Adsorption of chromate by surfactant-modified zeolites and MCM-41 molecular sieve

Synthetic and natural zeolites, modified by the quaternary amines, i.e. hexadecyltrimethylammonium (HDTMA) bromide and n-cetylpyridinium bromide (CPB) as well as MCM-41 molecular sieve were employed for removal of chromate from aqueous solution. Obtained data from chromate adsorption experiments over the mentioned materials were compared. It was shown that adsorption data for modified zeolite using the amine was consistent with Langmuir isotherm equation. The maximum chromate adsorption over as synthesized MCM-41 was much greater than that of the natural clinoptilolite and ZSM-5 zeolites.     

WO3-ZSM-5/MCM-41催化剂的合成 及其催化氧化脱硫研究

以氢氧化钠溶液处理微孔沸石ZSM-5来提供硅铝源,合成了ZSM-5/MCM-41复合结构型分子筛。采用XRD、N2吸附脱附、TEM等方法对其进行了表征,考察了其水热稳定性。实验结果表明,碱处理合成的ZSM-5/MCM-41同时具有微孔孔道和介孔孔道结构,并具有优于介孔MCM-41分子筛的水热稳定性。以ZSM-5/MCM-41为载体负载三氧化钨后应用于噻吩/正辛烷模拟油体系,双氧水为氧化剂,催化氧化脱硫,WO3-ZSM-5/MCM-41（三氧化钨质量分数为10%）表现出良好的催化性能,脱硫率可达到93.6%。     

Selective synthesis of triacetin from glycerol catalyzed by HZSM-5/MCM-41 micro/mesoporous molecular sieve

HZSM-5/MCM-41 molecular sieve(H-ZM) catalysts with well-defined micro/mesoporous structures were synthesized and showed high performance for selective synthesis of triacetin via the esterification reaction of glycerol with acetic acid. The conversion of glycerol was demonstrated to be 100% and the triacetin selectivity was over 91%, which can be attributed to the synergistic effect regarding suitable acidic property, excellent diffusion efficiency and good stability derived from the combined advantages of microporous molecular sieve HZSM-5 and mesoporous molecular sieve MCM-41.     

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.     

Methanol-to-Olefins Reaction over Large-Pore Zeolites: Impact of Pore Structure on Catalytic Performance

In the methanol-to-olefins (MTO) reaction, product flexibility is important for meeting the fluctuating chemicals demands. In this paper, the catalytic performance of recently reported zeolites having 12-ring pores, such as boroaluminosilicate CON-type zeolite ([Al,B]-CON), MCM-68, and YNU-5 zeolites, in the MTO reaction was compared to understand the relationship between zeolite framework and product selectivity. The catalytic performance of the synthesized zeolites was compared with that of Beta, mordenite, and ZSM-5. The highest selectivities for propylene and butylenes were achieved over MCM-68. The highest propylene-to-ethylene ratio in the products was obtained over [Al,B]-CON. ZSM-5 and [Al,B]-CON exhibited a superior ability to suppress coke formation compared to Beta, mordenite, MCM-68, and YNU-5.     

Ordered Mesoporous Materials with Improved Stability and Catalytic Activity

Microporous crystals of zeolites such as Y, Beta, and ZSM-5 are widely used commercial catalysts, but their applications are strongly limited by their small pore sizes. Recent progress in solving this is used to ordered mesoporous materials such as MCM-41, HMS, and SBA-15. These mesoporous materials have pore diameters of 2.0–30 nm and exhibit good catalytic properties for the catalytic conversion of bulky reactants. However, when compared with microporous crystals of zeolites, the catalytic activity and hydrothermal stability are relatively low, which severely hinders their practical applications in industrial catalytic reactions such as petroleum cracking. The relatively low catalytic activity and hydrothermal stability can be attributed to the amorphous nature of the mesoporous walls. In this account, we systemically review the routes for improving catalytic activity and hydrothermal stability of mesoporous materials, which include (1) acidic sulfated zirconia supported in mesoporous materials; (2) strongly acidic and thermally stable mesostructured sulfated zirconia with tetragonal crystalline phase; (3) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in alkaline media; (4) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in strongly acidic media; (5) hydrothermally stable mesoporous titanosilicates with catalytically active titanium species in oxidations; (6) high-temperature generalized synthesis of ultrastable ordered mesoporous silica-based materials by using fluorocarbonhydrocarbon surfactant mixtures.     

