Gaseous ozone decomposition over high silica zeolitic frameworks

For several decades, it has been known that ozone emissions are harmful to humans, plants, and animals. Heterogeneous catalytic decomposition is an efficient process for removing ozone from air. This study examines the effect of the zeolite's framework and pore width on efficiency for decomposing gaseous ozone. Four highly hydrophobic zeolites are used: a large cavity zeolite (Faujasite/H‐FAU), a medium pore zeolite with parallel channel (Mordenite/H‐MOR), and two medium pore zeolites with interconnected channels (H‐ZSM‐5/H‐MFI and Na‐ZSM‐5/Na‐MFI). Experiments were conducted in fixed‐bed flow reactors loaded with zeolite at ambient conditions (20 °C and 101 kPa). Zeolite surfaces were analyzed during the experiments in order to understand the influence of physical and chemical surface properties on the ozone decomposition mechanism. A higher amount of ozone is eliminated using H‐MOR, compared with the zeolite samples H‐FAU, H‐MFI, and Na‐MFI. Pore width and micropore framework size distribution (channel and cages) appear to be key factors. A narrow channel or cage, slightly larger than the ozone molecule size, seems to promote ozone interactions with Lewis acid sites. Fourier transform infrared spectroscopy shows that Lewis acid sites (LAS), located on the walls of zeolite pores, decompose ozone. This leads to the formation of atomic oxygen species that could react with another ozone molecule to form dioxygen. Hence, LAS are regenerated, ready to decompose another ozone molecule once more.

     

Hexane Isomerization over Hierarchical Pt/MFI Zeolite

The contribution focuses on the pore structure of mesoporous MFI and its catalytic properties in hexane isomerization. Base post treatment creates defected pore channels in MFI structure, thus enhances catalytic activity and unprecedentedly high dimethylbutane (DMB) yield far beyond shape selectivity restrictions. On the other hand, re-crystallization post synthesis method forms a MFI/MCM-41 composite with MFI zeolite aggregates homogeneously supported inside MCM-41 channel and has the same global activity as MFI zeolite but having higher 23DMB product selectivity. The pore structures of both post treated MFI zeolite are elucidated from the changes in the product selectivity and sorption measurements.     

t-Butylation of 1,2-dihydroxybenzene over acidic zeolites

t-Butylation of 1,2-dihydroxybenzene (DHB) with isobutene as alkylating agent was carried out over various acidic zeolites such as USH-Y, H-beta, and H-ZSM-5. USH-Y zeolite exhibits the highest catalytic activity and considerable selectivity of 4-t-butylcatechol (4-TBC). The selectivity of 4-TBC is increased in the order of H-ZSM-5>USH-YH-beta. 3-t-Butylcatechol (3-TBC) is well produced over catalyst with high SiO₂/Al₂O₃ ratio and large pore aperture. 3,5-Di-t-butylcatechol (3,5-DTBC) selectivity is maximum in zeolite which contains strong acidity and large pore channel. The influences of various reaction parameters such as reaction temperature, space velocity, reactant molar ratio are discussed. In order to improve 4-TBC formation and decrease in 3,5-DTBC selectivity simultaneously, USH-Y zeolite was silylated by tetraethylorthosilicate (TEOS) resulting in the decrease of 3,5-DTBC selectivity over modified catalysts by about 25%. USH-Y zeolite shows high stability in the t-butylation for at least 350 h. The coke formed during the reaction was identified by FT-IR and the USH-Y zeolite could be regenerated through oxidative thermal treatment.     

复合分子筛的发展现状

复合材料通过将几种单一材料性能上互相取长补短,产生良好的协同效应和催化性能,使其综合性能优于原组成材料。这种具有多重结构和叠加功能的分子筛可以避免单一孔结构的缺陷,多级孔道体系能同时提供尺寸不同的孔道,对解决传质等问题将会有很大帮助,而被广泛使用。通过合成方法、影响因素、表征技术和催化性能评价等几个方面详细地介绍了复合分子筛,并进行了展望。     

Disproportionation and Methylation of Toluene with Methanol Over Zeolite Catalysts

Zeolites TNU-9, SSZ-33, mordenite (MOR) and ZSM-5 were evaluated for their activities in toluene disproportionation and methylation reaction of toluene with methanol. The medium-pore zeolite TNU-9 was found to possess the highest conversion in toluene disproportionation as compared with SSZ-33, mordenite and ZSM-5 based catalyst. Zeolite mordenite with the highest Si/Al ratio of 135.9 (the lowest concentration of active sites) exhibited the highest toluene conversion and maximum xylene yield in toluene methylation. On mordenite, the presence of channel intersections allows more reaction space for the formation of bulky intermediates and/or products and the 12-ring channels on the other hand, allow diffusion without trapping, since the channel diameter is large enough. In toluene methylation, xylene selectivity at the same conversion level follows the order: ZSM-5 > TNU-9 > MOR > SSZ-33, which implies that xylene selectivity is directly related to the size of channels from medium to large pore zeolites. The medium-pore zeolite ZSM-5, with 10-ring channels, shows the lowest reactivity for further alkylation of xylene, while mordenite with 12-ring channel shows the highest reactivity for further alkylation of xylene.     

Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan

Pozzolanic activity of clinoptilolite, the most common natural zeolite mineral, was studied in comparison to silica fume, fly ash and a non-zeolitic natural pozzolan. Chemical, mineralogical and physical characterizations of the materials were considered in comparative evaluations. Pozzolanic activity of the natural zeolite was evaluated with various test methods including electrical conductivity of lime-pozzolan suspensions; and free lime content, compressive strength and pore size distribution of hardened lime-pozzolan pastes. The results showed that the clinoptilolite possessed a high lime-pozzolan reactivity that was comparable to silica fume and was higher than fly ash and a non-zeolitic natural pozzolan. The high reactivity of the clinoptilolite is attributable to its specific surface area and reactive SiO₂ content. Relatively poor strength contribution of clinoptilolite in spite of high pozzolanic activity can be attributable to larger pore size distribution of the hardened zeolite-lime product compared to the lime-fly ash system.     

分子筛疏水改性对CO2吸收强化的影响

Two methods of the modification of zeolite were employed:framework element modification and surface coating,and the influence of the zeolites before and after modification on the CO₂ absorption was investigated.It was found that although hydrophobicity of zeolite could be obtained by means of the surficial organic coating in the method of surface coating modification,partial channel of zeolite would be plugged,as a result,leading to the surface area reducing greatly.Distinctively,the framework element modification method could maintain not only complete lattice structure and adsorption capability of zeolite,but would also obtain a good hydrophobic property.Consequently,significant enhancement on gas absorption by this modified zeolite was achieved and up to a maxi-mum enhancement factor of 2.62.This shows that the solid particles with good enhancement role to gas absorption need not only good adsorptive capability but also certain hydrophobicity.An unsteady heterogeneous model was employed to predict enhancement factor and the calculated results agree well with the experimental data.     

Design of Optimum Zeolite Pore System for Central Hydrocracking of Long-Chain <Emphasis Type="Italic">n</Emphasis>-Alkanes based on a Single-Event Microkinetic Model

Model based catalyst design is an emerging methodology in the development of new catalytic materials with properties tailored to the needs of specific industrial applications. A Single-Event MicroKinetic model (SEMK) was used to assess the hydrocracking behavior of n-dodecane, 4,4,6-trimethyl nonane and 2,5,8-trimethyl nonane, on a non-selective USY zeolite. The differences in cracking pattern exhibited by the various feed molecules provide guidelines for the control of the cracked product distribution through modifications of the zeolite pore structure. The connection of ZSM-22 type channels to the zeolite Y super cage is considered in this work. The percentage of C₆ products obtained by central cracking in the chain can be increased from 25% up to 93% by the design of an appropriate zeolite topology combining USY-like super cages with ZSM-22 like channel segments. This is a promising approach for the development of zeolite catalysts for the selective hydrocracking of Fischer Tropsch waxes into middle distillates.     

负载金属沸石去除水中污染物的研究进展

近年来,沸石在污水处理领域得到了广泛的应用.但由于沸石的孔径小,通道易堵塞,对污染物的去除效果不理想,其吸附能力往往达不到要求.为了进一步提高沸石的离子交换、吸附等性能,从而提高对水中污染物的去除效率,须对沸石进行处理.简述了Fe、Mn、Cu、Ag、Ce、Al、La、Zn、Na和Ti 10种金属在天然沸石上的负载方法,...     

沸石补强硅酮建筑密封胶的应用

考察了用沸石和焙烧沸石作为补强剂用于制备硅酮建筑密封胶的工艺过程,分析了粉体用量对密封胶热稳定性、拉伸强度、断裂伸长率、干燥时间的影响;用扫描电镜(SEM)、X射线衍射(XRD)、氮气吸-脱附等温测试(BET)和脱附孔径测试(BJH)方法对沸石和焙烧沸石的微观形貌、物相、比表面积、孔容和孔径进行了表征;研究结果表明,它们是一种具有多孔结构的铝硅酸盐矿物,主要成分分别为KNa2Ca2(Si29Al7)O72和K(Si3Al)O8,孔径分别为10.68 nm和14.02 nm,孔体积分别为0.465 5 mL/g和0.587 1 mL/g,比表面积分别为153.6 m2/g和191.4 m2/g,孔径分布宽、孔体积和比表面积大有利于补强,焙烧沸石的补强性优于沸石,揭示了它们的补强作用是硅烷偶联剂表面改性、孔道效应和锚固效应共同作用的结果。     

