Effect of zeolite pore geometry on isomerization of n-butane

A comparative study of isomerization of n-butane over bifunctional catalysts based on zeolites with different pore geometry (ZSM-5 and mordenite) and with metal particles located inside and/or outside the zeolite main channel system has been carried out. 1,1,1,3,3,3-hexamethyldisilazane was used in order to obtain catalysts with external Brönsted acid sites poisoned. TPDA, FTIR, TPR and TEM techniques were used to characterize the catalysts. ZSM-5 catalysts were quite resistant to poisoning, mainly when metal sites were located inside the pore system. However, isomerization activity was virtually suppressed for the poisoned mordenite catalysts. It is proposed that the isomerization via C₈ formation cannot take place inside the one-dimensional pore system of mesopore-free mordenite catalysts, but this is not the case for isomerization on ZSM-5.     

Synergism between Brønsted acid sites and metal sulfide particles in the hydrodesulfurization of thiophene on ultrastable Y zeolite catalysts W/USY and Ni/USY

The influence of the acidity of ultrastable Y (USY) zeolite-supported tungsten or nickel sulfide catalysts, prepared at different pH values, on thiophene hydrodesulfurization activity has been studied. The acidity affects the catalysts' deactivation. The results of the initial activity clearly show a synergic effect between the metal sulfide centers and the Brønsted acid sites present in the zeolites. © 1998 SCI     

Partial oxidation of butane to syngas using nano-structure Ni/zeolite catalysts

In this study, performance of nano-structure Ni over different zeolite supports in partial oxidation of butane was investigated. First, partial oxidation process was performed without catalyst to evaluation of optimal conditions. For in situ reduction of catalysts, H₂ produced from homogenous reaction was used. Catalytic partial oxidation was carried out using nano-structure nickel catalysts supported by ZSM5, mordenite and Y. Each catalyst was synthesized through reverse microemulsion method. The catalysts were characterized by BET surface area, XRD, SEM and TGA. Highest butane conversion (≈89%) observed in the presence of Ni/Y catalyst. Also Ni/Y shows the highest overall selectivity to CO and H₂ as the most desired partial oxidation products. Results from TGA showed that the minimum quantity of formatted coke was related to Ni/Y, which confirmed the stability of butane conversion versus time for this catalyst.     

分子筛在双功能催化剂中催化CO/CO2加氢研究进展

双功能催化剂可将CO/CO_2加氢直接合成低碳烯烃、芳烃和汽油等,具有工艺流程短、能耗低的优势。双功能催化剂由金属氧化物和分子筛两部分组成,分子筛特定的腔体结构、酸性质及与金属氧化物的结合方式等均可显著影响其催化性能。该文综述了近年来分子筛在双功能催化剂中用于CO/CO_2加氢反应的研究进展,简述了分子筛的类型、酸性质、形貌及颗粒尺寸、金属改性、分子筛与金属氧化物的结合方式等对双功能催化剂催化性能的影响规律,展望了双功能催化剂中分子筛的发展趋势。     

Iron ion-exchanged zeolite: the most active catalyst at 473 K for selective reduction of nitrogen monoxide by ethene in oxidizing atmosphere

Among various metal ion-exchanged zeolites, metal loading alumina, and oxides, iron ion-exchanged mordenite was the most active for the selective reduction of nitrogen monoxide to nitrogen by ethene in the presence of oxygen at the temperature as low as 473 K. The catalytic activities of iron ion-exchanged zeolites depended on the zeolite structure and the iron ion exchange level. The effects of the zeolite structure are in the order of MOR > FER > MFI > Y > LTL at 473 K. The activity of iron ion-exchanged mordenite increased with the increment in the exchange level and levelled off above about 60%.     

Investigation on the textural characteristics of supported nickel hydrogenation catalysts

Nickel catalysts supported on a range of carriers such as kieselguhr, silica, γ-alumina, silica-alumina and mordenite were investigated in order to gain an understanding of their structural properties. The surface area and pore distribution characteristics of the carriers and unreduced catalysts obtained from nitrogen adsorption isotherms gave strong indications that the formation of the nickel salt submerged the carrier. Metallic nickel produced after reduction at high temperature was perhaps present in the macropores or on the outer surface of the carrier forming a microporous network of fine crystallites. The metal surface area of the catalyst in its reduced state, calculated from hydrogen chemisorption data, was not influenced by the specific surface area of the carrier. Among the different carriers, the nickel-carrier interaction was mainly found with kieselguhr and silica. Activity of the different catalysts in the hydrogenation of unsaturated fatty acid was found to be directly related to the metal area.     

