载铂多级孔ZSM-5分子筛用于邻二甲苯的“吸附-催化燃烧”循环脱除

首先利用F127作为软模板, 采用蒸汽辅助晶化法合成出具有一定介孔结构的多级孔ZSM-5分子筛, 然后采用等体积浸渍法负载铂, 成功制备了载铂的多级孔ZSM-5分子筛催化剂。利用X射线衍射(XRD)、氮气吸附等温线(N₂ isotherm)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对制备的催化剂进行了表征, 并将催化剂用于邻二甲苯的吸附和催化燃烧反应, 最后考察了催化剂“吸附-催化燃烧”循环脱除邻二甲苯的性能。结果表明, 与传统ZSM-5分子筛相比, 多级孔ZSM-5分子筛结晶度略有下降, 但是介孔度和孔体积明显提升。介孔结构与微孔结构并存, 极大提升了多级孔ZSM-5分子筛对邻二甲苯的吸附能力, 其饱和吸附量达到了传统ZSM-5分子筛的约8倍。此外, 介孔结构的存在提高了铂的分散度, 使得载铂多级孔ZSM-5分子筛具有最佳的催化燃烧邻二甲苯性能, 三次“吸附-催化燃烧”循环使用后的吸附容量依然基本保持不变, 并且在催化燃烧过程中无二次污染物生成, 具有较高的吸附容量和循环使用稳定性。     

载铂多级孔ZSM-5分子筛用于邻二甲苯的“吸附?催化燃烧”循环脱除

首先利用F127作为软模板,采用蒸汽辅助晶化法合成出具有一定介孔结构的多级孔ZSM-5分子筛,然后采用等体积浸渍法负载铂,成功制备了载铂的多级孔ZSM-5分子筛催化剂。利用X射线衍射(XRD)、氮气吸附等温线(N2 isotherm)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对制备的催化剂进行了表征,并将催化剂用于邻二甲苯的吸附和催化燃烧反应,最后考察了催化剂"吸附-催化燃烧"循环脱除邻二甲苯的性能。结果表明,与传统ZSM-5分子筛相比,多级孔ZSM-5分子筛结晶度略有下降,但是介孔度和孔体积明显提升。介孔结构与微孔结构并存,极大提升了多级孔ZSM-5分子筛对邻二甲苯的吸附能力,其饱和吸附量达到了传统ZSM-5分子筛的约8倍。此外,介孔结构的存在提高了铂的分散度,使得载铂多级孔ZSM-5分子筛具有最佳的催化燃烧邻二甲苯性能,三次"吸附?催化燃烧"循环使用后的吸附容量依然基本保持不变,并且在催化燃烧过程中无二次污染物生成,具有较高的吸附容量和循环使用稳定性。     

ZSM-5分子筛介孔的构筑

在微孔结构的ZSM-5沸石分子筛中构筑介孔,可以有效地解决ZSM-5分子筛在催化反应过程中的扩散传质和催化剂失活问题.重点阐述了在初始的合成体系中加入炭黑、介孔碳、表面活性剂等作为模板剂来构筑含介孔结构的ZSM-5和利用碱液或酸液对已合成的微孔的ZSM-5进行后处理来构筑介孔,并对含有介孔结构的ZSM-5的性质和相关的应用做了评价和展望.     

Co-Mo/ZSM-5的制备与加氢脱硫性能研究

采用Na_2CO_3溶液分别处理二氧化硅∶三氧化二铝物质的量比为50∶1、80∶1、150∶1的ZSM-5分子筛,采用XRD、SEM和NH3-TPD等进行表征。结果表明,经Na2CO3处理后,形成了微孔-介孔多级孔ZSM-5分子筛。在多级孔分子筛上负载Co、Mo制备Co-Mo/ZSM-5催化剂并进行加氢脱硫反应;研究了工艺条件对最佳催化剂加氢脱硫性能的影响。结果表明,二氧化硅∶三氧化二铝物质的量比为50∶1的催化剂加氢脱硫率最高;该催化剂在反应温度为350℃,压力3.0MPa,空速2.0h-1时,脱硫率达90.8%。     

