In Situ Delamination of Ferrierite Zeolite and its Performance in the Catalytic Cracking of C4 Hydrocarbons

Ferrierite (FER) zeolites were synthesized by solid transformation at different alkalinities (OH⁻/Al₂O₃ molar ratios). The in situ delamination of FER zeolites were achieved and their catalytic performances in the catalytic cracking of C₄ hydrocarbons were examined. The relationships among the OH⁻/Al₂O₃ molar ratio, FER structure, composition, surface acidity and catalytic performance in C₄ hydrocarbon cracking were investigated. The results of X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, N₂ adsorption, NH₃ temperature-programmed desorption and catalytic cracking showed that with increasing OH⁻/Al₂O₃ molar ratio in the synthesis gel, the SiO₂/Al₂O₃ molar ratio of the as-synthesized FER zeolite decreased, the amount of acid sites in the corresponding H-FER increased, and the acid strength weakened. Additionally, the FER zeolite was delaminated at the mesoscale. H-FER5 synthesized at the highest alkalinity had the largest number of acid sites and exhibited the highest catalytic activity in C₄ hydrocarbon catalytic cracking among three of the prepared catalysts. H-FER3 synthesized at the second-highest alkalinity showed that the highest yield of benzene and toluene because of the secondary pores resulted from the gaps between the layers, which were beneficial to the diffusion and formation of large molecules.     

Characterization of Pd catalysts supported on USY zeolites with different SiO2/Al2O3 ratios for the hydrogenation of naphthalene in the presence of benzothiophene

A series of ultra-stable Y-type (USY) zeolites with different SiO₂/Al₂O₃ ratios in the range of 10–80 were used as supports for preparing Pd/USY at 2 wt% Pd loading. The FT-IR of hydroxyl groups of USY zeolites, the n-butylamine chemisorption and the temperature-programmed desorption were used in combination to characterize the zeolite acidity. TPR, H₂-TPD and chemisorption using H₂ were used to characterize the Pd reduction and dispersion. The hydrogenation of naphthalene was conducted at 200 °C in the presence of benzothiophene at different sulfur/metal ratios. The hydrogenation activity, selectivity, and the sulfur tolerance strongly depended on the SiO₂/Al₂O₃ ratio (thus the acidity) of the zeolites. The activity decreased with increasing SiO₂/Al₂O₃ in this range. The IR and n-butylamine TPD showed that both the amount and strength of Brönsted acidity decreased with the increase of the SiO₂/Al₂O₃ ratio. The good relationship between the acidity modification and catalytic performance suggests that the sulfur tolerance of Pd/USY zeolite might be due to the desired metal-support interaction, which resulted in larger amount of electron-deficient Pd. However, as shown in TGA and TPO-IR studies, the higher hydrogenation performance on more acidic zeolite also caused higher amount of carbonaceous species on the catalyst.     

Catalytic cracking of isobutane over HZSM-5, FeHZSM-5 and CrHZSM-5 catalysts with different SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ratios

Several systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with different ratios of SiO₂/Al₂O₃ (25,38,50,80, and 150) were prepared and they were characterized by means of X-ray diffraction (XRD), UV–Vis, NH₃-TPD and BET techniques. The results indicated that, compared with uncalcined HZSM-5 zeolites, the total acid amounts, acidic site density and acidic strength of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts obviously decreased, while those of weak acid amounts obviously enhanced with the decrease of SiO₂/Al₂O₃ molar ratio. When the ratio of SiO₂/Al₂O₃ is less than 50, the three systems of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolite catalysts with same ratio of SiO₂/Al₂O₃ gave similar and high isobutane conversions. However, when the ratio of SiO₂/Al₂O₃ was equal to or greater than 80, these three systems of catalysts possessed different altering tendencies of isobutane conversions, thus their isobutene conversions were different. High yields of light olefins were obtained over the FeHZSM-5 and CrHZSM-5 zeolite catalysts with high ratio of SiO₂/Al₂O₃ (≥80). The ratio of SiO₂/Al₂O₃ has large effects on the surface area, and acidic characteristics of HZSM-5, FeHZSM-5 and CrHZSM-5 zeolites catalysts, and thus further affect their catalytic performances for isobutane cracking. That is the nature of SiO₂/Al₂O₃ ratio effect on the catalytic performances.     

