V.V. Yuschenko

Design of composite micro/mesoporous molecular sieve catalysts*

Two series of composite micro/mesoporous materials with different contributions of micro- and mesoporosity were prepared by dealumination and recrystallization of mordenite zeolite. The materials were characterized by X-ray diffraction, infrared spectroscopy, 27Al magic angle spinning (MAS) NMR, nitrogen adsorption–desorption, and temperature-programmed desorption of ammonia (TPD NH3). Catalytic properties were studied in transalkylation of biphenyl with diisopropylbenzene. Both types of composite materials showed remarkably high activity, stability, and selectivity toward formation of di-isopropylbiphenyls with respect to both pure microporous and mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores.

Micro/mesoporous catalysts obtained by recrystallization of mordenite

Micro/mesoporous composite materials with different contribution of micro- and mesoporosity were prepared by recrystallization of mordenite. The materials were characterized by XRD, IR spectroscopy, nitrogen adsorption — desorption and TPD NH3. Catalytic properties were studied in transalkylation of biphenyl (BP) with para-diisopropylbenzene (p-DIPB) and cracking of 1,3,5-triisopropylbenzene (TIPB). Composite materials showed remarkably high activity, stability and selectivity with respect to both pure microporous and pure mesoporous materials. The effect is due to high zeolitic acidity combined with improved accessibility of active sites and transport of bulky molecules provided by mesopores.

Chemical tuning of adsorption properties of titanate nanotubes

A conventional hydrothermal method widely used for the preparation of titania-based nanotubes still generates many unsolved questions. One of them is definitely connected with the influence of a posthydrothermal treatment of titania nanotubes on their micromorphology, structure, and adsorption characteristics. Here, it was analyzed systematically by a group of methods including nitrogen adsorption and temperature-programmed desorption of ammonia and carbon dioxide. It is proved that adsorption characteristics and the surface state of titania nanotubes correlate with a sodium content, since sodium ions act as Lewis acid sites and shield Ti4+ acid sites of the nanotubes. To obey a balance between chemical and heat treatments of the nanotubes to design their functional properties has been suggested.

Aniline methylation on modified zeolites with acidic, basic and redox properties

Four series of molecular sieve catalysts of different structural types, ZSM-11, L, Y and MCM-41 have been prepared. Each type of materials was modified to obtain acidic (H-forms), basic (Cs-forms impregnated with CsOH) and redox (modified with V2O5) catalysts. The catalysts were characterized by AES, XRD, FTIR, 29Si, 27Al, 1H and 133 Cs MAS NMR, NH3-TPD, CO2-TPD, TPR and nitrogen adsorption. The catalytic activities of the materials in aniline methylation was evaluated in a continuous-flow microreactor system at temperatures of 523 to 723 K, a WHSV of 1.8 h−1 and a molar aniline/methanol ratio of 1:5. In situ13C MAS NMR was applied to study the mechanisms of N-and C-alkylation on acidic, basic and redox catalysts and to determine key parameters responsible for the catalyst activity, selectivity and stability. The best catalyst performance was observed on zeolite CsNaY/CsOH, which showed an aniline conversion of 99%, a selectivity to N-methylaniline of 98.7% and a high time-on-stream stability.

Dehydrogenation of ethylbenzene over Ga- and Fe-containing MCM-41

Abstract Incorporation of Ga and Fe in the silica network of MCM-41 followed by calcination produces active, selective and stable catalysts for the dehydrogenation of ethylbenzene into styrene. Best preformance was observed over Fe-MCM-41 at 600°C which led to a stryrene yield of 38% per pass, amounting to 64% of the equilibrium value. The dehydrogenation activity is associated with the presence of immobilized oxide nanoparticles generating the reducible species able to split C-H bonds and to allow the recombinative dissociation of hydrogen. Under oxidative dehydrogenation conditions the catalysts demonstrate also good activity and stability but the selectivity in styrene is lower due to the contribution of total oxidation reactions.

11-P-06 - Dealumination of zeolite KL

Publisher Summary This chapter describes the dealumination of zeolite KL. Zeolite KL is dealuminated by combining hydrothermal, ion exchange, and acid-attack treatments. The dealumination process is governed by the removal of potassium ions from cationic sites located inside the cancrinite cages, which exert a long-range inductive stabilization of the framework. Deep bed calcination of the partly exchanged samples promotes migration of these cations toward exchangeable sites. Steam dealumination and acid attack allow producing highly crystalline materials, with a global silicon/aluminum (Si/Al) ratio close to 10 and featuring strong acid sites.

Hydroalkylation of benzene and ethylbenzene over Ru-and Ni-containing zeolite catalysts : novel catalytic route for ethylcyclohexylbenzene synthesis

Abstract The reaction of benzene and ethylbenzene has been studied over zeolite catalysts with different structural type (BEA, MFI), Si/Al ratio (10 – 200 for BEA) and Ru and Ni contents (0.5 – 1%) in the temperature range of 150 – 230 0 C, under 0.2 – 1 MPa and WHSV of 1 – 64 g/g*h. The main reaction pathways were found to include benzene and ethylbenzene hydrogenation towards cyclohexane and ethylcyclohexane, hydroalkylation into cyclohexylbenzene, ethylcyclohexylbenzene and diethylcyclohexylbenzene and formation of ethylbiphenyls or diethylbiphenyls followed by hydrogenation. The major reaction products were para- and meta-ethylcyclohexylbenzenes. The results have demonstrated that hydroalkylation of benzene and ethylbenzene over metal containing zeolites is a perspective route for synthesis of ethylcyclohexylbenzene, which can find application in production of phenylstyrene.

Aniline Methylation Over Modified Micro- And Mesoporous Catalysts

Methylation of aniline is an industrially important process, aimed at the synthesis of mono-N-methylaniline (NMA), di-N-methylaniline (NNDMA) and toluidines which are useful raw materials for organic syntheses as well as important intermediates in the dye-stuff production and in the pharmaceutical and agrochemical industries. Up till now, industrial processes leading to these products are based on the application of corrosive liquid acids as catalysts [1,2] and should be replaced by environmentally more benign processes using solid catalysts such as oxides, clays and zeolites. It is known that alkylation of aniline may take place on acidic [3, 4, 5, 6] and on basic zeolites [7,8]. Moreover, this reaction was performed even on zeolites with redox properties [3,9,10]. A detailed study of reaction mechanisms over zeolite catalysts pointed to existence of two mechanistic pathways: on acidic catalysts, the reaction proceeds via a methanol dehydration leading to surface methoxy groups as intermediates of N- alkylation, while on basic and redox catalysts, the reaction pathway includes methanol dehydrogenation leading to formaldehyde species, alkylation of aniline with formaldehyde to give N-methyleneaniline and hydrogenation of N- methyleneaniline to N-methylaniline [11, 12]. In this contribution, aniline methylation has been studied on various molecular sieve catalysts. The effects of both catalyst structure and nature of active sites were investigated. The catalyst structures selected covered a broad range of pore sizes from 5.5 A to 30 A. The nature of the active sites was altered to obtain acidic, basic and redox materials.