Benzene to phenol oxidation over iron exchanged zeolite ZSM-5

Zeolite ZSM-5 of different Si/Al ratio, templated and non-templated ones were modified with iron cations introduced by means of ionic exchange from aqueous solution and by solid state procedure. The modified samples calcined in the range of temperatures from 500 to 1000 °C were applied for benzene to phenol hydroxylation. Interaction of benzene and N₂O oxidant with Fe-ZSM-5 was searched by IR spectroscopy. The acidity of the samples was characterised by means of activity for cumene cracking and by IR spectra of adsorbed pyridine. Some correlations between oxidative activity, rate of deactivation and acidity of iron modified zeolites ZSM-5 were discussed.     

The contribution of the methanol-to-aromatics reaction to benzene methylation over ZSM-5 catalysts

The methanol to aromatics conversion is shown to contribute significantly to the benzene methylation with methanol at 400 °C over acidic ZSM-5 catalysts but such contribution over all catalysts is negligible at 250 °C. Benzene-only conversion shows only negligible contribution at both temperatures over the catalysts studied. However, it appears that the methanol-only conversion can be minimised, to enhance the benzene methylation with methanol (and indirectly the oxidative benzene methylation with methane), by using NaZSM-5 with highly reduced Brönsted acidity.     

Diffusion and reaction in ZSM-5 and composite catalysts for the methanol-to-olefins process

Diffusion and reaction in composite catalyst particles were calculated using the dusty-gas-model, Monte Carlo and Molecular dynamics calculations for the determination of multicomponent diffusivities of molecules participating in the methanol-to-olefins synthesis. A three-dimensional model of zeolite structures is presented. Without a fitting parameter, the diffusivities calculated in silicalite give a good approximation to the experimental data. Diffusion and reaction of the MTO synthesis is described with a model employing about 4000 particles.     

负载型ZSM-5分子筛催化剂再生方法研究

吡啶合成中所用的催化剂为负载铅ZSM-5分子筛（Pb-ZSM-5）,活性很好,但反应过程中催化剂很易发生积炭失活。通过对O₂烧炭再生、水蒸汽再生和甲醇再生处理的催化剂进行评价以及进行BET、XRD和TPD 表征,结果表明,甲醇再生方法效果明显,提高了催化剂的寿命。催化剂再生过程要抑制“飞温”现象发生。     

Mn and Zn doped ZSM-5 zeolite catalysts

Manganese was incorporated into a ZSM-5 zeolite by a special impregnation method which practically prevented the deposition of the metal ions on the internal surface of the zeolite pores. As a result, the production of light olefins increased sharply while that of aromatics did not significantly change. The double incorporation of Zn (by ion-exchange) and of Mn (by this impregnation technique) led to catalysts which could produce more aromatics and more light olefins (mainly ethylene and propylene) than the parent ZSM-5 zeolite.     

Phenylhydrazine rearrangement revisited over modified ZSM-5 catalysts

The rearrangement of phenylhydrazine too- andp-phenylenediamines was carried out over ZSM-5 and its modified catalysts. Sm and V showed the promoting effect. In presence of ammonia flow Ga and Cr modified ZSM-5 catalysts gave good yields ofo- andp-phenylenediamines. The better temperature and WHSV for this reaction are found to be 400°C and 0.25 h^–1 respectively. The SiO₂/Al₂O₃ catalyst showed very low ortho-para selectivity when compared with zeolite catalysts.IICT Communication No. 3372.     

Phosphorus poisoning of ZSM-5 and Pt/ZSM-5 zeolite catalysts in diesel exhaust gas conditions

Powdered ZSM-5 and Pt/ZSM-5 catalysts were studied as fresh and after two treatments: hydrothermal ageing and phosphorus poisoning in hydrothermal conditions. The results showed that the deactivating effect of phosphorus was stronger than the effect of the hydrothermal treatment alone. Phosphorus had accumulated in the samples during the ageing. The decrease in specific surface area and increase in Pt particle size indicated the possible reasons for deactivation.     