Synthesis and ion exchange of zeolites produced from kaolin for separation of oxygen from atmospheric air

Lithium-based zeolites are the most commonly used materials in PSA (pressure swing adsorption) oxygen concentration from atmospheric air. Synthesizing these adsorbents using mineral raw materials adapts to worldwide environmental requests, as only high-purity chemical reactants such as aluminates and silicates are usually used. The present work aims to synthesize and characterize zeolites using kaolin as raw material by studying the influence of the metakaolinization temperature and SiO₂/Al₂O₃ and H₂O/Na₂O molar ratios by experimental design. Ion exchange was used to incorporate lithium into synthesized zeolites. Kaolin was treated thermically and characterized, and zeolites were synthesized by a hydrothermal reaction. After synthesis, ionic exchange of Na⁺ ions by Li⁺ was performed. The results indicated the presence of three main phases, zeolites A, X, and P. Using ANOVA, it was found that the factors that contributed significantly to the formation of zeolite X were the H₂O/Na₂O and SiO₂/Al₂O₃ molar ratios. For zeolite A, the major influence was by the metakaolinization temperature and for zeolite P none of the factors was influential. Zeolites that incorporated higher amounts of lithium showed higher N₂ adsorption potential, indicating that even without pure phases formed, it was possible to obtain similar adsorption efficiency to commercial zeolite.     

Synthesis of ZSM-5 zeolite and silicalite from rice husk ash

Local rice husk was precleaned and properly heat treated to produce high purity amorphous SiO₂ for use in the synthesis of ZSM-5 zeolite and silicalite by hydrothermal treatment (150 °C) of the precursor gels (pH 11) under autogenous pressure in a short reaction time (4–24 h). A wide range of SiO₂/Al₂O₃ molar ratios (30–2075) and a small template content were employed to fully exploit the potential of rice husk ash (RHA). The mineralogical phases, morphology, specific surface area and pore volume of the synthesized products were investigated by XRD, FT-IR, SEM and BET analyses, respectively. Under the employed conditions, it was found that the gels with a low range of SiO₂/Al₂O₃ molar ratios (<80) produced an amorphous phase to poorly crystalline ZSM-5 zeolite; those with a medium range (80–200) favored well crystalline ZSM-5 zeolite production with a large surface area; whilst those with a high range of SiO₂/Al₂O₃ molar ratios (>200) yielded silicalite. The increase in Na₂O content, which was derived from the addition of NaAlO₂ to attain the desired SiO₂/Al₂O₃ molar ratio of the gel, did not significantly enhance the crystallization rate, crystallinity, or yield of products. On the contrary, these properties were greatly affected by the increase in the SiO₂/Al₂O₃ molar ratio.     

Surface Acidity of H-Beta and Its Catalytic Activity for Alkylation of Benzene with Propylene

The acidity of H-beta zeolites with SiO₂/Al₂O₃ ratios ranging from 20 to 350 was characterized by NH₃-TPD profiles and FTIR spectra of adsorbed pyridine. As SiO₂/Al₂O₃ ratios of the H-beta zeolites increased, NH₃-TPD acidic amount of the samples is decreased. The IR bands of the adsorbed pyridine on the zeolites are also decreased with the increased SiO₂/Al₂O₃ ratios. The batch reaction of propylene and benzene was carried out in liquid phase at 423 K over H-beta zeolites. The selectivity to isopropylbenzene was high. The catalytic activity of H-beta zeolites is in direct proportion to the acidic amount of the zeolites in general. H-beta zeolite of SiO₂/Al₂O₃=27, which contains the highest amount of Brønsted acid sites as indicated by FTIR spectra of adsorbed pyridine, is the most reactive catalyst in the alkylation reaction. In continuous liquid-phase reactions, high propylene conversion and isopropylbenzene selectivity can be achieved at 413–453 K with benzene to propylene mole ratio from 4 to 8. The catalytic activity and selectivity of the H-beta zeolite do not change after 1100 h of reaction.     

Alkali-treatment of ZSM-5 zeolites with different SiO2/Al2O3 ratios and light olefin production by heavy oil cracking

Four kinds of ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios are alkali-treated in 0.2 M NaOH solution for 300 min at 363 K. Changes to the compositions, morphologies, pore sizes, and distributions of the zeolites are compared before and after alkali-treatment. The changes observed are largely influenced by the SiO₂/Al₂O₃ ratios with which the zeolites are synthesized. A possible mechanism of desilication during alkali-treatment is proposed. The SiO₂/Al₂O₃ ratio of zeolites is found to influence the yield of light olefins that use heavy oil as feedstock. Alkali-treated ZSM-5 zeolites produce higher yields of light olefins compared to either untreated zeolites or the industry catalyst CEP-1. It is believed that alkali-treatment introduces mesopores to the zeolites and improves their catalytic cracking ability. ZSM-5 zeolites with SiO₂/Al₂O₃ ratios of 50 also present superior selectivity toward light olefins because of their optimized hierarchical pores.     

