Fe-zeolites as catalysts for chemical oxidation of MTBE in water with H2O2

The heterogeneous catalytic wet oxidation of methyl tert-butyl ether (MTBE) with hydrogen peroxide, catalyzed by the iron-containing zeolites Fe-ZSM5 and Fe-Beta, was studied at ambient conditions and pH 7. The kinetics of MTBE degradation could be well-fitted to a pseudo-first-order model. Using Fe-ZSM5, the dependence of the reaction rate constant on hydrogen peroxide and catalyst concentration was determined. Furthermore, the formation and oxidation of tert-butyl alcohol and tert-butyl formate as intermediates of MTBE oxidation were studied. A comparison of the reaction rates of MTBE, trichloroethylene and diethyl ether in the Fe-ZSM5/H₂O₂ system revealed that adsorption plays a positive role for the degradation reaction.Comparing the two types of Fe-containing zeolites applied in this study, Fe-Beta showed a lower catalytic activity for H₂O₂ decomposition and also MTBE degradation. However, in terms of utilization of H₂O₂ for MTBE degradation Fe-Beta is advantageous over Fe-ZSM5. This could be explained by the stronger adsorptive enrichment of MTBE on the Fe-Beta zeolite. This study shows that Fe-containing zeolites are promising catalysts for oxidative degradation of MTBE by H₂O₂.     

Dimethyl Ether as a Source of Reactive Species for Alkylation of Benzene

The co-reaction of dimethyl ether and benzene has been investigated on pure and promoted-ZSM-5 catalysts at 473–773 K. It was found that the addition of benzene to dimethyl ether markedly increased the formation of toluene, xylene and C₉ aromatics on ZSM-5 at and above 623 K. This feature is attributed to the reaction of benzene with the reactive hydrocarbon species formed in the decomposition of dimethyl ether on the acidic sites of ZSM-5 zeolite. The extent of the enhancement was further increased by ZnO and Mo₂C promoters.     

The Effect of Different Active Sites on the Catalytic Activity of Fe-ZSM-5 Zeolite for N2O Direct Decomposition

Fe-modified ZSM-5 zeolites (Si/Al = 25) were prepared by adopting the liquid ion-exchange method with nitrate and oxalate of iron as Fe precursors and their catalytic performance was studied in the N₂O decomposition reaction. The results of FT-IR and H₂-TPR investigations indicated that (i) part of the iron ions could replace Brönsted acid protons at the straight channel wall (α sites), intersection of straight and sinusoidal channels (β sites), and sinusoidal channel wall (γ sites) within the ZSM-5 zeolite; and (ii) different Fe precursors gave rise to various distributions of α, β, and γ sites. We observed that the Fe-ZSM-5 catalyst prepared with iron oxalate as Fe precursor outperformed the ones prepared with iron nitrate as Fe precursor in the direct decomposition of N₂O. Furthermore, the catalytic activity of iron ions located at the α sites was higher than those of iron ions located at the β and γ sites.     

Development of catalysts based on pentasil-type zeolites for selective synthesis of lower olefins from methanol and dimethyl ether

Using an integrated physicochemical approach to the study of zeolites and catalysts, scientific foundations for the targeted synthesis of catalysts based on ZSM-5 type zeolites for selective production of lower olefins from methanol and dimethyl ether have been developed. The selective synthesis of the C₂₌ and C₃₌ olefins takes place on medium-strength acid sites. The domination of strong acid sites increases the extent of the secondary oligomerization, aromatization, and cracking reactions and intensifies the deactivation of the catalyst. The effects of reaction conditions (feed partial pressure and temperature) on the outcomes of the process have been investigated. High-efficiency Zn-containing catalysts based on modified pentasils and promoted with magnesium and phosphorus have been developed for C₂₌–C₄₌ olefin synthesis. These catalysts compare well with the industrial catalyst used in the Lurgi process.     

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.     

Characteristics of Fe-exchanged natural zeolites for the decomposition of N2O and its selective catalytic reduction with NH3

Natural zeolites obtained from various regions of Turkey and their iron-exchanged forms were characterised by XRD, BET, H₂-TPR and NH₃-TPD methods. Transient experiments with N₂O showed that the iron introduced into natural zeolites have appreciable oxygen deposition capacity due to isolated iron species involved. Atomic surface oxygen species in these zeolites are formed at 250 °C, which is released through increasing the temperature until 900 °C, similar to Fe-containing ZSM-5 zeolite. The steady-state experiments indicate that the iron-containing zeolite of the Yavu-Sivas region, in particular, has high activity in selective catalytic reduction of N₂O with NH₃ as a consequence of isolated cationic and/or dimeric iron content.     

Fischer-Tropsch synthesis and the generation of DME in situ

Ternary physical mixtures comprised a Fischer-Tropsch catalyst, a methanol synthesis catalyst and a zeolite employed in the hydrocarbon synthesis from syngas. Two Fe-based catalysts (i.e., one promoted by K and the other by Ru), two HY zeolites with different acidities, a commercial HZSM-5 and Cu/ZnO/Al₂O₃ (methanol synthesis catalyst) were used in these systems. The main products obtained were dimethyl ether, methanol and hydrocarbons. First of all, it was observed that by adding Cu/ZnO/Al₂O₃ catalyst to a binary physical mixture comprised of a Fischer-Tropsch catalyst and HZSM-5, the CO conversion increases more than 20 times. Second, during the reaction transient period the dimethyl ether selectivity decreases as the conversion increases. Third, the hydrocarbons synthesized followed the ASF distribution in the C₁-C₁₂ range and finally, it was also verified that the Y zeolites and the Fischer-Tropsch synthesis catalyst promoted by Ru generated the most active physical mixtures. The results showed that the role of zeolites in the ternary physical mixture is only associated with the dimethyl ether synthesis. The following reaction pathway was suggested: first, methanol is synthesized from syngas using Cu/ZnO/Al₂O₃ catalyst; after that, this alcohol is dehydrated by an acid catalyst generating DME; and lastly, DME initiates Fischer-Tropsch synthesis, which is then propagated by CO.     

Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

Kinetics of dimethyl ether oxidation over Pt/ZSM-5 catalyst

A kinetic study of dimethyl ether (DME) combustion over Pt/ZSM-5 was performed below 423 K. Power law model and Langmuir-Hinshelwood model were established to predict the reaction rate. Reaction orders for DME and O₂ were 0.28 and 2.30, respectively. Activation energies for the two models were 99.35 and 109.30 kJ/mol. The reaction orders and adsorption constants suggested DME was more strongly adsorbed on Pt/ZSM-5 than O₂ at low temperatures. The reliability of the models was confirmed by the comparison between the predicted and experimental conversions of DME.     

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.     

Isomerization of α-Pinene Oxide Over Iron-Modified Zeolites

Fe-modified mordenite, ferrierite, Y, ZSM-5, ZSM-12 and beta zeolite catalysts were prepared by solid state ion-exchange and conventional liquid phase ion-exchange methods from aqueous solutions. Sn- modified H-beta-300 zeolite catalyst was prepared by the later method. The characterization of proton form, Fe and Sn modified zeolites was carried out using X-ray powder diffraction, scanning electron microscopy, Mössbauer spectroscopy with magnetic measurements, transmission electron microscopy, nitrogen adsorption, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma spectroscopy, thermo-gravimetric analysis and FTIR spectroscopy using pyridine as a probe molecule. Isomerization of α-pinene oxide over the Fe and Sn modified zeolite catalysts was carried out in the liquid phase using a batch-wise glass reactor. Formation of campholenic aldehyde and fencholenic aldehyde were observed to be influenced by the structure, acidity of zeolite and contents of Fe and Sn, reaction temperature and the catalysts pretreatment.     

Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

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.     

Investigation on the morphology of hierarchical mesoporous ZSM-5 zeolite prepared by the CO2-in-water microemulsion method

A series of hierarchical mesoporous ZSM-5 zeolites with different morphology were successfully synthesized by the CO₂-in-water microemulsion method, and mesoporosity was formed without organotemplate. The different synthesis conditions, including silica alumina molar ratio, stirring time and compressed CO₂ pressure, were systematically investigated to discuss the influence of these conditions on the morphology of ZSM-5 zeolite. The resulting samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP) and nitrogen adsorption-desorption measurement. XRD results indicated that compressed CO₂ route for the synthesis of MFI zeolites had a fast crystallization rate and good crystallinity. SEM images showed that the ZSM-5 hierarchical mesoporous ZSM-5 zeolite had a uniform chain-like crystal morphology, whereas silicalite-1 displayed a monodisperse crystal morphology. In addition, the nitrogen adsorption-desorption measurement provided sufficient evidence for the presence of hierarchical mesopores in ZSM-5 zeolite.     

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.     

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。     

以纯天然矿物为硅铝原料水热合成ZSM-5分子筛

以纯化硅藻土和热活化高岭土为硅铝原料,在水热条件下一步合成纯相ZSM-5分子筛。考察分子筛合成参数对产物的影响,得到合成ZSM-5分子筛的适宜条件:硅藻土与高岭土质量比32∶1,晶化温度170℃,晶化时间48 h,合成体系pH=13. 0。采用XRD、SEM及N2吸附-脱附等对样品进行表征。结果表明,最适宜条件下合成的ZSM-5分子筛晶型完整,具有与工业ZSM-5分子筛相似的六棱柱形貌以及相近的总比表面积和总孔容。     

Synthesis,characterization of Al-rich ZSM-12 zeolite and their catalytic performance in liquid-phase tert-butylation of phenol

Al-rich ZSM-12 zeolites were synthesized using N,N,N′,N′-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium diiodide as template under hydrothermal conditions. Their physico-chemical properties were characterized using XRD, ICP-AES, SEM, N₂ adsorption, ²⁷Al MAS NMR and NH₃-TPD. The results indicated that Al-rich ZSM-12 zeolites with low Si/Al ratios of 8–23 were successfully crystallized. Catalytic properties of the prepared zeolites were studied in the tert-butylation of phenol. Higher para selectivity was obtained on the Al-rich ZSM-12 zeolites compared with other types of zeolites.     

Phosphorus induced hydrothermal stability and enhanced catalytic activity of ZSM-5 in methanol to DME conversion

The change in properties of ZSM-5 samples was achieved by treatment with phosphorus compounds (trimethyl phosphite or phosphoric acid) and the resultant materials were characterized by N₂ adsorption, NH₃-TPD, ²⁷Al, and ³¹P MAS NMR techniques. The phosphorus-treated HZSM-5 (P/ZSM-5) samples exhibited lower acidity, higher hydrothermal stability and improved dimethyl ether (DME) selectivity in methanol conversion when compared to the phosphorus-free HZSM-5. ²⁷Al, and ³¹P MAS NMR results revealed that the added P indeed interacted with the ZSM-5 framework and is responsible for the changes observed in the catalytic properties. The interaction caused the decrease in strong acid sites on one hand and creation of new acid sites (NH₃-TPD) on the other, in P/ZSM-5 samples. The studies indicated the need of optimizing the P loading, where the positive role of P on the catalytic activity was observed to be maximum at P/Al molar ratio of 1.05.     

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。