ZSM-5催化剂成型条件对其性能的影响

采用X射线衍射(XRD)、N_2吸附-脱附和激光粒度分析等方法对不同成型条件下的ZSM-5分子筛催化剂的晶相、孔结构和粒度进行了表征,并对比分析了优化成型条件后制备的催化剂与进口催化剂的催化性能。结果表明,使用不同厂家生产的SB粉成型后的催化剂晶相结构未出现明显变化,但强度差异较大。成型后的催化剂强度随着分子筛原粉粒度的减小和硝酸用量的增加呈显著递增趋势,孔结构和相对结晶度均无明显变化。在一定范围内,挤出速度及强度都随着水粉比的增加呈先增加后降低的趋势。催化结果显示,优化成型条件后制备的催化剂性能与进口催化剂相当。     

浸渍方式对挤条成型Mo/ZSM-5催化剂甲烷无氧芳构化反应性能的影响

以SiO_2为粘结剂,通过不同浸渍方式制备了挤条成型的Mo/ZSM-5催化剂,考察其催化甲烷无氧芳构化的反应性能。采用扫描电镜(SEM)、紫外拉曼光谱(UV-Raman)及程序升温还原法(H_2-TPR)等对催化剂进行了表征。结果表明,碱性浸渍液有利于成型催化剂中Mo物种的分散,促进了Mo物种的还原,芳烃增加约13%,积碳量下降约8%。     

浸渍方式对挤条成型Mo/ZSM-5催化剂甲烷无氧芳构化反应性能的影响

以SiO_2为粘结剂,通过不同浸渍方式制备了挤条成型的Mo/ZSM-5催化剂,考察其催化甲烷无氧芳构化的反应性能。采用扫描电镜(SEM)、紫外拉曼光谱(UV-Raman)及程序升温还原法(H_2-TPR)等对催化剂进行了表征。结果表明,碱性浸渍液有利于成型催化剂中Mo物种的分散,促进了Mo物种的还原,芳烃增加约13%,积碳量下降约8%。     

ZSM-5分子筛蜂窝状成型工艺及其吸附甲苯的性能研究

为解决现有涂覆式催化剂涂层易脱落、难回收等问题,以ZSM-5分子筛为基体,添加黏合剂、田菁粉和羟丙基甲基纤维素,采用共混挤出法制备了整体式ZSM-5蜂窝状分子筛。XRD和BET等表征方法和甲苯吸附-脱附实验结果表明,以硅溶胶为黏结剂制备的蜂窝状分子筛相对结晶度较高、机械性能优异、疏水和吸附性能良好,对甲苯的脱附性能优于活性炭。     

不同载体成型的ZSM-5催化剂上甲醇芳构化反应性能

以ZSM-5分子筛为活性组分,采用不同的氧化物载体挤条制备催化剂,并对催化剂的甲醇芳构化反应性能进行评价。采用X射线衍射、氨程序升温脱附和N₂低温吸附-脱附等方法对催化剂进行表征。结果表明,添加氧化物载体后,催化剂的芳构化反应性能明显提高,催化剂芳构化反应性能与其酸性质有着密切联系,Zn/La-ZSM-5(Al₂O₃)催化剂的芳构化反应性能较好,主要归因于催化剂具有适宜的酸分布和孔结构。在反应压力0.1 MPa、空速0.8 h^-1、反应温度437 ℃和反应时间240 min条件下,轻质芳烃收率为42.36%.     

ZSM-5分子筛的研究进展

介绍了ZSM-5分子筛的基本结构,比较了ZSM-5分子筛在不同条件下合成情况,阐述了ZSM-5分子筛的改性的现状,促进ZSM-5分子筛催化剂的研发工作进一步发展。     

ZSM-5分子筛膜合成条件对膜脱硫性能的影响

采用正交实验,考察了ZSM-5分子筛膜制备过程中合成液碱量、硅铝比、模板剂用量对成膜的影响,并采用单组分模拟汽油进行脱硫实验。从脱硫效果看,得出了用于脱除噻吩和苯并噻吩各自的最佳合成液配比。按最佳配比制备出两膜,用XRD、SEM对膜进行表征,确定了所合成的膜为ZSM-5分子筛膜,并估算出两膜的孔径分别为0.58 nm、0.64 nm。结果表明,合成液配比主要影响膜的孔径大小,从而影响着ZSM-5分子筛膜的分子筛分性能,最后指出当ZSM-5分子筛膜的孔径略小于硫化物分子动力学直径时,脱硫效果最佳。     