Kinetics of geopolymerization: Role of Al2O3 and SiO2

The early-stage reaction kinetics of metakaolin/sodium silicate/sodium hydroxide geopolymer system have been investigated. The setting and early strength development characteristics, and associated mineral and microstructural phase development of mixtures containing varying SiO₂/Al₂O₃ ratios, cured at 40 °C for up to 72 h, were carefully studied. It was observed that setting time of the geopolymer systems was mainly controlled by the alumina content. Essentially, the setting time increased with increasing SiO₂/Al₂O₃ ratio of the initial mixture. Up to a certain limit, the SiO₂/Al₂O₃ ratio was also found to be responsible for observed high-strength gains at later stages. An increase in the Al₂O₃ content, i.e. for low SiO₂/Al₂O₃ ratio, led to products of low strength, accompanied by microstructures with increased amounts of Na-Al-Si-containing “massive” phases (grains). EDAX analyses showed that the SiO₂/Al₂O₃ ratios of geopolymer gel phases were quite similar to those of the starting mixtures, but with an overall lower Na content. Most importantly, this study clearly demonstrates that the properties of resulting geopolymer systems can be drastically affected by minor changes in the available Si and Al concentrations during synthesis.     

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.     

The conversions of 1,3,5-trimethylbenzene over beta zeolite: Effect of SiO2/Al2O3 ratio

A series of beta zeolites with various SiO₂/Al₂O₃ ratios has been synthesized. These samples were characterized with respect to crystallinity, particle size, acidity and sorption capacities of water, n-hexane and cyclohexane. The conversion of 1,3,5-trimethylbenzene (TrMB) was conducted in a fixed bed reactor at 493–743 K and atmospheric pressure. The conversion of 1,3,5-TrMB decreased with an increase in the SiO₂/Al₂O₃ ratio of the zeolite. The zeolites with low SiO₂/Al₂O₃ ratio favored the disproportionation and the zeolites with high SiO₂/Al₂O₃ ratio favored the isomerization. These can be interpreted by the acid concentration of zeolite. In the isomerization, all zeolites produced more 1,2,4-TrMB than 1,2,3-TrMB. In the disproportionation, the selectivity of tetramethylbenzene (TeMB) was in the order of 1,2,3,5->1,2,4,5->1,2,3,4-TeMB. The concentration of 1,2,4,5-TeMB is greater than that at equilibrium. The results show that shape selectivity comes into effect. The reaction temperature and the reaction time on stream also affect the selectivity significantly due to coke formation in the zeolites. © 1998 SCI     

Benzylation of benzene to diphenylmethane using zeolite catalysts

The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl chloride (BC) is investigated over a number of zeolite catalysts at 358 K and under atmospheric pressure. Conventional homogeneous Lewis acid catalyst, AlCl₃, is also included for comparison. Zeolite H-β is found to be more selective but less active compared to HY and H-ZSM-5 zeolites in the benzylation of benzene. The conversion of BC, rate of BC conversion and selectivity to DPM over H-β after 6 h of reaction time are 33.3 wt%, 4.7 × 10⁻³ mmol g⁻¹ h⁻¹ and 89.1 wt%, respectively. For comparison, the conversion of BC, rate of BC conversion and selectivity to DPM over AlCl₃, under identical reaction condition, are found to be 100 wt%, 170 × 10⁻³ mmol g⁻¹ h⁻¹ and 58 wt%, respectively. Higher amounts of consecutive products are obtained over AlCl₃ due to its non shape selectivity. The acidity of the zeolite catalysts is measured by temperature programmed desorption method. The effect of the duration of the run, SiO₂/Al₂O₃ ratio of H-β, catalyst concentration, reaction temperature and benzene to BC molar ratio on the catalyst performance is also investigated in order to optimize the conversion of BC and selectivity for DPM. The conversion of BC using H-β is increased with the increase in the reaction time, catalyst concentration, reaction temperature and molar ratios whereas it decreases with the increase in SiO₂/Al₂O₃ molar ratio of H-β. H-β is recycled two times and a slight decrease in BC conversion is observed after each cycle, which is related to the minor dealumination of the zeolite catalyst by HCl, which is produced during the reaction as by product. The formation of DPM is explained by an electrophilic attack of the benzyl cation (C₆H₅CH₂⁺) on the benzene ring, which is produced by the polarization of BC over acidic sites of the zeolite catalysts.     

