Atomistic simulations for adsorption and separation of flue gas in MFI zeolite and MFI/MCM-41 micro/mesoporous composite

Adsorption of pure CO₂ and N₂ and separation of CO₂/N₂ mixture in MFI zeolite and MFI/MCM-41 micro/mesoporous composite have been studied by using atomistic simulations. Fully atomistic models of MFI and MFI/MCM-41 are constructed and characterized. A bimodal pore size distribution is observed in MFI/MCM-41 from simulated small- and broad-angle X-ray diffraction patterns. The density of MFI/MCM-41 is lower than MFI, while its free volume and specific surface area are greater than MFI due to the presence of mesopores. CO₂ is preferentially adsorbed than N₂, and thus, the loading and isosteric heat of CO₂ are greater than N₂ in both MFI and MFI/MCM-41. CO₂ isotherm in MFI/MCM-41 is similar to that in MFI at low pressures, but resembles that in MCM-41 at high pressures. N₂ shows similar amount of loading in MFI, MCM-41 and MFI/MCM-41. The selectivity of CO₂ over N₂ in the three adsorbents decreases in the order of MFI>MFI/MCM-41>MCM-41. With increasing pressure, the selectivity increases in MFI and MFI/MCM-41, but decreases in MCM-41. The self-diffusivity of CO₂ and N₂ in MFI decreases as loading increases, while in MFI/MCM-41, it first increases and then drops.     

VPT法制备MCM-22分子筛催化剂颗粒及其烷基化性能

采用汽相法（VPT）制备了以成型干胶颗粒为基体的MCM-22分子筛催化剂.利用XRD、SEM和BET测试技术对所制备催化剂进行了物相表征、形貌观察和织构分析,并以苯和丙烯烷基化合成异丙苯为模型反应,在液-固固定床反应器上对所制备催化剂的性能进行了评价.结果表明：汽相法制备的MCM-22分子筛催化剂不仅具有较好的结晶度和较高的微孔表面积,而且具有更好的晶体生长取向性和更加致密的结构;在烷基化反应中也具有很好的活性、选择性和稳定性,特别是对目的产物异丙苯的选择性明显高于水热法（HTS）合成的催化剂,在异丙苯合成上具有很好的应用前景.     

Catalysis of Zeolite in the Amidation of Alcohols with Nitriles for the Synthesis of N-Alkylacrylamides

The catalytic applicability of zeolites in the Ritter reaction of acrylnitrile (AN) with various alcohols for the synthesis of N-alkylacrylamide was studied. In terms of the maximum amide selectivity, the optimum zeolite structure was FAU for the reaction of AN with tertiary alcohol and MFI for that with secondary alcohols. A reaction scheme involving nucleophilic substitution of carbocation intermediates is proposed. It was suggested that the Ritter reaction is acidity demanding, hydrophobicity favorable and pore size sensitive. Accordingly, amide product selectivity and yield can be improved by using zeolites with strong acidity, or with mesopores generated by base treatment, enhancing hydrophobicity by tuning appropriate silica/alumina ratio or by silica vapor deposition. Base post treatment can promote amide product selectivity effectively.     

Synthesis, characterization, and catalytic properties of a hydrothermally stable Beta/MCM-41 composite from well-crystallized zeolite Beta

A Beta/MCM-41 composite has been synthesized with a new method by using well-crystallized zeolite Beta as silica and aluminum source. The prepared composite was characterized by XRD, FTIR, N₂ adsorption/desorption at 77 K, FE-SEM, DTG, ²⁹Si MAS NMR spectral techniques. It was shown that the composite consisted of a highly ordered mesoporous MCM-41 phase and a zeolite Beta phase. Its hexagonal mesoporous structure was still retained after statically treated for 120 h in boiling water. In contrast, the structure of generally synthesized Al-MCM-41 nearly completely collapsed. This might be attributed to the assembly of the dissolved fragments such as the first and/or secondary structural units of zeolite Beta into the mesoporous structure around surfactant micelles. This is supported by the catalytic result that the prepared composite showed higher activity and selectivity for medium fraction in hydrocracking of Daqing vacuum residue than the parent zeolite Beta, the Al-MCM-41 as well as the mechanical mixture of these two materials.     

Impact of accessibility and acidity on novel molecular sieves for catalytic cracking of hydrocarbons

The catalytic properties of extra-large pore aluminosilicate MCM-41, silicon containing VPI-5 and aluminium containing ETS-10 were investigated by MAT (Micro Activity Test) using n-hexadecane and 1,3,5-triisopropylbenzene as the model feeds and were then compared with the results obtained from Y zeolite in the H-form and a commercial FCC (Fluid Catalytic Cracking) catalyst. It could be demonstrated that not only the acidic properties of the investigated materials, but also the accessibility to the internal active sites of the investigated materials have a significant influence on activity and selectivity. It can be assumed that, by optimising structural and chemical properties, the mesoporously organised MCM-41 and related materials are suitable as active components in cracking catalysts for “deeper” cracking of high boiling hydrocarbons.     

