Conversion of methanol to light olefins over zeolite H-T

The conversion of methanol over zeolite H-T was investigated in a fixed bed reactor. H-T was prepared from Na-T by ion exchange with HCl and NH₄Cl solutions. The HCl solution caused appreciable dealumination. High yields of ethene were obtained with NH₄Cl exchangeed zeolites Na-T with 45% decationization, high proprne yields with low HCl or NH₄Cl Exchanged catalysts. Low methanol partial pressures and short residence times favoured the formation of lower olefins. Lowest coking rates were observed at a reaction temperature of 693 K. The catalytic activity decrased slowly with the number of reaction/regeneration cycles. The distribution of procucts > C₂ could be described by the most probable distribution of Schulz and Flory.     

Deactivating species in the transformation of crude bio-oil with methanol into hydrocarbons on a HZSM-5 catalyst

A study has been carried out by using different techniques (TPO, FTIR, Raman, ¹³C NMR, GC/MS of the coke dissolved in CH₂Cl₂) on the nature of the coke deposited on a HZSM-5 catalyst modified with Ni in the transformation of the crude bio-oil obtained by flash pyrolysis of lignocellulosic biomass (pine sawdust) into hydrocarbons. The reaction system has two steps in-line. In the first one, the components of crude bio-oil derived from the pyrolysis of biomass lignin are polymerized at 400 °C. In the second one, the remaining volatile oxygenates are transformed into hydrocarbons in a fluidized bed catalytic reactor at 450 °C. The reaction has been carried out with different bio-oil/methanol mass ratios in the feed (from 100/0 to 0/100). Co-feeding methanol significantly attenuates coke deposition, and the nature of the coke components varies according to the bio-oil/methanol ratio in the feed. When bio-oil is co-fed, the coke deposited on the catalyst has a significant content of oxygenates and oxo-aromatics and consists of two fractions, identified by temperature programmed oxidation, corresponding to external and internal coke in the zeolite crystals. The fraction of external coke is soluble in CH₂Cl₂, with a high content of oxygenates and oxo-aromatics, and is generated by polymerization of products derived from biomass lignin pyrolysis activated by the zeolite acid sites. The fraction of coke retained within the zeolite crystals is partially insoluble and is formed by several routes: from the intermediates in the transformation of both methanol and bio-oil oxygenates into hydrocarbons; by evolution of the other coke fraction; from the hydrocarbons (with high aromatics content) in the reaction medium.     

Stabilization of CuZSM-5 NOx reduction catalysts with lanthanum

The effects of high temperature steam treatment on the activity and selectiv ity of CuZSM-5 catalysts for the selective catalytic reduction of NO with propene have been examined. Loss of activity and selectivity on steam treatment is due to framework dealumination of the zeolite, which causes migration of Cu out of the zeolite pores to the external surface. Pre-exchange of the zeolite with La³⁺ cations inhibits the dealumination, preventing migration of Cu to the surface and allowing the catalyst to retain high activity and N₂ selectivity after steam treatment. The deactivation of the catalysts was monitored using X-ray powder diffraction, magic angle spinning²⁷Al and²⁹Si nuclear magnetic resonance, X-ray photoelectron spectroscopy and ion scattering spectroscopy.     

Catalysts based on ferrierite for the selective hydrocracking of <Emphasis Type="Italic">n</Emphasis>-hexane

Supported platinum catalysts based on ferrierite type zeolite with Pt content in the range of 1.3–2.8 wt % are prepared. The localization of Pt in zeolite channels is studied for the first time. It is shown that the platinum localized in them increases the yield of products from the selective hydrocracking of n-hexane. Platinum on the outer surface of the zeolite crystals participates in the transformation of n-hexane in the direction of forming hydrocarbons with isomeric structure. The catalysts can be used to improve the octane rating of reformed gasoline, owing to the selective removal of low-octane n-paraffin hydrocarbons and the increase of the portion of high-octane isoparaffin hydrocarbons in the catalytic reforming gasolines.     

One Pot Direct Catalytic Conversion of Cellulose to Hydrocarbon by Decarbonation Using Pt/H-beta Zeolite Catalyst at Low Temperature

We investigated one pot direct catalytic conversion of cellulose to light hydrocarbon selectively at low temperature in the presence of Pt and solid-acid zeolite catalysts. Results revealed that Pt/H-beta zeolite catalyst prepared by ion exchange enabled selective production of C₃ and C₄ hydrocarbons.     