Preparation of discrete colloidal ZSM-5 crystals with high Al-content

A new method for synthesis of discrete colloidal ZSM-5 particles with SiO₂/Al₂O₃ M ratios as low as 30 and sizes .4–1 micrometer has been developed. The relation between the synthesis parameters and synthesis yield, crystal structure, crystallinity, particle size and morphology was investigated. The synthesis yield increases and the deviation of the SiO₂/Al₂O₃ ratio in the product from that in synthesis mixture decreases with increasing autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that temperature determines the lower limit of the SiO₂/Al₂O₃ ratio. The SiO₂/Al₂O₃ ratio in the synthesis mixture decreases with autoclave temperature suggesting that the introduction of aluminium into the zeolite structure is favoured by high autoclave temperature during the synthesis and that the temperature determines the lower limit of SiO₂/Al₂O₃ ratio. Synthesis mixture, aimed to yield a high SiO₂/Al₂O₃ ratio, gives smaller zeolite crystals, higher specific surface areas, higher geometric areas (external surface area of the crystals) and a more oval crystal shape compared with lower ratios, synthesised at the same temperature. Higher autoclave temperature during the synthesis gives larger zeolite crystals and a more hexagonal crystal shape compared with zeolites synthesised at lower temperatures, for the same SiO₂/Al₂O₃ ratios.     

Synthesis and characterization of hollow zeolite microspheres with a mesoporous shell by O/W/O emulsion and vapor-phase transport method

Hollow microspheres of ZSM-5 with a mesoporous shell have been synthesized through formation of amorphous hollow SiO₂/Al₂O₃ microspheres by sol–gel process in multiple oil–water–oil emulsions and transformation of the amorphous species into zeolite by water–organic vapor-phase transport treatment at 160 °C for 8 days. The morphology of the amorphous and zeolite spheres observed by scanning electron microscopy shows no significant change whereas the molar ratio of Si/Al increases from 6 to 20 during the transformation. The structural feature of zeolite was characterized by X-ray diffraction and ²⁹Si and ²⁷Al magic-angle spinning nuclear magnetic resonance. Transmission electron microscopy and N₂ adsorption–desorption isotherms indicate that uniform mesopores in the shell of zeolite spheres arise from the interstices among zeolite crystallites.     

Two-step process for synthesis of a single phase Na–A zeolite from coal fly ash by dialysis

Using the amorphous aluminosilicate in coal fly ash (FA), a single phase Na–A zeolite was synthesized from FA by dialysis. The FA and NaOH solution added into the tube made by semipermeable membrane were pretreated in the same NaOH solution at 85 °C for 24 h. After the pretreatment, the tube was removed and NaOH–NaAlO₂ solution was added into the residual solution to control SiO₂/Al₂O₃ molar ratio of the solutions from 0.9 to 4.3. The precipitates thus formed were aged for 24 h at 85 °C. The amorphous aluminosilicate in FA was dissolved during the pretreatment. When the NaOH–NaAlO₂ solution was added into the solution after the pretreatment and then aged, white precipitates were yielded over the whole SiO₂/Al₂O₃ range. At SiO₂/Al₂O₃=0.9, the material formed was identified as a single phase Na–A zeolite. The Na–X zeolite was slightly produced at SiO₂/Al₂O₃≥1.7.     

Effect of Water Content of Synthetic Hydrogel on Dehydration Performance of Nanoporous LTA Zeolite Membranes

Nanoporous LTA‐type zeolite membranes were synthesized on α‐Al₂O₃ disk as substrate using secondary growth method. A gel formula of 1 Al₂O₃: 2 SiO₂: 3.4 Na₂O: W H₂O in molar basis was chosen while its water content (W) was varied. Four levels of water contents of 140, 155, 175, and 200 were selected for membrane synthesis. The results showed that the best membrane was synthesized with water content of 155. The most efficient zeolite membrane showed a permeation flux of 0.5 kg/m²/h and a separation factor of 3800 in dehydration of a 5/95 (wt%) water/isopropanol mixture at 298 K.     

Design and preparation of BaO–Al2O3–SiO2–B2O3/Quartz LTCC composites with tailored coefficient of thermal expansion

In this work, by focusing on widespread problem of thermal mismatch caused by different coefficients of thermal expansion (CTE) in electronic packaging materials, low-temperature co-fired ceramic (LTCC) materials with tunable CTE values were designed. By substituting Ba²⁺ with Sr²⁺ and replacing quartz with alumina and zirconia, respectively, BaO–Al₂O₃–SiO₂–B₂O₃/quartz LTCC composites with CTE of 7.05–9.52 × 10^?6/°C were developed. Results show that major crystalline phases of LTCC composite materials are quartz and hexacelsian. By replacing quartz with alumina or zirconia, sintering behavior and subsequently thermal expansion and dielectric properties were modulated. On the other hand, substituting Ba²⁺ with Sr²⁺ can be beneficial to the densification of composite materials. The introduction of Sr²⁺ triggered mixed alkali effect and hindered the crystallization of hexacelsian phase, which can further improve mechanical properties. Finally, sandwich structure module of BaO–Al₂O₃–SiO₂–B₂O₃/quartz with gradient CTE values was obtained, which showed potential for electronic packaging with sustained thermal compatibility under cyclic temperatures.     

