Detemplation with H2O2 and characterization of MCM-56

Detemplation of zeolite MCM-56 was successfully realized by controlled oxidation of the template using H₂O₂ at 363 K. The resulting material (denoted as MCM-56(H₂O₂)) shows larger surface area (micropore and external), higher micropore volume, more Lewis acid and Brønsted acid sites in comparison with the sample detemplated by calcination (denoted as MCM-56(C)). Moreover, two Mo-containing catalysts of Mo/H-MCM-56(H₂O₂) and Mo/H-MCM-56(C) were prepared, and their catalytic properties for the reaction of methane aromatization were investigated. Compared with Mo/H-MCM-56(C), the sample of Mo/H-MCM-56(H₂O₂) shows higher conversion of methane and yield of benzene, with lower selectivity to benzene and higher selectivity to coke. The relatively high benzene yield might be mainly assigned to the existence of more 10-ring channels, while the high selectivity of coke should be due to the presence of large amounts of 12-ring pockets and acid sites exposed to the crystal exterior over Mo/H-MCM-56(H₂O₂).     

Pyrolysis of Polyethylene over Aluminum-Incorporated MCM-41 Catalyst

Aluminum-containing MCM-41 catalysts were synthesized in this study by impregnation of aluminum into hydrothermally synthesized MCM-41. Aluminum was loaded into the porous framework of silica with different Al/Si ratios, using aluminum isopropoxide as the aluminum source. These catalysts exhibited Type IV adsorption–desorption isotherms and had a pore diameter of 2.4 nm. Aluminum species were coordinated tetra- and octahedrally in the structure of catalysts. Diffuse Reflectance Fourier Transform Infrared Spectra (DRIFTS) analysis of the pyridine-adsorbed catalysts revealed the existence of Brönsted acid sites in the synthesized catalysts in addition to the Lewis acid sites. The performance of these catalysts was tested in the degradation of polyethylene using a thermogravimetric analyzer. Pure MCM-41 did not show a significant reduction in the degradation temperature of polyethylene, whereas aluminum-impregnated catalysts were successful in decreasing the temperature.     

Synthesis,characterization and catalytic evaluation of zirconia-pillared montmorillonite for linear alkylation of benzene

Zirconia-pillared montmorillonite was synthesized by an ultrasonication method and characterized by XRD, FT-IR of adsorbed pyridine, XPS, XRF and low temperature nitrogen adsorption techniques. The basal spacing of d(0 0 1) reflection of the pillared clay estimated by XRD was found to be 20 Å. XRD study showed well distribution of pillars without any non-pillared portion of the clay. FT-IR studies showed the formation of both Lewis and Brönsted acid sites due to pillaring. Pyridine desorption studies revealed that the Brönsted sites were stronger than Lewis acid sites. The activity of the Zr-PILC for the alkylation of benzene with long chain α-olefins [C₁₀–C₁₃] was investigated. The Brönsted acid sites played major role in this reaction.     

Effect of surface Na+ or K+ ion exchange on hydrodesulfurization performance of MCM-41-supported Ni–W catalysts

Ni–W hydrodesulfurization (HDS) catalysts supported on MCM-41 synthesized from two different silica sources (sodium silicate hydrate and tetraethylorthosilicate) as well as on Na⁺ or K⁺ ion exchanged MCM-41 were prepared. These catalysts were used to investigate the influence of the surface properties of MCM-41 on the performance of HDS catalysts with DBT as the model molecule. The XRD and N₂ adsorption results indicated that the MCM-41 prepared from tetraethylorthosilicate (MCM-41(T)) exhibited the best structural properties. The mesostructure of MCM-41 synthesized from sodium silicate (MCM-41(S)) remained after ion exchange with Na₂C₂O₂ and K₂C₂O₂. Both pyridine FT-IR and Hammett indicators showed that only MCM-41(S) possessed some Brönsted and Lewis acid sites. Ni–W/MCM-41(S) showed the highest HDS and hydrogenation activities. The introduction of Na⁺ and K⁺ strongly inhibited the hydrogenation activity of Ni–W/MCM-41(S) but enhanced its hydrogenolysis activity. UV–vis and TPR studies indicated that the introduction of Na⁺ and K⁺ into MCM-41(S) may lead to the segregation of surface Ni species and may hinder the reducibility of the supported Ni–W oxides. Spillover hydrogen, which is “trapped” by Na⁺ and K⁺, may play an important role in the HDS activity and selectivity of Ni–W catalysts.     