FTIR spectroscopic and1 H MAS NMR studies of the influence of lattice chemistry and structure on Brønsted acidity in zeolites

The influence of the Si/Al ratio, of the nature of the T-atom and of the pore size on the acidic strength of Brønsted sites in zeolites has been investigated using changes of the vibrational properties of Brønsted OH(OD) groups and a shift change of Brønsted protons in nuclear magnetic resonance upon adsorption of weak bases. Deuterated acetonitrile and trichloro-acetonitrile have been chosen to probe the acidic strengths of ZSM-5, FeZSM-5, mordenite and zeolite Y, which are often used as catalysts. From the results of the FTIR and 1 H MAS NMR studies it can be concluded that the chemical composition of the lattice dominates the acidic strength of the Brønsted sites in zeolites. Differences in structure or pore size play a much smaller role.     

Transesterification of sunflower oil over zeolites using different metal loading: A case of leaching and agglomeration studies

The aim of this study was to analyse the catalytic performance of several heterogeneous catalysts in the transesterification of sunflower oil with methanol. In order to characterize the different catalysts, nitrogen adsorption/desorption and CO₂ temperature programmed desorption were used. The transesterification of sunflower oil was carried out using three different zeolites: mordenite, beta and X, to determine the influence of the kind of zeolite on the methyl ester production. The influence of the metal incorporation technique was studied using both impregnation and ion-exchange methods. Also, the transesterification reaction was carried out using catalysts with different metal loading. Finally, zeolite X was agglomerated with a binder, sodium bentonite, to study how the presence of a binder could change the catalytic performance of the zeolite. A methyl ester content of 93.5 and 95.1 wt% was obtained at 60 °C employing zeolite X with or without sodium bentonite, respectively. All biodiesel synthesized were characterized using the standard UNE-EN 14214. A complete deactivation study was carried out in order to check the sodium leaching from the catalyst. The results supported the hypothesis of a homogeneous-like mechanism where the alkali methoxide species were leached out.     

The hydrogenation of toluene over nickel loaded Y zeolites

The catalytic activities of a range of hydrogen reduced nickel Y zeolites for the hydrogenation of toluene were measured and correlated with the following catalytic parameters: reaction temperature; reaction time; coke deposition. The role of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺) in influencing the overall hydrogenation activity of the supported nickel metal was probed. The effect of poisoning the surface Bronsted acidity by the adsorption of ammonia is discussed. For comparative purposes, data on the hydrogenation of benzene over the same catalysts are included.     

Generation, Characterization, and Impact of Mesopores in Zeolite Catalysts

Amongst the current developments in the field of hierarchical pore structures, the creation of mesopores in zeolite crystals is the most frequently employed way to combine micropores with mesopores in one material. In this review an overview is presented of the different approaches to generate and characterize mesopores in zeolite crystals and establish their impact on the catalytic action. Mesopores can be created via several routes from which steaming and acid leaching are the most frequently applied. Novel approaches using secondary carbon templates that are removed after synthesis have recently been launched. For the characterization of mesopores, nitrogen physisorption and electron microscopy are commonly used. More recently, it was shown that electron tomography, a form of three-dimensional transmission electron microscopy, is able to reveal the three-dimensional shape, size, and connectivity of the mesopores. The effect of the presence of mesopores for catalysis is demonstrated for several industrially applied processes that make use of zeolite catalysts: the cracking of heavy oil fractions over zeolite Y, the production of cumene and hydroisomerization of alkanes over mordenite, and synthesis of fine chemicals over Y, ZSM-5, and Beta. For these processes, the mesopores ensure an optimal accessibility and transport of reactants and products, while the zeolite micropores induce the preferred shape-selective properties.     

Esterification of oleic acid in soybean oil on zeolite catalysts with different acidity

The catalytic activity of zeolites was studied in the esterification of oleic acid with methanol in soybean oil. The influences of acidity and pore structure of the zeolites were investigated in relation to conversion of the oleic acid on the zeolite catalysts. H⁺ ion exchanged ZSM-5 (HMFI) and mordenite (HMOR) zeolites conducted with different Si/Al ratio were employed to examine an influence of acidity in the reaction. Conversion of oleic acid was about 80% on HMOR zeolites and HMFI(25) zeolite. The conversion of oleic acid was improved as the amount of acid site increased. The amount of acid site of the zeolites affected significantly the catalytic activity in the esterification of oleic acid.     

