Deactivation mechanism of beta-zeolite catalyst for synthesis of cumene by benzene alkylation with isopropanol

The alkylation of benzene with isopropanol over beta-zeolite is a more cost-effective solution to cumene production. During the benzene alkylation cycles, the cumene selectivity slowly increased, while the benzene conversion presented the sharp decrease due to catalyst deactivation. The deactivation mechanism of betazeolite catalyst was investigated by characterizing the fresh and used catalysts. The XRD, SEM and TEM results show that the crystalline and particle size of the beta-zeolite catalyst almost remained stable during the alkylation cycles. The drop in catalytic activity and benzene conversion could be explained by the TG, BET,NH_3-TPD and GC–MS results. The organic matters mainly consisted of ethylbenzene, p-xylene and 1-ethyl-3-(1-methyl) benzene produced in the benzene alkylation deposited in the catalyst, which strongly reduced the specific surface area of beta-zeolite catalyst. Moreover, during the reaction cycles, the amount of acidity also significantly decreased. As a result, the catalyst deactivation occurred. To maintain the catalytic performance,the catalyst regeneration was carried out by using ethanol rinse and calcination. The deactivated catalyst could be effectively regenerated by the calcination method and the good catalytic performance was obtained.

Study on Mechanism for Alkylation of Benzene with Propylene over β Zeolite and MCM-22 Zeolite by In-situ IR Spectrometry

The reaction mechanism for alkylation of benzene with propylene over the β zeolite and the MCM-22 zeolite were investigated respectively by in-situ IR spectrometry. Three types of experiments were carried out. （1） IR spectra of the gas-phase propylene, benzene and isopropyl benzene were recorded. （2） IR spectra of the above-mentioned substances as adsorbates that have combined with the zeolite wafer were recorded. （3） IR spectra of the reaction modes were recorded. The test results showed that the alkytation reaction over the zeolite β was ascribed to the mechanism of carbonium ions, whereas the alkylation reaction over the zeolite MCM-22 was ascribed to the synchronous reaction mechanism.

Elucidating the effect of oxides on the zeolite catalyzed alkylation of benzene with 1-dodecene

In the present work, the effect of oxides on the alkylation of benzene with 1-dodecene was comprehensively investigated over MCM-49 n-heptanol, n-heptaldehyde and n-heptanoic acid were selected as the model oxides herein, and obvious decrease of lifetime could be caused by only trace amount of oxides added in the feedstocks. However, the deactivated catalysts were difficult to be regenerated by extraction with hot benzene. Additionally, coke-burning was also proved to be incapable to regenerate the deactivated catalysts mainly for the dealumination during calcination. Further characterizations complementary with DFT calculations were conducted to demonstrate that the deactivation was mainly due to the firm adsorption of oxides on the acid sites.

Lean methane combustion over zeolite-supported Pd catalysts:Structure-performance relationship and deactivation mechanism

Zeolites are a promising support for Pd catalysts in leanmethane(CH_(4))combustion.Herein,three types of zeolites(H-MOR,H-ZSM-5 and H-Y)were selected to estimate their structural effects and deactivation mechanisms in CH_(4)combustion.We show that variations in zeolite structure and surface acidity led to distinct changes in Pd states.Pd/H-MOR with external high-dispersing Pd nanoparticles exhibited the best apparent activity,with activation energy(Ea)at 73 kJ/mol,while Pd/H-ZSM-5 displayed the highest turnover frequency(TOF)at 19.6×10^(−3)sec^(−1),presumably owing to its large particles with more step sites providing active sites in one particle for CH_(4)activation.Pd/H-Y with dispersed PdO within pore channels and/or Pd2+ions on ion-exchange sites yielded the lowest apparent activity and TOF.Furthermore,Pd/H-MOR and Pd/H-ZSM-5 were both stable under a dry condition,but introducing 3 vol.%H_(2)O caused the CH_(4)conversion rate on Pd/H-MOR drop from 100%to 63%and that on Pd/H-ZSM-5 decreased remarkably from 82%to 36%.The former was shown to originate fromzeolite structural dealumination,and the latter principally owed to Pd aggregation and the loss of active PdO.

