DFT方法研究酸性沸石上苯与乙烯烷基化反应的机理

采用B3LYP/6-31G*水平计算来研究酸性沸石上苯与乙烯的烷基化反应历程,从生成能和反应活化能角度分析并讨论了苯与乙烯的反应机理.选取4T簇模型模拟分子筛的酸性位,使用密度泛函理论对烷基化反应三种不同的反应机理(两个联合反应机理和一个分步反应机理)进行计算分析.结果表明,在联合反应机理中,乙烯的质子化和苯与乙烯间C-C键的形成同时发生;分步反应机理中,首先形成一个稳定的乙醇盐中间物种,然后与苯分子反应形成乙苯.联合机理速控步骤的活化能约为160kJ/mol,分步机理速控步骤的活化能为190.24kJ/mol,因此,酸性沸石上苯与乙烯烷基化反应机理主要以联合机理为主,但分步机理与其有一定程度的竞争。     

Kinetic model for anisol synthesis by methanol alkylation of phenol on a zeolite catalyst

A kinetic model for the reaction of phenol alkylation by methanol on a zeolite catalyst tested is suggested. Estimate of the kinetic parameters confirms the proposed reaction mechanism.

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Densification products in conversion of ethylene on a high-silica zeolite catalyst

Russian Journal of Applied Chemistry - Fundamental aspects of the conversion of ethylene on a high-silica zeolite catalyst in the temperature range 200–400°C were studied. The methods of...     

Effect of zeolite pore morphology on solvent-less alkylation of benzene with 1-hexene

In an attempt to convert the carcinogenic benzene which is almost restricted for its use in gasoline, alkylation reaction with olefin 1-hexene has been conducted on various zeolites. Four zeolites having different pore topology and pore size have been applied as solid acid catalysts for effective production of alkylate in a liquid phase, solvent-less low temperature reaction. The textural properties of all the four zeolites (ZSM-5, MOR, BEA, HY) have been characterized for crystal morphology by TEM, crystal structure by XRD and FTIR, BET for surface area, N₂ sorption for porosity and TPD for acidity. Among the zeolite, BEA possessed high surface area (600.61 m²/g) and enhanced meso pores volume (0.3956 cm³/g) as compared to other zeolite samples. The performance of BEA was also observed to be superior in the liquid phase alkylation of benzene with 1-hexene in a batch reactor under autogenous pressure without using any solvent. At the optimum reaction conditions, the benzene conversion was 86.6 wt% and 3-Phenylhexane, 2-Phenylhexane yield were about 47.9 wt% and 38.7 wt% respectively on this catalyst. The BEA also exhibited longer time-on-stream and reusability performance, thus offers an attractive route for converting benzene into valuable (3-Phenylhexane, 2-Phenylhexane) alkylate product useful for the manufacturing of fine chemicals, dyestuff, detergents and scents.     

Shaped binderless ZSM-11 zeolite catalyst prepared via a dry-gel conversion method:Characterization and application for alkylation of benzene with dimethyl ether

Shaped binderless ZSM-11 zeolite catalysts were synthesized via a dry-gel conversion technique from 70ZSM-11/30 SiO_2mix extrudates. 1,6-hexanediamine combined with tetrabutylammonium bromide was proved to be the best structure directing agent for the synthesis of the binderless ZSM-11 catalyst, without adding other alkaline materials. The 70HZSM-11/30 SiO_2mix serials materials crystallized for different times were detected by X-ray diffraction(XRD), nuclear magnetic resonance(NMR), scanning electron microscopy(SEM), transmission electron microscopy(TEM), scanning transmission electron microscopy–energy dispersive spectroscopy(STEM–EDS) techniques, and so on. In order to investigate the possible crystallization mechanism, the textural and structural properties of 70HZSM-11/30 SiO_2mix serials samples were further characterized by N_2 adsorption–desorption. Acid properties were determined by temperature-programed desorption of NH_3(NH_3-TPD) and pyridine adsorption-infrared(Py-IR) measurements. In the alkylation of benzene with dimethyl ether, the serials catalysts exhibited different benzene conversions. 70HZSM-11/30 SiO_2mix showed the lowest benzene conversion while sample 70HZSM-11/30 SiO_2mix-6.5h synthesized only for 6.5h displayed a higher benzene conversion, even higher than the value over 70HZSM-11/30Al_2O_3mix. Extending the crystallization time, the obtained samples displayed the increased benzene conversion in general under the same reaction conditions. In the end, the relation of physicochemical properties with the reaction performance was investigated.     

Study of the acidity of zeolite alkylation catalysts by temperature programmed ammonia desorption

The temperature programmed desorption (TPD) spectrum of ammonia from HLaCaNaY alkylation catalysts shows a strong band with maximum at 389°C, which virtually coincides with the optimal sample activation temperature (380°C). The TPD spectrum was found to account for the specific features of the acidity of these alkylation catalysts. Institute of Bioorganic and Petroleum Chemistry, National Academy of Sciences of Ukraine, 1 Murmanskaya ul., Kiev 02094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 4, pp. 247–250, July–August, 2000.     