ZSM-5/SBA-15复合分子筛催化热解稻壳制备芳烃化合物研究

通过后合成法制备了ZSM-5/SBA-15复合分子筛,利用X射线衍射、透射电子显微镜、BET比表面积测试法和傅里叶变换红外光谱等表征方法对合成的分子筛催化剂进行了表征,在立式固定床反应器进行稻壳热解实验,分析了ZSM-5/SBA-15复合分子筛催化热解制备芳烃化合物的性能。结果表明:ZSM-5/SBA-15具有微-介孔复合结构;与未添加催化剂相比,催化剂的加入使得热解油中芳烃化合物(主要是苯、甲苯、二甲苯、萘和甲基萘等)的产率得到有效提高。此外,与ZSM-5相比,ZSM-5/SBA-15的加入提高了液体产物的产率,降低了气体产物的产率;而且单环芳烃(苯、甲苯和二甲苯)的产率和选择性都得到提高,单环芳烃选择性达到84.6%,与之相应的是多环芳烃的产率明显下降。     

以聚乙二醇为模板凝胶转化制备介孔ZSM-5沸石及其催化性能

以聚乙二醇为介孔导向剂, 通过凝胶转化制备了介孔ZSM-5沸石。研究表明, 在TPA⁺/SiO₂=0.1时经过9~15 h溶剂挥发制得的凝胶, 在160℃处理24 h可得到介孔ZSM-5沸石; 挥发时间太短或太长会得到纯的ZSM-5沸石或介孔材料, 说明在凝胶的制备过程中, 通过控制溶剂的挥发程度, 既可为沸石生长过程提供所需的水分, 又能避免沸石晶体形成过程中无定型相的产生, 从而在较低的TPA⁺浓度下获得介孔ZSM-5沸石。与传统的ZSM-5沸石相比, 利用该方法制备的介孔ZSM-5沸石不仅具有微孔/介孔多级孔结构, 同时具有沸石材料较强的酸性、较高的水热稳定性和择形催化性能, 使其在苯甲醛与正丁醇的大分子醇醛缩聚反应中能有效地克服传统沸石孔径限制的缺点, 收率高达42.4%。     

介孔材料在生物柴油合成中的应用

生物柴油是一种绿色可再生能源,一般是通过酸或碱催化酯化或酯交换反应来制备。综述了介孔金属氧化物、介孔分子筛及介孔磷酸盐等不同类型介孔材料催化剂用于制备生物柴油的研究进展,并对制备生物柴油的介孔催化剂研究方向进行展望。     

磺酸基有序介孔炭的一步合成及其催化性能

采用一步法直接制备磺酸基有序介孔炭材料,利用FT-IR、酸量、XRD、TEM和BET等对其结构与形貌进行表征,以苯甲醛与原甲酸三甲酯的缩醛反应为模型反应,并考察其催化性能。结果表明,在原料酚醛树脂∶硫酸∶F127质量比为1∶2∶0.3,炭化温度为600℃时,所制磺酸基介孔炭呈有序结构、较大的比表面积和均匀的孔径。采用上述条件合成介孔炭材料作催化剂时,反应收率可达87.1%,明显高于相同条件下传统分子筛固体酸催化剂HY与未加入磺酸基的介孔炭材料的催化效果。     

汽相转化法制备纳米晶组成的块状ZSM-5多孔沸石

在ZSM-5沸石前驱体中加入羧甲基纤维素钠并制得干胶, 然后通过蒸汽相转化制得了大块状ZSM-5沸石。由于羧甲基纤维素钠与硅铝物种之间的相互作用干扰了沸石晶体的正常生长, 这种干扰所产生的“键阻断”作用导致合成的大块状ZSM-5沸石由100~150 nm的初级ZSM-5沸石晶体组成, 在这些初级粒子之间存在2~20 nm的二次介孔结构。异丙苯催化裂化结果表明, 由于纳米沸石具有较高的外表面积和较大的介孔孔容, 比参比催化剂表现出更高的异丙苯转化率。     

Cu含量对Cu/ZSM-5催化剂氨选择性催化还原NO影响的研究

采用浸渍法将铜(Cu)负载在ZSM-5分子筛上,制备了一系列不同Cu含量的Cu/ZSM-5分子筛催化剂。对ZSM-5及Cu/ZSM-5分子筛催化剂的氨选择性催化还原一氧化氮(NO)性能进行评价,并对Cu/ZSM-5分子筛催化剂进行表征分析。结果表明,Cu含量变化对Cu/ZSM-5分子筛催化剂的氨选择性催化还原反应(NH3-SCR)活性影响较大,Cu含量为0.75%(wt,质量分数)制得的Cu/ZSM-5具有最佳的中低温活性,在190℃条件下对NO的转化率为91%。     