Side-chain alkylation of 2,6-lutidine to 2,6-divinylpyridine over basic zeolites

Synthesis of 2,6-divinylpyridine (2,6-DVP) and 2-methyl-6-vinylpyridine (2M6VP) was achieved for the first time by side-chain alkylation of 2,6-lutidine using formaldehyde (37 wt/v) as alkylating agent in heterogeneous conditions at atmospheric pressure, and at a reaction temperature of 300 °C over alkali and alkaline metal ion modified zeolites. A mixture of 2,6-divinylpyridine and 2-methyl,6-vinylpyridine were formed by the alkylation of the 2,6-lutidine over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of 2,6-lutidine was studied over various potassium metal ion modified zeolite molecular sieves like ZSM-5 (30), X, Y, mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2,6-lutidine when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) gave best conversion of 2,6-lutidine and selectivity to 2-methyl,6-vinylpyridine. K-ZSM-5 (30) catalyst was employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2,6-lutidine. The effect of potassium metal ion content and precursors of potassium ion on catalytic activity in side-chain alkylation of 2,6-lutidine was studied. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed mechanism. The selectivities of 2,6-DVP were 45.2, 40.0, and 30.7% at 73.4, 66.0 and 60.5% conversion at 300 °C from 2,6-lutidine and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and Cs-K-ZSM-5 (30), respectively.     

New effective catalysts based on mesoporous nanofibrous carbon for selective oxidation of hydrogen sulfide

The systems based on granular mesoporous nanofibrous carbonaceous (NFC) materials synthesized by decomposition of hydrocarbons over nickel-containing catalysts are promising catalysts for selective oxidation of hydrogen sulfide. Sample series of nanofibrous carbon with three main types of their fiber structures and different contents of metal catalysts inherited from the catalysts for their synthesis were studied in this reaction. The correlation between NFC structure and its activity and selectivity in hydrogen sulfide oxidation was determined. The metal inherited from the initial catalysts for the synthesis of NFC influences the activity and selectivity of the resulting carbon catalysts. A particular influence is observed in the case of the catalyst withdrawn from the synthesis reactor at the stage of stationary operation of the metal catalyst (low specific carbon yields per unit weight of the catalyst). The presence of the metal phase results in an increase in the carbon catalyst activity and in a decrease in the selectivity to sulfur. NFC samples with the highest activity and selectivity are nanotubes and those with graphite planes perpendicular to the axis of the fibers. Carbon nanotubes have high selectivity, while samples obtained on copper–nickel catalysts also possess high activity. The promising NFC catalysts provide high conversion and selectivity (almost independent of the molar oxygen/hydrogen sulfide ratio) when a large excess of oxygen is contained in the reaction mixture.     

Nitrous oxide as an oxidant for ethane oxydehydrogenation

Waste nitrous oxide was used as an oxidant for ethane oxydehydrogenation performed at the range of temperature from 350 to 450 °C over iron modified zeolite catalysts. Different zeolite matrices (zeolite ZSM-5 of different Si/Al ratio, H-Y, mordenite) modified with iron cations introduced into zeolite by means of ionic exchange were applied as catalysts for the reaction under study. Additionally, amorphous silica and alumina silica as well as silicalite of MFI structure were also used as a matrix for iron ions accommodation and they were tested for oxydehydrogenation reaction. It was found that only iron modified zeolites showed activity for reaction under study. Amorphous oxide supports and crystalline neutral silicalite modified with iron cations by means of impregnation were completely inactive for oxydehydrogenation reaction. The best catalytic performance was found on iron modified zeolites of MFI structure. The Si/Al ratio of the ZSM-5 matrix influenced the activity for ethane oxydehydrogenation reaction insignificantly. N₂O oxidant was partly utilized for ethane oxidation (towards ethene or carbon oxides), while some part of the oxidant was decomposed to nitrogen and oxygen. Performing the reaction at 450 °C resulted in a high ethene yield and complete N₂O removal.     

