Synthesis methods for preparing microporous carbons with a structural regularity of zeolite Y

As reported in previous communications, novel porous carbons were synthesized by using zeolite Y as a template. The carbons possess a periodic ordering structure and high BET surface area with large micropore volume. In this work, the details of the synthesis methods for preparing the ordered microporous carbons were examined. It was found that the following two-step process, the filling of carbon into zeolite channels by impregnation of furfuryl alcohol and then chemical vapor deposition (CVD) of propylene, was indispensable for preparing carbon with highly periodic ordering. In addition, low-temperature CVD and the further heat treatment of zeolite/carbon composite after the CVD are key points for the appearance of both good long-range periodicity and very high BET surface area with almost no mesoporosity in the carbons.     

分子筛催化γ-丁内酯气相胺化合成N-乙烯吡咯烷酮单体

研究了ZSM-5、NaY分子筛对γ-丁内酯与乙醇胺气相反应的催化性能,结果表明,ZSM-5与Y型分子筛的初始产物收率分别为29·8%和43·0%以上。反应产物收率随温度升高而增大,然后趋于平缓,当超过280℃以后呈降低趋势;选择性在较低温度时变化不明显,温度较高时明显降低,合适的反应温度为260~270℃。再生性实验表明,两种分子筛的失活都是由于水蒸气使其部分结构遭到破坏而引起的,是不可恢复的失活。     

Activity of different zeolite-supported Ni catalysts for methane reforming with carbon dioxide

The catalytic performance of Ni based on various types of zeolites (zeolite A, zeolite X, zeolite Y, and ZSM-5) prepared by incipient wetness impregnation has been investigated for the catalytic carbon dioxide reforming of methane into synthesis gas at 700 °C, at atmospheric pressure, and at a CH₄/CO₂ ratio of 1. It was found that Ni/zeolite Y showed better catalytic performance than the other types of studied zeolites. In addition, the stability of the Ni/zeolite Y was greatly superior to that of the other catalysts. A weight of Ni loading at 7 wt.% showed the best catalytic activity on each zeolite support; however, the 7% Ni catalysts produced a higher amount of coke than that of two other Ni loadings, 3 and 5%.     

Synthesis and characterization of microporous carbons templated by ammonium-form zeolite Y

Emerging applications such as gas storage require porous carbon materials with tailored structural and surface properties. Template synthesis approach to porous carbons offers opportunities for tailoring these properties. In this study, ammonium-form zeolite Y (NH₄Y) was used as a template and furfuryl alcohol (FA) was employed as a carbon precursor to prepare microporous carbons by simple impregnation method. The effects of synthesis conditions such as carbonization temperatures and heating rates on the pore structure of the microporous carbons were investigated. The thermal behaviors of FA-NH₄Y mixtures and zeolite/carbon composites were studied by thermogravimetric analysis (TGA). The physical, structural, and surface properties of the microporous carbons were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM), elemental analysis, and physical adsorption of nitrogen. Microporous carbons with high surface areas, pore volumes and nitrogen-containing surface functional groups can be readily synthesized.     

Adsorption of Carbon Dioxide on High-Silica Zeolites with Different Framework Topology

Adsorption isotherms of carbon dioxide were measured on six high-silica zeolites TNU-9, IM-5, SSZ-74, ferrierite, ZSM-5 and ZSM-11 comprising three-dimensional 10-ring (8-ring for ferrierite) at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO₂ adsorption, isosteric heats of adsorption were calculated. The obtained adsorption capacities and isosteric adsorption heats related to the amount of CO₂ adsorbed have provided detailed insight into the carbon dioxide interaction with zeolites of different framework topology. The zeolites TNU-9 and ferrierite are characterized by pronounced energetic heterogeneity whereas due to the location of Na⁺ cations in the same positions the isosteric adsorption heats of CO₂ adsorption on IM-5, ZSM-5 and ZSM-11 zeolites are rather constant for molecular ratio CO₂/Na⁺ < 1. As IM-5 zeolite has a maximum adsorption capacity, it appears to have optimum properties for carbon dioxide separation.     