Obtainment of hierarchical ZSM-5 zeolites by alkaline treatment for the polyethylene catalytic cracking

Great efforts have been applied in order to achieve the synthesis of hierarchical zeolites through post-synthesis alkaline treatment. In this case, the use of hierarchical ZSM-5 zeolites as acid catalysts in the catalytic cracking of polyolefins overcomes some diffusional limitations and expands the selectivity of products. Thus, the purpose of work was to promote a secondary porosity in ZSM-5 zeolite by NaOH treatment (using conventional electric and microwave heating methods), applying cetyltrimethylammonium bromide as pore-directing agent. Both heating methods generated additional secondary porosity, with microwave heating promoting a narrow pore size distribution, when compared to conventional. All hierarchical ZSM-5 have been showed low-density polyethylene conversions superior to the purely microporous ZSM-5, however the hierarchical zeolite processed by conventional electric heating reached the higher temperature reduction (42.6 K). It was evidenced through measurements of morphological and textural properties, ion exchange capacity and catalytic activity in the LDPE cracking that the CTAB cations exerts a protective effect at alkaline treatment avoiding the desilication process. The additional secondary porosity promoting the generation of compounds of lower molecular mass in LDPE catalytic cracking, by thermogravimetric analysis, proving that the alkaline treatment increases the accessibility to the active acidic sites of zeolitic catalysts for bulky molecules.     

Study on using cellulose derivatives as pore directing agent for preparation of hierarchical ZSM-5 zeolite catalyst

Cellulose derivatives such as hydroxyethylmethylcellulose (HEMC), and hydroxypropylmethylcellulose (HPMC), which are originated from biomass, were used as mesoporous directing agent for the synthesis of hierarchical ZSM-5 zeolite. Hierarchical ZSM-5 zeolites with outstanding mesoporosity and high hierarchy factors were achieved by hydrothermal method in the presence of bio-mesoporogen. The as-synthesized hierarchical ZSM-5 zeolites were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption (BET), scanning electron microscope (SEM) to determine the structure of samples. The influences of different mesoporogens with different dosage in the synthetic process on the physicochemical and catalytic properties of hierarchical ZSM-5 zeolite were investigated. Possession of the high mesopores, high surface areas and abundant accessible acid sites, the hierarchical zeolites exhibited excellent catalytic performance in the alkylation reaction of benzene and benzyl alcohol.     

Effects of concentration on the alkali-treatment of ZSM-5 zeolite: a study on dividing points

Alkali-treatment for modification or dissolution has attracted extensive attention as an innovative means of preparing porous materials. The hierarchical porosity of modified zeolite is highly dependent on its treatment conditions. However, studies on critical alkali-treatment concentrations, specifically those that discuss the dividing points, have not yet been reported. In this article, the pore and crystalline properties of ZSM-5 zeolite samples modified by different concentrations of alkali-treatment are investigated. The experimental results show that the pore properties of the samples change as a function of the alkaline concentration. The total surface, mesopore surface area, total pore volume, mesopore volume, and average pore diameter of ZSM-5 zeolites increase and then decrease with increasing alkaline concentrations. The micropore surface area, micropore volume, and crystallinity of the samples decrease monotonously. The following dividing points are proposed: 0.40 mol/L as the threshold for alkali-modification and 1.00 mol/L as the starting point for alkali-dissolution. A possible desilication mechanism is also proposed.     

Study on the structural formation of new useful multiporous material ‘nano–meso ZSM-5’ and its application in producing biofuel

New ‘nano–meso ZSM-5’ (NM-ZSM-5) material was successfully synthesised by hydrothermal treatment using silica derived from rice husk. The synthesis of the material involves two steps of crystallisation, including the formation of ZSM-5 zeolite seed and mesoporous structure. The effect of crystallisation time on the formation of mesoporous structure was studied in the range 0–40?h. Samples were characterised by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller and ²⁷Al-NMR methods. The results show that the best time for crystallisation is 14?h. The synthesised material has a multiporous structure, including micropore system of ZSM-5 zeolite, mesopore system of MCM-41 and another pore system which has a diameter in the range 10–50?nm (mesoporous system) due to the burning of organic compounds that remain in the material during the calcination process. In addition, the synthesised NM-ZSM-5 achieves crystallinity of approximately 100%. The catalytic performance of NM-ZSM-5 material was evaluated by the catalytic cracking reaction to produce biofuel from vegetable oil sludge. The research proved that NM-ZSM-5 is one of the most suitable catalysts for this process. The catalytic cracking reaction over NM-ZSM-5 yields products that are similar to those of the petroleum cracking process, such as dry gases, liquefied petroleum gas, gasoline, light cycle oil and heavy cycle oil.     