NaOH改性ZSM-5分子筛在苯、甲醇烷基化反应中的应用

用NaOH溶液对高硅ZSM-5分子筛进行处理,考察其应用于苯-甲醇烷基化反应过程的最佳处理条件,并用XRD、SEM、XRF、NH3-TPD、TPO、BET等手段对试样进行表征。结果表明,NaOH在脱除分子筛硅物种的同时,也会脱出晶粒表面附着物,暴露出更多的酸性位,形成一定量的介孔,进而影响苯-甲醇烷基化性能。当NaOH处理量为2.4 mmol/gcat时,在液体积空速为85 h-1下,烷基化反应中苯的转化率达到38%,相比处理前提高了近16%,且积炭量低,稳定性好。     

改性HZSM-5分子筛上噻吩烷基化反应和失活再生性能的研究

采用不同碱单独处理和两种碱不同方式联合处理HZSM-5分子筛,制备微孔-介孔多级孔HZSM-5分子筛催化剂并应用于噻吩烷基化反应中。结果表明,不同碱单独处理和两种碱不同方式联合处理HZSM-5分子筛后,均能够在分子筛上造出介孔孔道且能够调变分子筛的酸性,其中,采用Na₂CO₃溶液和TPAOH溶液分开处理得到的分子筛催化剂织结构最适合噻吩烷基化反应;其次考察具有最佳织结构分子筛催化剂的噻吩烷基化反应稳定性,并分析催化剂失活的原因和再生条件。结果表明,当噻吩烷基化反应进行到1050 h后,催化剂已基本失活,催化剂失活的主要原因是,在反应过程中原料中反应组分间发生烯烃齐聚、环化、脱氢和芳烃烷基化等副反应生成的大分子化合物沉积在催化剂上,堵塞催化剂的孔道和遮盖催化剂的活性中心所致;对失活催化剂进行高温再生,从高温再生的能耗较大以及多次高温再生对催化剂酸性和骨架结构不利的角度考虑,选定催化剂的再生温度为550 ℃。     

Distribution of the products from the alkylation of isobutane with butenes at a zeolite catalyst and the reaction mechanism

The mechanisms of formation are proposed on the basis of the distribution of the intermediate and final products of zeolite alkylation of isobutane with butenes. The mechanisms are based on activation of the isobutane molecule at the methyl groups, simultaneous intermolecular and intramolecular hydride transfer, and β dissociation during skeletal isomerization of the carbonium ions.     

Selective alkylation of xylenes by alcohols on zeolite catalysts

The peculiarities of catalytic performance of crystalline aluminosilicates of different types and compositions (X, Y including dealuminated Y, mordenite, pentasil ZSM-5), as well as of amorphous aluminosilicate catalyst in conversion of xylene + alcohol mixtures were studied. New data were obtained for alkylation ofo-xylene withtert-butyl alcohol, concerning controlling the selectivity and stability of the zeolite catalysts in reactions proceeding with the participation of water, including the water evolved during the reaction, in particular by controlling the acidic properties and hydrophobycity of the zeolites. A catalyst ensuring production of 1,2-dimethyl-4-tert-butylbenzene (DMTBB) with a 94% yield and selectivity of alcohol conversion to the target product of 94–97% was developed. The catalyst can be used as the basis for a high-performance and environmentally safe method for the synthesis of DMTBB. The catalysts developed can be also used for selective alkylation ofo-xylene by C₃-C₅ alcohols and for alkylation ofm-xylene bytert-butyl alcohol.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No, 12, pp, 2912–2917, December, 1996.     

Activity and regenerability of dealuminated zeolite Y in liquid phase alkylation of benzene with 1-alkene

HY-zeolite and its deep-bed dealuminated and EFAL-extracted forms were tested in liquid phase alkylation of benzene with 1-hexadecene in a batch reactor at 120°C. Deep-bed dealumination of the HY-sample at 560 °C followed by careful selective extraction of extra-framework aluminium by hydrochloric acid increased the catalytic activity as well as oxidative regenerability of Y-zeolite.     

Catalytic benzene alkylation over mesoporous zeolite single crystals: improving activity and selectivity with a new family of porous materials

Mesoporous zeolite single-crystal catalysts are shown to be both more active and more selective than conventional zeolite catalysts in the alkylation of benzene with ethene. The superior catalytic properties are ascribed to improved mass transport in the mesoporous zeolite crystals. Thus, mesoporous zeolite single-crystal catalysts combine the high acidity, shape-selectivity, and hydrothermal stability of zeolites with the efficient mass transport that is typically achieved in mesoporous materials.     

The alkylation reaction of benzene with methanol to produce toluene: Y-C and Y-CCs catalyst

The secondary reaction of toluene is difficult to be suppressed in benzene alkylation with methanol over conventional acidic zeolite catalysts. Moreover, the formation of coke yet remains a challenging problem. In this study, Na-Y zeolites were modified with ammonium carbonate (AC), citric acid (CA) and caesium nitrate(CN) to evaluate the alkylation of benzene with methanol, which was also characterized by XRD, SEM, FT-IR, N₂ adsorption and Py-IR. For the Na-Y treated with AC-CA-CN, not only the catalytic selectivity for the alkylation of benzene with methanol was improved (the total selectivity of toluene and xylene was 97.9% and toluene selectivity was 86.4%), but also the quantity of coke was greatly decreased.