Preparation and characterization of Beta/MCM-41composite zeolite with a stepwise-distributed pore structure

A Beta/MCM-41 composite zeolite with a stepwise-distributed pore structure was prepared with a silica-alumina source originated from alkaline treatment of zeolite Beta. The material was characterized by various techniques. The results indicated that this composite possesses a mesopore system of MCM-41 and the microporous structure of Beta zeolite. Hydrothermal stability and acidity was improved over MCM-41 due to the introduction of Beta building units into the mesopore walls. The composite was used as the support of a Pd-Pt catalyst for the hydrogenation of naphthalene in the presence and absence of 4, 6-dimethyldibenzothiophene. It was demonstrated that the catalyst has an enhanced activity and sulfur tolerance during naphthalene hydrogenation.     

Comparative Study of the Acidic and Catalytic Properties of the Mesoporous Material H-MCM-41 and Zeolite H-Y

The objective of this work is to give a comparative characterization of aluminosilicate MCM-41 and zeolite Y, in particular with respect to acidity and catalytic properties in hydrocarbon cracking. These studies are compared to a well investigated amorphous aluminosilicate, based on the fact that the new mesoporous MCM-41 materials are a mixture of ordered material with amorphous pore walls. Characterization of differently treated MCM-41 materials and zeolite Y for comparison by N₂ sorption, XRD, TPAD (Temperature Programmed Ammonia Desorption) with in situ FT-IR in combination with catalytic testing by MAT (Micro Activity Test) is discussed. Combination of the characterization data and the catalytic testing gives an interesting explanation of the surface properties especially in comparison with zeolite Y.     

Co掺杂对Ce/MCM-41和Ce/SBA-15催化剂催化氧化甲苯性能的影响

以分子筛为载体,采用等体积浸渍法制备Ce/SBA-15、Ce/MCM-41、Ce Co/SBA-15和Ce Co/MCM-41催化剂。用N2吸附-脱附、X射线衍射、扫描电子显微镜、H2程序升温还原、X射线光电子能谱和傅立叶变换红外光谱等对载体和催化剂进行表征,并考察催化剂催化氧化甲苯的活性。结果表明,与载体相比,随着Ce和Co的浸渍,催化剂的比表面积和孔容下降,但仍然保持了载体的有序介孔结构。引入的Ce和Co没有进入分子筛骨架,而是以立方相固溶体形式存在于分子筛表面和孔道中。催化剂催化氧化甲苯活性顺序依次为:Ce Co/SBA-15>Ce Co/MCM-41>Ce/MCM-41>Ce/SBA-15。共浸渍Ce和Co的催化剂活性明显优于只浸渍Ce的催化剂,活性与其还原性能直接相关,Ce Co/SBA-15催化剂具有最低的还原温度和最好的供氧能力,从而表现出最优的催化性能。     

Esterification of bioplatform molecules over 12-tungstophosphoric acid anchored to MCM-41

The catalytic conversion of bio-platform molecules into desired products can be an important unit for the future biorefinery. The present contribution consists of synthesis of solid acid catalyst comprising 20 % 12-tungstophosphoric acid (TPA) and MCM-41 and its characterization by various physico-chemical techniques such as fourier transform infrared, X-ray diffraction surface area measurement (BET method), transmission electron microscopy and total acidity. The use of synthesized catalyst was explored for esterification of bio-platform molecules such as succinic acid and malonic acid with different alcohols. The catalyst shows high activity in terms of higher yields towards all diesters. The product selectivity towards the mono and diester was found to be the same for TPA alone and supported system, TPA₂/MCM-41, that also confirms the uniform distribution of the TPA on MCM-41. The excellent catalytic performance is attributed to the large surface area and pore diameter of the mesoporous support, MCM-41 as well as the Bronsted acid strength of TPA, as active sites. The catalyst shows the potential of being used as a recyclable catalytic material after simple regeneration without significant loss in activity.     

