Surface P and Al Distribution in P-modified ZSM-5 Zeolites

The surface composition of two commercial ZSM-5 zeolites with and without PO₄ modification was examined by X-ray photoelectron spectroscopy. Both zeolites were slightly enriched in aluminum on the surface. The surface silica/alumina ratio (SAR) was about half of that of the bulk. Calcination at 600^∘C decreased slightly this enrichment. After drying with H₃PO₄ followed by calcination, both zeolites showed surface enrichment of PO₄. The surface of the zeolite with large crystal was more enriched. Steaming resulted in enrichment of aluminum on the surface, in agreement with migration of extra-framework alumina. Increasing phosphate content decreased this enrichment. This paper was presented in the 5th Brazilian Meeting on Adsorption, held at Natal, Brazil, 18-21 July, 2004.     

不同硅铝比ZSM-5的合成及其吸附脱除柴油中苯胺和吡啶的性能

合成了一系列不同硅铝比的ZSM-5分子筛,采用XRD、FT-IR、ICP、SEM、NH_3-TPD和N_2吸附-脱附等方法对其进行了表征,研究了不同硅铝比ZSM-5分子筛对模拟柴油中苯胺和吡啶的吸附脱除性能。结果表明,所合成的ZSM-5分子筛均具有典型MFI结构;与合成原料混合物中的硅铝比相比,实际硅铝比稍有降低。ZSM-5分子筛的酸量随硅铝比的增加而降低,硅铝比较小的ZSM-5(1)和ZSM-5(2)的吸附脱除苯胺或吡啶的效果明显优于其他样品,并且所有样品吸附脱除吡啶的效果均优于苯胺。ZSM-5(2)上苯胺和吡啶的吸附等温线符合Langmuir-Freundlich混合模型。     

Targeted Synthesis of Ultrastable High‐Silica RHO Zeolite Through Alkali Metal–Crown Ether Interaction

High‐silica RHO zeolite was directly synthesized using an alkali metal‐crown ether (AMCE) complex as organic structure‐directing agent (OSDA). Derived from the UV‐vis spectra and zeolite patterns, the crown ether‐cesium cation interaction was found to have crucial effect on the enhancement of silica content within the zeolite framework. The synthesized RHO zeolites possess up to four times larger silica/alumina ratio (SAR) values than that in their conventional form, which gives them extraordinarily rigid frameworks even after hydrothermal aging under 800 °C. Compared to commercial zeolites, copper‐exchanged high‐silica RHO zeolites demonstrate considerably high reaction activity in NO_X removal, making them promising candidates for diesel exhaust treatment.     

碱处理脱硅与提高Y型分子筛硅铝比——矛盾的对立与统一

考察了 "水热处理"以及"碱处理+水热处理"两种方法所制得的超稳 Y 分子筛的骨架硅铝比、孔结构特征以及酸量, 并探讨了"碱处理+水热处理"方法对起始 NaY 分子筛的适应性. 结果表明, 在水热处理前, 对 NaY 分子筛进行碱处理脱硅可在不改变最终样品的骨架超稳化水平和酸量的同时, 样品的介孔体积显著增加. 直接水热处理 NaY 分子筛所得样品介孔体积不超过 0.14 cm3/g, 而先碱处理后水热处理, 所得样品介孔体积可达 0.22 cm3/g. 该法适用于制备骨架硅铝比高的 NaY 分子筛. 起始原料的骨架硅铝比较低时, 所得样品的介孔体积增幅小, 而且微孔受损严重.     

Ultra-high-Silica ZSM-5 Zeolites: Synthesis and Properties

ZSM zeolites with silica ratios of 100–260 were synthesized with hexamethylenediamine (HMDA) as the structure former. IR spectroscopy and X-ray powder diffraction identified the products with ZSM-5 zeolites with more than 90% crystallinity. The unit cell parameters, specific surface area, and morphology were determined for zeolite samples. The composition of precursor alumina—silica gel was shown to influence the physicochemical characteristics of zeolites.     