Exploring suitable ZSM-5/MCM-41 zeolites for catalytic cracking of n-dodecane: Effect of initial particle size and Si/Al ratio

In this study, various ZSM-5/MCM-41 micro/mesoporous zeolite composites have been prepared by alkalidesilication and surfactant-directed recrystallization of ZSM-5. The effects of particle size and Si/Al ratio of initial ZSM-5 zeolites on the structure and catalytic performance of ZSM-5/MCM-41 composites are studied. The results of XRD, TEM N₂-adsorption-desorption, NH₃-TPD and in situ FT-IR revealed that ordered hexagonal MCM-41 mesopores with 3-4 nm pore size were formed around ZSM-5 crystals, and the specific surface area and mesopore volume of composites increased with increasing the Si/Al ratio of initial ZSM-5. Catalytic cracking of n-dodecane (550 ℃, 4 MPa) showed that the ZSM-5/MCM-41 composites obtained from the high Si/Al ratio and nano-sized initial ZSM-5 zeolites exhibited superior catalytic performance, with the improvement higher than 87% in the catalytic activities and 21% in the deactivation rate compared with untreated zeolites. This could be ascribed to their suitable pore structure, which enhanced the diffusion of reactant molecules in pores of catalysts.     

Side-chain alkylation of 2,6-lutidine to 2,6-divinylpyridine over basic zeolites

Synthesis of 2,6-divinylpyridine (2,6-DVP) and 2-methyl-6-vinylpyridine (2M6VP) was achieved for the first time by side-chain alkylation of 2,6-lutidine using formaldehyde (37 wt/v) as alkylating agent in heterogeneous conditions at atmospheric pressure, and at a reaction temperature of 300 °C over alkali and alkaline metal ion modified zeolites. A mixture of 2,6-divinylpyridine and 2-methyl,6-vinylpyridine were formed by the alkylation of the 2,6-lutidine over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of 2,6-lutidine was studied over various potassium metal ion modified zeolite molecular sieves like ZSM-5 (30), X, Y, mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2,6-lutidine when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) gave best conversion of 2,6-lutidine and selectivity to 2-methyl,6-vinylpyridine. K-ZSM-5 (30) catalyst was employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2,6-lutidine. The effect of potassium metal ion content and precursors of potassium ion on catalytic activity in side-chain alkylation of 2,6-lutidine was studied. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed mechanism. The selectivities of 2,6-DVP were 45.2, 40.0, and 30.7% at 73.4, 66.0 and 60.5% conversion at 300 °C from 2,6-lutidine and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and Cs-K-ZSM-5 (30), respectively.     

改性介微孔ZSM-5分子筛催化剂制备及催化甲苯甲醇烷基化反应性能

将微孔ZSM-5分子筛通过不同浓度的氢氧化钠溶液处理不同的时间制备不同的介微孔ZSM-5分子筛,然后负载五氧化二磷制备介微孔ZSM-5分子筛催化剂,对介微孔ZSM-5分子筛负载五氧化二磷催化剂进行甲苯甲醇烷基化反应评价。其中氢氧化钠溶液浓度为1.0 mol/L、处理时间为30 min得到的介微孔ZSM-5分子筛负载五氧化二磷催化剂催化甲苯甲醇烷基化反应的活性较高。对介微孔ZSM-5分子筛负载五氧化二磷催化剂进一步采用铂进行改性,将制备的催化剂用于甲苯甲醇烷基化反应,在460 ℃条件下连续反应505 h,甲苯转化率保持在10.9%,二甲苯中对二甲苯的选择性保持在96%以上。研究结果表明,五氧化二磷、铂改性的介微孔ZSM-5分子筛催化剂具有优异的甲苯甲醇烷基化反应性能。     

Properties of Desilicated ZSM-5, ZSM-12, MCM-22 and ZSM-12/MCM-41 Derivatives in Isomerization of α-Pinene

Limited information is available on the isomerization of α-pinene proceeding on zeolites and related desilicated materials. We wish therefore to report on the title reaction proceeding over ZSM-5, ZSM-12 and MCM-22 type zeolites, parent and modified by the sodium hydroxide treatment. The NaOH solutions of various concentrations (0.05–1 M) were used as a desilicating agent. Such treatments with basic solutions were applied: (i) under atmospheric pressure, and (ii) under hydrothermal conditions. It was shown that ZSM-12 was more resistant towards the basic solutions treatment, and its structure was retained over a whole range of NaOH concentrations studied. Nitrogen sorption revealed strong influence of the desilication process on the pore structure of modified materials—the mesopores system was formed in the zeolite crystals. Finally, catalytic studies were carried out using ZSM-5, ZSM-12, MCM-22, their desilicated derivatives and a ZSM-12/MCM-41 composite material. Catalytic properties of the samples studied were affected to a large extent by the NaOH treatment.     

