Noble metal catalysts highly-dispersed on Sm-doped ceria for the application to internal reforming solid oxide fuel cells operated at medium temperature

The synthesis of MTBE was studied in the gas phase at elevated temperatures (up to 175°C) and low pressures (150 kPa) where the MTBE formation rate is limited by thermodynamic equilibrium, using various solid acid catalysts (Amberlyst-15 resin, silica-alumina, HY and H-ZSM-5 zeolites). All the zeolites studied were found to exhibit better selectivities to MTBE than the commercially used Amberlyst-15 resin catalyst. The formation of byproducts increased with increasing temperature and appeared to have a strong enhancing effect on catalyst deactivation. H-ZSM-5 seems to be more suitable for high temperature formation of MTBE because of its excellent selectivity towards MTBE and low deactivation behavior.     

生物基乳酸（酯）制丙烯酸的工艺研究

以乳酸（酯）脱水反应为模型反应,分别考察了X、Y、ZSM-5和SBA等分子筛、硫酸盐、磷酸盐以及复配催化剂的催化性能。结果表明,适当调节分子筛催化剂的酸碱度,实现多种催化剂的复配应用,催化剂性能较好,丙烯酸及其酯的总选择性达80.3%。     

分子筛催化剂脱除重整油中微量烯烃的研究

以Hβ分子筛、HY分子筛和经水蒸汽处理后的HY分子筛为脱烯烃催化剂活性主体,研究了不同分子筛、分子筛酸性和水蒸汽处理时间等对催化剂的脱烯烃性能影响。结果表明,催化剂表面酸性对催化剂脱烯烃性能有重要影响,B酸是主要活性中心,L酸起辅助催化剂作用,B酸中心密度过高会加速催化剂结焦失活。水蒸汽处理可以有效改善分子筛的表面酸量和酸强度,可延长催化剂的单程寿命达到工业白土的6倍。脱烯烃催化剂有更好的容焦能力,其表面的积碳属于轻质焦碳,易于再生。     

Producing triacetylglycerol with glycerol by two steps: Esterification and acetylation

A two-step method is proposed to obtain high selectivity and high conversion rate for producing additive triacetylglycerol of biofuel from its byproduct glycerol. The esterification of glycerol with acetic acid was carried out over resin and zeolites. Amberlyst-35 was found to be an excellent catalyst. The reaction conditions were optimized by testing catalysts, temperatures, feedstock ratios as well as loads of catalysts. The optimal conditions are temperature of 105 °C and an acetic acid to glycerol molar ratio of 9:1 with 0.5 g catalyst. After the 4 hour reaction of the optimal condition, the selectivity of triacetylglycerol reaches almost 100% in 15 min by adding thereto acid anhydride. Recycling experiments indicate that no significant deactivation of Amerlyst-35 occurred during the reaction.     

不同结构分子筛的甲醇制丙烯催化性能

在常压、空速为1.5 h^-1、反应温度为450℃条件下,考察了4种具有不同拓扑结构的分子筛(SAPO-34、ZSM-48、ZSM-5和beta)在甲醇转化制丙烯(MTP)反应中的催化性能,并对催化剂的积炭失活行为进行了研究。结果表明,从8元环到12元环,分子筛孔口尺寸越小,低碳烯烃(乙烯+丙烯)选择性越高,积炭失活速率也越快。孔道尺寸越大,丙烯/乙烯(P/E)比越高,但产物分布向C₄以上组分偏移,丙烯选择性降低。10元环分子筛具有较高的丙烯选择性,但催化剂的积炭失活速率随孔道体系的不同有很大差异。一维直通孔道的ZSM-48容易积炭失活,而具有三维交叉孔结构的ZSM-5表现出了优异的抗积炭失活性能。不同结构分子筛在MTP反应中催化性能的差异主要归因于分子筛的过渡态择形和产物择形作用的不同。     

Catalyst design and development for upgrading aromatic hydrocarbons

Background and strategy of catalyst development for upgrading aromatic hydrocarbons are intensively discussed. Originally prepared catalysts (hydrogenation and hydrocracking catalysts) were used for accelerated aging tests. Though each catalyst showed superior catalytic performance as compared to commercially available catalysts, a severe deactivation was observed on the hydrocracking (HC) catalysts. A new type of HC catalyst was designed and prepared, based on the understanding of catalyst deactivation. High silica NaY zeolites were synthesized using crown-ether. USY zeolites were then prepared by ion exchange, steaming and calcining. Surface properties and catalytic functions of well-crystallized USY zeolites were investigated to develop practical HC catalysts. The Ni–W catalyst prepared using the newly prepared USY zeolite showed a considerable improvement in the HC activity.     