Investigation of catalytic degradation of high-density polyethylene by hydrocarbon group type analysis

Catalytic degradation of waste high-density polyethylene (HDPE) to hydrocarbons by ZSM-5, zeolite-Y, mordenite and amorphous silica–alumina were carried out in a batch reactor to investigate the cracking efficiency of catalysts by analyzing the oily products including paraffins, olefins, naphthenes and aromatics with gas chromatography/mass spectrometry (GC/MS). Catalytic degradation of HDPE with zeolite-Y, mordenite and amorphous silica–alumina yielded 71–82 wt.% oil fraction, which mostly consisted of C₆–C₁₂ hydrocarbons, whereas ZSM-5 yielded much lower 35% oil fraction, which mostly consisted of C₆–C₁₂ hydrocarbons. Both all zeolites and silica–alumina increased olefin content in oil products, and ZSM-5 and zeolite-Y particularly enhanced the formation of aromatics and branched hydrocarbons. ZSM-5 among zeolites showed the greatest catalytic activity on cracking waste HDPE to light hydrocarbons, whereas mordenite produced the greatest amount of coke. Amorphous silica–alumina also showed a great activity on cracking HDPE to lighter olefins in high yield, but no activity on aromatic formation.     

The Influence of Silica to Alumina Ratio on Y Zeolite Activity by Simultaneous TG and DSC Analysis

Simultaneous TG and DSC analyses of n-butylamine adsorption/desorption were carried out over several zeolites with different degrees of dealumination. The samples used consisted of high crystalline zeolites, preparedvia steam/leaching sequential treatments, and characterized by various techniques. Catalyticactivity measured as the initial rate of cracking of 1,3,5-triisopropylbenzene did not correlate with total acidity, however, the energy required to the complete desorption of the probe molecule, determined by integration of DSC curves, correlates with the catalytic activity of zeolites with any or little extra-framework alumina content. High amounts of extra-framework alumina give significant constraint effect to acessibility to acid sites as shown by applying the Crank's method to the TG curves. This method allowed to determine the intra-crystalline diffusivity of the probe molecule, which seems to be the controlling step to the cracking reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and characterization of NaA zeolite powder/film deposited on alumina beads by dip-coating method

Linde Type A (LTA) zeolites have been synthesized in the current study by simple sol–gel technique. The crystal growth has been controlled by varying the hydrogel synthesis time and annealing temperature. The resulting products obtained at various crystallization times and temperatures have been studied using X-ray powder diffraction (XRD) method, High resolution transmission electron microscopy images, scanning electron microscopy (SEM) micrographs, energy dispersive study and Brunauer–Emmett–Teller (BET) analysis. The TEM images of the final LTA zeolite annealed at 500 °C revealed the formation of cubic structure. XRD analysis revealed that the crystallinity improved with annealing. BET analysis revealed that the synthesized LTA is a well crystallized 4A zeolite. LTA zeolites were dispersed in poly ethylene glycol in the ratio 3:100 and 5:100 and coated on porous alumina beads for the formation of membrane. The SEM images revealed excellent formation of fine structure LTA zeolite membrane with uniform coating. The membrane consisted of a top layer with thickness of 1.14–2.0 µm. Crystals in the top layer showed cubic morphology and amorphous phase was observed at the grain boundaries present between LTA zeolite and alumina substrate.     

Preparation and characterization of alumina supported silicalite membranes by sol–gel hydrothermal method

Two types of unsupported zeolites (silicalite-1 and silicalite-2) and porous alumina discs supports were prepared by the hydrothermal sol–gel synthesis method. The influence of the raw materials used as SiO₂ source, the temperature of the thermal treatment and the presence of the ceramic support on the crystallization of zeolites were studied. The reaction products were characterized by X-ray diffraction (XRD), IR spectroscopy (IR) and scanning electron microscopy (SEM) studies. The SiO₂ source had a significant effect on the final zeolite obtained: the use of colloidal silica sol (ZCS) as SiO₂ source in the synthesis led to ZSM-11 (silicalite-2) crystals, while the sodium silicate solution (ZSS) produced the ZSM-5 (silicalite-1) type. The presence of the alumina support influences the crystallization process of ZSM-5, as it improves nucleation and the ordering of the crystals.     

TMEDA-Na2O-SiO2-Al2O3-H2O系统沸石的水热结晶

在四甲基乙基二胺(TMEDA)-Na2O-SiO2-Al2O3-HO2系统中,水热反应产物的沸石相,随配料硅铝比提高,依次为Md(丝光沸石),TMEDA-Md,ZSM-35,ZSM-5,ZSM-39及一种我们称为CF-3的新沸石.从沸石的组成,性质,晶体结构与"模极分子"的构型等方面,讨论了TMEDA对诱导上述沸石的生成所起的电荷平衡与孔道充填的共同作用向笼的充填作用的转变.     