ZSM-5分子筛择形催化剂的工业应用

详细介绍了ZSM-5分子筛催化剂的结构特点,及其在有机合成、精细化工、环保等领域的应用。     

不同条件下合成的ZSM-5分子筛的SEM研究

考察了不同的pH值、模板剂用量、用水量和升温程序等条件下合成的ZSM-5分子筛的形貌变化。结果表明：pH值在9．5～12．5范围内,随pH值逐渐变大,合成的分子筛晶粒尺寸逐渐增大,晶粒表面逐渐由粗糙趋于光滑;模板剂用量与硅源摩尔比从0．25：1增加到0.4：1时,分子筛由晶面较光滑的单个立方体晶粒变成表面粗糙的球形晶粒。用水量与硅源摩尔比(简称水硅比)由高到低时,分子筛由尺寸较小、均匀规整的无团聚晶粒渐变为粒径较大、晶形不规整且团聚严重的晶粒。无低温诱导期时,合成的分子筛晶粒尺寸较大,晶形呈立方体形,晶粒表面较光滑,部分晶粒表面出现明显的台阶纹;随着低温诱导期增长,晶粒表面的台阶纹长大,分子筛的晶形逐渐由立方体形变成圆球形,但表面台阶纹仍很明显;当低温诱导期达到一定时间,分子筛晶粒完全变成圆球形．且尺寸变小．表面粗糙,已无明显的台阶纹．即无明显的晶面。当晶体生长阶段温度逐渐升高时,晶体粒径逐步变大,结晶度逐渐升高。     

ZSM-5分子筛在MTP反应中的催化性能

合成了3种不同晶粒尺寸的ZSM-5分子筛,并制得MTP催化剂,对ZSM-5分子筛催化剂在MTP反应中的性能进行系统研究。采用XRD、SEM、N2物理吸附和TGA等对ZSM-5分子筛催化剂进行表征,发现小晶粒的ZSM-5分子筛具有良好的抗积炭性能,在MTP反应中具有较高的稳定性。采用小晶粒分子筛制成的催化剂,考察反应工艺条件对催化剂催化性能的影响,结果表明,丙烯选择性随反应温度和空速提高而增加,降低反应压力和提高水醇质量比也有利于提高丙烯选择性,为调整MTP工艺的产物分布和优化反应工艺条件提供了技术依据。     

ZSM-5硅烷化改性对临氢降凝催化剂的影响

采用液相沉积法对ZSM-5分子筛进行硅烷化改性,以改性后的分子筛为原料制备了变压器油临氢降凝催化剂,通过N₂-BET、NH₃-TPD和By-IR等方法对催化剂进行表征。以环烷基原油加氢改质柴油为原料油,在固定床反应器上对催化剂进行性能评价。结果表明,通过控制SiO₂的沉积位置和沉积量,可以降低外表面酸性、修饰孔口尺寸,阻止非择形裂解反应,提高反应的择形性能。在反应温度280 ℃、压力8 MPa、空速1.0 h^-1和氢油体积比500∶1的条件下,使用自制的催化剂,可得到倾点小于-50 ℃的40^#变压器油馏分。     

ZSM-5催化剂催速失活的研究

分析了合成甲基叔丁基醚时结焦是ZSM-5失活的主要原因。本实验通过“连续试验法”对ZSM-5分子筛催化剂的失活规律进行了实验研究。通过检测不同温度下异丁烯的转化率来考察ZSM-5催化剂的稳定性，并得出最佳反应温度为75℃。     

Ag/ZSM-5催化剂上甲醇芳构化过程

详细研究了Ag负载ZSM-5催化剂上甲醇芳构化反应过程.考察了反应温度、催化剂酸性、甲醇分压和Ag浸渍量对甲醇芳构化反应选择性的影响.高的甲醇分压有利于提高芳烃选择性,并显著改变芳烃产品组成.芳烃选择性先随着反应温度与银含量升高而升高,分别在475℃和3%Ag时达到最高值,然后随二者的进一步升高而降低.高的酸性对芳烃的生成反应非常关键.     

Xylene isomerization by ZSM-5 zeolite catalyst

The larger pore LaY zeolite catalyst resembles homogeneous metal chloride and heterogeneous silica-alumina acid catalysts since the results are consistent with isomerization being a series of intramolecular 1,2 shifts. On the other hand, isomerization with the smaller pore zeolite, ZSM-5, is very different and the relative rate constants appear to be influenced by diffusion and/or shape selectivity. Disproportionation is a significant reaction with LaY but not with ZSM-5 in the temperature range used for the present study. The small amount of trimethylbenzene formed at low conversions using ZSM-5 is 1,2,4-trimethylbenzene, also providing evidence of shape selectivity influencing the reaction products.     