Glycerol Valorization: Dehydration to Acrolein Over Silica-Supported Niobia Catalysts

The catalytic dehydration of glycerol to acrolein is investigated over silica-supported niobia catalysts in a continuous fixed-bed gas-phase reactor. Various supported niobia catalysts are prepared and characterized using surface analysis and spectroscopic methods (XRD, UV–Vis, XPS, N₂ adsorption), as well as with ammonia adsorption microcalorimetry. Good results are obtained with initial glycerol conversions of over 70% and with 50–70% selectivity to acrolein. We investigate the influence of changing the catalyst acid strength by varying the niobia content and catalyst calcination temperature. Glycerol conversion and acrolein selectivity depend on the surface acid strength. Catalyst deactivation by coking is also observed, but simple oxidative treatment in air restores the activity of the catalysts completely.     

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.     

Oligomerization of isobutene over solid acid catalysts

Oligomerization of isobutene has been carried out in the liquid phase at mild conditions using n-butane as a diluent. The reaction was studied at low temperatures (30–70 °C) and at pressures high enough to ensure that the reaction takes place in the liquid phase. A number of different resins and zeolites were evaluated as catalysts for the dimerization. The best performance was obtained with Amberlyst 15 whereas the zeolites (H-ZSM5, H-Mordenite, β and Y) all showed very rapid deactivation.     

分子筛上甲醇转化过程的热力学和拓扑结构

现代新型煤化工是我国当今基础有机化学工业发展的新亮点,也是世界化工界的又一次革命。煤制化学品路线经历气化、变换、甲醇合成、甲醇制烃类等过程,其中,最为重要的是分子筛上甲醇转化的过程。本文综述了分子筛上甲醇转化的相关研究,一方面从ZSM-5上甲醇转化的生成烃池及烯烃的热力学机制和产物分布出发,介绍了多甲基苯生成烯烃热力学平衡模型和其中的芳烃池生成烯烃热力学机制,另一方面,介绍了基于Ising模型的分子筛离散拓扑结构模型。利用分子筛孔道堵塞与围棋中“气”的有无的类似性,能够很好地再现SAPO-34上的相变失活现象和不均匀的积炭分布现象。以模型为指导,介绍了一些分子筛多级结构构筑的工作,这些工作很好地提升了催化剂选择性和寿命。这些概念对于准确理解甲醇在分子筛上的反应与失活机制、产品分布及提高选择性有指导意义。     

甲醇制丙烯反应中ZSM-5分子筛催化剂积炭失活介尺度机制研究

甲醇制丙烯（MTP）是当前煤化工领域亟需发展的关键催化技术,积炭被认为是导致催化剂失活的重要原因之一。以积炭分子筛为研究对象,通过IGA、FTIR及TG等多种表征手段,考察甲醇的吸附行为、分子筛表面酸性、积炭成分与MTP反应中甲醇反应活性之间的构效关系。研究结果表明,甲醇的吸附量随催化剂的失活而降低,其下降速率与甲醇转化率成正比。催化剂上滞留的碳物种的主要成分为轻烃、BTX芳烃、活性结焦和积炭,而其中积炭是引起分子筛失活的主要原因。完全失活的催化剂与新鲜催化剂相比仍保留一定的甲醇吸附能力,推测积炭主要存在于酸活性中心周围。积炭首先覆盖的是B酸中心的羟基和桥式羟基,随后是非骨架Al—OH;而催化剂的甲醇转化率与分子筛中可接触的B酸和L酸数量成正比。另外,基于催化剂的失活速率与转化率存在的正比关系,结合反应动力学,推导出了失活曲线的数学表达式,理论上解释了MTP反应过程中的积炭失活介尺度机制。     