Improvement of vapor-phase silylation and thermal stability of silylated MCM-22 zeolite

The method of vapor-phase silylation over as-made MCM-22 was improved through the replacement of deionized water with NaOH solution that absorbed HCl produced during the vapor-phase silylation. Also, the thermal stability of silylated MCM-22 was investigated by X-ray diffraction, N₂ adsorption–desorption, pyridine adsorption and desorption followed by infrared measurement and nuclear magnetic resonance techniques. The results showed that this improvement was beneficial for dichlorodimethylsilane molecules to enter the interlayer of MCM-22 zeolite to form pillaring structure. Both the interlayer pillaring structure and acidity of silylated MCM-22 varied with increasing thermal treatment temperature from 600 to 750 °C. Specifically, the interlayer pillaring Si groups were thermally stable below 650 °C, and damaged gradually with the increase of thermal treatment temperature from 650 to 750 °C, leading to gradual decrease of the specific surface area and volume corresponding to interlayer supercages. At 750 °C, the interlayer pillaring structure was destroyed completely, whereas the MWW structure was still maintained well. As to the variations of acid sites with thermal treatment temperature, different trend was observed. The amount of weak and strong Brönsted acid sites, as well as that of strong Lewis acid sites decreased gradually with increasing thermal treatment temperature to 650 °C, but remained almost unchanged when the temperature was further increased to 750 °C.     

Influence of synthesis method on the properties and catalytic performance of MCM-49 zeolites

Highly crystalline and pure MCM-49 was hydrothermally synthesized by dynamic and static methods, respectively. The properties of the samples were studied by N₂ adsorption, XRD, TEM and FT-IR techniques. The results indicated that MCM-49 synthesized by dynamic method showed much smaller crystal and lower concentration of acid sites. The Pd-supported catalyst on MCM-49 synthesized by static method showed higher acetone conversion in one-step synthesis of methyl isobutyl ketone from acetone, which was attributed to higher concentration of acid sites. While the higher selectivity to methyl isobutyl ketone for Pd-supported on MCM-49 synthesized by dynamic method might be related with the lower acidity and higher BET surface area.     

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.     

MCM-22 分子筛的合成及液相烷基化合成乙苯性能研究

对各种条件下合成的MCM-22沸石进行了表征研究。研究表明晶化时间对MCM-22沸石的层间结构有着显著的影响,晶化40 h后,其结构趋向稳定。MCM-22沸石沸石具有较高的B酸含量,强酸中心主要为B酸,MCM-22晶体呈片状结构,其结构中存在丰富的大孔。以MCM-22沸石为催化剂考察了其催化乙烯和苯的液相烷基化的反应性能。结果表明,MCM-22沸石催化剂具有优良的选择性,在低苯烯比(B/E)的反应条件下,其反应稳定性优良。在乙烯质量空速达到0.7 h~(-1),苯烯摩尔比(B/E)可以降低到2.0,乙苯选择性达到84%,二甲苯含量小于50 mg/kg。     

Competent,selective and high yield of 7-hydroxy-4-methyl coumarin over sulfonated mesoporous silica as solid acid catalysts