Differences between ZSM-5 and ZSM-11 zeolite catalysts in 1-hexene aromatization and isomerization

ZSM-5 and ZSM-11 zeolites with high crystallinity are synthesized and tested in the aromatization and isomerization reactions of 1-hexene at 370 °C in a continuous flow fixed bed. The results indicate that ZSM-5 and ZSM-11 zeolites possess similar acid site amount and strength, and most of the acid sites belong to Brønsted acid. When the ZSM-5 and ZSM-11 zeolites were used as catalysts, the aromatics selectivity over ZSM-11 catalyst was higher than that over ZSM-5 catalyst in contrast to i-paraffins selectivity, maybe attributed to that the C₇ and C₈ aromatics have an easier exit from the ZSM-11 zeolite. Moreover, the decrease of particle size can present superior aromatics selectivity and less i-paraffins selectivity in the aromatization and isomerization of 1-hexene over the ZSM-11 catalyst.     

不同双模板剂对ZSM-5分子筛催化剂形貌的影响

固定硅源、铝源和水用量,采用复合模板剂,其中一种模板剂为四丙基氢氧化铵,另一种模板剂为有机胺(乙二胺、1,6-己二胺、异丙胺或三乙胺),通过改变第二种模板剂用量和类型,制备系列ZSM-5分子筛催化剂。采用XRD和SEM进行表征,考察不同双模板剂对ZSM-5分子筛催化剂晶体结构和形貌的影响。结果表明,不同双模板剂合成的产物均为纯相ZSM-5分子筛,且具有较高的结晶度,晶粒外形保持不变,但晶粒尺寸有很大差异,顺序为:四丙基氢氧化铵+三乙胺四丙基氢氧化铵+异丙胺四丙基氢氧化铵+1,6-己二胺四丙基氢氧化铵+乙二胺,可见,只改变模板剂种类而不改变硅源、铝源和水的用量,即可合成相对结晶度高、外形相同但晶粒尺寸不同的ZSM-5分子筛催化剂。     

Catalytic dechlorination of C5 compounds over metal-oxide/ZSM-5 catalysts

In this research, the dechlorination of 2-chloro-2-butene in C5 oil from the fluid catalytic cracking (FCC) process was performed through a catalytic reaction. Metal oxides were used as active materials and ZSM-5 was used as the supporting material for the catalysts; the metal was cobalt, iron, or manganese. After the preparation of three types of metal-oxide/ZSM-5 catalysts through the ion-exchange method, the activities and characteristics of each catalyst were evaluated. Through screening tests, the Co₃O₄/ZSM-5 catalyst was selected as the dechlorination catalyst, and the performance of catalysts containing different amounts of Co₃O₄ relative to ZSM-5 were tested.     

Selective catalytic reduction of nitric oxide with ethane and methane on some metal exchanged ZSM-5 zeolites

The selective reduction of nitric oxide by methane or ethane, in the presence and in the absence of a large excess of oxygen, has been investigated on Cu/ZSM-5, Co/ZSM-5, Rh/ZSM-5 and Pt/ZSM-5 catalysts over a wide range of temperatures. It has been found that the maximum nitric oxide conversion is higher with ethane than with methane and the temperature of this maximum is lower with ethane. In the absence of oxygen the order of activity is Rh/ZSM-5>Pt/ZSM-5>Co/ZSM-5> Cu/ZSM-5 with the Cu/ZSM-5 being essentially inactive, while in the presence of oxygen the order is: Rh/ZSM-5>Co/ZSM-5>Cu/ZSM-5> Pt/ZSM-5 when ethane is used as reductant and: Rh/ZSM-5>Co/ZSM-5> Cu/ZSM-5>Pt/ZSM-5 when methane is used. The effect of the oxygen content has been investigated for the Co/ZSM-5 catalyst. It has been found that with a small quantity of oxygen the catalytic activity decreases markedly; with higher oxygen content the activity of the catalyst rises again. It appears that two different reaction schemes may be operative, one in the absence of oxygen the other in the presence of oxygen. It is concluded that neither carbonaceous deposits, nor nitrogen dioxide formation in the gas phase are important in the reaction mechanism on metal-containing zeolites. It is proposed that the reaction is essentially a redox process in which decomposition of nitric oxide occurs on reduced metallic or metal ion sites (the relative activity of each of these depending on the choice of metal), leading to the formation of gaseous nitrogen and adsorbed oxygen, followed by the removal of the adsorbed oxygen by the hydrocarbon, thus recreating the active centres.     