Stable and Selective Dehydrocondensation of Methane Towards Benzene on Modified Mo/HMCM-22 Catalyst by the Dealumination Treatment

A modified Mo/HMCM-22 catalyst by the dealumination treatment (Mo/HMCM-22-D) exhibited remarkable performance for the catalytic dehydrocondensation of methane with a higher selectivity of benzene and a lower selectivity of coke, in comparison with the same Mo catalyst supported on parent HMCM-22 (Mo/HMCM-22). Excellent catalytic stability as well as a high benzene formation rate of 1500 nmol/(g-cat·s) was obtained on a 6%Mo/HMCM-22-D catalyst at 1023 K, 3 atm and 2700 ml/(g·h) owing to the efficient suppression of coke formation. Dealumination of the HMCM-22 zeolite was characterized by XRD, ²⁷Al and ¹H MAS NMR and NH₃-TPD techniques. It was found that the dealumination treatment of HMCM-22 zeolite resulted in an effective suppression of acid sites, particularly the Brønsted acid sites (proton form in Al--O--Si) owing to the removal of tetrahedral framework aluminum, while the microporous structure and the zeolite framework remained unchanged. It was suggested that the stable and selective dehydrocondensation of methane towards benzene is based on the suppression of coke formation owing to the effective decrease of strong Brønsted acid sites by the dealumination treatment of the HMCM-22 zeolite.     

Transformation of methanol to gasoline range hydrocarbons using HZSM-5 catalysts impregnated with copper oxide

Various CuO/HZSM-5 catalysts were studied in a fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. The catalysts were prepared by wet impregnation technique. Copper oxide loading over HZSM-5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, BET surface area, metal oxide content, scanning electron microscopy (SEM) and thermogravimetric (TGA) techniques were used to characterize the catalysts. Higher yield of gasoline range hydrocarbons (C₅-C₁₂) was obtained with increased weight % of CuO over HZSM. Effect of run time on the hydrocarbon yields and methanol conversion was also investigated. The activity of the catalyst decreased progressively with time on-stream. Hydrocarbon products’ yield also decreased with the increase in wt% of CuO. Relatively lower coke deposition over HZSM-5 catalysts was observed compared to CuO impregnated HZSM-5 catalyst.     

Palladium-exchanged MFI-type zeolites in the catalytic reduction of nitrogen monoxide by methane. Influence of the Si/Al ratio on the activity and the hydrothermal stability

Pd-exchanged MFI-type zeolites containing 3.7 and 0.7 framework aluminium atoms per unit cell (corresponding to Si/Al ratios of 25 and 131) were found active in the selective reduction of nitrogen monoxide in the presence of excess oxygen. Upon steaming at 800°C, both catalysts exhibited the total loss of their catalytic activity in the reduction of NO. Such a behaviour was ascribed to the complete aggregation of Pd ions into large metal particles on the external surface of the zeolite crystals. Both supports, although maintaining their crystallinity, are shown to experience extended dealumination upon steaming. Although the loss of Pd exchange capacity could partially explain the Pd migration and sintering, a mechanism involving the formation of mobile Pd hydroxyl entities condensing into PdO particles outside the zeolite crystallites is preferred.     

Hydrothermal study of Pt–Sn-based SAPO-34 supported novel catalyst used for selective propane dehydrogenation to propylene

Catalyst's regeneration is unavoidable part during dehydrogenation. The hydrothermal treatment influence on the performance of Pt–Sn-based SAPO-34 supported novel catalyst, used for propane dehydrogenation to propylene is investigated in this study. The catalyst shows excellent stability for mild steaming (nitrogen mixed steam), during four consecutive runs (reaction–regeneration mode). On the other hand, Pt–Sn/ZSM-5 was largely affected on mild steaming due to severe dealumination. In order to get into mechanistic understanding, severe hydrothermal treatment was carried our using pure steam. The substation loss in catalyst activity was noted. Both fresh and severe hydrotreated catalysts were characterized by XRD, XRF, O₂-pulse analysis of coke, NH₃-TPD, IR spectrum of adsorbed ammonia, H₂-TPR, HR-TEM and XPS, to explore reasons for change in catalytic properties. The texture/topology is found stable. Changes in surface ensembles occur due to the loss of Sn, Al, formation of SnO_x species and in particular Pt sintering. This leads Pt active sites (zeolite–SnO–Pt) to inactive sites (zeolite–Pt, zeolite–PtO–Sn, Pt–Sn alloy, etc.) formation and reduced catalyst activity. TEM micrographs and H₂-chemisorption analysis confirms Pt particles agglomeration and/or sintering. About 98% catalyst activity is recovered by re-dispersed Pt using chlorination technique and credit goes to hydrothermally stable support (SAPO-34).     