Recent progress in the deactivation mechanism of zeolite catalysts in methanol to olefins

Methanol to olefins(MTO)as an important reaction in C1 chemistry can effectively transform non-petroleum carbon resources into value-added chemicals.Zeolites have been widely used as MTO catalysts.However,they usually suffer from a rapid deactivation due to bulky coke species production,and thus require continuous regenerations in industrial application.The key to design and develop highly stable zeolite catalysts for MTO process is to unravel the deactivation mechanism and clarify the structure–performance relationship of catalysts.Here,in this mini-review,we investigate the critical intermediate species inducing zeolite deactivation and analyze the formation and evolution pathways of polycyclic aromatic hydrocarbons(PAHs)that are the precursors of carbonaceous deposits.In addition,some methods to alleviate the coking mainly including acid regulation,morphology modification and process optimization,are also summarized.

Dimethyl ether carbonylation over zeolites

Syngas to ethanol, consisting of dimethyl ether(DME) carbonylation to methyl acetate(MA) over zeolites and MA hydrogenation to ethanol on copper catalyst, has been developed in recent years.DME carbonylation over zeolites, a key step in this new process, has attracted increasing attention due to the high reaction efficiency and promising industrial application.In recent years, continuous efforts have been made on improving the activity and stability of the zeolites.From a mechanistic point of view, DME carbonylation to MA, involving the formation of C–C bond, is achieved via the Koch-type CO insertion into DME within the 8-member ring(8-MR) pores of zeolites, typically HMOR and HZSM-35.The unique geometric configuration of the 8-MR pore endowed the formation of the key intermediate(acetyl, CH3CO^*), possibly by a spatial confinement of the transition state during CO insertion into the surface O–CH3 group.This review article summarizes the main progress on zeolite-catalyzed DME carbonylation, including reaction kinetics and mechanism, theoretical calculations, and experimental strategies developed for populating acid sites and engineering pore structure of the zeolites in order to enhance the overall performance.

Confinement effects in methanol to olefins catalysed by zeolites： A computational review

Small pore zeolites, containing 8-rings as the largest, are widely employed as catalysts in the process of methanol-to-olefins （MTO）. Reactants and products dif- fuse with constraints through 8-rings and this is one of the reaction bottlenecks related to zeolite micropore topology. Small pore zeolites and silicon-aluminophosphates （SAPOs） containing cavities, where olefins are mainly formed through the hydrocarbon pool （HP） mechanism, are frequently tested for MTO. Shape selectivity of transition states within the side-chain methylation will be reviewed as this is one of the controlling steps of the MTO process, with particular attention to the role of hexam- ethylbenzene （HMB） and heptamethylbenzenium cation （HeptaMB~）, which are the most tipically detected reaction intermediates, common to the paring and side-chain routes within the HP mechanism. The relative stability of these and other species will be reviewed in terms of confinement effects in different cage-based zeolites. The role of the different alkylating agents, methanol, dimethyl ether （DME）, and surface methoxy species （SMS） will also be reviewed from the computational viewpoint.

碳四烷基化离子液体催化剂失活机理和再生方法的研究进展

氯铝酸离子液体作为一种新型的绿色催化剂已用于催化碳四烷基化反应生产高品质汽油。然而,在长周期烷基化反应过程中,离子液体的催化活性逐渐下降,因此,明晰催化剂失活机理并恢复其催化活性对保证烷基化装置连续稳定运行至关重要。为此,综述了碳四烷基化离子液体催化剂的失活机理和再生方法,介绍了离子液体的组成、结构及其催化性能之间的关系,总结了离子液体中Br?nsted酸和Lewis酸中心的失活原因,烷基化副反应生成的酸溶油是Lewis酸性下降的主要原因。基于此,重点讨论了酸溶油的组成、结构及其与离子液体的作用机理,对比分析了从离子液体中脱除酸溶油的各类方法的优缺点,并提供了失活离子液体的活性恢复策略。

