分子筛的补铝及其催化性能研究

本文介绍了分子筛的补铝方法及其补铝后分子筛的催化性能｡按所用的补铝溶液性质可分为NaOH等碱性溶液补铝法､AlCl₃和HCl酸性溶液补铝法及含羟基有机酸溶液补铝法,补铝机理涉及晶格缺陷位补铝､非骨架位表面反应以及同晶取代三种｡补铝的分子筛表面酸性质发生了变化,改善了某些催化反应性能｡     

铝源对HZSM-5分子筛中骨架铝落位及其甲缩醛气相羰基化性能的影响

通过调控铝源合成了四种HZSM-5分子筛，并将其应用于催化甲缩醛(DMM)气相羰基化合成甲氧基乙酸甲脂(MMAc)反应。结果表明，改变合成凝胶体系中的铝源种类，可以制备出织构性质、酸性特征相近，但骨架铝分布不同、催化羰基化性能迥异的HZSM-5分子筛。其中，使用硝酸铝与硫酸铝作为铝源制备的分子筛HZ-N与HZ-S表现出更为优异的催化活性，HZ-N对应的DMM转化率与MMAc选择性分别为25.3%与58.9%,HZ-S对应的DMM转化率与MMAc选择性分别为28.7%与64.6%。采用Co-ZSM-5的UV-vis-DRS与²⁷Al MAS NMR等表征手段详细分析证实，硝酸铝与硫酸铝作为铝源时，更多的骨架铝优先落位于HZSM-5分子筛交叉孔道，其在催化DMM羰基化反应过程中起主导作用，落位比例高，更有利于反应的进行，反之可能导致较低的DMM转化率以及更高的副产物选择性。     

超稳Y分子筛脱铝改性的研究进展

超稳Y分子筛(USY)在石油化工催化领域应用广泛,尤其是作为加氢裂化和异构化反应的催化剂。随着工业化的发展,超稳Y分子筛逐渐满足不了催化剂的要求,达不到生产目的,而脱铝的超稳Y分子筛(DUSY)作为催化剂载体或活性组分的效果比母体USY分子筛要好,因此对脱铝改性的USY分子筛的研究引起关注。综述超稳Y分子筛的制备与脱铝改性方法的研究进展,改性方法包括水热法、化学法和水热-化学法,重点介绍化学脱铝改性对超稳Y分子筛的性质影响,展望超稳Y分子筛脱铝改性的发展方向。     

分子筛改性研究综述

综述了国内外分子筛的主要改性方法,阐述了脱铝改性、脱硅改性和金属改性的特点。脱铝改性主要有水蒸气改性法和酸处理改性法,相比于水蒸气处理分子筛需要大量的能量且难以掌握脱铝程度,酸处理脱铝以能耗低、环保、脱铝程度易控制的优势更加适用于低硅铝比分子筛脱铝,微波处理可以大幅缩短酸处理的时间。采用碱处理脱硅制备的介孔-微孔分子筛,结合了微孔的催化性能、择形选择性和介孔的优异扩散性能,提高了分子筛的综合价值。金属改性能在不改变分子筛结构的基础上,有效的提高目的产物的收率与选择性,延长分子筛的寿命。在总结目前分子筛改性研究进展的基础上,提出随着分子筛催化剂生产的产业化,应研究更适合大规模生产的改性条件。     

铁取代介孔磷铝分子筛的合成、表征及其催化性能

以水热晶化法合成了Fe取代介孔磷铝分子筛,并用XRD, FT-IR, N2吸附等对其进行了表征. 结果表明,合成的分子筛为缺乏长程有序的介孔结构,具有较高的比表面积. 在焙烧后的分子筛中,Fe3+离子主要以四配位的形式存在于骨架中. 该分子筛能有效催化氧化水溶液中苯酚,在反应温度60℃、苯酚起始浓度3 mmol/L、加入45 mmol/L H2O2、溶液起始pH值4.5的条件下,4 h后苯酚去除率达99.5%,COD去除率达87.9%,且催化剂性能稳定,反应过程中有极少量Fe3+离子流失.     