磷改性ZSM-5沸石的催化裂化性能

用磷改性ZSM-5沸石,并将其制备成催化剂。初步考察了其物化性能的变化,并在固定床重油微反装置上考察了其催化裂化反应特性。研究发现,磷能显著改善ZSM-5沸石的活性、稳定性和选择性。ZSM-5沸石上不同的磷含量和其与不同的Y型分子筛配伍对催化裂化反应有着显著的影响。合理调配催化裂化催化剂的活性组分,适当控制其氢转移能力和烷基化能力,对增产丙烯有着积极的意义。     

Deactivation of ZSM-5 additives in laboratory for realistic testing

ZSM-5 deactivates differently from Y zeolite. Dealumination of Y zeolite during deactivation causes UCS shrinkage and thereby decline in activity and changes in selectivity. For ZSM-5 instead deactivation removes alumina from the zeolite structure, but in spite of that the zeolite structure does not collapse. Therefore, deactivation causes activity decline due to loss of active alumina sites, but no significant changes in the strength and separation between acid sites. Unlike with FCC catalyst, physical properties of ZSM-5 additive do not change significantly with deactivation and surface area and pore volume measurements cannot be used as indications of additive performance. Yet, since both Y and ZSM-5 are used simultaneously in practice, the information on the relative rates of deactivation between the two zeolites is very important. Therefore, the question remains, what is the best way to deactivate and test ZSM-5 additives in the laboratory to obtain realistic performance, e.g. propylene yield and to obtain proper ranking of various additives. This paper discusses the effect of deactivation conditions as well as performance testing aspects of ZSM-5 additives. It is shown that choice of deactivation conditions has an effect on additive ranking and performance. By choosing the deactivation conditions properly ranking can be made clearer and more realistic additive performance is obtained.     

Adsorption of CO<Subscript>2</Subscript> and CO on H-zeolites with different framework topologies and chemical compositions and a correlation to probing protonic sites using NH<Subscript>3</Subscript> adsorption

Adsorption of CO₂ and CO at 25 °C has been conducted using commercially-available (Y, ZSM-5) and laboratory-synthesized (SSZ-13, SAPO-34) H-zeolites with different framework topologies and chemical compositions, and their textual and surface properties have been characterized by N₂ sorption and NH₃ adsorption techniques. All the zeolites were microporous, although ZSM-5 and SSZ-13 apparently showed a mesoporous sorption behavior due to the interparticle spaces. The zeolites had Si/Al values in the order of SSZ-13 (16.44) > ZSM-5 (16.08) ? Y (2.82) ? SAPO-34 (0.19). Regardless, high CO₂ adsorption capacity was obtained for SSZ-13 and SAPO-34 with a CHA framework. The FAU zeolite Y with the highest micropore volume showed less CO₂ adsorption than the CHA zeolites and the MFI-type ZSM-5 yielded the poorest performance. Probing acid sites in the H-form zeolites using NH₃ disclosed that these all contain both weak and strong acid sites with significant dependence of their strengths and amounts on the topology. The acid strength of the weak acid sites in the CHA zeolites was the weakest, which might allow a stronger interaction with CO₂. The H-zeolites gave CO₂/CO selectivity factors that were in the range of 4.61–11.0, depending on the framework topology.     

Adsorption of pharmaceuticals from aqueous solutions on synthetic zeolites

The objectives of this study were to measure the sorption capacity of a dilute solution of drugs in water on hydrophobic zeolites and to quantify aspects of their adsorption mechanisms for potential use in wastewater remediation. The removal of three drugs, erythromycin (ERY), carbamazepine (CBZ) and levofloxacin (FLX) from water using three organophilic zeolites (Y, mordenite (MOR), ZSM-5) was investigated. Adsorption isotherms show that these three drugs are adsorbed in remarkable amounts by Y. These data were confirmed by thermogravimetric analysis. The presence of these drugs inside the Y cage was revealed by unit cell parameter variations and structural deformations obtained by X-ray structure analyses carried out using the Rietveld method on zeolite after adsorption. Our results indicate that the adsorption properties of zeolitic materials do not only depend on micropore size and that zeolite shape selectivity also depends on structural features which are difficult to determine “a priori”. In order to test the ability of organophilic zeolites in removing drugs from wastewater, the adsorption of ERY, FLX and CBZ on zeolite Y from water samples collected at the outlet of a wastewater treatment plant located in Northern Italy was determined. These drugs were almost completely adsorbed by Y zeolite, confirming that this material is suitable for removing drugs from wastewater.     