ZSM-5/MCM-41复合分子筛的制备及对乙醇脱水的催化活性

以微孔ZSM-5分子筛为母体,采用NaOH溶液对其进行预处理,再在水热条件下以十六烷基三甲基溴化铵（CTMAB）为模板剂制备了ZSM-5/MCM-41介微孔复合分子筛,考察了预处理温度、晶化温度等因素对复合分子筛结构和形貌的影响。进一步考察了该复合分子筛催化剂在乙醇脱水反应中的催化活性。结果表明,ZSM-5分子筛在2.0 mol/L NaOH溶液中于110℃预处理20 h,再于110℃水热晶化20 h制备的分子筛具有良好的介微孔复合结构;该复合分子筛经NH4NO3溶液离子交换制备的氢型催化剂在乙醇脱水催化反应中表现出良好的性能。当乙醇WHSV=0.5 h-1时,最佳反应温度为240～255℃,乙醇转化率〉99%,乙烯选择性〉96%。     

Short overview on the application of metal-modified molecular sieves in selective hydrogenation of cinnamaldehyde

This article shortly overviews our recent work on the application of metal supported molecular sieve catalysts in liquid-phase hydrogenation of cinnamaldehyde. The topic covers catalyst deactivation, influence of the support, active metals as well as the influence of reaction conditions on catalytic performance. Acquired results demonstrate superior performance of microporous supports (zeolites) compared to mesoporous MCM-41, which was relatively unselective and less active. At optimised conditions, selectivity towards cinnamylalcohol of about 60–70% and reasonable activity were achieved.     

MCM-41介孔分子筛合成与改性的研究进展

简要介绍了MCM-41介孔分子筛的特点,应用和改性原因.综述了MCM-41介孔分子筛的合成方法,主要包括水热合成法,室温合成法,微波合成法等,列出了每种合成方法的优缺点和合成过程中的影响因素,pH值、晶化时间、晶化温度、模板剂的种类及用量等都会对MCM-41介孔分子筛的结构和孔径产生很大影响.阐述了MCM-41介孔分子筛的改性方法,包括金属杂原子取代法,如主族金属、过渡金属、稀土金属等,有机修饰或功能化法,负载型改性法,如负载金属氧化物、无机酸、杂多酸、有机碱、金属的配合物等.最后就MCM-41介孔分子筛的应用前景做了展望.     

Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO₂/Al₂O₃ = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively. Indian Institute of Chemical technology (IICT) communication no: 020707     

Active copper species in 1-butene skeletal isomerization: comparison between copper-modified MCM-41 and beta catalysts

The role of copper was studied in the skeletal isomerization of 1-butene over copper-modified mesoporous MCM-41 molecular sieve and Beta zeolite. The Cu–H-MCM-41 and Cu–H-Beta catalysts were synthesized in our laboratory and characterized by XRD, nitrogen adsorption, X-ray fluorescence, FTIR of adsorbed pyridine and direct current plasma atomic emission spectrometry. The oxidation state of copper after oxidation and reduction in Cu–H-MCM-41 was evaluated by FTIR with probe molecules. Copper ion-exchanged and the proton forms of MCM-41 and Beta catalysts were tested towards 1-butene skeletal isomerization by varying the weight hourly space velocity and temperature. Quantum chemical calculations at the B3LYP/6-31 + G^** level were performed in order to understand the role of copper at the molecular level.

Copper in Cu–H-MCM-41 pretreated in synthetic air was mostly in the form of Cu²⁺ but reduced during the catalytic experiment to the metallic form Cu⁰ via Cu⁺. Even if the copper exchange decreased the amount of Brønsted acid sites, Cu–H-MCM-41 pretreated in synthetic air was more active than H-MCM-41 towards 1-butene skeletal isomerization. The enhanced catalytic activity is due to copper Cu⁺, which was formed during the reaction. Introduction of copper into H-Beta, however, did not have any effect at all on the performance of the catalyst. The probable reason for this is the high initial activity of copper-modified H-Beta causing a very fast reduction of copper to the inactive metallic form Cu⁰.     

介孔分子筛MCM-41改性及应用研究进展

纯硅介孔分子筛MCM-41具有稳定的骨架结构、孔道规则排列有序、孔径分布窄等优点,但其水热稳定性较差、酸性弱、孔径不够大,难以用于大分子反应。本文综述了近几年国内外介孔分子筛MCM-41改性及应用研究的新进展,尤其是扩孔改性、金属掺杂改性以及杂多酸改性等方面的最新研究。     