The synthesis and testing of thin film ZSM-5 catalysts

The synthesis and catalytic testing of thin ZSM-5 films on glass and alumina beads is described. The thickness of the ZSM-5 films was controlled to 150, 350, 800 and . The samples were characterised by SEM, gas adsorption and p-xylene isomerisation and 1,3,5-tri-isopropyl benzene cracking test reactions. A reaction-diffusion model adequately described the p-xylene isomerisation data. Estimates of model parameters were obtained by fitting the model to the experimental data. In both cases, the reaction rate constant increased with increasing film thickness. The xylene reaction data showed that secondary reaction products increased as expected with increasing diffusion limitations, but the increase was less than that predicted by the variation of thickness only. The trends in the reaction data could be explained by more defects in the thicker films and/or partial poisoning of the zeolite by mobile support cations in thinner films and/or orientation effects.     

Infrared study of nitrogen monoxide adsorption on palladium ion-exchanged ZSM-5 catalysts

The adsorption of NO at room temperature on a H-ZSM-5 catalyst exchanged with Pd(NH₃) ₄ ²⁺ complex and activated in oxygen at 773 K has been examined by FTIR spectroscopy. After the oxidizing treatment, the Pd tetrammine complex decomposed into Pd(II) ions and/or Pd(II) hydroxyl complexes dispersed in the zeolite channels. The subsequent adsorption of NO at room temperature led to the reduction of Pd(II) to Pd(I) entities, resulting in the formation and adsorption of NO₂ on H-ZSM-5. The Pd(I) entities were shown to adsorb NO and form mononitrosyl complexes dispersed in the zeolite porosity and characterized by a single infrared absorption band at 1881 cm^–1. The Pd(I) mononitrosyl complex was shown to reversibly coordinate water and NO₂ molecules. The resulting nitrosyl complex was characterized by a single NO vibration band at 1836 cm^–1.     

Diffusion and catalytic reaction in zeolite ZSM-5

Rates of reaction and product-distributions for small and large pellets and for small and large crystals of the same zeolite-preparation (H-ZSM-5) were observed in order to evaluate the influence of diffusion (concentration-gradients) on the conversion of (CH₃)₂O to hydrocarbons with this catalyst. Diffusivities of (CH₃)₂O and C₆H₆ in the zeolite crystals were obtained from sorption kinetics. Macropore-diffusion affects activity and selectivity if pellets with dia > 2 mm are used; intracystalline mass-transfer does not seem to be important with respect to catalyst-activity and selectivity at temperatures below 600 K. The conventional model of diffusion and reaction in porous catalysts can not be applied to the entire reaction-network in the zeolite-crystals, because migration of olefins in the zeolite can not be understood as random-walk diffusion.     