Studies on acidity,activity and coke deactivation of ZSM-5 during n-heptane aromatization

In order to understand the effects of acidity and acid strength distribution on the nature of coke formed over ZSM-5 zeolite in n-heptane aromatization reaction, a series of ZSM-5 samples dealuminated to different degrees are prepared. Microcalorimetric ammonia adsorption studies indicated the presence of very strong acid sites (ΔH>140 kJ/mol) in the catalysts steamed at 400 and 500°C. ¹³C CP/MAS NMR along with dipolar dephasing is used to estimate the fraction of aromatic carbon and variation in aliphatic components with change in acidity of the ZSM-5 zeolites. Maximum selectivity to aromatics in n-heptane conversion is observed in the case of partly dealuminated ZSM-5 catalyst, whereas the aromatic nature of the coke is continuously decreased with steaming temperature, i.e. dealumination.     

用于MTP反应ZSM-5分子筛的磷改性研究

将P改性用于甲醇制丙烯(MTP)反应ZSM-5分子筛的改性研究,以提高丙烯选择性和分子筛活性稳定性。采用XRD、SEM和NH_3-TPD表征催化剂物化性能。对不同硅铝比ZSM-5分子筛P改性研究发现,3种不同硅铝物质的量比(50、150和300)ZSM-5分子筛进行P改性时,在n(P)∶n(Al)=0.5~0.7时,ZSM-5分子筛改性后丙烯选择性和寿命得到提升。研究分子筛晶粒尺寸与P负载量关系时发现,随着分子筛晶粒尺寸的增大,位于分子筛表面的P含量逐渐增加,并且分子筛晶粒越小,最佳的P负载量越小。     

Synthesis of nanostructured SiC by magnesiothermal reduction of silica from zeolite ZSM-5 and carbon: The effect of carbons from different sources

Nanostructured SiC was synthesized by magnesiothermal reduction of silica derived from zeolite ZSM-5 with a Si/Al ratio of about 80 and four carbons from different sources. The carbons were carbon black and three carbons synthesized by impregnating furfuryl alcohol or sucrose into three porous templates (ZSM-5, clinoptilolite and MCM-48). Magnesiothermal reduction was carried out by reacting mixtures of silica, carbon and magnesium powder at 600–800 °C in a flowing argon atmosphere. The starting materials and final products were characterized by X-Ray diffraction, thermogravimetric analysis, scanning electron microscopy and BET analysis. The results indicated that the synthesis of nanostructured SiC is influenced by the chemical nature of the carbon and its surface area.     

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.     

改性分子筛催化乳酸甲酯的脱水反应

通过生物基路线制备丙烯酸及酯具有潜在的经济效益.同时对化石资源的绿色替代具有重要意义.考察了X.Y.ZSM-5等沸石分子筛经过钾、钙、钻等金属离子交换改性后,在乳酸甲酯脱水制备生物基丙烯酸甲酯过程中的催化性能.试验结果表明K离子改性Y沸石分子筛对产物的选择性高,而ZSM-5类具有较高的转化率,但是选择性低.分析结果说明:Y分子筛催化剂的高选择性与其特有的骨架结构相关.沸石分子筛催化剂需要通过金属离子的交换才能调整到适当的酸碱性实现最佳催化的效果.在上述结论的基础上.以钾离子改性的NaY分子筛为催化剂,对反应温度.反应空适等反应条件进行了优化得到了较高的丙烯酸甲酯得率.     

Thermal-catalytic degradation kinetics of polypropylene over BEA,ZSM-5 and MOR zeolites

In this study, thermal degradation of additive-free polypropylene powder over different type of zeolite catalysts was investigated. BEA, ZSM-5 and MOR with different surface areas, pore structures, acidities and Si/Al molar ratios were used as solid catalysts for degradation of polypropylene (PP). Degradation rate of the PP over zeolites was studied by thermogravimetric analysis (TGA) employing four different heating rates and apparent activation energies of the processes were determined by the Kissinger equation. The catalytic activity of zeolites decreases as BEA > ZSM-5a (Si/Al = 12.5) > ZSM-5b (Si/Al = 25) > MOR depending on pore size and acidity of the catalysts. On the other hand, initial degradation is relatively faster over MOR and BEA than that over both ZSM-5 catalysts depending on the apparent activation energy. It can be concluded that acidity of the catalyst is the most important parameter in determining the activity for polymer degradation process as well as other structural parameters, such as pore structure and size.     

Synthesis, Characterization, and Catalytic Properties of Nu-1, FU-1, and Related Zeolites

The discovery of the striking catalytic properties of the Mobil zeolite ZSM-5 has been followed by a large and intensive research effort both in catalysis promoted by ZSM-5 and in the synthesis and properties of other highly siliceous zeolites. While the distinctions between ZSM-5 and some of the claimed new zeolites are barely perceptible (it would perhaps be invidious to name these zeolites), other new. highly-siliceous zeolites differ markedly from ZSM-5/ZSM-11 in structure and consequently in other properties as well. Zeolites Nu-1 and FU-1 have now been fairly well characterized in both physical and catalytic properties. Although their crystal structures have not yet been determined, it is clear that they are different from ZSM-5 (and indeed, any other published zeolite structure).     