The catalytic performance of methylation of naphthalene with methanol over SAPO-11 zeolites synthesized with different Si content

A series of SAPO-11 zeolites with different Si contents were prepared by hydrothermally synthesized method. They were characterized by ICP, XRD, SEM, FT-IR, N₂ adsorption-desorption, NH₃-TPD and ²⁹Si MAS NMR, and evaluated by the methylation of naphthalene with methanol to 2,6-dimethylnaphthalene (2,6-DMN). According to XRD and SEM results, the crystallinity of SAPO-11 sample increased with increase of the Si content until the SiO₂/Al₂O₃ ratio was up to 0.2. However, a reduction in the crystallinity was observed with further increase of the Si content of the synthesis. N₂ adsorption-desorption results showed that all the samples possessed micropores and secondary mesopores. SAPO-11 sample with SiO₂/Al₂O₃ ratio of 0.2 exhibited the largest secondary mesopores size distributions. NH₃-TPD and ²⁹Si MAS NMR showed that the Si content was incorporated into the framework affecting not only the acid sites but also the acid strength of SAPO-11. SAPO-11 with SiO₂/Al₂O₃ ratio of 0.2 presented the high catalytic performances for the methylation of naphthalene, which was mainly attributed to the amount of secondary mesopores in the SAPO-11 zeolite.     

Large-scale fine structural alumina matrix ceramic guideway materials improved by diopside and Fe2O3

Diopside and Fe₂O₃ were introduced in alumina matrix ceramic materials. Large-scale fine structural alumina matrix ceramic guideway materials were fabricated by the technology of pressureless sintering, during which liquid phase sintering took place and new phases such as 3Al₂O₃·2SiO₂, CaO·Al₂O₃·2SiO₂ and CaO·6Al₂O₃ were produced by the chemical reactions taking place among alumina and the additives. The hardness, the fracture toughness and the bending strength of the guideway products were tested. The influences of diopside and Fe₂O₃ additions were studied by microstructural observations and mechanical properties evaluations. Meanwhile, the expected improvement of mechanical properties compared with pure alumina was indeed observed. The fracture mechanism and porosity of large-scale fine structural alumina matrix ceramic guideway materials were analyzed.     

Dehydration of Ethanol into Ethylene over Solid Acid Catalysts

The dehydration of ethanol into ethylene was investigated over various solid acid catalysts, such as zeolites and silica–alumina, at temperatures ranging 453–573 K under atmospheric pressure. Ethylene was produced via diethyl ether during the dehydration process. H-mordenites were the most active for the dehydration. It was suggested that the catalyst activity could be correlated with the number of strong Br?nsted acid sites in the catalyst. Further, the H-mordenite was more stable with a SiO₂/Al₂O₃ ratio of 90 than with a SiO₂/Al₂O₃ ratio of 20.     

Grain boundary diffusion effect on mineral transition of calcium sulpho-aluminate with sodium dopant

The mineral formation-transition mechanism, microstructure morphology evolution, pulverization property and chemical reactivity of calcium sulpho-aluminate with sodium dopant are systematically studied with the molar ratio of CaO to Al₂O₃ is 0.8, the molar ratio of CaO to SiO₂ is 1.5, the mass ratio of Al₂O₃ to SiO₂ is 2.0, and the SO₃ accounts for 4%. The results show that sodium dopant could promote 3CaO·3Al₂O₃·CaSO₄, CaO·2Al₂O₃ and 2CaO·Al₂O₃·SiO₂ transform into 2CaO·SiO₂, CaO·Al₂O₃, 12CaO·7Al₂O₃ and 2Na₂O·3CaO·5Al₂O₃, and it also can decrease the decomposition temperature of reactive materials and the initial phases formation temperature significantly. Sodium diffusion can destroy the clear grain boundary of calcium aluminate and calcium silicate phases, change the macro-microstructure morphology, improve the crystalline degree of the samples, and then improve the pulverization and alumina leaching property. However, excessive sodium dopant can decrease the melting temperature, inhibit the transformation process of 2CaO·SiO₂ from β to γ, and then deteriorate the pulverization property significantly again.