碱改性介-微孔HZSM-5分子筛催化乙醇脱水制乙烯性能

对两种不同硅铝比的HZSM-5分子筛进行碱处理,制备介-微孔复合HZSM-5分子筛,研究乙醇脱水制乙烯的催化性能,并考察碱溶液浓度和处理温度对HZSM-5分子筛孔结构和表面酸性的影响。结果表明,适宜的碱处理条件有利于分子筛发生骨架脱硅和脱铝,从而形成介孔。碱处理对硅铝比低的HZSM-5分子筛酸性质影响明显,而硅铝比高的HZSM-5分子筛在碱处理过程中酸性质变化不明显,更易发生脱硅和脱铝而形成更多介孔。碱改性介-微孔HZSM-5分子筛催化剂使乙醇脱水制乙烯催化性能得到改善,尤其低温催化活性提高,这主要归功于碱处理中介孔的形成和表面酸性的调变。     

USY分子筛表面酸性的调变及其在催化脱除芳烃中烯烃的应用

详细论述了柠檬酸对USY分子筛的改性作用,以脱除高溴指数芳烃中烯烃的反应为例对其催化活性进行了评价。实验结果表明:0.2mol/L柠檬酸溶液酸性适宜,对分子筛的骨架铝以及非骨架铝进行了有效的脱除,脱除的铝在分子筛中以无定形的非骨架铝形式存在。柠檬酸改性过程可使分子筛的介孔面积以及介孔孔容增大,这十分有利于减缓分子筛的失活速率。柠檬酸改性过程使分子筛表面的强B酸减少,强L酸增多,这有助于减缓分子筛上积炭的生成速率。经过柠檬酸改性的USY分子筛对脱除芳烃中微量烯烃的催化效果明显高于目前工业中在用的普通白土和改性白土。再生实验说明,经3次焙烧再生后,改性分子筛的活性依然在90%以上,具有很好的可再生性。     

高硅铝比小晶粒分子筛的合成及应用进展

小晶粒分子筛具有较大比表面积和短孔道,在炼油和石油化工反应中表现出优异的催化性能。分子筛晶粒越小,热稳定性和水热稳定性越差。结晶度相近的沸石分子筛结构稳定性主要受粒径和骨架硅铝比的影响。综述了小晶粒分子筛的合成方法,认为提高硅铝比可以提高小晶粒分子筛的热稳定性和水热稳定性。介绍了高硅铝比小晶粒沸石分子筛的制备及研究进展,认为高硅铝比小晶粒分子筛的合成仍是未来研究趋势。     

不同硅铝比纳米ZSM-5分子筛的合成及表征

纳米ZSM-5分子筛由于其特殊的孔道和表面性质,显示出优异的吸附与催化性能,但粒径小于100 nm的ZSM-5分子筛极易发生团聚。以正硅酸乙酯为硅源、偏铝酸钠为铝源、四丙基氢氧化铵为模板剂,合成硅铝物质的量比分别为25、50、100、200和400的纳米ZSM-5分子筛。通过X射线衍射(XRD)、扫描电镜(SEM)、N_(2)物理吸附-脱附、^(27)Al固体核磁共振(^(27)Al MAS NMR)表征,结果表明,在硅铝物质的量比为25~400范围,均可合成粒径小于100 nm的ZSM-5分子筛。同时随着硅铝物质的量比增加,分子筛结晶度变强,分散性变好,比表面积和孔容增加,非骨架铝减少。     

硅铝比对Cu/SSZ-13分子筛低温催化性能的影响

采用水热法和液态离子交换法制备了一系列硅铝比(摩尔比)不同的Cu/SSZ-13分子筛[n(Si)/n(Al)=47,30,20,15],探究了硅铝比对NH_3选择性催化还原(NH_3-SCR)的影响,并通过XRD,ICP,N_2吸脱附,SEM,H_2-TPR,NH_3-TPD等表征分析对样品的物化性质进行了系统研究。活性测试结果表明,不同硅铝比分子筛的NH_3-SCR性能具有显著差异,特别是低温范围,其中催化剂起燃温度T_(50)(转化效率≥50%时的温度)顺序为n(Si)/n(Al)=20 n(Si)/n(Al)=15 n(Si)/n(Al)=30 n(Si)/n(Al)=47。从表征结果可知,硅铝比会影响分子筛催化剂的表面形貌、晶体结构,进而影响样品中Cu物种的分布和数量及酸性。4种分子筛催化剂中n(Si)/n(Al)-20具有最多的孤立Cu~(2+)以及弱L酸位数量,有利于低温NH_3-SCR反应的进行。     

