesoporosity of the sample. The catalytic activity of VHMA was evaluated, under mild reaction conditions, for the oxidation of cyclohexane reaction, which mainly gave cyclohexanol and cyclohexanone along with a very small amount of a secondary product, viz., cyclohexyl acetate. A comparative study, with other vanadium containing molecular sieves, viz., VMCM-41, VAPO-5 and VS-1, on the application of VHMA catalyst reveal that the latter exhibits excellent activity, selectivity and stability to leaching for the oxidation reaction of cycloalkanes, including bulkier molecules such as cyclododecane.     

Synthesis of ITQ-2 Zeolites and Catalytic Performance in n-Dodecane Cracking

ITQ-2 zeolites were prepared by sequential alkali-swelling and ultrasonic-delamination of precursor MCM-22 and characterized by X-ray powder diffraction, scanning electron microscopy, nitrogen adsorpti...     

The Synthesis and Properties of Two Catalytically Important Zeolites

With his discovery of stilbite in 1756, Cronstedt [1] recognized the existence of a new group of minerals consisting of hydrated “aluminosilicates” of the alkali and alkaline earth cations. While several members of the group may have similar or nearly identical compositions, each possesses its own, unique crystal structure. At present there are 35 known naturally occurring zeolites. The crystal structures have been determined for 27 and all but about 10 have been prepared synthetically. This paper will present the definition of zeolites and focus on the synthesis and physicochemical properties of two catalytically and commercially important synthetic zeolites, zeolite Y and zeolite ZSM-5.     

The State and Catalytic Properties of Platinum and Palladium in Faujasite-type Zeolites

The extensive body of literature published on the physicochemical and catalytic properties of metal zeolites has been reviewed in detail by Minachev and Isakov [1]. Industrial processes in petroleum chemistry involving metal zeolite systems have been examined by Bolton [2], Quite recently Rudham and Stockwell [3] presented a review covering many aspects of catalysis by faujasites. The scope of the present review is far more limited since only platinum and palladium faujasites will be considered and the subject will be further restricted by deliberately ignoring the important domain of bifunctional catalysis. So far little attention has been paid to the rapid progress made in the knowledge of very small particles supported on zeolites. During the past few years improved methods of particle size measurements, and new methods of evaluating the location, the structure, and the electronic properties of metal, and reliable measurements of intrinsic rates of reaction have provided much information on highly dispersed metal in zeolites which deserves to be known not only by people in the zeolite club but also by all those concerned with very small supported particles. Indeed, the choice of focusing our attention on palladium and platinum in faujasites was governed by the fact that these materials are the best known and the best suited to investigate the properties of highly divided metals. Thus, even with high loading, platinum in faujasites can be obtained in very homogeneous states of dispersion with particle sizes ranging down to nearly atomic scale. This is not true for most of the metal-zeolite systems where encaged species are always found together with unreduced cations and/or larger particles. This is not true either for platinum on other supports where wider size distribution and larger sizes are present and where minute loadings prevent detailed structural investigations.     

The Effect of Silanization on the Catalytic and Sorption Properties of Zeolites

Silanizing a zeolite can result in significant beneficial changes to their catalytic and sorptive properties. It has been shown, however, that it is necessary to carefully control the reaction conditions when silanizing a zeolite. Apart from considerations such as the different effects of using vapor or liquid deposition procedures and static or flow systems, deposition temperature and the number of silanization/calcination cycles are of great importance. By careful control of the number of cycles it is possible to systematically modify the diffusional properties of the zeolite while at the same time inertizing the external surface acidity. On the basis of the changes in adsorption properties of the silanized zeolite it is suggested that diffusional changes are more likely due to blockage of pore entrances,resulting in a greater diffusion pathway, than due to a controlled narrowing of the pore openings. By careful control of the number of cycles (i.e., silanization followed by calcination)it is possible to systematically change the diffusional properties to whatever extent is desired. It is shown that the amount of Si deposited/nm2 is a good indicator of the process of silanization. The conversion of TEOS and the products of the silanization reaction at different temperatures have been used to propose a reaction pathway. Results shown for a variety of reactions indicate that silanized zeolites are able to significantly increase the yield of particular isomers as a result of the diffusional constraints resulting from the silanization process.     

The Synthesis and Properties of Two Catalytically Important Zeolites

Abstract

With his discovery of stilbite in 1756, Cronstedt [1] recognized the existence of a new group of minerals consisting of hydrated “aluminosilicates” of the alkali and alkaline earth cations. While several members of the group may have similar or nearly identical compositions, each possesses its own, unique crystal structure. At present there are 35 known naturally occurring zeolites. The crystal structures have been determined for 27 and all but about 10 have been prepared synthetically. This paper will present the definition of zeolites and focus on the synthesis and physicochemical properties of two catalytically and commercially important synthetic zeolites, zeolite Y and zeolite ZSM-5.     

Ti-HMS合成、表征及其催化氧化性能研究

以有机金属二氯二茂钛为钛源,六方介孔二氧化硅分子筛(HMS)为载体,采用嫁接法合成了含钛量(mol)分别为2.8%、3.8%和4.8%的Ti-HMS,HMS合成原料组成中H2O/EtOH(v/v)分别为0.5、1、2、5、9.合成材料用X射线粉末衍射(XRD)、N2吸附-脱附等温线、漫反射紫外可见光谱(UV-VIS)进行了表征,并考察了它们以叔丁基过氧化物(TBHP)为氧化剂在对叔丁基甲苯液相氧化中的催化性能.结果表明,表面钛嫁接后的HMS介孔结构有所损失,比表面积和孔体积减少.载体HMS合成原料中的H2O/EtOH(v/v)影响介孔织构和钛的配位环境.UV-VIS资料表明,H2O/EtOH(v/v)=0.5和9时不利于钛着床于分子筛骨架,H2O/EtOH(v/v)=1、2和5的HMS适合作为嫁接钛的载体.催化剂的活性主要受四配位Ti、介孔织构的影响.钛嫁接的HMS在氧化反应中表现出较好的催化活性,载钛量为4.8%Ti、H2O/EtOH(v/v)=1的Ti-HMS显示最好催化活性,对叔丁基甲苯转化率为21.8%.     

Synthesis, Characterization and Catalytic Properties of Chiral BINOL Functionalized Mesoporous Silicas for Enantioselective Morita-Baylis-Hillman Reaction

Several Chiral BINOL functionalized mesoporous silicas were prepared by post grafting of organosilane derivatives of (S)-BINOL (1,1′-bi-2-naphthol) on SBA-15 and characterized by ¹³C CP/MAS NMR, FT-IR, UV–visible absorption spectra, elemental analysis, powder XRD, nitrogen adsorption–desorption isotherms and TEM techniques. Their catalytic properties were demonstrated in enantioselective Morita-Baylis-Hillman reaction of 3-phenylpropanal and cyclohexenone. Among them, 3BSBA-15 linked through the 3 position of BINOL exhibit higher enantioselectivity (26% e.e.) and yield (88%) which are similar to the homogeneous catalyst (S)-BINOL (27% e.e. and 92% yield) as Brønsted acids catalyst, while complex of 3BSBA-15 and calcium 3BSBA-15-Ca show lower enantioselectivity (21% e.e.) than its homogeneous complex (S)-BINOL-Ca (32% e.e.) as ligand catalyst. 3BSBA-15 and 3BSBA-15-Ca can be reused with no significant decrease in enantioselectivity and yield.