The Effect of Acid Strength on the Conversion of Methanol to Olefins Over Acidic Microporous Catalysts with the CHA Topology

The present work addresses the influence of acid strength on the stability and product selectivity of microporous catalysts with CHA framework type. The two studied catalysts, H-SAPO-34 and H-SSZ-13, have the same topology, density of acid sites (approximately one acid site per cage), and crystal size (0.2–2 microns), but their acid strength differ due to the framework composition. The difference in acid strength was determined by infrared spectroscopy, using CO as probe molecule. Catalytic tests were performed in a fixed bed flow reactor at 300–425 °C and WHSV = 6.0 h⁻¹. It was observed that the acid strength has significant influence on reaction rates, enhancing the production rate of olefins in the reactor effluent as well as aromatics retained in the catalyst pores and leading to a lower optimal temperature of operation for the more acidic H-SSZ-13 catalyst. The activation and deactivation patterns and the intermediates formed are very similar for the two materials. The ethene to propene ratio increases with temperature and time on stream for both catalysts, and is higher over the more acidic H-SSZ-13 catalyst at similar reaction conditions.     

Characterizations of Ru/ZnO catalysts with different Ru contents for selective hydrogenation of crotonaldehyde

Ru catalysts supported on ZnO with different Ru contents were prepared by an impregnation method and were applied to the vapor-phase selective hydrogenation of crotonaldehyde. The catalysts were characterized by X-ray powder diffraction (XRD), NH₃ temperature-programmed desorption (NH₃-TPD), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). It was found that with increasing Ru contents in the Ru/ZnO catalysts, the activity (TOF), surface acidity amount and deactivation rate increased and the selectivity to crotyl alcohol increased first and then decreased. The 3Ru/ZnO catalyst showed the highest selectivity to crotyl alcohol (up to 88.0%) for the hydrogenation of crotonaldehyde. The initial TOF values of the catalysts depended on the strength of surface acidity and the Ru particle sizes. The more Lewis acid sites made catalysts deactivate more easily. It was assumed that the deactivation was due to the formation of organic compounds deposition and poison effect of CO strongly adsorbed on the Ru atoms.     

Zeolite-catalyzed chlorination of toluene by sulfuryl chloride: activity, selectivity and deactivation of NaX and NaY zeolites

Chlorination of toluene with sulfuryl chloride was studied using NaX and NaY zeolites as catalysts under conditions where ring chlorination predominates. The zeolites are more selective than conventional Lewis acid catalysts with initial para-chlorotoluene : ortho-chlorotoluene ratios of 1.2. Both faujasites studied underwent rapid deactivation under reaction conditions. The deactivation of NaX was much more rapid than that of NaY. The accumulation of polychlorinated toluenes in the pores of the catalyst may be initially responsible for the loss of activity. In the case of NaY, this lost activity can be partially recovered by soaking the catalyst in fresh toluene, whereas attempts to regenerate by burning out the deposited materials cause a rapid disintegration of the catalyst. Zeolite fouling is accompanied by a more severe dealumination process that eventually leads to structural collapse and complete loss of activity.     

MWW型分子筛的高效清洁合成及其在苯与乙烯烷基化反应中催化性能

研究了MWW型分子筛合成过程中模板剂六亚甲基亚胺加入量对产物晶相、结晶度、形貌、孔结构和酸性等物化性能的影响。结果表明,通过加入晶种,利用晶种的导向作用,能有效提高MWW型分子筛的晶化速率,大幅降低配料中有毒模板剂六亚甲基亚胺用量,达到分子筛高效清洁生产的目的。在制得的MWW型分子筛中加入黏结剂制成催化剂,工业装置操作条件下评价其在苯与乙烯液相烷基化反应中的活性、选择性、产物分布及稳定性等,并进行了2 000 h寿命试验,结果表明,乙烯转化率接近100%,乙基化选择性大于99.7%,催化剂性能稳定,满足工业应用要求。     

