循环流化床粉煤灰可控制备高纯F型八面沸石研究

利用粉煤灰制备沸石分子筛是其高值化利用的重要方向之一.以循环流化床粉煤灰为原料,采用酸浸预处理-氢氧化钠碱熔活化-水热晶化法制备F型八面沸石,并用于吸附亚甲基蓝.考察酸浸温度、碱熔温度及碱灰质量比对粉煤灰结构的影响及碱熔温度、碱灰质量比、液固比及晶化时间对沸石的结构和形貌的影响.通过XRD和SEM对粉煤灰沸石的晶体结构和形貌进行表征.结果表明,利用循环流化床粉煤灰制备高纯F型八面沸石适宜条件为碱熔温度550℃,碱灰质量比1.5:1,液固比12 mL/g,晶体导向剂用量10;,晶化温度100℃,晶化时间20 h.其比表面积高达357 m2/g,且对亚甲基蓝的饱和吸附量高达178 mg/g.     

Effect of ultrasound on the synthesis of low-modulus zeolites from a metakaolin

It was studied the effect of ultrasonic processing (22 kHz) of the aqueous suspension of metakaolin, sodium hydroxide and alumina with a molar ratio 2Al₂Si₂O₇:12NaOH:2Al₂O₃ on the low-modulus zeolite synthesis processes. To investigate the XRD, SEM, IR, EDS had been used. It was shown that after ultrasonic processing, sodium aluminates are formed, what leads to a change in process of further synthesis. It was found that without ultrasonic processing on the stage of thermal treatment at 650 °C, SOD zeolite (|Na₆|[Al₆Si₆O₂₄]) and sodium aluminosilicate (Na₆Al₄Si₄O₁₇) are synthesized. In the sample after ultrasound during thermal treatment, only sodium aluminosilicates of cubic syngony (Na₆Al₄Si₄O₁₇ and Na₈Al₄Si₄O₁₈) are formed. It was demonstrated that sodium aluminosilicates are precursors for the formation of LTA zeolite (|Na₁₂|[Al₁₂Si₁₂O₄₈]). As a result zeolitization of sodium aluminosilicates after the hydrothermal crystallization in alkaline solution, the sonicated sample contained 97 wt% LTA. Without ultrasonic processing, the product of synthesis contained 50 wt% SOD and 40 wt% LTA.     

ZSM-5分子筛膜的研究进展

本文分析了ZSM-5分子筛膜的主要合成方法和研究现状,总结了ZSM-5分子筛膜的缺陷与修饰方法,指出了ZSM-5分子筛膜的表征手段是以XRD、SEM、TEM和单组分气体渗透等为主,对ZSM-5分子筛膜的应用和前景进行了展望。     

A high-resolution MAS NMR study on the potential catalysts Mo/HBeta for olefin metathesis: The interaction of Mo species with HBeta zeolite

The interfacial interaction of Mo species with the HBeta zeolite was studied by multinuclear MAS NMR, XRD and N₂ adsorption. As proved by the quantitative ²⁷Al MAS NMR, this interaction is so strong as to dealuminate the framework of HBeta, and leads to a new peak appearing at −14 ppm, which indicates the formation of crystalline Al₂(MoO₄)₃. This can also be detected by XRD measurements when the Mo loading is as high as 9.0 wt.%. The corresponding quantitative ²⁹Si and ¹H MAS NMR spectra show that the amount of silanols and Brønsted acidic sites decrease obviously with increasing Mo loading. This also reveals an interaction between Mo species and HBeta support through an oxygen bridge resulting from condensation with the hydroxyls on the support. At higher Mo loadings, the interaction is so strong that it results in an extraction of aluminum from the zeolite framework, and subsequently appearance of Al₂(MoO₄)₃ and loss of Brønsted acidic sites. These can be correlated to the low catalytic activity of Mo/HBeta in metathesis of ethylene and 2-butylene to propylene.     