Pd-β/MCM-41复合分子筛加氢裂解废食用油性能研究

以碱处理β沸石作为硅铝源,以CTAB为模板剂,合成了β/MCM-41介孔-微孔复合分子筛,以其为载体制备Pd-β/MCM-41复合分子筛催化剂,利用XRD、N₂吸附-脱附、NH₃-TPD和XRF等技术对其进行了表征,并与γ-Al₂O₃、USY、ZSM-5等载体制备的催化剂比较了废食用油加氢裂解活性。结果表明：β/MCM-41复合分子筛同时具备β沸石和MCM-41分子筛的结构,β/MCM-41为载体时,Pd-β/MCM-41催化剂具有适宜的中强酸性中心,适宜的孔道分布结构,催化剂加氢裂解废食用油的活性最高。此外还考察了催化剂制备条件对废食用油加氢裂解反应的影响,结果表明：采用离子交换法制备负载量2%的Pd-β/MCM-41复合分子筛催化剂、焙烧温度为500 ℃时,催化剂对废食用油加氢裂解的效果最好。此时,原料油的转化率可以达到85.9%,生物汽油的收率可以达到16.4%,生物柴油的收率达到17.8%,且此催化剂水热稳定性较好,再生性能良好,工业化应用前景较好。     

Preparation of mesoporous MCM-41 from natural sepiolite and its catalytic activity of cracking waste polystyrene plastics

Mesoporous MCM-41 was prepared by leaching of sepiolite and sequent hydrothermal synthesis in NaOH solution with hexadecyltrimethylammonium bromide as template. Small-angle X-ray diffraction patterns, Scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller were performed to characterize the resulting compounds. The results showed that the crystallinity and pore size of MCM-41 increased with increase of crystallization time, ratios of surfactant to SiO₂ and decrease of Mg content. The experimental results of catalytic cracking of polystyrene waste showed that the MCM-41 with MgO from natural sepiolite had high catalytic activity and good selectivity to monomer styrene for the catalytic cracking of polystyrene when the ratio of waste plastics to MCM-41 was 200. The side reactions yielded ethylbenzene, isopropylbenzene, isopropenylbenzene and secondary cross-linking were suppressed by basic species MgO in MCM-41.     

Transformation of ethylbenzene–m-xylene mixture on zeolites with different structures

Hierarchical zeolite ZSM-5 synthesized by applying amphiphilic organosilane as mesopore template, nanosized zeolite Beta and zeolite MCM-22 have been studied, for the first time in the conversion of mixed ethylbenzene–m-xylene feed. The effects of the channel structure, nanosizing and presence of mesopores in these zeolite materials with close Si/Al molar ratio on the catalytic activity and selectivity have been discussed. It was found that the diverse zeolites have different advantages and disadvantages in dependence on their structure and morphology. MCM-22 zeolite provides promising ethylbenzene conversion at low xylene loss with high production of the p-isomer among xylene.     

13X微孔沸石和MCM-41介孔材料的合成及用于处理含Cd2+废水

以天津蓟县钾长石矿粉为主要原料,经选矿、煅烧、水热处理等工艺成功合成了13X微孔沸石. 以气相氧化硅、氢氧化钠、十六烷基三甲基溴化铵等为主要原料,在水热条件下合成了MCM-41有序介孔材料. 采用XRD和N2吸附-脱附等手段对合成的13X沸石和MCM-41介孔材料的物相、比表面积、孔径、孔体积等进行了分析对比. 在此基础上,对13X沸石和MCM-41介孔材料处理含Cd2+废水的效果和机理进行了对比研究,确定了不同分子筛用量、不同初始pH值、不同混合时间下13X沸石和MCM-41介孔分子筛对水中Cd2+的吸附率和吸附量. 研究发现,尽管MCM-41的比表面积和孔径远大于13X沸石,但其对水中Cd2+的处理效果却低于13X沸石,这与13X沸石和MCM-41的孔道结构类型、化学组成、表面荷电性质等有关.     

Structural and catalytic properties of Ti–MCM-41 synthesised at room temperature up to high Ti content

A study of the pore structural properties and catalytic activity of MCM-41 containing titanium, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium alcoxides, cationic surfactants and ammonia is presented. The influence of different metal sources (titanium ethoxide, isopropoxide or n-butoxide), alcohols (ethanol or propan-2-ol), metal content (2  Si/Ti  100) and surfactants (tetra-, hexa- or octadecyltrimethylammonium bromide) is considered. The materials were characterised by X-ray diffraction, nitrogen adsorption at 77 K and diffuse reflectance UV–Vis spectroscopy. The catalytic activity was evaluated in the model reaction of oxidation of cyclohexene with anhydrous tert-butylhydroperoxide, for representative samples. It is concluded that this method allows the preparation in a short period of time of well structured and catalytically active Ti–MCM-41. Down to Si/Ti = 10 the materials have high pore volumes and very uniform pore size, with highest conversion and excellent selectivity demonstrated in the compositional range 30  Si/Ti  100, corresponding to materials containing predominantly isolated and tetracoordinated Ti. The increase in Ti content to Si/Ti ratios of 10 and 5 implied a reduction both in conversion and selectivity, although the MCM-41 structure was still observed for Si/Ti = 2.     