Continuous mode linoleic acid hydrogenation on Pd/sibunit catalyst

Catalytic hydrogenation of linoleic acid and oleic acid to stearic acid over palladium on mesoporous carbon sibunit (Pd/sibunit) catalyst was studied in a continuous trickle-bed reactor with the weight hourly space velocity 5.4 h⁻¹ at 120°C and 30 bar using tall oil fatty acid (TOFA) as reactor feed. Stearic acid preparation using TOFA as a raw material is of industrial importance. Pd/sibunit catalysts with spherical particle shape of the size 1.62 mm were synthesized with the palladium loadings 0.5, 1, and 2 wt %. The metal dispersion (%), metal particle size (nm), as well as metallic surface area (m²/g metal) of the three synthesized Pd/Sibunit samples were measured by CO chemisorption. The Pd/C catalysts were tested in linoleic acid hydrogenation, showing promising behavior in terms of activity, selectivity and stability to be used in fixed bed applications. The product stream from the fixed bed reactor was saved and analyzed by X-ray fluorescence (XRF) and direct current plasma (DCP) spectroscopy. The catalyst activity increased with the Pd loading. The lowest metal loading of 0.5 wt % gave the least prone to initial deactivation and thus the most stable catalyst. This catalyst can be recommended for farther pilot testing.     

ETBE synthesis over silicotungstic acid and tungstophosphoric acid catalysts calcined at different temperatures

Vapor phase ethyl tertiary butyl ether synthesis was investigated using heat treated heteropoly acid catalysts, namely silicotungtsic acid (STA) and tungstophosphoric acid-Keggin (TPA-K) and these results were compared with the results obtained with untreated catalysts. ETBE synthesis experiments showed that heat treatment of TPA-K at temperatures over 473 K had caused significant decrease of its catalytic activity. Activity of STA was more stable and deactivation of this catalyst was observed by heat treatment at 673 K and above. Heat treatment at high temperatures caused loss of constitutional water of STA and TPA-K, causing loss of protons, consequently the loss of acidity of the catalysts, resulting deactivation. FT-IR, TGA-DTA and DRIFTS analyses on pyridine-adsorbed catalysts supported the conclusions related to structural changes of STA and TPA-K with heat treatment. Highest ETBE yields were obtained at around 368 K, while at temperatures over 423 K formation of DEE and ethylene were observed due to dehydration of ethanol.     

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.     

n-Pentane Hydroisomerization on Pt Containing HZSM-5, HBEA and SAPO-11

Hydroisomerization of n-pentane over platinum promoted acids zeolites was studied. The effect of structure and acidity of the support was investigated at atmospheric pressure between 250 and 400 °C. Pt/HDBEA catalyst showed the best performance at 300 °C with high activity and selectivity to isopentane, due to its structure and a proper balance between acid and metallic sites. This catalyst has a high catalytic stability and regeneration under air flow after deactivation by coking, restores its activity and selectivity.     

Modified Beta Zeolite as Catalyst for Fries Rearrangement Reaction

Modified beta zeolites were applied as catalysts for the Fries rearrangement reaction. The properties of the modified zeolites were characterized by NH₃-TPD, n-hexane and 1,2,4-trimethylbenzene adsorption. Modification with SiO₂ did not block the pores of the beta zeolite but reduced the number of acid sites on the surface. However, when the beta zeolite was modified with Ce₂O₃, the number of acid sites determined by NH₃-TPD increased, which indicated that new acid sites are created by the interaction of cerium oxide and zeolite. Modified beta zeolites and H-beta were applied as catalysts for the Fries rearrangement of phenol acetate. Reaction over H-beta has low selectivity and the catalyst is easily deactivated. SiO₂ modification of the catalyst increases the selectivity of the reaction but decreases the conversion. Ce₂O₃-modified beta zeolites show higher catalytic activity and rearrangement selectivity in the reaction than other catalysts. The stability of the catalyst is also improved after Ce₂O₃ modification. About 70% selectivity and 60-80% conversion can be achieved over 16 wt% Ce₂O₃-modified beta zeolite.