沸石补强硅酮建筑密封胶的应用研究

详述了用沸石和焙烧沸石作为补强剂用于制备硅酮建筑密封胶的工艺过程,分析了粉体用量对密封胶热稳定性、拉伸强度、断裂伸长率、干燥时间的影响;用扫描电镜（SEM）、X射线衍射（XRD）、氮气吸附—脱附等温测试（BET）和脱附孔径测试（BJH）方法对沸石和焙烧沸石的微观形貌、物相、比表面积、孔容和孔径进行了表征;研究结果表明它们是一种具有多孔结构的铝硅酸盐矿物,主要成分KNa2Ca2(Si29Al7)O72和K(Si3Al)O8,孔径分别为10nm和14nm,孔体积0.4655cc/g和0.5871cc/g,比表面积153.6m2/g和191.4m2/g,孔径分布宽、孔体积和比表面积大有利于补强,焙烧沸石的补强性优于沸石,揭示了它们的补强作用是硅烷偶联剂表面改性、孔道效应和锚固效应共同作用的结果。     

Enhancement of the photocatalytic reactivity of TiO2 nano-particles by a simple mechanical blending with hydrophobic mordenite (MOR) zeolite

The photocatalytic oxidation of gaseous acetaldehyde with O₂ on commercial TiO₂ nano-particles could be successfully enhanced by a simple mechanical blending with a high-silica mordenite (MOR) zeolite, the surface of which showed high hydrophobic properties. When the TiO₂ nano-particles of ca. 5–20 wt% were mixed with the MOR zeolite powders in an agate mortar for only 5 min, the blended TiO₂/MOR samples showed higher photocatalytic reactivity as compared to the pure TiO₂ nano-particles. Since the high-silica zeolite powders are highly transparent in UV light regions, the incident UV light is effectively irradiated onto the whole part of the TiO₂ nano-particles without any loss of light intensity. Furthermore, the siliceous MOR zeolite powders effectively adsorb the gaseous acetaldehyde molecules and supply them onto the surfaces of the blended TiO₂ nano-particles, resulting in an enhancement of the photocatalytic reactivity.     

Zeolite Beta with hierarchical porosity prepared from organofunctionalized seeds

Beta zeolite with hierarchical porosity has been obtained by a new synthesis strategy, based on perturbing the growth of the zeolite crystals by functionalization of the zeolitic seeds with organosilanes in order to hinder and prevent their further aggregation and agglomeration. As a consequence, a secondary porosity in the supermicropore region has been generated in zeolite Beta, leading to a considerable increase in both the total surface area and the pore volume of the material. The enhancement of the textural properties can be controlled by changing the silanization agent molecular size and its quantity added to the synthesis medium. This type of hierarchical Beta zeolites presents interesting applications as catalysts in reactions involving bulky molecules. Thus, their catalytic activity in the catalytic cracking of LDPE has been found to be strongly enhanced compared to a standard Beta zeolite sample, due to the higher accessibility to the acid sites caused by the presence of the secondary porosity.     

Mathematical modelling of diffusion and reaction in blocked zeolite catalysts

A mathematical model for diffusion and reaction in blocked zeolites is developed which takes into account nonidealities arising from interaction between sorbed molecules as well as the effect of pore and surface blocking. The model combines a microscopic approach, in which expressions for chemical potential and diffusive fluxes are calculated within the lattice-gas framework, with the more traditional continuum approach which takes into account the effect of surface blocking. The effect of pore blocking on the diffusive fluxes in accounted for through an effective medium approximation. The effects of crystal size and blocking on the activity-selectivity characteristics of the crystal are illustrated through an example that is qualitatively similar to industrially important reactions such as alkylation of toluene in blocked ZSM-5 zeolite.     