Skeletal isomerization of 1-butene over ferrierite and ZSM-5 zeolites: influence of zeolite acidity

Three ferrierite (FER) and five ZSM-5 (MFI) zeolites with SiO₂Al₂O₃ ratio ranging from 27 to 2000 are tested as catalysts for the skeletal isomerization of 1-butene at 350–450°C and atmospheric total pressure in order to study the influence of acidity and pore structure of zeolite on conversion and selectivity. The catalytic and NH₃ temperature-programmed desorption results from FER and MFI catalysts with the same SiO₂/Al₂O₃ ratio reveal that the pore structure of FER zeolite rather than its acidity may play an important role in achieving high selectivity for the skeletal isomerization of 1-butene to isobutene.     

PEG2000对MCM-22分子筛结构特性和催化性能的影响

以六亚甲基亚胺为模板剂,在动态水热合成MCM-22分子筛的过程中,加入有机辅助剂聚乙二醇2000(PEG2000),考察有机辅助剂PEG2000对MCM-22分子筛结构、酸性以及催化性能的影响。由X射线衍射谱图可以看出,合成时加入适量的PEG2000,可以得到结晶较好的MCM-22晶体,但结晶度稍微有些降低。由氮吸附脱附测试结果可以看出,适量助剂PEG2000的加入,改变了分子筛的最可几孔径分布,最可几孔径由0.556 nm提高至0.587 nm,孔容由0.35 m3/g增加到0.59 m3/g,BET比表面积由410 m2/g增加到456 m2/g。NH3-TPD方法测试样品的酸性结果显示,加入适量的PEG2000后,分子筛的强酸位得到加强。另外用合成的分子筛作为催化剂,以苯与丙烯烷基化为模型反应,考察了MCM-22分子筛的活性以及选择性,结果显示催化剂的活性有较大提高,然而对异丙苯的初始选择性降低,随着反应的进行,异丙苯的选择性却很快地增长。     

Chemical Stability of Ti-Modified MCM-41 Catalysts in the Hydroxylation of Benzene in the Liquid Phase

Ti-substituted MCM-41 and Ti-grafted MCM-41 materials possessing both well-ordered long-range and pore structures have been used as catalysts for the hydroxylation of benzene in the liquid phase. The stability of the catalytic performance and the changes in the structural characteristics of Ti-modified MCM-41 resulting from the hydroxylation reaction have been investigated. It has been found that Ti-grafted MCM-41 exhibits better stability of catalytic performance than Ti-substituted MCM-41. For the Ti-substituted MCM-41, the migration of framework Ti into non-framework sites results in a decrease in the catalytic performance and the partial collapse of the pore structure. For the Ti-grafted MCM-41, the hydroxylation of benzene induces a smaller decrease in the pore volume and specific surface area than that observed for Ti-substituted MCM-41.     

Catalytic Activity of Cobalt Containing MCM-41 and HMS in Liquid Phase Oxidation of Diphenylmethane

Cobalt containing MCM-41 and HMS were synthesized by direct hydrothermal (DHT) and post synthesis methods (grafting and immobilization). The catalytic activity of these materials was investigated in the liquid phase oxidation of diphenylmethane at 80 °C with TBHP (70 wt%) as oxidant. Comparative study of cobalt containing MCM-41 and HMS was carried out to reveal the catalytic performance of framework, extraframework and immobilized cobalt species. The role of the solvent in the performance of catalyst was examined with different polar and non polar solvents. Oxidation of diphenylmethane in solvent free media (under similar reaction conditions) shows formation of hydroxy derivatives of benzophenone in addition to main product (benzophenone). Hundred percent selectivity to benzophenone was obtained when the reaction was carried out in solvent.     

Self-Bonded Zeolite Beta/MCM-41 Composite Spheres

Self-bonded zeolite Beta/MCM-41 composite spheres were prepared using a two-step synthesis procedure. In the first step, mesoporous zeolite Beta spheres were obtained using anion exchange resin as macrotemplate. In the second step, the MCM-41 or Al-MCM-41 was grown both on sphere surfaces and in the pore structure of the pre-formed zeolite Beta spheres. Finally, the templating agents used in the synthesis of mesophase were removed by calcination leaving behind self-bonded Beta/MCM-41 composite spheres. Beta/MCM-41 composites were characterized by XRD, SEM and nitrogen adsorption measurements. Materials with controlled macroshape, composition and complex porosity were prepared by the approach.     

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.