Deactivation of metal exchanged zeolite catalysts during exposure to chlorinated hydrocarbons under oxidizing conditions

Deactivation of modified cation exchanged zeolite catalysts was studied during complete oxidation of methylene chloride, trichloroethylene and carbon tetrachloride over a temperature range of 175 to 400°C. Coking was found to be the cause of deactivation. However, the catalysts could be completely regenerated by oxidation in air at 450°C. Two different formulations of modified cobalt exchanged Y zeolite catalysts were tested to determine the coking and deactivation rates. Increased cation content increased deactivation and coking over a period of about 1000 hours. Changing the type of zeolite from larger pore Y to medium pore mordenite increased deactivation. The type of chlorinated feed also affected coking and deactivation with the rate of deactivation increasing in the order of trichloroethylene> methylene chloride> carbon tetrachloride. Both coking and deactivation increased with decreasing temperature. Higher space velocity produced more deactivation for trichloroethylene oxidation at 275°C. Based on these results a mechanism for coking is proposed with CO as the possible reaction intermediate that leads to the formation of coke.     

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.     

Template synthesis of novel porous carbons using various types of zeolites

As previously reported, high surface area microporous carbons with long-range order can be synthesized by using zeolite Y as a template. In this work, an attempt is made to synthesize porous carbon using several other types of zeolites (zeolite β, ZSM-5, mordenite and zeolite L). Special attention is paid to whether the structural regularity of each zeolite can be transferred to the carbon structure as well as with the case of zeolite Y. The carbon filling method was then examined to see which gives the highest regularity to the carbon structure. It has been found that the optimum carbon filling method for zeolite Y is not an optimum one for the other zeolites and the degree of the regularity of long-range ordering in the carbons strongly depends on zeolite type. The order of the regularity in the resultant carbons is zeolite β>>zeolite L>mordenite>ZSM-5. The effect of zeolite type on the regularity is discussed in relation to the size and the shape of the zeolite channels.     

Preparation and Application of Faujasite-Type Y Zeolite-based Catalysts for Coal Pyrolysis using Sodium Silicate Solution and Colloidal Silica as Silicon Source

Using zeolites as catalysts of coal pyrolysis for production of valuable chemical compounds such as aromatics is being widely investigated and has shown promising results. In this study, pure faujasite-type Y zeolite crystals were successfully synthesized by a direct hydrothermal method with sodium silicate solution and colloidal silica as the silicon sources, without any seeding gel. A novel approach was adopted to directly synthesize zeolites impregnated with nickel oxide. Moreover, a batch reactor was designed to increase the silica/alumina ratio (SAR) of the zeolites by dealumination process without causing significant damage to the zeolite structure. The various analysis methods were employed to characterize the parent and modified zeolites, and the fabricated zeolites were applied in coal pyrolysis experiments. The results are presented in order to show the catalytic performance of the faujasite-type Y zeolites for application in coal pyrolysis process.     

Y型分子筛介孔改性的研究进展

Y型分子筛在催化裂化领域有着极其重要的应用,对其的介孔改性研究也引起了国内外研究者的广泛关注。本文综述了近年来Y型分子筛介孔改性的方法,指出了各种方法的优缺点,重点评述了高温水蒸气脱铝过程以及使用孔导向剂脱硅过程中介孔的形成机理,分析了通过脱铝和脱硅向Y型分子筛引入介孔时对其酸性和水热稳定性产生的影响。对介孔改性后的Y型分子筛的应用进行了总结,认为介孔改性的Y型分子筛将广泛应用于煤、生物质及其他含碳原料催化转化等领域。     

Methane Combustion over Pd Catalysts Loaded on Medium and Large Pore Zeolites

Methane combustion was conducted over Pd catalysts supported on medium (ZSM-5, ferrierite, TNU-9, TNU-10) and large (USY, mordenite, beta) pore zeolites. Among the catalysts studied here, Pd/H-TNU-10 exhibited the highest combustion activity, together with excellent durability in the presence of water vapor. A combination of TEM and Pd K-edge XAFS measurements reveals the formation of highly dispersed PdO particles within the TNU-10 pores. This is also the case of Pd/H-ferrierite, while frequently there are large particles (60–100 Å) on its outer surface. In contrast, most of PdO on zeolites other than these two medium pore materials were found to exist as aggregated particles (>50 Å) on their outer crystallite surface. It appears that zeolite structures with intersecting 10- and 8-ring pores may be better supports for stabilizing nanometric PdO particles than those with the uniform 10-ring size or with the 12-ring pore system.