CO2 and CO adsorption equilibrium on ZSM-5 for different SiO2/Al2O3 ratios

CO₂ and CO adsorption on MFI type zeolites with different SiO₂/Al₂O₃ ratios (ZSM-5(30), ZSM-5(50), ZSM-5(280), and silicalite) were investigated in this study by a static gravimetric analyzer for pure isotherms at 30°C, 65°C, 100°C, and 135°C over the pressure range of 0–10 atm. Adsorption capacity of CO increases with decreasing SiO₂/Al₂O₃ ratios within ZSM-5. The adsorption of CO₂ for decreasing SiO₂/Al₂O₃ ratios, showed stronger adsorption at lower pressures and at higher pressures, the highest capacity varied from ZSM-5(50) to ZSM-5(30). ZSM-5(280) was found to have the highest selectivity for CO₂ within the widest range of pressures and temperatures tested.     

Enhancing the Production of Light Olefins by Catalytic Cracking of FCC Naphtha over Mesoporous ZSM-5 Catalyst

The enhanced production of light olefins from the catalytic cracking of FCC naphtha was investigated over a mesoporous ZSM-5 (Meso-Z) catalyst. The effects of acidity and pore structure on conversion, yields and selectivity to light olefins were studied in microactivity test (MAT) unit at 600 °C and different catalyst-to-naphtha (C/N) ratios. The catalytic performance of Meso-Z catalyst was compared with three conventional ZSM-5 catalysts having different SiO₂/Al₂O₃ (Si/Al) ratios of 22 (Z-22), 27 (Z-27) and 150 (Z-150). The yields of propylene (16 wt%) and ethylene (10 wt%) were significantly higher for Meso-Z compared with the conventional ZSM-5 catalysts. Almost 90% of the olefins in the FCC naphtha feed were converted to lighter olefins, mostly propylene. The aromatics fraction in cracked naphtha almost doubled in all catalysts indicating some level of aromatization activity. The enhanced production of light olefins for Meso-Z is attributed to its small crystals that suppressed secondary and hydrogen transfer reactions and to its mesopores that offered easier transport and access to active sites.     

Characterization and application of a Pt/ZSM-5/SSMF catalyst for hydrocracking of paraffin wax

The microstructured Pt/ZSM-5/SSMF catalysts, for hydrocracking of paraffin wax, have been developed by impregnation method to place Pt onto thin-sheet ZSM-5/SSMF composites obtained by direct growth of ZSM-5 on the sinter-locked stainless steel microfibers (SSMF). The best catalyst is the one with ZSM-5 having a SiO₂/Al₂O₃ weight ratio of 200, delivering ~ 95% conversion with 77.5% selectivity to liquid products or 64.4% selectivity to naphtha at 280 °C. This new approach is capable of increasing the naphtha selectivity with high activity maintenance in comparison with the literature catalysts.     

Effect of Calcination Temperature of Kaolin Microspheres on the In situ Synthesis of ZSM-5

ZSM-5 zeolite has been successfully synthesized in-situ on calcined kaolin microspheres by the hydrothermal method using n-butylamine as a template. The supported ZSM-5 was characterized by X-ray diffraction and scanning electron microscopy. The effect of calcination temperature of kaolin microspheres on the in-situ synthesis of ZSM-5 was investigated. The influence of the pretreatment temperature on the properties of kaolin microspheres including phase transformation, amounts of active SiO₂ and Al₂O₃, and pore structures, was studied using fourier transform infrared (FT-IR), nitrogen adsorption and chemical analysis. The results showed that when the calcination temperature increased from 300 to 900 °C, the amount of active SiO₂ in the kaolin microspheres increased slightly and the amount of active Al₂O₃ initially increased rapidly and then decreased steadily. The surface area and pore volume of the kaolin calcined at both low and high temperatures was less than those of kaolin calcined at a medium temperature. The property changes of kaolin caused the relative crystallinity of in situ synthesized ZSM-5 to vary.     

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.     

Synthesis of ZSM-5 at low temperature and atmospheric pressure in a pilot-scale batch reactor

The synthesis of ZSM-5 was carried out at 100°C and atmospheric pressure in a 30 l batch reactor. The results show that a quality of ZSM-5 can easily be synthesized with a well-developed framework structure within 72 h of reaction. The crystallinity readily reached almost 100% and the yield was well over 70% for samples having various SiO₂/Al₂O₃ ratios. As the SiO₂/Al₂O₃ ratio decreased, the morphology changed from euhedral to spherulite along with an increase of aggregation. The average BET surface area of the samples was 371 m² g⁻¹ and nuclear magnetic resonance spectroscopic studies showed a quality of ZSM-5 with the least defect sites in the framework structure.     