Influence of the calcination treatment on the catalytic properties of hierarchical ZSM-5

The effect of the calcination conditions on the properties and catalytic performance of hierarchical ZSM-5 zeolite has been investigated using different reactions as catalytic tests: acylation of aromatic substrates and rearrangement of linear and cyclic epoxides. The hierarchical h-ZSM-5 material was prepared by crystallization of silanized protozeolitic units. The removal of the organics present in the as-synthesized ZSM-5 samples has been carried out using two different calcination procedures: (i) directly under air atmosphere; (ii) following a two-step (nitrogen-air) treatment.Clear differences are noticed related to the textural properties of the ZSM-5 samples, since the h-ZSM-5 presents higher BET and external surface area than standard ZSM-5 zeolite. Whereas the calcination method does not affect the properties of the reference ZSM-5 sample, noticeable changes were observed over the hierarchical zeolite. The concentration of Brønsted acid sites decreases by half for one-step air calcination, but only a quarter when using a two-step nitrogen/air calcination, showing that the aluminium present in hierarchical ZSM-5 is very sensitive to the calcination conditions as it may undergo framework extraction and dehydroxylation phenomena. For all the studied reactions, the hierarchical sample, calcined by a two-step treatment, presents higher activity than when using direct air calcination.     

Effect of calcination temperature on catalytic properties of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

The effect of calcination temperature on catalytic performance of PtSnNa/ZSM-5 catalysts for propane dehydrogenation was studied. It was found that when the calcination temperature was in the range of 400–500 °C, structure and acidity of the catalyst did not change obviously. In contrast to this, with the increase of calcination temperature, the specific surface area and pore volume dramatically decreased, while the mean pore diameter increased. Under these conditions, more framework aluminum atoms were removed from tetrahedral positions, which weakened the interactions between Sn species and carrier. Meantime, the degree of Pt sintering and the destruction of Pt active sites with “sandwich structure” were aggravated, which was disadvantageous to the reaction. When the catalyst was calcined at 500 °C, the interactions between Pt and Sn were strengthened, thus improving the catalytic stability and reaction selectivity evidently. Moreover, it should be remarked that the phenomenon of slow Pt sintering was not clearly observed even though the reaction temperature of it was higher than the calcination one.     

Direct partial oxidation of methane over ZSM-5 catalyst: Zn-ZSM-5 catalyst studies

Extended studies on Zn-ZSM-5 catalyst for the production of liquid hydrocarbons in the direct partial oxidation (DPO) of CH₄ with O₂ are reported. Previously, it was reported that metal-containing ZSM-5 catalysts could produce C₅₊ hydrocarbons from pure CH₄/O₂ feeds without feed additives. Zn-ZSM-5 produced the highest C₅₊ yields of the catalysts tested. This work shows that the method of introducing Zn onto the catalyst, ion-exchange versus impregnation, does not significantly alter C₅₊ yields if low Zn content is maintained ( 0.4–0.5 wt%). Liquid hydrocarbon yields in this system doubled after 8 h on stream while overall C₂₊ yields increased by over 300%. Mechanistic implications of these findings are discussed. Finally, processing a natural gas feed over Zn-ZSM-5 gave higher C₅₊ yields over CH₄ feed but these yields were not improved over previously published results using HZSM-5.     

Effect of hydrothermal treatment temperature on FCC gasoline upgrading properties of the modified nanoscale ZSM-5 catalyst

Nanoscale HZSM-5 zeolite was hydrothermally treated with ammonia water at different temperatures and then loaded with La₂O₃ and ZnO. The parent and the modified nanoscale HZSM-5 catalysts were characterized by SEM, NH₃-TPD, IR and XRF. The performance of the modified HZSM-5 catalysts for FCC gasoline upgrading was evaluated in a fixed bed reactor in the presence of hydrogen. The results indicated that the modified catalyst which was hydrothermally treated at 400 °C exhibited excellent aromatization activity, isomerization activity and higher ability of reducing olefin content in FCC gasoline. Under the given reaction conditions, the olefin content in FCC gasoline could be decreased from 49.6 to 8.1 vol.%. The catalytic performance of the modified nanoscale ZSM-5 catalyst hardly changed within 300 h time on stream, and the research octane number (RON) of gasoline was preserved.     

Vanadia loaded hierarchical ZSM-5 zeolite: a promising catalyst for epoxidation of cyclohexene under solvent free condition

Hierarchical ZSM-5 zeolite with composite micro and mesoporous was obtained by alkali treatment of parent ZSM-5 for 60 min. Vanadia was loaded on modified zeolite by wetness impregnation technique (VDZ). The prepared samples were characterized by various techniques including XRD, FTIR, TGA, UV-DRS, TEM, XPS and nitrogen adsorption–desorption. Vanadia loaded sample was found to exhibit excellent catalytic activity for the epoxidation of cyclohexene by tertiary butyl hydroperoxide. A controlled reaction was carried out to demonstrate the utility of hierarchical topology of the catalyst. A free radical mechanism was proposed for the reaction with rate constant of 6.91 × 10^?2 L mol^?1 min^?1 and activation energy of 41.81 kJ mol^?1. The reaction was carried out without the use of any solvent and the catalytic activity of VDZ was retained even after five runs.