Effects of zeolites on volatile products of beech wood using analytical pyrolysis

Five unmodified basic and acidic zeolites have been tested in the thermo-chemical conversion of beech (Fagus sylvatica L.) using an on-line pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system to study their effects on lignocellulose thermal degradation products. The catalysts employed were SN-27, MSN-15, MSM-15, H-ZSM-5-28 and H-ZSM-5-80 with varying Si/Al ratio between 11 and 80. Thoroughly mixed samples of the biomass with different catalysts loading were pyrolysed at 500 °C. The catalyst exhibited varying degree of selectivity on individual volatile products. The selectivity was largely controlled by the nature of zeolites’ active sites and alumina contents. The acidic catalysts mostly influenced the condensable organic products; induced high yields of furfural and levoglucosan. Their yields increased up to five and nine times respectively in samples spiked with 40% MSM-15 and H-ZMS-5 on the basis of feedstock weight. H-ZSM-5 with lower alumina content proved most effective in enhancing high yield of furfural due to better diffusion of molecules through the pores. A slight reduction in polysaccharide derived low molecular volatiles such as hydroxyacetaldehyde, acetic acid, hydroxypropanone was observed in all catalysts. The overall result indicated that the acidic catalysts largely induced cleavage of glycosidic bonds through protonation predominantly on zeolites’ surface area. This was followed by the modification of free hydroxyl groups through dehydration process. All zeolites revealed no significant effect on most lignin derived products except indenes.     

含有乙醚的无胺无氟反应物体系中高硅丝光沸石的合成

本文研究含有乙醚的Na2O-Al2O3-SiO2-H2O反应物中高硅丝光沸石在413-453K下的水热合成。乙醚的存在能有效促进丝光沸石的结晶过程,且有助于提高产物结晶度和硅铝比。反应物胶体中硅铝比与碱度对产物的生成有关键作用。合成原料使用不同铝源,体系结晶规律相近,但产物的形貌和硅铝比有差异。在优化的反应条件下合成的高硅丝光沸石硅铝比达30左右。低温氮吸附与27Al魔角旋转核磁谱表征证实该沸石骨架结构完美,孔道开放畅通,其水热稳定性优于低硅丝光沸石。     

Hβ/MCM-41复合分子筛催化剂上苯甲醚与乙酸酐酰化反应研究

以β沸石为硅源,制备了不同硅铝比的Hβ/MCM-41复合分子筛,考察了该复合分子筛对苯甲醚与乙酸酐酰化反应的催化效果,并与介孔MCM-41、微孔Hβ分子筛的催化效果进行了比较,研究了分子筛硅铝比、酸性及孔道结构对酰化反应催化性能的影响。结果表明,对于苯甲醚和乙酸酐酰化反应,Hβ/MCM-41复合分子筛具有较好的催化稳定性,反应过程中的积炭量较少,积炭的碳氢比较低。该复合分子筛不仅具有微孔沸石的强酸性,而且具有较大孔径的介孔,产物分子能及时从孔道中扩散出来,催化活性位不易中毒失活。     

Some observations on the liquid immiscible nature of the Iron-Indium and Aluminium-Indium Systems

Hydroxide Groups on Zeolites. IV. Formation of Hydroxide Groups by Reduction of Y-Zeolites Containing Transition Metal Ions The formation of hydroxide groups as result of the reduction is studied by IR spectroscopy on NiNaY, CuNaY, and ZnNaY zeolites. After transformation of the OH groups into OD groups it was found that D₂ reduces the transition metal ions at 350°C and that simultaneously the concentrations of two types of the hydroxides groups which are already present before this treatment are increased markedly, viz. the concentration of an acid species and that of a weakly acid species. In NiNaY and CuNaY zeolites, the reduction at 350°C proceeds much more slowly than in ZnNaY zeolites. The reduction of ZnNaY zeolites is connected with their transformation to ultrastable zeolites.     

Stability of hydrogen peroxide during perhydrolysis of carboxylic acids on acidic heterogeneous catalysts

This paper describes a study of the stability of hydrogen peroxide in the presence of different aluminosilicate materials, in connection with an investigation of carboxylic acid perhydrolysis. During the reaction, aluminosilicate materials such as H-β zeolites, mesoporous material H-MCM-41 and alumina initiate the decomposition of hydrogen peroxide. The reason of the spontaneous decomposition of H₂O₂ is related to the partial dealumination of these zeolites. However, in the case of experiments carried out with H-ZSM-5 zeolite catalysts, a slight catalytic effect on the perhydrolysis and no spontaneous decomposition of hydrogen peroxide were noticed. The use of cation exchange resins as catalysts is more kinetically beneficial than H-ZSM-5 zeolite catalysts.     

