后处理法合成高热稳定性的中孔Ti-P-Al材料

 以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂,采用水热合成法制备了中孔氧化钛原粉,再采用磷酸和氯化铝溶液依次对中孔氧化钛原粉进行后处理,得到了具有高热稳定性的中孔Ti-P-Al材料. 通过粉末X射线衍射、透射电子显微镜和氮物理吸附等方法对样品进行了表征. 结果表明,反应凝胶组成对样品的中孔结构有较大的影响,当反应凝胶配比为Ti(SO4)2∶CTAB∶H2O=1∶0.54∶430, 温度为363 K, 处理时间为10～20 min时,所得的TiO2原粉具有较规整的中孔结构. 此样品经过0.25 mol/L的磷酸处理后有序性有较大程度的提高. 将磷酸处理过的样品进一步用氯化铝溶液处理,得到了中孔结构的Ti-P-Al材料,此材料经过873 K焙烧后仍具有典型的中孔特征,其比表面积为 382 m2/g, 孔径为3.13 nm.     

Effect of Alkali Treatment on the Structure and Catalytic Properties of ZSM-5 Zeolite

Catalytic properties of ZSM-5 zeolite samples pretreated with NaOH solution have been investigated. The samples are characterized by XRD, SEM, chemical analysis, and N2 adsorption.The results indicate that mesopores are created in ZSM-5 crystals under alkali treatment without change the microporous structure and acidic strength of the zeolite, but the crystallinity is greatly decreased under severe treatment. IR indicates that the concentration of silanol is greatly enriched by alkali treatment. The etherification activities of ZSM-5 zeolites are greatly increased byalkali-treatment. The noticeably improved catalytic activity of treated samples is ascribed to the formation of mesopores and greatly enriched silanol group.     

液晶模板合成多级孔ZSM-5分子筛及其催化应用

以哌嗪基丙基甲基二甲氧基硅烷偶联剂(PZPMS)和阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为复合液晶模板,在水热条件下合成多级孔ZSM-5分子筛.采用XRD、 SEM、 BET、 XRF、 FT-IR和NH_3-TPD对催化剂的性能进行了表征.结果表明, PZPMS/CTAB复合液晶模板的加入可以减小颗粒尺寸,增加外表面积,有利于合成多级孔ZSM-5分子筛.加入液晶模板可以有效调整催化剂表面B酸与L酸量比例,改善催化剂表面酸性.对合成的催化剂样品在MTA反应中进行了催化性能测试,样品在反应中对芳烃表现出较高的选择性,催化寿命有不同程度的提高.     

Incorporation of Silicon into AlPO-5 Framework Sites: Higher Thermal Stability and Lower Extra-Framework Aluminum Concentration

Diffuse reflectance spectroscopy was used to investigate the structural modification of AlPO-5 microporous aluminophosphate synthesized in the presence of a silicon source and subjected to calcination in air. Extra-framework aluminium species, formed upon calcination and expulsion of aluminium from the framework, are detected by DRS because they are involved in aluminium-oxygen charge transfer transitions. Impregnation of the calcined AlPO-5 and SAPO-5 samples with ethanolic acetylacetone converted all the extra-framework aluminium atoms with distorted symmetry to a highly ordered symmetry, as evidenced by a distinct and well-defined 280 nm band in the DR spectra. The intensity of the 280 nm absorption band in AlPO-5 is much higher than those of all SAPO-5 samples with different silicon content. This is an indication of the presence ofa considerably higher amount of extra-framework aluminium in AlPO-5. Washing the acetylacetone treated samples with hot ethanol leads to extraction of some of the complexed aluminium. The progress of extraction could be monitored by both DR and UV-vis spectrophotometry.     

The Influence of Temperature on Ethene Diffusion in H[Al]ZSM-5 Studied by Molecular Dynamics

Molecular dynamics(MD) simulation of ethene diffusion in the lattice of H[Al]ZSM-5 was performed at the temperature ranging from 300 K to 700 K. The calculated diffusion coefficients increase with the temperature from 2.60×10-9 m2/s at 300 K to 12.78×10-9 m2/s at 700 K. The Arrhenius plot gives an activation energy of 6.31 kJ/mol. The anisotropy of the diffusion process was examined.     

TPAOH/NaOH混合碱体系对ZSM-5沸石的改性及其催化性能研究

采用四丙基氢氧化铵和氢氧化钠有机无机混合碱TPAOH/NaOH体系对ZSM-5分子筛进行改性处理,得到了具有介孔和微孔的ZSM-5分子筛。用XRD、N₂吸附脱附、NH₃-TPD、SEM等手段对改性后的产物进行表征。结果表明,碱处理ZSM-5分子筛会使分子筛同时脱硅和脱铝。当混合碱体系中总OH^-浓度一定时,随TPA⁺/OH^-比值的降低和处理时间的延长,均会使分子筛的微孔结构数量减少,介孔结构数量增加。同时,还会改变分子筛的酸性,TPA⁺/OH^-比值适合的混合碱体系可在生成介孔的同时最大限度保留微孔结构,并减少分子筛的强酸数量,在甲醇制烯烃反应(MTO)中表现出较高的丙烯选择性。与无机碱NaOH相比,TPAOH对分子筛的改性速率较慢而且温和,具有可控性,可以起到孔道生长调节剂的作用。