硅铝沸石分子筛晶化过程再思考

目前针对沸石分子筛的晶化过程已经进行了大量研究,但是近年来硅铝分子筛的合成显示其晶化过程超出了传统的沸石分子筛晶化理论,特别表现在硅铝沸石分子筛的模板作用、水的作用以及沸石晶体之间的转化等.本文讨论了上述作用的本质,并通过研究模板法作用提出了无有机模板法合成硅铝沸石的策略,通过了解水的作用提出了无溶剂法合成沸石分子筛,通过表征沸石之间的转化过程发现不仅低骨架密度可以向高骨架密度晶体转化,而且高骨架密度也可以向低骨架密度晶体转化.

SDS与CTAB混合表面活性剂体系对合成4A沸石的影响

研究了阴离子表面活性剂十二烷基硫酸钠(SDS)和阳离子表面活性剂十六烷基三甲基氯化铵(CTAB)同时加入反应体系时对以硅酸钠、氢氧化铝、氢氧化钠为原料的化学法水热合成4A沸石分子筛的合成过程的影响。考察了两种表面活性剂单独存在时和复配使用时对沸石晶化速率、产品粒度分布的影响。结果表明,SDS和CTAB的加入可以缩短4A沸石晶化过程中的诱导期,加快晶化速率,并且两种表面活性剂复配使用时可以更加显著的加快晶化速率。

表面活性剂和水溶性聚合物对合成A型沸石的影响(待续)

研究了不同表面活性剂———十二烷基硫酸钠(K 12)、二辛基磺基琥珀酸钠(AOT)、辛基三乙基溴化铵、Nonidet(P40)和聚乙二醇对A型沸石晶化影响 ,并与没有添加剂的A型沸石晶化做了比较。通过对反应的水热体系不同时间点采样的X衍射 ,得出了晶化动力学曲线 ;对样品通过扫描电镜(TEM) ,可以得出粒度分布和线性晶化成长速率 ,从这些数据可以绘制出粒度分布直方图 ;通过等离子体原子发射光谱(ICP/AES) ,测出了水热体系液体中不同时间硅、铝浓度的变化情况。研究表明 :加入添加剂后使预成核时间增长、成核时间缩短 ,加快了晶化速率 ;除了AOT外 ,均可增加核数量 ,减小粒度并使粒度分布变窄。这些影响可能是由于添加剂的加入 ,使水热体系中水含量的降低而引起的。而AOT的加入使核数量减少、粒度增大 ,可能是由于它与铝之间有特殊的作用。水热体系液体中铝的浓度在晶体成长期显著下降。

膨润土碱溶法制备4A沸石

本文以四川盐亭膨润土为原料，经提纯后采用直接碱溶法制备了4A沸石。通过实验研究，获得了膨润土直接碱溶法制备4A沸石的工艺技术条件。X射线衍射分析和扫描电镜分析结果表明，所获沸石样品纯度高，晶形呈发育完善的立方体连生体，粒径一般小于2μm；样品的钙离子吸附量达301．25mg CaCO2／g，白度为79．06％，分别达到了企业一级和二级产品的质量标准。直接碱溶法与酸化膨润土法相比具有成本低、工艺简单、环保等优势。

反应物浓度对硅铝酸盐聚合反应的影响

研究硅铝酸盐聚合反应是探讨沸石分子筛形成机理的关键问题之一,同时对于改善现有沸石晶化导向剂的性能和发现新型沸石晶化导向剂具有指导意义。关于单纯的硅酸及其盐或单纯的铝酸盐的聚合反应研究报道较多,但是对于硅铝酸盐的聚合反应研究报道较少,至于高浓度和高硅铝比条件下硅铝酸盐的聚合反应研究尚未见报道。本文以沸石分子筛液相成核和沸石晶化导向剂为应用背景,研究了高浓度高硅铝比条件下反应物浓度对硅铝酸盐聚合反应的影响。

Alcohol-assisted synthesis of high-silica zeolites in the absence of organic structure-directing agents

In this work,we show for the first time that high-silica zeolites(MFI,TON,MTT,and*MRE)could be synthesized from a combined strategy of both zeolite seeding and alcohol filling in the absence of organic structure-directing agents(OSDAs).High-silica ZSM-5 zeolites with Si/Al ratios ranging from 38 to 240(TF-Al-ZSM-5)could be synthesized via this route.The key to the success of this technique was the employment of an aluminosilicate precursor with a fully 4-coordinated aluminum species as the initial source,wherein the rearrangement and condensation of the silicate species,rather than the aluminate species,occurred during zeolite crystallization.In addition,heteroatoms,such as Fe and B,could be incorporated into the zeolite frameworks.Catalytic tests for the methanol-to-propylene(MTP)reaction exhibited good catalytic performance for TF-Al-ZSM-5,which was comparable to that of the aluminosilicate ZSM-5 zeolite synthesized with OSDAs.Hence,this method offers viable opportunities for the industrial production and catalytic application of high-silica zeolites in the future.