Y型分子筛应用于双环芳烃加氢裂化多产轻芳烃过程研究进展

催化柴油富含双环芳烃,可通过加氢裂化过程选择性多产高价值轻质芳烃（BTX）产物,现有研究已对此过程所需的工艺条件和催化剂性质进行了大量考察。工业应用中催化剂的酸性组分以Y型分子筛为主,研究分子筛性质和反应结果的关系成为重点内容。本文主要介绍了双环芳烃多产BTX产物经历加氢饱和、开环、断侧链等主要反应过程,金属组分及其与分子筛的协同作用;总结了Y型分子筛的性质如孔道性质、小晶粒、酸性质、核壳结构等因素对上述反应过程的影响。初步表明分子筛孔性质、酸性质直接影响目标反应选择性,通过对分子筛性质进行调变,可以达到促进反应物有效转化及提高BTX产物收率的目的。     

Seed-assisted, OSDA-free synthesis of MTW-type zeolite and “Green MTW” from sodium aluminosilicate gel systems

Recently, the seed-assisted methods have provided a new route for the organic structure-directing agent (OSDA)-free synthesis of industrially useful zeolites under environmentally-friendly conditions. In this paper, the various parameters are investigated in the OSDA-free synthesis of MTW-type zeolite by the hydrothermal treatment of sodium aluminosilicate gel with the aid of calcined ZSM-12 seed crystals prepared using tetraethylammonium hydroxide (TEAOH). More importantly, the green production of MTW-type zeolite referred as “Green MTW” is achieved for the first time, by using the product of OSDA-free synthesis as seeds. The X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and solid-state ²⁷Al MAS NMR results exhibit better crystallinity of MTW-type zeolite and Green MTW than those of calcined ZSM-12 seeds. MTW-type zeolite is not obtained when seeds are absent in the initial reactant gel while ZSM-5 (MFI-type zeolite) and/or mordenite (MOR-type zeolite) are formed. The results of thermogravimetric (TG) analysis of hydrated samples confirm the enough micropore volume in MTW-type zeolite whereas nitrogen adsorption-desorption measurements of MTW-type zeolite and Green MTW show nitrogen adsorption capacity lower than that of the seeds, which might be attributed to the partial pore blocking in the one-dimensional channel systems of the MTW framework.     

Molecule sieving catalysts for NO reduction with hydrocarbons in exhaust of lean burn gasoline and diesel engines

NO oxidation catalysts with small pores and low hydrocarbon oxidation activity owing to molecular sieving were prepared by dispersing platinum in the pores of ferrierite and chabazite zeolites. These small pore platinum zeolite crystals were physically mixed with large pore silver mordenite zeolite crystals and evaluated as HC-SCR catalysts for selective catalytic reduction of NO in a synthetic gas mixture doped with octane or isooctane, mimicking exhaust from lean burning engines with unburned hydrocarbons. A synergetic effect on N₂ formation and hydrocarbon efficiency was obtained in these physical zeolite mixtures. In the pores of the small pore zeolite where the diffusion of NO, O₂ and NO₂ molecules with small kinetic diameters was rapid, NO was effectively oxidized by the platinum into NO₂, while the small window apertures suppressed the diffusion and reaction of the hydrocarbon. The silver plated large pore zeolite catalyzed the reaction between the NO₂ formed in the small pore zeolite and the hydrocarbon. The importance of molecular sieving was demonstrated in experiments with permutation of pore sizes and catalytic functions.     

多级孔沸石分子筛的制备及其催化应用研究进展

多级孔沸石分子筛在保留了微孔沸石优异的催化活性与择形性的同时,能够从本质上大幅提升沸石分子筛的传质与扩散效率,改善催化剂因积炭问题失活较快的弊端。本文介绍了当前阶段多级孔沸石分子筛的研究现状,主要基于孔径大小的差异,重点综述了微孔-介孔、微孔-大孔以及微孔-介孔-大孔三类具有多级孔道结构的沸石分子筛在制备及催化应用方面的最新研究进展,综合分析了各种制备方法在性能、成本、可操作性及应用上的利弊关系,并且指出,设计并可控地制备出具有多级孔道结构且在三维空间高度贯通的多级孔沸石分子筛材料以最大限度地提高催化效率,将会是未来多级孔沸石分子筛领域的研究重点。     

The effect of acid treatment on the reactivity of natural zeolites used as supplementary cementitious materials

This work investigated the use of acid treatment as a method for increasing the reactivity of natural zeolite used as a supplementary cementitious material. The effects of treating a natural clinoptilolite zeolite with nine acid solutions, 0.1 M, 0.5 M, or 1 M hydrochloric or nitric acid or 0.1 M, 0.5 M, or 0.87 M acetic acid, were measured using x-ray diffraction, particle size analysis, pore size distribution and surface area analysis. The zeolite pozzolanic reactivity was determined by measuring the quantity of portlandite in hydrated zeolite-cement paste after 28 and 90 days. Results showed that acid treatment increased zeolite surface area, resulting in increased zeolite pozzolanic reactivity, independent of the solution concentration used. Cement hydration was also increased, evidenced by greater rates of heat evolution from cement-zeolite pastes. Additionally, although reductions of portlandite occurred most quickly in pastes with zeolites treated with strong acids, by 90 days the zeolites treated with acetic acid solutions showed comparable portlandite reductions.