补铝改性β沸石对烷基化反应的影响

制备出补铝β沸石催化剂样品。从样品的红外表征结果讨论了补铝对表面羟基结构的影响和不同状态铝含量的改变。通过程序升温脱附(TPD)对样品进行了各种酸量的测定，结合反应活性评价实验,证明了加铝可使催化剂酸量增加并能提高反应活性。结构测定数据表明补铝样品有较多的微孔表面积和微孔孔容。采用加速失活方法考察了两个样品。结果表明，只加铝的β沸石样品具有较好的稳定性。     

Realumination of dealuminated HZSM-5 zeolite by citric acid treatment and its application in preparing FCC gasoline hydro-upgrading catalyst

This article describes a novel citric acid treatment method for realuminating dealuminated HZSM-5 zeolite and its application in enhancing the performance of the zeolite derived FCC gasoline hydro-upgrading catalysts. A series of modified HZSM-5 zeolites were prepared by streaming and/or acid treatments and the influences of the different modification methods on the acidity, pore structure and catalytic performance of the modified HZSM-5 zeolite supported catalysts were compared in the present investigation. The results showed that compared with the single HCl or citric acid treatment, the steaming treatment, and the steaming/HCl treatments, the citric acid treatment after steaming exclusively increased the amount of framework Al species due to its realumination effect on the steamed HZSM-5 zeolite. This realumination effect of the citric acid treatment could optimize the ratio of framework Al to extra-framework Al in the steamed HZSM-5 zeolite and thus greatly improve the acidity distribution and pore structure of the corresponding catalyst. The catalytic performance assessments of the different zeolite supported catalysts for FCC gasoline hydro-upgrading revealed that the catalyst supported on the steaming/citric acid treated HZSM-5 zeolite had balanced initial and long-term activities in hydrodesulfurization, hydroisomerization and aromatization, high liquid yield and improved gasoline road octane number. The superior catalytic performance of the catalyst could be closely related to its suitable ratio of framework Al to extra-framework Al achieved by the combinational use of the steaming dealumination and the citric acid realumination, fully demonstrating the effectiveness of the steaming and citric acid treatments in optimizing the physicochemical properties and catalytic performance of HZSM-5 zeolite supported catalysts.     

Comparing Al-SBA-15 Support and Pt/Al-SBA-15 Catalyst: Changes in Al Speciation and Acidic Properties Induced by the Introduction of Pt via Aqueous Medium

Differences between the acidic properties of silicoaluminic Pt-containing catalysts and those assessed on their parent supports have been reported in the literature and attributed to the presence of the metal nanoparticles and to their influence on the acid sites. It is shown here that for mesoporous materials containing various types of Al species, an alternative explanation can be proposed. ²⁷Al NMR spectroscopy, FTIR of adsorbed CO and probe catalytic tests suggest the redistribution of aluminium atoms upon contact of the parent support with the aqueous solution containing the Pt precursor. Upon contact with water and thermal treatment, strong and mild Brønsted sites (Si–O(H)–Al) transform into strong Lewis sites (isolated tetracoordinated Al atoms). As a consequence, it may not be straightforward to deduce the acidic properties of metal-containing catalysts supported on Al-containing mesoporous materials from those of the bare support, because the surface species may differ significantly.     

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity.     

Synthesis of hydrothermally stable, hierarchically mesoporous aluminosilicate Al-SBA-1 and their catalytic properties

Hydrothermally stable mesoporous aluminosilicates Al-SBA-1 with hierarchical pore structure have been successfully synthesized under alkaline condition at 120 °C by employing organic mesomorphous complexes of polyelectrolyte (poly(acrylic acid) (PAA)) and cationic surfactant (hexadecyl pyridinium chloride (CPC)) as template. The Si/Al ratio could be as high as 5 and the incorporation of Al into the silica framework did not disturb the well-ordered cubic Pm ?3n mesostructure. Meanwhile, the incorporation of Al could greatly increase the specific surface area and pore volume of the samples. The Al-SBA-1 materials exhibited a high hydrothermal stability and remained stable even after being treated in boiling water for 10 days. The catalytic activity of the Al-SBA-1 materials was investigated by employing the Friedel-Crafts alkylation of toluene with benzyl alcohol as a model reaction and they exhibited excellent catalytic property due to the incorporated acid sites and the hierarchically mesoporous structure.     