Synthesis and characterization of calcium aluminate compounds from gehlenite by high-temperature solid-state reaction

The mineral transition mechanism and self-pulverization property of the sintered products in the Ca₂Al₂SiO₇-CaO system were systematically studied using pre-synthesized gehlenite determined by XRD, SEM, FTIR and particle size analyses. The minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄, Ca₃SiO₅ and Ca₂SiO₄ are formed by the direct reactions of Ca₂Al₂SiO₇ with CaO. CaAl₂O₄ reacts with CaO to form Ca₁₂Al₁₄O₃₃ or Ca₃Al₂O₆, while Ca₃SiO₅ reacts with Ca₂Al₂SiO₇ to form Ca₂SiO₄ and calcium aluminate compounds. The sintered products mainly contain CaAl₂O₄, Ca₁₂Al₁₄O₃₃ and Ca₂SiO₄ at 1350?°C or above 1500?°C when the molar ratio of CaO to Al₂O₃ is 1.0. Increasing the sintering duration or the CaO consumption promotes the transition of Ca₂Al₂SiO₇ to Ca₂SiO₄ and calcium aluminate compounds when sintered at 1350?°C, which accordingly improves the self-pulverization property of the sintered products. The formed minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄ and Ca₂SiO₄ transform into Ca₂Al₂SiO₇ again when the sintering temperature is between 1400?°C and 1450?°C, and the corresponding self-pulverization property of the sintered products deteriorates sharply.     

Direct Synthesis of ZSM-5 and Mordenite Using Poly(ethylene glycol) as a Structure-Directing Agent

ZSM-5 (SiO₂/Al₂O₃ = 55) and mordenite (SiO₂/Al₂O₃ = 48) were synthesized directly using poly(ethylene glycol) (PEG 200) as a structure-directing agent. The PEG 200 molecules were occluded in the pores of ZSM-5 but not in mordenite. It is expected that the formation of ZSM-5 occurs via a layered phase such as magadiite.     

In-situ synthesis and catalytic activity of ZSM-5 zeolite

ZSM-5 zeolite has been hydrothermally synthesized in-situ on the external surface of calcined kaolinite in the presence of n-butylamine. This supported zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N₂ adsorption. Several synthesis variables were systematically investigated, including SiO₂ to Al₂O₃ ratio, pH, crystallization time, and crystallization temperature. After mixing the ZSM-5 with a Fluid Catalytic Cracking (FCC) catalyst, catalytic performance was evaluated by cracking vacuum gas oil (VGO) in a micro-fixed bed reactor. ZSM-5 addition was favorable for the production of light olefins by catalytic cracking of VGO.     

Kinetics of the Syntheses of Mesityl Oxide (MO) and Methyl Isobutyl Ketone (MIBK) in a Fixed-Bed Flow Reactor (FBR)

Nb₂O₅/SiO₂ and Pd/Nb₂O₅/SiO₂ catalysts were studied for the liquid phase syntheses of mesityl oxide (MO) and methyl isobutyl ketone (MIBK) in a fixed bed flow reactor (FBR). Catalyst activities as high as 1.7 g/h g_cat and selectivities ranging from 93.4 to 100% for MO synthesis were observed. The catalyst activity was found to be a strong function of space velocity likely due to product inhibition. A synergistic effect was observed whereby the catalyst activity for all organic products increased by 22% and the MIBK productivity increased by 20% at 160 °C and WHSV = 8.6 h^?1 from the introduction of hydrogen to the reactor. However, the MIBK selectivity was constrained to less than 83.5% due to competing reactions.     