Hydrothermal stability of HZSM-5 catalysts modified with Ni for the transformation of bioethanol into hydrocarbons

The hydrothermal stability of catalysts prepared from HZSM-5 zeolites doped with Ni (by impregnation) has been studied in the transformation of bioethanol into hydrocarbons, in order to remove the main barrier for the use of HZSM-5 zeolite catalysts in this process, which is the irreversible deactivation by dealumination of the zeolite above 400 °C with water in the reaction medium. The main effect of doping is the attenuation of the zeolite acid strength from 135 to 125 kJ (mol of NH₃)⁻¹ for a Ni content of 1 wt.%. The catalysts maintain a high level of activity and a high selectivity of propene and butenes, and Ni doping significantly attenuates irreversible deactivation of the catalyst by dealumination of the zeolite. The zeolite catalyst doped with 1 wt.% of Ni maintains its kinetic behaviour in reaction-regeneration cycles when the reaction step is carried out at 500 °C and with 5 wt.% of water in the feed. This catalyst allows operating at 400 °C without irreversible deactivation with bioethanol containing 75 wt.% of water.     

Performance of modified H-ZSM-5 zeolite for dehydration of methanol to dimethyl ether

The conversion of methanol to dimethyl ether was carried out over various commercial zeolites and modified H-ZSM-5 catalysts to evaluate their catalytic performance. A series of commercially available zeolite samples were used for vapor-phase dehydration of methanol to DME. Catalyst screening tests were performed in a fixed-bed reactor under the same operating conditions (T = 300 °С, P = 16 barg, WHSV = 3.8 h⁻¹). It was found that all the H-form zeolite catalysts in this study were active and selective for DME synthesis. According to the experimental results MDHC-1 catalyst exhibited the highest activity in dehydration of methanol.After finding the most active catalyst, the H-MFI90 zeolite was modified with Na content varying from 0 to 120 mol%, via wet-impregnation method to further improve its selectivity. All of catalysts were characterized by BET, XRD, NH₃-TPD, ICP, TGA, SEM, FT-IR and TPH techniques. It was found that these materials affected activity of MDHC-1 zeolite by changing its acidity. Ultimately, among all the catalysts studied, Na₁₀₀-modified H-MFI90 zeolite exhibited optimum activity, selectivity and stability at methanol dehydration reaction.     

甲醇气相脱水制二甲醚催化剂研究进展

甲醇气相脱水制二甲醚反应为固体酸催化反应,常用的固体酸催化剂有γ-Al₂O₃和分子筛类。γ-Al₂O₃表面存在弱酸中心或中等强度酸中心,催化剂有较好的初始催化活性,但活化所需的反应温度较高,耐水稳定性差;分子筛类催化剂表面有许多强酸性位,低温下催化活性较高,但在高温反应条件下易产生烃类副产物和积炭,热稳定性差。为改善这两类催化剂的催化性能,对催化剂进行了各种改性研究,改性后催化剂的活性、选择性和稳定性均有一定程度提高。综述了近年来在γ-Al₂O₃和分子筛催化剂上进行的改性研究,总结并展望了甲醇脱水催化剂的发展方向。     

Controlled coke deposition on zeolite ZSM5 and its influence on molecular transport

The influence of coke deposited from n-hexane and mesitylene on HZSM5 on the transport characteristics of probe molecules was investigated by measuring both the intracrystalline self-diffusion coefficients and tracer desorption coefficients using NMR methods. Coking with n-hexane involves an initial period in which coke is deposited in the intracrystalline channel network and a final period in which deposition is mainly on the outer surface of the zeolite crystals. In contrast, coke from mesitylene is predominantly deposited on the outer surface of the zeolite crystals from the very beginning. These results are explained by a model of controlled coking which implies that coke deposition is simultaneously determined by the size of the hydrocarbon molecule and the amount of coke already deposited.     