Investigation of the catalytic wet peroxide oxidation of phenol over different types of Cu/ZSM-5 catalyst

In this work oxidation of phenol with hydrogen peroxide on Cu/ZSM-5 catalysts was studied. The catalysts samples were prepared by two different methods: by ionic exchange from the protonic form of commercial ZSM-5 zeolite, and by direct hydrothermal synthesis. Characterization of the catalysts extends to X-ray diffraction (XRD), while the adsorption techniques were used for the measurement of the specific surface area. The catalytic tests were carried out in a stainless steel Parr reactor in batch operation mode at the atmospheric pressure and the temperature range from 50 to 80 degrees C. The mass ratio of the active metal component on the zeolite was in the range of 1.62-3.24 wt.%. for catalyst prepared by direct hydrothermal synthesis and 2.23-3.52 wt.% for catalyst prepared by ion exchange method. The initial concentration of phenol and hydrogen peroxide was 0.01 and 0.1 mol dm(-3), respectively. The influence of different methods of Cu/ZSM-5 preparation on their catalytic performance was monitored in terms of phenol conversion and degree of metal leached into aqueous solution.     

Catalytic cracking of light naphtha over hierarchical ZSM-5 using rice husk ash as silica source in presence of ultrasound energy: Effect of carbon nanotube content

Hierarchical structured ZSM-5 was prepared by sonochemical assisted carbon nanotube templated method and their catalytic activity was examined in catalytic cracking of light naphtha. Different amounts of carbon nanotubes (5, 15, 30?wt%) was introduced into the synthesis gel, as a hard template, for mesopore creation. The rice husk ash was used as a silica source. In order to analyse physicochemical properties of synthesized catalysts, multi-techniques such as XRF, XRD, BET, FE-SEM, NH₃-TPD and TGA were used. The obtained results revealed that by adjusting the amount of carbon nanotube, catalyst properties can be favorably tuned. The XRD analysis confirmed successful synthesis of high crystalline ZSM-5 zeolite. According to the FE-SEM analysis, small rough spheres of ZSM-5 were synthesized in all samples. The use of carbon nanotube led to creating new mesopores in the ZSM-5 structure. However, increase in carbon nanotube content led to destruction of micropores of ZSM-5. The acidity of ZSM-5 slightly changed. Results from catalytic activity test showed that high catalyst stability can be achieved in presence of mesopores along with the micropores. The highest olefin yield (54?wt%) and the best catalytic stability were obtained over the synthesized ZSM-5 with 15?wt% carbon nanotube.     

Synthesis of mesoporous ZSM-5 from rice husk ash with ultrasound assisted alkali-treatment method used in catalytic cracking of light naphtha

A series of mesoporous ZSM-5 zeolite was synthesized with ultrasonic assisted alkali-treatment technique and their catalytic activity was investigated in catalytic cracking of light naphtha. ZSM-5 zeolite was synthesized from rice husk ash without using any organic template. Effect of alkali-treatment conditions on physicochemical properties of synthesized zeolite was investigated with XRD, FESEM, TEM, N2 adsorption-desorption isotherm, NH3-TPD and TGA technique. It was found that ultrasound energy facilitates the creation of hierarchical structure of ZSM-5 during alkali-treatment. According to XRD analysis, zeolite structure was preserved after 20 min ultrasonic assisted alkaline treatment. However, prolonged dessilication time led to the destruction of MFI zeolite structure. The synthesized ZSM-5 represented highly ordered hexagonal-shape morphology. With increasing alkali-treatment time, the plough land roughness appeared on the surface of zeolite. Comparison of the textural properties samples revealed that the mesopore surface area of alkali-treated samples increased considerably with the increase of ultrasonic assisted alkali-treatment time. Results from catalytic activity tests showed that ultrasound energy has great influence on the activity of ZSM-5. The sample had the highest activity after alkali-treated for 20 min in presence of ultrasound energy which was due to their appropriate hierarchical structure.