Combustion of methane over palladium ZSM-5 and mordenite catalysts

The effect of Pd-loading on Pd-NaZSM-5 and Pd-NaMordenite catalysts prepared by ion exchange was studied for methane combustion with excess oxygen (1% CH₄, 18% O₂, balance N₂) in the temperature range 40–500°C. Fresh and calcined samples (3 h, 450°C) showed methane conversions proportional to Pd-loading on Pd-NaZSM-5 catalysts, while conversions decreased with Pd-loading on calcined Pd-NaMordenite catalysts. TOF (number of methane molecules converted per second per Pd²⁺ ion) for over exchanged Pd-NaZSM5-116 was low as compared to under exchanged Pd-NaZSM5-80 and Pd-NaZSM5-58 samples. Close TOF's were found for the last two samples at 330°C. TOF differences in Pd-NaMordenite catalysts demonstrate the heterogeneity of Pd⁺² sites due to structurally nonidentical locations of cations. TOF's appear to be related to Na/Pd ratios in both catalyst types. Apparent activation energies for Pd-NaZSM-5 materials are higher than those for Pd-NaMordenite catalysts.     

不同载体成型的ZSM-5催化剂上甲醇芳构化反应性能

以ZSM-5分子筛为活性组分,采用不同的氧化物载体挤条制备催化剂,并对催化剂的甲醇芳构化反应性能进行评价。采用X射线衍射、氨程序升温脱附和N₂低温吸附-脱附等方法对催化剂进行表征。结果表明,添加氧化物载体后,催化剂的芳构化反应性能明显提高,催化剂芳构化反应性能与其酸性质有着密切联系,Zn/La-ZSM-5(Al₂O₃)催化剂的芳构化反应性能较好,主要归因于催化剂具有适宜的酸分布和孔结构。在反应压力0.1 MPa、空速0.8 h^-1、反应温度437 ℃和反应时间240 min条件下,轻质芳烃收率为42.36%.     

碱酸处理ZSM-22分子筛催化剂的MTO性能研究

首先用一定浓度的Na_2CO_3溶液处理ZSM-22分子筛,然后再用HCl溶液进行酸洗,得到多级孔ZSM-22分子筛。采用XRD、SEM、BET、FTIR、NH3-TPD等手段研究碱酸处理对ZSM-22分子筛物化性能的影响,并将其作为催化剂用于甲醇制低碳烯烃(MTO)反应。结果表明,碱酸处理后的样品结晶度维持较好,且拥有较高的比表面积和微孔-介孔结构。碱酸处理可选择性地脱除分子筛的部分强酸中心。其中利用0. 2 mol/L Na_2CO_3处理后再用0. 1 mol/L HCl酸洗得到的ZSM-22分子筛催化剂,在其低碳烯烃选择性基本保持不变的基础上,MTO反应寿命可显著提高。     

碱酸处理ZSM-22分子筛催化剂的MTO性能研究

首先用一定浓度的Na_2CO_3溶液处理ZSM-22分子筛,然后再用HCl溶液进行酸洗,得到多级孔ZSM-22分子筛。采用XRD、SEM、BET、FTIR、NH3-TPD等手段研究碱酸处理对ZSM-22分子筛物化性能的影响,并将其作为催化剂用于甲醇制低碳烯烃(MTO)反应。结果表明,碱酸处理后的样品结晶度维持较好,且拥有较高的比表面积和微孔-介孔结构。碱酸处理可选择性地脱除分子筛的部分强酸中心。其中利用0. 2 mol/L Na_2CO_3处理后再用0. 1 mol/L HCl酸洗得到的ZSM-22分子筛催化剂,在其低碳烯烃选择性基本保持不变的基础上,MTO反应寿命可显著提高。     

Hydrogen back-spillover effects in the aromatization of ethylene on hybrid ZSM-5 catalysts

The involvement of hydrogen back-spillover is confirmed for the aromatization of ethylene. Using hydrogen monitoring during catalytic reactions with ethylene, it has been observed that the amount of hydrogen in the gaseous effluents is much more important on hybrid catalysts than on pure ZSM-5 zeolites. The active sites on ZnO based co-catalysts are believed to be partial reduction zinc sites created during the induction period. ZnO precipitate favors the release of hydrogen species as ethane. ZnO/Al₂O₃ co-precipitate favors hydrogen recombination.