Highly ordered mesoporous MCM-41 and SBA-15 have been synthesized and functionalized with different amounts of propyl sulfonic acid groups using 3-mercaptopropyltrimethoxysilane as sulfur source. The synthesized catalysts have been well-characterized by different techniques such as XRD, FTIR and BET surface area and pore size distribution by BJH method. FTIR spectra of chemisorbed pyridine and temperature programmed desorption of NH₃ techniques have been successfully used to characterize the acidic sites. The results showed that, both surface area, mean pore diameter and pore volume decrease as the extent of sulfonation increase. XRD results and TEM images confirm the stability of mesoporous long range order even after sulfonation process done. In addition, the study also showed that, sulfonation enhances the surface acidity and new moderate and strong acid sites were created. All the sulfonated catalysts under investigations have been found to be highly active and selective for the Pechmann condensation reaction of resorcinol with ethyl acetoacetate. More than 98% yield of 7-hydroxy-4-methyl coumarin was obtained with 100% selectivity. Presence of high number of moderate and strong Brönsted acid sites in sulfonated catalysts help in achieving high yields. Furthermore, the MCM-41 sulfonated catalysts showed higher catalytic performance due to their higher surface acidities.     

Synthesis of Ru-modified MCM-41 Mesoporous Material, Y and Beta Zeolite Catalysts for Ring Opening of Decalin

Ru modified MCM-41 mesoporous material, Y and Beta zeolites were synthesized, characterized and investigated in ring opening of decalin. Ru-MCM-41 catalysts were prepared using ion-exchange, impregnation and in situ synthesis methods. Ru-MCM-41, Ru-Y and Ru-Beta zeolite catalysts were characterized using XRD, SEM, EDXA, FTIR, XRF and nitrogen adsorption. Ru modification of MCM-41, Y and Beta zeolites did not influence the parent phase purity of materials. Microporous H-Beta and H-Y catalysts showed larger number of Brønsted acid sites than H-MCM-41 mesoporous material. Method of Ru introduction in MCM-41 was observed to influence conversion of ring opening of decalin and selectivity to ring opening products. Ru-MCM-41-IE catalyst prepared by ion-exchange method exhibited higher conversion of decalin than Ru-MCM-41-IMP and Ru-MCM-41-IS catalysts prepared by impregnation and in situ synthesis methods. Ru-MCM-41-IS catalyst prepared by in situ method showed higher selectivity to ring opening products than Ru-MCM-41-IE and Ru-MCM-41-IMP catalysts.     

Quantitative Determination of Brönsted Acid Sites on Zeolites: A New Approach Towards the Chemical Composition of Zeolites

An original quantitative method based on H/D exchange between H₂O/D₂O molecules and the OH groups of different zeolites has been developed for the titration of the Brönsted acid sites present on the solid surface. The measured Brönsted acid sites density appears to be in good agreement with the theoretical amount estimated by the Si/Al ratio. In contrary to classical methods, this non-destructive anhydride method titrates the whole quantity of Brönsted acid sites of zeolites.     

均三甲苯在MCM-22和MCM-56分子筛上的吸附和扩散

以MCM-22和MCM-56分子筛为研究对象,考察烃类均三甲苯在MWW型分子筛上的吸附和扩散,同时对分子筛进行XRD、N2吸附和TEM等表征,探究分子筛的结构特性与吸附和扩散之间的关系。研究表明,均三甲苯在MWW型分子筛中的吸附和扩散位置为外表面半超笼。单层和错层结构使MCM-56较MCM-22分子筛拥有更多的外表面酸性位,有利于均三甲苯的吸附。与MCM-22相比,MCM-56分子筛片层结构较薄,焙烧导致晶体外部结构的卷曲使烃类大分子均三甲苯在MCM-56分子筛中的扩散受阻。     

Pillared MWW zeolites MCM-36 prepared by swelling MCM-22P in concentrated surfactant solutions