Insight into the mechanisms of the ethylbenzene disproportionation: transition state shape selectivity on zeolites

The direct experimental evidence shows that ethylbenzene disproportionation is a transition state shape selective reaction on zeolites: a bimolecular reaction mechanism via diphenylethane-mediated pathway on large-pore zeolites X and Y (ca. 0.74 nm) and a monomolecular reaction mechanism on medium-pore zeolites ZSM-5 (ca. 0.56 nm) via the ethoxy-mediated intermolecular ethyl group transfer. The lifetime of bulky diphenylethane species was prolonged by a fine-tune of FAU-zeolites, which makes this transition state detectable by 13C MAS NMR spectroscopy. Due to tunable catalytic properties and pore shapes, zeolites are promising catalysts toward emulating the efficiency and selectivity in desired reactions.     

Effects of the types of zeolites on catalytic upgrading of pyrolysis wax oil

Because zeolites play an important role in an upgrading catalyst for heavy hydrocarbons in industrial refinery processes, the effects of the zeolite type on the upgrading of pyrolysis wax oil are investigated in this study. Raw pyrolysis wax oil was obtained from the pyrolysis of municipal plastic wastes in a commercial rotary kiln pyrolysis plant (Dongmyong RPF Co.). The catalystic experiments are performed for the three different types of commercial zeolites with different physicochemical properties in a continuous fixed bed reactor at 450 °C for 1 h as a MAT(micro-activity test) method: HZSM-5 (pure), zeolite Y (HY; pure or including 20% clay) and mordenite (HM; including 20% clay or alumina) catalysts. The highest conversion of pyrolysis wax oil into light hydrocarbons such as gas products and gasoline-range hydrocarbons is obtained for the HZSM-5 catalyst among them, and the composition of liquid products is found to become in the main aromatic components due to a shape selectivity. For the case of zeolite Y(HY), medium activity and the highest fraction of branched hydrocarbons with a high octane number, as well as a high fraction of aromatic products are shown. However, the mordenite (HM) with one-dimensional pore structure shows the lowest conversion of pyrolysis wax oil into light hydrocarbons and a very high fraction of paraffin product in the liquid product like the characteristics of raw pyrolysis wax oil.     

Molecular simulation of adsorption of alkanes in sodium MOR-type zeolites using a new force field

The applicability of a recently proposed force field of Calero et al. (J. Am. Chem. Soc., 2004, 126, 11377) to Na-MOR zeolites is evaluated. The Henry law coefficients of ethane and C(5)-C(9) as well as the adsorption isotherms of ethane, propane, butane, and hexane in various Na-MOR zeolites are computed and compared with experimental values. These comparisons show that the new force field is suitable for Na-MOR zeolites. Furthermore, this force field is used to study the effects of sodium cations on the adsorption behavior of larger alkanes, such as C(4)-C(7), in MOR-type zeolites. These simulations give a better understanding of the underlying mechanisms of the cations' position and density influence on adsorption. In addition, a characteristic pressure named "reversal pressure" is introduced which characterizes the efficiency of the presence of cations in zeolites.     

柠檬酸对USY分子筛的化学改性研究

在非缓冲体系下用柠檬酸对USY分子筛进行分子结构修饰,详细考察了各反应因素对分子筛改性效果的影响;并且用XRD,DTA,DTG,FT-IR,N~2静态容量吸附法等物理手段对改性分子筛样品的结构及性能进行了表征,用MAT法评价了其催化裂化反应性能和对低碳烯烃的选择性能。发现改性后分子筛硅铝比、结晶度和热稳定性显著提高,晶胞常数相应减小;具有更加发达的孔结构,尤其二次孔含量明显增多;对低碳烯烃有较高的选择性和收率,酸性质取得了与文献一致的结论。     

Analysis of the Micropore Structure of Various Microporous Materials from Nitrogen Adsorption at 77 K

The micropore structure of four microporous materials (two zeolites, ZSM-5 and Y-82; an activated carbon and an alumina pillared clay) and their binary physical mixtures (50-50 wt%) have been examined by nitrogen adsorption at 77 K. Various micropore sizes have been considered from the stages on the micropore filling mechanism in the microporous materials. The application of the Dubinin-Astakhov (DA) equation to characterize and obtain the adsorption potential distributions of the microporous materials is presented.