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。     

Syngas to iso-paraffins over Co/SiO2 combined with metal/zeolite catalysts

Selective production of gasoline ranged iso-paraffins from synthesis gas was performed in a consecutive dual reactor system, in which Fischer–Tropsch reaction was carried out over Co/SiO₂ catalyst in the upper reactor and hydroconversion of the Fischer–Tropsch hydrocarbons occurred over precious metal/zeolite catalyst in the lower reactor. Results indicate that the product distribution of traditional Fischer–Tropsch synthesis was significantly modified and high selectivity to iso-paraffins was achieved with the presence of metal/zeolite catalyst in the lower reactor. A significant effect of metals (Pt and Pd), zeolites (zeolites of β and USY), and the preparation methods (impregnation and ion exchange) of the metal/zeolite catalyst on the iso-paraffins selectivity and product distribution was clearly observed. This was explained based on the property of the metal for hydrogen spillover and the acidic and structural properties of the zeolite in the bifunctional metal/zeolite catalyst.     

On the localization of tetrahedral aluminum in MCM‐22 zeolite

The distribution of aluminum in MCM‐22 zeolite has been studied by ²⁷Al solid‐state nuclear magnetic resonance. Three different aluminum species in tetrahedral position were observed. Surface selective dealumination with oxalic acid causes the disappearance of one of the NMR signals at 50.5 ppm. The corresponding species have been attributed to aluminum atoms located in the 12‐T large cavities located on the external surface of the zeolite crystals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and catalytic cracking performance of mesoporous zeolite Y

Mesoporous zeolite Y (denoted as meso-Y) was synthesized using hydrothermal synthesis method using pluronic P123 block copolymer as template. Furthermore, stabilized Y (USY) was prepared through ion exchange and ultra-stabilization process of the meso-Y. The catalysts were prepared and characterized by XRD, SEM, TEM, N₂ adsorption–desorption, NH₃-TPD and Py-IR. These catalysts were evaluated by determining the micro-activity using the light diesel oil as sample. The results showed that the Meso-CAT-3 catalyst had the highest micro-activity and lowest coke yield. It could be ascribed to the mesoporous structure which is known to improve the mass transfer of the larger molecules.     

Catalytic Activity of Copper Oxide Impregnated HZSM‐5 in Methanol Conversion to Liquid Hydrocarbons

A number of CuO/HZSM‐5 catalysts have been studied in a small scale fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. All the catalysts were prepared by wet impregnation technique. The copper oxide loading over HZSM‐5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, surface area analyzer, metal trace analyzer, SEM techniques and TGA were used to characterize the catalysts. Incorporation of CuO onto HZSM‐5 zeolite significantly increased conversion and liquid hydrocarbon product yields. The major liquid products of the reactions were ethyl benzene, toluene, xylene, isopropyl benzene, ethyl toluene, trimethyl benzene and tetramethyl benzene. The maximum methanol conversion and hydrocarbon product yield was obtained at a copper oxide loading of 7 wt%. Effect of run time on conversion and product distribution was also investigated to compare the performance of these catalysts and coke on the catalyst was determined. Effect of space‐time and temperature on methanol conversion and products yield with 7 wt% CuO/HZSM‐5 has also been investigated and analyzed qualitatively.     

MTO工艺中分子筛催化剂的研究和应用进展

从分子筛的工业制备、工业应用和再生等方面介绍分子筛催化剂在MTO工艺过程中的应用现状。认为开发出烯烃收率高、抗积炭能力强、耐磨损、活性良好、选择性高、再生间隔期长和寿命高而价格低廉的MTO工艺中分子筛催化剂是当务之急。采用廉价模板剂或少用模板剂,甚至不用模板剂是分子筛合成的研究重点。     

Hydrogenation of carbon dioxide by hybrid catalysts,direct synthesis of aromatics from carbon dioxide and hydrogen

Direct synthesis of aromatics from carbon dioxide hydrogenation was investigated in a single stage reactor using hybrid catalysts composed of iron catalysts and HZSM-5 zeolite. Carbon dioxide was first converted to CO by the reverse water gas shift reaction, followed by the hydrogenation of CO to hydrocarbons on iron catalyst, and finally the hydrocarbons were converted to aromatics in HZSM-5. Under the operating conditions of 350°C, 2100 kPa, and CO₂/H₅ = 1/2, the maximum aromatic selectivity obtained was 22% with a CO₂ conversion of 38% using fused iron catalyst combined with the zeolite. Together with the kinetic studies, thermodynamic analysis of the CO₂ hydrogenation was also conducted. It was found that unlike Fischer Tropsch synthesis, the formation of hydrocarbons from CO₂ may not be thermodynamically favored at higher temperatures.