Lamellar zeolite forms like layered MCM-22 precursor, MCM-22P, offer unprecedented opportunities for creating diversity of more open zeolite structures prepared post-synthesis by expanding and modifying the interlamellar space. This is a relatively unexplored area with regard to procedures ensuring easy, least destructive and most efficient expansion of layered zeolites. Herein we explore concentrated surfactant solutions with high pH for their ability to provide swollen MCM-22 that can be converted to the pillared MCM-36. High pH of the swelling solutions was obtained by addition of tetrapropylammonium hydroxide and by partial conversion of the surfactant chloride into hydroxide by ion exchange. The products were evaluated based on their X-ray diffraction characteristics, sorption properties, scanning electron microscopy and IR spectra as indicators of catalytic potential. The swelling/pillaring efficiency was judged based on BET surface area and depended on swelling conditions, especially the apparent basicity. There was an overall decrease in acid site concentration due to incorporation of inert silica pillars. The MCM-36 zeolite with the highest BET showed increased uptake of 2,6-di-tert-butyl-pyridine by 75% compared to the parent MCM-22 suggesting enhanced accessibility of acid sites for bulky probe molecules. We conclude that concentrated surfactant solutions can be effective in swelling MCM-22P even at room temperature but an optimal approach must balance many factors including yield and activity of the final product.     

Mono- and bifunctional MFI,BEA and MCM-41 titanium-molecular sieves. Part 1. Synthesis and characterization

A series of mono- and bifunctional titanium-molecular sieves containing different trivalent ions, e.g. Al³⁺, B³⁺ and Ga³⁺ with MFI, BEA and MCM-41 topologies has been prepared and characterized. Various techniques including XRD, N₂ adsorption, UV–visible and MAS-NMR were used to monitor the physico-chemical properties of these materials. The results revealed that the Ti and the trivalent ions are mostly incorporated into catalyst framework. The acidic properties of these catalysts were studied by FTIR spectra in the OH as well as in the pyridine regions. These results revealed that no Brönsted acid sites were present in TS-1, Ti-MCM-41 and B–Ti-MCM-41. The FTIR spectra in the pyridine regions at different temperatures indicate that the acidic strength is in the following order: TS-1<B-TS-1≪Ga-TS-1⩽Al-TS-1 and Ti-MCM-41<B–Ti-MCM-41≪Ga–Ti-MCM-41<Al–Ti-MCM-41. This work illustrates how redox catalysts such as TS-1 and Ti-MCM-41 can be modified by introducing acid sites of controlled acid strength through lattice insertion of different trivalent cations.     

Effect of different synthesis methods on the structural and catalytic performance of SBA-15 modified by aluminum

Two different aluminum-containing mesoporous Al/SBA-15 were prepared by post-synthesis method and direct synthesis method using P123 as structure directing agent and aluminum isopropoxide as the aluminum source. Samples were characterized in detail by XRD, N₂ adsorption, TEM,²⁷Al MAS NMR, and the acidic properties were performed by FT-IR of pyridine adsorption (Py-IR). The results show that Al/SBA-15 prepared by the direct synthesis method possessed higher BET surface area and larger pore volume. The acidic properties were investigated in Friedel–Crafts alkylation of phenol tert-butylation. The different synthesis method leads to distinct coordination of Al and intensity of acidity. Kinetics of the alkylation over Al/SBA-15 was also investigated. These results indicated that Al/SBA-15, prepared by post-synthetic grafting method, has more activity ability than the corresponding one synthesized by direct method since they contain more Lewis acid sites and Brönsted acid sites. The catalysts preserved almost their initial catalytic activity after four reuses.     

Hydrogen storage characteristics of metal oxide doped Al–MCM-41 mesoporous materials

The feasibility and perspectives of Al–MCM-41 as hydrogen storage systems were evaluated. The Al–MCM-41 with varying content of aluminum was synthesized by hydrothermal process. Different metal oxides were impregnated over Al–MCM-41 by incipient wetness impregnation (IWI) method. The crystallnity of the samples were interrogated by powder X-ray diffraction. The textural properties were measured by N₂ sorption method. The structural properties were established by Transmission Electron Microscope (TEM). The gas chromatogram indicates that hydrogen uptake in Al–MCM-41 is strongly dependent on density of Brønsted acid sites and the amount of metal oxide (especially NiO).     