Enhanced selectivity to benzaldehyde in the liquid phase oxidation of benzyl alcohol using nanocrystalline ZSM-5 zeolite catalyst

In the present paper, nanocrystalline hierarchical ZSM-5 zeolites were successfully synthesized by the hydrothermal method in the presence of tetrapropylammonium hydroxide as a single template with the gel composition of 58SiO₂:Al₂O₃:20TPAOH:1,500H₂O. The prepared zeolite catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Nitrogen adsorption–desorption (BET), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM) techniques. The formation of pure and highly crystalline ZSM-5 zeolite phase is confirmed by XRD. The IR vibration band at 550 cm^?1 is assigned to the double 5-rings of MFI-type zeolites. N₂ adsorption–desorption isotherms showed that the synthesized product had high BET surface area and possessed composite pore structures with both micro and mesopores. The catalytic performance of hierarchical ZSM-5 zeolite was investigated in the selective oxidation of benzyl alcohol (BzOH) with hydrogen peroxide (H₂O₂) under mild conditions. The results showed that the conversion of BzOH and the selectivity to benzaldehyde were about 94 and about 99 % respectively, when using 0.08 g ZSM-5 catalyst with acetonitrile as the solvent and H₂O₂ as the oxidant at 90 °C. This catalyst can be retrieved and reprocessed for five times without a significant loss in its activity and selectivity.     

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.     

Aromatization of n-Butane Over Supported Mo2C Catalysts

Similarly to the case of methane, ethane and propane, Mo₂C deposited on ZSM-5 significantly enhanced the aromatization of n-butane observed on ZSM-5 (SiO₂/Al₂O₃ ratio of 80) alone. The catalytic performance of Mo₂C/ZSM-5 sensitively depended on its preparation and pretreatment. The selectivity of aromatics measured for pure ZSM-5 increased from 11-13% to 28-34% at the conversion level of 60-65%. The formation of aromatics was also observed over Mo₂C/SiO₂.     

Characteristics and evaluation of synthetic 13X zeolite from Yunnan’s natural halloysite

High purity microporous 13X zeolitic materials with octahedral microstructure were successfully synthesized by using Yunnan’s natural halloysite as silica and aluminum sources through hydrothermal method in alkaline media. The effects of various factors such as the molar ratio of SiO₂/Al₂O₃, alkalinity, crystallization time and crystallization temperature were investigated. In addition, the characteristics of its structure and porosity were studied. The optimum synthesis conditions were SiO₂/Al₂O₃ molar ratio of 4.3, NaOH solution concentration of 2 mol/L, aging time at room temperature 12 h and crystallization temperature of 100 °C/8 h. The optimum 13X zeolitic materials were fully characterized by chemical analysis, X-ray diffraction, field emission scanning electron microscopy, thermogravimetry and N₂ adsorption–desorption. The as-synthesized 13X zeolitic products exhibited high thermal stability and Langmuir surface area of up to 726 m²/g, value much higher than elsewhere reported.     

Vapour phase synthesis of 3,5-dipropylpyridine over modified zeolites

3,5-Dipropylpyridine was synthesized selectively in vapour phase with valeraldehyde, formaldehyde and ammonia over modified ZSM-5 (SiO₂/Al₂O₃=30) catalysts at 400 °C. High conversion (>90%) and high yield (72%) were obtained over PbZSM-5(30). The activity was correlated with the acidity of the catalyst. The modified catalysts were characterized by XRD, FT-IR, ICP-MS, BET-surface area and temperature programmed desorption (TPD) of NH₃.     

Synthesis of SUZ-4 zeolite by a dry gel conversion method

SUZ-4 zeolite was synthesized by the dry gel conversion (DGC) process with water vapor as gas phase, and characterized by XRD, SEM and N₂ adsorption. The dry gel was prepared with the assistance of a small amount of crystalline seed and organic template tetraethylammonium hydroxide (TEAOH). Molar ratios of SiO₂/Al₂O₃, KOH/SiO₂, TEAOH/SiO₂ and H₂O/SiO₂, amounts of seed and dry gel, types of silica sources, and crystallization temperature and time, were changed to optimize synthesis conditions. The results show that the DGC method leads to formation of SUZ-4 zeolite in a broad range of crystallization temperature 120–180 °C. Under the optimal conditions, i.e., SiO₂/Al₂O₃ = 22.5, KOH/SiO₂ = 0.44, TEAOH/SiO₂ = 0.044, H₂O/SiO₂ = 22.2, seed amount = 0.1 wt%, fumed silica as the silica source, 160 °C and 5 days, SUZ-4 zeolite is obtained with a high crystallinity. Compared to hydrothermal synthesis, the present DGC approach employs far less amount of organic template and allows using inert fumed silica as silica source, producing smaller rod-like SUZ-4 zeolite crystals.     

Screening of Catalysts for Acrylonitrile Decomposition

The catalytic decomposition of acrylonitrile over various metal components (Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, and Pt) supported on several metal oxides (Al₂O₃, SiO₂, TiO₂, ZrO₂, and MgO) and ZSM-5 was studied. The most promising catalyst was Cu-ZSM-5, which exhibited 100% conversion and at least 80% N₂ selectivity above 350 °C.     