On the exceptional time-on-stream stability of HZSM-12 zeolite: relation between zeolite pore structure and activity

ZSM-12 and several other 12-membered ring large-pore zeolites have been tested for the reforming of naphthenic hydrocarbon mixtures. It was found that ZSM-12 possesses a surprisingly higher coking resistance than other large pore zeolites tested such as USY, L-zeolite, mordenite, and β=zeolite for reforming of hydrocarbon mixtures. This superior performance is due to the unique non-interconnecting tubular-like linear channels of ZSM-12, which do not allow trapping/accumulation of coking precursors. ZSM-12 zeolite also demonstrated excellent structural stability even under severe acid dealumination. From this work, we found that the decrease of the aluminum content of a zeolite is not sufficient to ensure low rates of coke deposition. We also concluded that zeolites with channel intersections (cavities) of comparable size with the zeolite apertures do not favor coke formation. For these types of zeolites the strong acid sites carry out other acid-catalyzed reactions, rather than forming coke. In contrast, zeolites with relatively large supercages are inherently favorable to coking reactions, which in turn lead to the fast deactivation. The appropriate combination of the zeolite pore structure and acidity (controlled via dealumination) showed superior TOS behavior (time-stable activity and product selectivities). For zeolites which are susceptible to coking due to pore structure, the increase of the Brønsted acid strength results in fast deactivation. Contrary to what one would commonly expect and previous reports, we found that one-dimensional zeolites, such as, ZSM-12, can exhibit significantly higher tolerance to coking than multidirectional zeolites.     

Catalytic pyrolysis of woody biomass in a fluidized bed reactor: Influence of the zeolite structure

Catalytic pyrolysis of biomass from pine wood was carried out in a fluidized bed reactor at 450 °C. Different structures of acidic zeolite catalysts were used as bed material in the reactor. Proton forms of Beta, Y, ZSM-5, and Mordenite were tested as catalysts in the pyrolysis of pine, while quartz sand was used as a reference material in the non-catalytic pyrolysis experiments. The yield of the pyrolysis product phases was only slightly influenced by the structures, at the same time the chemical composition of the bio-oil was dependent on the structure of acidic zeolite catalysts. Ketones and phenols were the dominating groups of compounds in the bio-oil. The formation of ketones was higher over ZSM-5 and the amount of acids and alcohols lower than over the other bed materials tested. Mordenite and quartz sand produced smaller quantities of polyaromatic hydrocarbons than the other materials tested. It was possible to successfully regenerate the spent zeolites without changing the structure of the zeolite.     

Oligomerization of α-octene catalyzed by zeolites

The oligomerization of octene-1 was studied in the presence of zeolites of different structural types (e.g., Y, Beta, ZSM-12, and ZSM-5). It was shown that at 150–200°C, wide-pore zeolite catalysts Y, Beta, and ZSM-12 exhibit high catalytic activity in the reaction. The conversion of catalyzed octene can be as high as 96%, and the yield of oligomers is 88–100 wt %. Zeolite ZSM-5 at 150–180°C has low activity and mainly catalyzes the isomerization of octene-1. As the temperature rises to 250°C, low molecular weight oligomers resulting from the cracking process are the main products of this reaction. The activity and selectivity of zeolite catalysts in the oligomerization of octene-1 are conditioned by their acidic properties and structural characteristics, as well as by the reaction conditions. It was revealed that the main oligomerization products are octene dimers having an alkylnaphthene structure and containing unsaturated hydrocarbons with tri- and tetra-substituted double bonds in amounts of 2.2–3.2%. The properties of the octene oligomers synthesized in the presence of zeolite Beta are similar to the characteristics of hydrogenated poly-α-olefins, the oligomerization of which was performed on AlCl₃ complexes.     

Aldol condensation in gaseous phase by zeolite catalysts

Vapour-phase reactions of, in situ, prepared formaldehyde with methyl propionate were studied using X, Y and ZSM-5 zeolite catalysts. Base properties of these zeolites were enhanced by KOH or NaN₃ treatment. The niobium and molybdenum ZSM-5 zeolite supported oxides were also tested for their catalytic activity. The results are discussed in terms of an ability of zeolite catalysts to synthesize methyl methacrylate.