In-situ Synthesis of ZSM-5 Zeolite from Metakaolin/Spinel and Its Catalytic Performance on Methanol Conversion

ZSM-5 zeolite was in-situ synthesized from metakaolin or s alumina sources, respectively. The ZSM-5 zeolite was characterized pinel by incorporating additional silica and by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, Fourier transform infrared （FT-IR） spectroscopy and N2 adsorption measurement. This supported zeolite was tested on the methanol to propylene （MTP） processes. Experimental results showed that the ZSM-5 zeolite exhibited high selectivity for propylene. The yield of propylene on ZSM-5 zeolite made from metakaolin was increased by 17.73%, while that on ZSM-5 zeolite made from spinel was raised by 9.90%, compared to that achieved with the commercial ZSM-5 zeolite. The significant increase in propylene production is probably due to the distinctive morphology of the ZSM-5 zeolite, which possessed a rough external surface covered with sphere-like particles and distribution of small crystals sized at around 400--500 nm. This morphology could help to generate more crystal defects so that more active centers could be exposed to the reaction mixture. In addition, the zeolite product had a gradient pore distribution and many medium Brǒnsted acid sites, both of which might also contribute to the increased propylene production.

Design of fast crystallization of nanosized zeolite omega crystals at higher temperatures

Fast crystallization of nanosized zeolite crystals is a very popular process used for practical zeolite catalyst applications. Herein, we report a designer crystallization process for nanosized zeolite omega crystals based on the relationship between the crystallization time and temperature in the Arrhenius equation. Compared to the conventional hydrothermal synthesis of zeolite omega(72 h at room temperature and 240 h at 100℃, MAZ-100), the crystallization of zeolite omega presented in this work only requires a very short time interval(5 h at 180℃, MAZ-180). Physicochemical characterizations, including XRD, SEM, N2 sorption isotherms, and 27 Al MAS NMR show that the product of zeolite omega(MAZ-180) has good crystallinity and uniform nanocrystals. More importantly, after the loading of Pt nanoparticles(0.5 wt%), the Pt/H-MAZ-180 catalyst exhibits higher isomer selectivity and lower cracking selectivity than those of the Pt/H-MAZ-100 catalyst in the hydroisomerization of n-dodecane. These results suggest the potential applications of these omega nanocrystals as supporting catalyst compounds in industrial processes.

Hydrothermal synthesis and catalytic performance of bulky titanium silicalite-1 aggregates assembled by bridged organosilane

A facile and effective method to synthesize TS‐1zeolite aggregates has been presented.The crystallization of silanized seeds and nanocrystallites led to large and irregular TS‐1zeolite aggregates ranging from5to40μm in size,based on the special sol‐gel chemistry of bridged organosilane.Epoxidation of1‐hexene and cyclohexene was used as a probe reaction to investigate the catalytic performance of the resulting materials.These TS‐1zeolite aggregates possessed both the conventional nanoparticle properties of TS‐1zeolites and variable surface hydrophilic/hydrophobic features,which enhanced the catalytic properties of hydroperoxides for alkene epoxidation.Moreover,the large aggregates effectively simplified the separation procedure during preparation and catalytic reactions.

Study on Crystallization of Titanium Silicalite Zeolite (Ⅱ)

In order to investigate the rules on formation of zeolite during crystallization of titanium silicalite zeolite (TS-1) the X-ray diffractometry and Foulier transform infra-red spectrometry were applied to track the process of crystallization of titanium silicalite zeolite. The research results revealed that at the initial stage of crystallization the interactions between silica gel and titania gel in the polymer blend could gradually lead to the formation of tiny crystal nuclei with complicated structure that could slowly grow up to form molecular sieves. Quite different from the conventional zeolites that use the acid sites as the catalytically active centers, the oxidative reactivity of the titanium silicalite zeolite was not proportional to its crystallinity and is associated with the oxidative centers of titanium contained in the zeolite.