Catalytic behavior of CoMo/ZSM5 catalysts for CS2 conversion

Catalysts based upon ZSM-5 zeolites (SiO₂/Al₂O₃ molar ratio of 30 and 150) were synthesized and tested for the carbon disulfide (CS₂) conversion. First, the zeolites were shaped in pellets using alumina (20 wt%) as binder. The pellets containing ZSM5 (SiO₂/Al₂O₃ = 30) were exchanged with Co²⁺. Afterwards, this material and the other one, having the zeolite with SiO₂/Al₂O₃ ratio of 150, were co-impregnated with Mo and Co salts. The structural variations were explored by means of X-Ray Diffraction. The progressive reduction of the metal phases was studied by Thermal Programmed Reduction (TPR); the acidity distribution was evaluated by FTIR-pyridine adsorption and the aggregation state of the crystalline phases was characterized by High Resolution Transmission Electron Microscopy (HRTEM) and EDS. The catalytic properties were evaluated in a fixed bed reactor at 350 °C, P = 20 kg/cm² with a H₂/CS₂ molar ratio equal to 2. The results suggest a hindering of catalytic activity by the metal phase, which is deposited either on the alumina or over the external surface of the zeolite crystallites.     

HYDROTHERMAL REACTION OF FLY ASH/HYDRATED LIME: CHARACTERIZATION OF THE REACTION PRODUCTS

Class F coal fly ash was slurried with hydrated lime at 90°C in 1/3, 5/3, 9/3, and 15/3 weight ratios and for 3, 5, 7, and 9 hours of hydration, in a process to prepare sorbents for SO₂ removal. The amounts of aluminum, silicon, and calcium in the product of the pozzolanic reaction were determined in order to study the evolution of product composition with the initial raw materials ratio and hydration time and to relate this composition to the desulfurization capability of the material. Al, Si, and Ca were present in the solid product for any raw materials ratio and hydration time, showing that calcium silicates, calcium aluminates, and/or calcium aluminum silicates were obtained simultaneously. The products formed show a nearly constant molar ratio of Al₂O₃/SiO₂ independent of the experimental conditions tested and similar to the Al₂O₃/SiO₂ ratio in the fly ash. The SiO₂/CaO molar ratio in the products decreased as the initial fly ash/Ca(OH)₂ ratio decreased, being approximately constant for each ratio with respect to hydration time after 5 hours of hydration. The maximum moles of CaO, SiO₂, and Al₂O₃ per gram of sorbent in the reaction product were found for any hydration time for the 5/3 sorbents, meaning that at this initial ratio the pozzolanic reaction takes place at the highest rate. The capacity of the sorbent for SO₂ removal depends not only on the amount of products produced by the pozzolanic reaction but also on the specific surface area of the sorbent.     

Effect of Al2O3/SiO2 ratio on iron-based catalysts for Fischer–Tropsch synthesis

A systematic study was undertaken to investigate the effects of Al₂O₃/SiO₂ ratio on reduction, carburization and catalytic behavior of iron-based Fischer–Tropsch synthesis (FTS) catalysts promoted with potassium and copper. The catalysts were characterized by N₂ physical adsorption, CO₂ temperature-programmed desorption (TPD), H₂ temperature-programmed reduction (TPR) and Mössbauer effect spectroscopy (MES). CO₂-TPD indicated that Al₂O₃ binder has stronger acidity than SiO₂ binder and weakens the surface basicity of the catalysts. H₂-TPR profiles suggested that the lower Al₂O₃/SiO₂ ratio promotes the reduction of Fe₂O₃→Fe₃O₄. With further increasing Al₂O₃/SiO₂ ratio, the transformation of Fe₂O₃→Fe₃O₄ shifts to higher temperatures. The MES results showed that the increase of Al₂O₃/SiO₂ ratio leads to the relatively large crystallite size of α-Fe₂O₃ and inhibits carburization of the catalyst. During reaction tests in a fixed bed reactor it was found that a maximum in catalyst activity is noted at the Al₂O₃/SiO₂ ratio of 5/20 (weight basis). The selectivity to olefins shows a rapid decrease and the formations of methane and light hydrocarbons are promoted with increasing Al₂O₃/SiO₂ ratio. The oxygenate selectivity in total products increases with increasing Al₂O₃/SiO₂ ratio.