n‐Butane Monomolecular Cracking on Acidic Zeolites: A Density Functional Study

采用5T簇模型,利用密度泛函理论在B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d)水平下研究正丁烷在酸性分子筛上的单分子催化裂解反应。本文重点详细研究了正丁烷在分子筛表面不同C位的脱氢反应。在B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d)水平下计算所得第一和第二位C-C键裂解的活化能垒分别为 238、217 kJ/mol。而第一第二序位脱氢反应能垒分别为296、242 kJ/mol。正丁烷不同序位脱氢反应的活化能垒相差54 kJ/mol。从计算结果可以看出,正丁烷在分子筛上催化裂解脱氢反应优先发生在第二位C原子上。此外,本文还讨论了簇模型结构与酸性的关系,结果显示改变封端Si-H键的键长的方法可以用来模拟分子筛酸性变化。最后研究了分子筛酸性变化与正丁烷催化裂解反应能垒的关系。     

MCM-41-HY复合分子筛的合成及其在深度加氢脱硫中的应用

在水热条件下合成了包覆型MCM-41-HY复合分子筛.采用XRD、N2气吸附和SEM等方法对其进行了表征.结果表明,MCM-41-HY复合分子筛和MCM-41与H型Y沸石(HY)的机械混合物明显不同,在复合分子筛MCM-41-HY中,中孔相MCM-41附晶生长在HY沸石上,将HY包覆起来.以二苯并噻吩为模型化合物,考察了该材料担载NiMo催化剂的加氢脱硫活性.结果表明,MCM-41-HY复合分子筛与MCM-41和HY的机械混合物担载NiMo催化剂的加氢脱硫(HDS)活性相当,但MCM-41-HY复合分子筛担载NiMo催化剂的裂化活性较低.其裂化活性不同的原因在于其载体孔道结构和酸性位的分布不同.     

Pt/CeL重整催化剂的制备及其石脑油芳构化性能

为克服常规氧化铝重整催化剂氯离子流失及其对设备的腐蚀等问题,通过离子交换法制备了Ce~(3+)改性的L分子筛,采用浸渍法制备了Pt/CeL重整催化剂;用XRD、N_2吸附-脱附、NH_3-TPD和Py-FTIR等手段对载体和催化剂进行了表征,并以硫含量为0.50μg/mL的工业精制石脑油为原料,在固定床微型反应装置上评价了Pt/CeL催化剂的重整芳构化性能。结果表明,Ce~(3+)离子交换可提高载体的酸量和酸强度,而不会破坏L分子筛的骨架结构;Ce~(3+)改性后的Pt/CeL催化剂其重整芳构化性能明显提高,活性与选择性达到氧化铝型商业重整催化剂的水平,说明适当的酸性对重整催化剂芳构化反应有显著的促进作用。     

烯烃对噻吩在介孔分子筛Al-MCM-41活性位物种上吸附脱硫机制的影响

采用后嫁接法制备了不同铝负载量的Al-MCM-41分子筛。运用XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR等方法对分子筛进行物性表征,利用固定床评价其对噻吩的吸附性能。通过将分子筛吸附噻吩能力与分子筛的酸性质及织构性质进行关联,考察烯烃存在对Al-MCM-41活性位物种吸附脱硫机制的影响。结果表明,铝物种的引入即产生了B酸中心,也同时产生了两种类型的L酸中心L₁和L₂。引入低含量铝物种利于形成B酸中心和L₁型酸中心,引入高含量铝物种利于形成L₂型酸中心。其中,L₂型酸中心对噻吩的吸附效果最佳。烯烃和噻吩在B酸中心发生竞争吸附和催化转化反应,且催化转化反应占主导地位。L₂酸中心的存在促进了B酸中心上的催化转化反应,其所生成的大分子硫化物取代噻吩吸附在分子筛酸活性中心上提高了Al-MCM-41分子筛的饱和吸附硫容量。     

以微孔β沸石为硅铝源合成强酸性介孔分子筛

以微孔β沸石为硅铝源,通过碱处理和以十六烷基三甲基溴化铵为模板剂,合成了具有较强酸性的六方结构介孔分子筛材料B-MCM-41,并采用XRD、N₂吸附脱附、FT-IR、²7Al MAS NMR、HRTEM和水热处理等手段对其进行了结构表征,采用NH₃-TPD对其进行了酸性表征。实验结果表明,B-MCM-41具有明显强于常规介孔分子筛的酸性,且在C⁺₁0混合芳烃加氢脱烷基化反应中表现出了良好的催化性能。这主要是由于碱溶液将β沸石降解为沸石结构单元,在表面活性剂作用下五元环次级结构单元被引入了介孔铝硅酸盐B-MCM-41的结构。