Positive effect of secondary structure creation in mordenites on alkylation of benzene with 1-tetradecene

The liquid-phase alkylation of benzene with 1-tetradecene was realized over dealuminated mordenites with different mesoporous surface areas and three different levels of acidity. The mordenite catalysts were characterized by N₂-sorption, FTIR pyridine adsorption, and TPDA. The number of Brønsted acid sites decreases; however, it represents a higher proportion of the total acidity. Alkylation results demonstrated that the mordenite activity in alkylation accelerated with increasing mesoporous surface area in spite of the lower total acidity. This fact indicates that the accessibility of acid sites and the internal mass transport in mordenite channels play a significant role in liquid-phase alkylation of aromatics with 1-alkenes.     

MCM-36 zeolites tailored with acidic ionic liquid to regulate adsorption properties of isobutane and 1-butene☆

Adsorption properties of an adsorbent or a catalyst towards adsorbates are crucial in the process of adsorption separation or catalytic reaction. Surface morphology and structure of adsorbents have a significant impact on the adsorption properties. In this study, a novel acidic ionic liquid, 1-butyl-3-(triethoxysilylpropyl)imidazolium hydrogen sulfate(i.e., [BTPIm][HSO_4]), was synthesized and subsequently grafted onto the MCM-36 zeolite for the regulation of its adsorption properties towards isobutane and 1-butene. The resultant [BTPIm][HSO_4]-immobilized MCM-36(i.e., MCM-36-IL) was characterized by FT-IR, XPS, XRD, SEM, TG/DTG and N_2 adsorption–desorption measurement. It was found that the specific surface area, micropore volume and mesopore volume of the MCM-36 support underwent a reduction upon the immobilization of ionic liquid,while the surface density of acid increased from 0.0014 to 0.0035 mmol·m~(-2). The adsorption capacity of isobutane and 1-butene on the MCM-36-IL was determined by a static volumetric method. Results demonstrated that the interaction between isobutane and MCM-36-IL was enhanced and the interaction between 1-butene and MCM-36-IL was reduced. As a result, a tunable adsorption ratio of isobutane/1-butene on MCM-36 was achieved.With the increase in surface density of acid and the tunable adsorption ratio of isobutane and 1-butene on the functionalized MCM-36, the acidic ionic liquid-immobilized zeolites are beneficial to obtain an improved reaction yield and a prolonged catalyst life in the reactions catalyzed by solid acid.     

Synthesis of mesoporous aluminosilicates with low Si/Al ratios using a single-source molecular precursor under acidic conditions

A single molecular precursor, bis(sec-butoxy)-aluminoxy-triethoxysilane, was used as aluminum source for the synthesis of mesoporous aluminosilicates with Si/Al ratios ranging from 1 to 10 under acidic conditions. Aluminum can be stoichiometrically incorporated into the mesoporous materials at pH = 1.5. The mesoporous aluminosilicates synthesized with the single molecular precursor display larger unit cell parameter and pore diameter than that of the materials prepared with aluminum sulfate, aluminum nitrate, aluminum hydroxide, and aluminum isopropoxide as the aluminum sources. IR spectra of adsorbed pyridine and NH₃-TPD showed that both Brönsted acidic sites and Lewis acid sites with medium strength are present in the materials. However, no direct relationship between the acidic properties and the content of aluminum was observed when the Si/Al ratios of the mesoporous aluminosilicates are lower than 10.     

NO x reduction by ethanol on Pd/zeolites-effect of oxygen

The reduction of NO by ethanol on palladium catalysts supported on NaZSM-5 and HZSM-5 zeolites was studied. Temperature programmed techniques, such as desorption of ethanol, NO and surface reaction (TPSR) analyses, besides NH₃ (NH₃–TPD), as well as, FTIR after pyridine adsorption were used to accomplish reaction products and surface properties. Results show that NaZSM5 and HZSM5 present different amounts of Lewis and Brönsted acid sites, which affect strongly the carbon product distribution, but not the nitrogen selectivity. NO reaction with ethanol in the presence of oxygen occurs only over the metal and is independent of the acid sites.