ZSM-5沸石催化剂的失活历程和活性稳定性

研究了 ZSM-5分子筛催化剂上苯 /乙烯烷基化制乙苯反应体系的结焦失活历程。结果表明 ,失活历程经历高水平活性稳定期、活性衰退期和低水平活性稳定期 3个阶段。通过考察失活催化剂的孔结构及酸性质 ,分析了失活机理 ,认为采用降低强酸活性位和晶粒表面活性位这两种手段来改性催化剂 。

β-沸石催化剂上苯与丙烯烷基化催化剂的失活机理

通过分析失活催化剂积炭的组成，表征失活催化剂的酸性质及孔结构的变化，考察反应条件对催化剂寿命的影响等手段，得出了β－沸石催化剂上苯与丙烯烷基化反应过程催化剂失活机理：催化剂失活主要是由深度烷基化造成的，失活从晶内孔开始，并且随着失活程度的加深，失活逐渐向外扩展。这也说明烷基化反应主要是在晶内进行的。

超临界反应条件下Y型分子筛催化剂失活的研究

对苯烷基化过程中Y型分子筛催化剂的失活进行了多方面的实验研究.结果表明,超临界条件下该催化剂的活性寿命比液相条件下长达四倍以上.借助色-质谱联用机分析两种操作的反应产物,发现含有多环物质,并且它们的种类和数量随条件而不同.根据热力学原理,建立了多环物在超临界流体中的溶解模型,并以并四苯、并五苯和并六苯作为焦前物模拟物进行了计算.

AB-97型分子筛催化剂上苯与乙烯烷基化Ⅱ.副产物二甲苯的生成规律

在AB -97型分子筛催化剂上对苯 /乙烯烷基化制乙苯的重要副产物二甲苯的生成规律进行了系统研究 ,建立了反应动力学模型。降低温度及乙烯分压可抑制二甲苯的生成 ,并提出了二甲苯生成的机理。试验证实了结焦过程生成的微量游离氢的存在是生成二甲苯的必要条件。二甲苯生成反应的模拟计算结果与工业生产的结果相吻合 ,二甲苯的质量分数可控制在 0 2 %以内。

苯与丙烯烷基化失活沸石催化剂氢再生机理

对工业中试用于苯与丙烯烷基化失活β 沸石改性催化剂进行了H2 再生研究。通过对失活、新鲜和再生后催化剂的TPO、TPD、孔结构测定和活性评价以及失活和再生催化剂样品上炭组成的GC MS分析 ,讨论了H2 再生后催化剂催化性能的恢复状况。解释了虽然仍有部分炭未被除去 ,但酸性和活性恢复良好的原因。提出了本文体系失活催化剂H2 再生过程的作用机理。

不同粒径ZSM-5分子筛在苯与甲醇烷基化反应中催化性能及反应条件优化

采用水热合成法合成了不同粒径的ZSM-5分子筛催化剂,系统考察了分子筛粒径变化对苯与甲醇烷基化反应的影响。研究结果表明,随着ZSM-5分子筛粒径增大,不但苯的转化率和二甲苯选择性降低,而且催化剂稳定性明显下降。其中,粒径为0.25μm的ZSM-5分子筛在苯烷基化反应中的催化性能最佳,且催化剂稳定性最好。另外,采用拉曼光谱和热重等方法对催化剂积碳物种和失活机理进行了深入研究,发现催化剂失活主要是由于反应过程中生成的大分子稠环芳烃堵塞了分子筛孔道并覆盖活性位点造成的。最后,考察了反应温度、原料组成及空速对苯烷基化反应的影响并优化出最佳的苯烷基化反应条件。