Acetylation of 2-methoxynaphthalene with acetic anhydride over a series of dealuminated HBEA zeolites

The liquid phase acylation of 2-methoxynaphthalene with acetic anhydride was carried out in a batch reactor at 120°C over a series of HBEA zeolites resulting from dealumination of a commercial sample by treatment with chlorhydric acid or with ammonium hexafluorosilicate. Lewis acid sites which correspond to extraframework aluminium species and to transient-state species (aluminium atoms which are leaving the framework) were preferentially removed. With all the HBEA samples, acetylation of 2-methoxynaphthalene leads preferentially to 1-acetyl-2-methoxynaphtalene, this compound undergoing isomerization into 2-acetyl-6-methoxynaphthalene and 1-acetyl-7-methoxynaphthalene as well as deacylation. A maximum in acetylation and isomerization activities is found for a Si/Al ratio between 20 and 35. The low activity of the commercial sample can be related to limitations in the desorption of acetylated products from the zeolite micropores caused by the large amount of extraframework aluminium species present on this sample. Lewis acid sites were shown to be completely inactive for acetylation and isomerization reactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization and catalytic performance of mesoporous molecular sieves Al-MCM-41 materials

Mesoporous Al-MCM-41 materials of different Si/Al ratios have been synthesized and characterized by X-ray powder diffraction, ²⁷Al and ²⁹Si MAS NMR, differential thermogravimetric analysis, N₂ adsorption measurements, FT-IR and catalytic cracking of alkanes. The experimental results show that the incorporation of aluminium into the framework of MCM-41 has a great effect on the degree of long-distance order, the surface acidities and the mesoporous structures of the materials. With increase of the aluminium content, the amounts of tetrahedral framework aluminium and the acid sites on the samples increase, but the acid strength decreases. Al-MCM-41 materials exhibit high activity for n-C₁₆ ⁰ cracking and good selectivity for producing low carbon alkylenes, particularly for i-C₄ ⁼.     

Characterization and catalytic behaviors of methylamine modified FAU zeolites

The methylamine (MA) modified FAU zeolites with 5.8 and 80 of silica alumina molar ratio were successfully prepared by the treatment of original FAU zeolites with MA. The obtained materials were investigated with diffuse reflectance infrared Fourier transform spectroscopy, X-ray diffraction, magic-angle spinning nuclear magnetic resonance, thermogravimetry, temperature-programmed desorption of CO₂ and NH₃ (CO₂-TPD and NH₃-TPD), nitrogen content analysis, and specific surface area analysis. The formations and thermal stabilities of different Si–N–C groups in the MA modified FAU zeolites were confirmed. The changing of aluminium species due to the interaction of MA and framework/extraframework aluminium (FAL/EFAL) in the modified samples was discovered. The acidity and basicity of the MA modified FAU zeolites were correlated to the hybrid aluminium species and variation of Si–N–C groups, respectively. The catalytic behaviors of the MA modified FAU zeolites were explored by Knoevenagel condensation reaction of benzaldehyde and malonic acid.     

Realumination of zeolite Y under acidic conditions

Dealuminated zeolites Y were treated with aqueous solutions of various acids and ammonium salts to investigate the realumination behavior under acidic conditions. From the results of ²⁷Al MAS NMR, ²⁹Si MAS NMR and FT-IR measurements, it was found that a part of non-framework aluminum species in the dealuminated zeolite Y is effectively reinserted into the zeolite framework in CH₃COONH₄ and C₆H₅COONH₄ aqueous solutions. Pyridine adsorption experiments also revealed that most of incorporated aluminum species generate tetrahedrally coordinated framework aluminum species, namely Brönsted acid sites. Although the realumination also proceeded in H₂SO₄ and CH₃COOH aqueous solutions, large amounts of incorporated aluminum species were not necessarily responsible for generation of Brönsted acid sites. Framework connected aluminum species, presumably as 3-fold-coordinated Lewis acidic framework aluminum species, were mainly generated. In the TEM image of the realuminated zeolite Y, needle-like crystals with ca. 25–80 nm in length were observed, which are probably due to AlOOH generated from non-framework aluminum species.