分子筛催化剂上催化裂化汽油掺混甲醇的改质研究

以实现甲醇制取低碳烯烃转化工艺和FCC汽油降烯烃工艺的有效组合为目的,在固定床微型反应装置上,使用SAPO-34、ZSM-5、DOCO以及分子筛组合催化剂,对FCC汽油掺混甲醇改质进行了研究。主要对反应温度、空速和混炼比等影响因素进行了考察。结果表明,SAPO-34分子筛上甲醇制取低碳烯烃效果较好,高烯烃含量汽油在SAPO-34分子筛上的氢转移和芳构化效果显著,ZSM-5分子筛上的芳构化反应效果和DOCO的异构化反应效果较显著,甲醇转化与汽油转化反应间的相互协同作用,既有利于甲醇转化成低碳烯烃又能提高汽油降烯烃转化深度。适宜的混炼条件:反应温度400℃,m(甲醇):m(汽油)=0.05,空速3h~(-1),组合催化剂上,产物汽油中烯烃含量较FCC粗汽油下降23%以上。     

介孔分子筛MCM-41—SO3H 催化木糖脱水制备糠醛的研究

采用在MCM-41分子筛上先嫁接—SH,再经氧化和酸化的方法制备了介孔分子筛固体酸催化剂MCM-41—SO3H,对催化剂进行了表征,并对其用于木糖脱水环化生成糠醛的反应进行了研究。当木糖与催化剂的质量比为0.8、反应温度为170 ℃、反应时间为4 h时,木糖的转化率为83.4%,生成糠醛的选择性为76.7%,糠醛收率为64.0%。该催化剂的优点是糠醛收率高于硫酸作催化剂时的收率;不产生酸性废水;催化剂经再生处理后能重复使用,但糠醛收率降为39.7%。     

Utilization of ZSM-5/MCM-41 composite as FCC catalyst additive for enhancing propylene yield from VGO cracking

A micro-mesoporous ZSM-5/MCM-41 composite molecular sieve (ZM13) was synthesized and tested as an FCC catalyst additive to enhance the yield of propylene from catalytic cracking of vacuum gas oil (VGO). The catalytic performance of the additive was assessed using a commercial equilibrium USY FCC catalyst (E-Cat) in a fixed-bed micro-activity test unit (MAT) at 520?°C and various catalyst/oil ratios. MCM-41, ZSM-5 and two ZSM-5/MCM-41 composites were systematically characterized by complementary techniques such as XRD, BET, FTIR and SEM. The characterization results showed that the composites contained secondary building unit with different textural properties compared to pure ZSM-5 and MCM-41. MAT results showed that the VGO cracking activity of E-Cat did not decrease by using these additives. The highest propylene yield of 12.2 wt% was achieved over steamed ZSM-5/MCM-41 composite additive (ZM13) compared with 8.6 wt% over conventional ZSM-5 additive at similar gasoline yield penalty. The enhanced production of propylene over composite additive was attributed to its mesopores that suppressed secondary and hydrogen transfer reactions and offered easier transport and accessibility to active sites. Gasoline quality was improved by the use of all additives except MCM-41, as octane rating increased by 6?C12 numbers.     

The preparation of Fe<Superscript>3+</Superscript> ion-exchanged mesopore containing ZSM-5 molecular sieves and its high catalytic activity in the hydroxylation of phenol

A series of Fe³⁺ containing catalysts were synthesized using ion-exchange technique over hierarchically porous ZSM-5 (M-ZSM-5) and micro-mesoporous composite ZSM-5/MCM-41 (ZSM-5/MCM-41), respectively. The prepared catalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, N₂ adsorption–desorption, UV–Vis spectroscopy, temperature programmed reduction and inductively coupled plasma-optical emission spectroscopy. The characterization results exhibit that the hierarchically porous ZSM-5 was synthesized with intracrystalline mesopores, while the micro-mesoporous composite ZSM-5/MCM-41 was prepared with the well-ordered mesopores. Furthermore, the results also prove that the existence of iron in the catalysts was mainly presented in the form of Fe³⁺ ions. Catalytic performances of the samples for phenol hydroxylation were compared by using H₂O₂ as oxidant. Under the optimized conditions, Fe³⁺ ion-exchanged M-ZSM-5 (Fe-M-ZSM-5) shows that a phenol conversion of 42.3% obtained with 92.5% selectivity to dihydroxybenzenes, whereas Fe³⁺ ion-exchanged ZSM-5/MCM-41 (Fe-ZSM-5/MCM-41) give 46.2% phenol conversion and 90.1% dihydroxybenzenes selectivity, which are all better than most reported results. The recyclability tests show that Fe-ZSM-5/MCM-41 with ordered mesoporous structure and bigger surface area has better anti-deactivation performance than Fe-M-ZSM-5. The excellent catalytic performances were due to the improved diffusion performance with newly created mesopores and the highly active Fe³⁺ species obtained by ion-exchange technique.