催化噻吩类硫化物与烯烃烷基化硫转移反应的固体酸催化剂的失活机理

催化裂化 (FCC)汽油中的硫化物多以噻吩类硫化物的形式存在 ,而且相对集中在沸程较高的馏分中 .通过固体酸催化剂催化噻吩类硫化物与烯烃的烷基化反应生成多烷基噻吩 ,可较大程度地提高其沸点 ,再经精馏将硫化物转移至FCC汽油的重馏分中 ,从而达到脱硫目的 .考察了AlCl3 CT175树脂催化剂催化模型硫化物如噻吩、2 甲基噻吩及 2 乙基噻吩与异丁烯的烷基化反应性能 ,采用GC FPD和GC MS技术研究了AlCl3 CT175树脂催化剂的失活机理 .结果表明 ,原料中的二烯烃杂质在固体酸催化剂作用下发生聚合反应结焦 ,覆盖在催化剂表面 ,堵塞孔道 ,从而导致催化剂失活 .

TH-06催化剂合成直链烷基苯Ⅱ.催化剂的失活及再生

对直链烷基苯合成过程中ＴＨ－ ０６ 催化剂的失活及再生进行了研究。通过对失活催化剂进行表征发现，导致催化剂失活的原因主要是萘、１ ，４ － 二丁基－ １ ，２ ，３ ，４ － 四氢化萘、１ － 甲基－ ３ － 壬基茚满及１ － 乙基－ ３ － 庚基－ ２ ，３－ 二氢化茚等大分子在催化剂孔道中的积累。失活从晶内开始，然后逐渐向外扩展。经苯反复洗涤再生，催化剂寿命超过１０００ ｈ 。

β沸石催化剂上二异丙苯与苯反应机理及催化剂失活

采用Ｉｎ－ｓｉｔｕＩＲ和ＴＰＤ－ＩＴＤ研究了二异丙苯（ＤＩＰＢ）、异丙苯（ＩＰＢ）、苯和丙烯在改性β沸石催化剂上的吸附和反应。考察了１，３－ＤＩＰＢ和１，４－ＤＩＰＢ与苯烷基转移的反应性能、催化剂的酸性质和催化剂的稳定性。结果表明，１，３－ＤＩＰＢ与苯烷基转移反应主要按双分子反应ＳＮ２－１机理进行，而１，４－ＤＩＰＢ与苯主要按单分子反应ＳＮ１机理进行；１，３－ＤＩＰＢ和１，４－ＤＩＰＢ之间存在着异构化反应。改性β沸石催化剂失活原因是：（１）焦炭覆盖在部分酸性中心上，使得催化剂的活性下降；（２）烷基萘等相对分子质量较大、沸点较高的化合物沉积在催化剂的孔口或表面。

碱性X分子筛催化甲苯与甲醇侧链烷基化自由基机理研究（英文）

苯乙烯是重要的工业原料,年消耗量约3000万吨.传统工艺中,苯乙烯由乙苯催化脱氢得到.由于传统工艺高能耗,高污染,甲苯与甲醇侧链烷基化合成苯乙烯引起了人们广泛关注,但是目前该路线进入工业化还有很多问题需要解决,甚至催化机理仍不明确.本文对甲苯侧链烷基化机理及提高反应选择性等方面进行了研究.采用离子交换法制备CsX分子筛,在固定床反应器上进行甲苯与氘代甲醇的同位素示踪实验和硝基甲苯的侧链烷基化实验,结合量子计算明确反应机理.采用IGA-002系统测定甲醇在CsX,KX和Na X上的等温吸附线,考察甲醇在分子筛不同笼结构中的吸附情况.将氘代甲苯与甲苯在CsX,KX和活性炭催化下进行氢氘交换实验,检验自由基在不同催化剂上的稳定性.以CO2为载气进行甲苯与甲醇侧链烷基化实验,考察CO2对反应的影响.甲苯与氘代甲醇进行侧链烷基化反应时,大多数氘出现在甲苯上,仅少数氘存在于苯乙烯及乙苯上,表明甲苯氢与甲醇的甲基氘进行了氢氘交换.量子化学计算表明,甲苯与甲醇的氢氘交换沿自由基路径的能垒远小于沿离子路径的.氘代实验和量子计算结果表明,甲苯侧链烷基化过程中存在自由基,但并不能证明侧链烷基化是自由基反应.为了验证甲苯侧链烷基化反应是否为自由基机理,以4-硝基甲苯(NO2-Ph-CH3)代替甲苯与甲醇进行侧链烷基化反应.硝基是强吸电子基团,能稳定苄基负离子,如果甲苯侧链烷基化是离子反应,硝基甲苯侧链烷基化产物收率会升高.另外,硝基又能与活泼自由基生成稳定自由基,若反应为自由基机理,则硝基甲苯不发生侧链烷基化反应.分析结果表明,反应液中不存在侧链烷基化产物,确定了甲苯侧链烷基化反应为自由基机理,而不是离子机理.热力学上甲醇更容易进行生成CO和H2等的副反应,从而减少CH·3与H·碰撞甲醇的几率.甲醇等温吸附线显示甲醇在Na X和KX上的吸附容量相近且远大于CsX上的,表明Cs+阻碍了甲醇进入X分子筛的β-笼.由于甲苯不能进入β-笼,Na X和KX的β-笼内甲醇与甲基自由基接触发生副反应.CsX催化时Cs+阻碍甲醇进入β-笼而抑制了副反应的发生,提高了甲醇利用率.甲苯与氘代甲苯在CsX,KX和活性炭上进行氢氘交换,反应物用GC-MS分析.结果表明,在CsX上氢氘交换进行得更彻底,在活性炭上几乎没有氢氘交换.X分子筛活化甲苯为自由基的效果优于活性炭,这可能是推拉效应造成的.当甲苯进入分子筛后,Lewis酸性阳离子与苯环络合并吸引电子,催化剂阴离子骨架与甲苯的甲基作用并供给电子,推电子与吸电子共同作用使甲苯更容易生成苄基自由基,并使其更稳定.CsX对甲苯的活化作用强于KX,表明CsX的酸碱搭配更有助于甲苯生成自由基.这也是CsX催化甲苯与甲醇侧链烷基化效果优于KX的原因.以CO·2替代N2作为载气能显著提高苯乙烯的选择性,这是由于CO2的存在降低了H·和CH3的浓度,提高了·CH2OH的浓度.·CH2OH与甲苯生成苯乙烯,H·的减少降低了苯乙烯加氢生成乙苯.

甲苯与甲醇侧链烷基化合成苯乙烯KX催化剂失活现象的研究

考察了甲苯、甲醇侧链烷基化反应KX催化剂的稳定性及失活现象。并采用XRD、N2物理吸附、DTG、SEM、NH3-TPD、CO2-TPD和ICP等方法对反应前后的催化剂进行了表征。结果表明,反应前后活性位变化和积炭不明显,对催化剂失活影响很小。随着反应时间延长,反应过程中产生大量的水导致分子筛骨架脱铝,晶体结构被严重破坏,这是催化剂失活的主要原因。增强催化剂骨架的水热稳定性是解决催化剂失活问题的关键。

不同条件下苯与丙烯烷基化反应的催化剂失活研究

对不同条件下苯与丙烯烷基化反应Hβ催化剂的寿命、失活催化剂的积炭量和积炭性质进行了研究。在5.7MPa下,随反应温度变化,反应介质在反应过程中所经历的相态变化不同,导致催化剂的寿命、失活催化剂的积炭量和积炭的性质也存在着较大差异。300℃时,反应介质处于接近于体系临界点的超临界相或高压液相状态,催化剂寿命最长,积炭量大。失活催化剂积炭的元素分析及TPO-MS表征结果发现,积炭的碳氢比与反应温度有关,温度越高,碳氢比越高;而积炭的脱炭温度与反应时间(催化剂寿命)相关,催化剂寿命越长,相应的脱炭温度也越高。