O. A. Ponomareva

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.

Hydroalkylation of benzene and ethylbenzene over metal-containing zeolite catalysts

The hydroalkylation reaction of benzene and ethylbenzene over BEA zeolites with a Si/Al ratio of 9–190, MOR with Si/Al = 48, and MFI with Si/Al = 25 containing ruthenium, rhodium, platinum, or palladium was studied, as well as over the Ru/BEA zeolites with Si/Al = 42 doped with a second metal: nickel, cobalt, or rhodium. The catalytic experiments were conducted under flow conditions in the temperature range 130–190°C, a pressure of 1 MPa, a feed weight hourly space velocity of 2–64 h−1, and a stoichiometric reactant ratio. It was shown that the main reaction routes are the complete hydrogenation of benzene and ethylbenzene yielding cyclohexane and ethylcyclohexane, respectively; hydroalkylation yielding cyclohexylbenzene, para- and meta-ethylcyclohexylbenzenes, and diethylcyclohexylbenzenes; and alkylation resulting in dicyclohexylbenzenes and ethyldicyclohexylbenzenes. The ruthenium-promoted (1 wt %) zeolite BEA with Si/Al = 42 displayed the highest activity and selectivity in the benzene and ethylbenzene hydroalkylation reactions. Doping of the catalyst with cobalt and rhodium did not improve its catalytic properties, presumably, owing to the fact that the dopant metals largely occur in the cationic form according to the IR data for adsorbed CO. An admixture of nickel (0.5 wt %) to the catalyst increases the catalyst operation stability without reducing the yield of ethylcy-clohexy lbenzenes.

Hydroisomerization of n-octane over Pt-containing micro/mesoporous molecular sieves

Abstract Hydroisomerization of n-octane over Pt-containing micro/mesoporous catalysts obtained by recrystallization of zeolites BEA and MOR was investigated in the temperature range of 200–250 °C under 1–20 bar. Composite materials showed remarkably high activity 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.

Microporous crystalline silicoaluminophosphates: Effect of synthesis conditions on the physicochemical and catalytic properties in the reaction of methanol to C2-C4 olefins conversion

Effect of the synthesis parameters (reaction mixture composition, crystallization temperature and duration) on the physicochemical and catalytic properties of microporous crystalline silicoaluminophosphates (SAPOs) has been studied. Methods for the directional control of phase composition, degree of crystallinity, morphology and size of SAPO crystals crystallized from colloidal silicoaluminophosphate sols stabilized in tetraethylammoniun hydroxide solution as a template have been developed. It has been determined that the use of more severe synthesis conditions (increase in temperature and duration of crystallization) leads to the formation of larger crystals and a growth in the concentration of medium strength sites in the samples, which causes a rapid deactivation of the samples in the reaction of methanol conversion to C2-C4 olefins. Crystallization under milder conditions (a decrease in pH and temperature) promotes the acid formation of CHA/AEI intergrowth crystals exhibited a high and steady performance in the methanol conversion for more than 8 h at a total yield of olefins of 95 wt %.

Benzene alkylation with dodecene-1 over micro-mesoporous molecular sieves

The alkylation of benzene with dodecene-1 has been studied over catalysts with a combined micro-mesoporous structure with different amounts of mesopores obtained by the hydrothermal recrystallization of Beta and mordenite zeolites. The main features of the reaction of benzene alkylation with dodecene-1 over the micro-mesoporous catalysts have been established. The formation of transport pores and an increase in the accessibility of acid sites as a result of recrystallization under mild conditions facilitate an increase in the activity, with a high selectivity for linear phenyldodecanes being retained; a higher degree of recrystallization to MCM-41 leads to a decrease in the conversion and selectivity; the mordenite-based catalysts are more active than zeolite Beta.

Hydroisomerization of n-octane on platinum-containing micro-mesoporous molecular sieves

The hydroisomerization reaction of n-octane at atmospheric pressure and a temperature of 230°C on platinum-containing catalysts with a combined micro-mesoporous structure synthesized on the basis of MOR and BEA zeolites was studied. The influence of the nature of zeolite, the relative amount of micropores, the platinum content, and the Si/Al ratio on the catalytic activity was examined. The microporous materials showed a considerably higher n-octane conversion and a higher isomerization selectivity as compared to both starting zeolites and mesoporous catalysts. It was found that the BEA-based micro-mesoporous materials are more active and selective than mordenites. An increase in platinum loading from 0.2 to 0.7 wt % leads to a rise in the yield of octane isomers, and a further increase in the platinum content does not result in a substantial change in the characteristics of the processes. It was shown that a change in the Si/Al ratio has a considerable effect on the formation of polybranched C8 isomers.

The mechanism of phenol methylation on acid and basic zeolite catalysts

The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by 13C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins.

Catalytic synthesis of cumene from benzene and acetone

The reaction of benzene hydroalkylation with acetone on bifunctional catalysts has been studied and the principal features of the process have been revealed, wherein the catalysts contain a copper oxide-copper chromite binary system as a hydrogenating component and BEA, MOR, FAU, or MFI zeolite as an alkylating component. It has been found that the use of the catalyst based on the mixed copper-chromium oxide and mordenite, running the process at 150°C and 3 MPa, and feedstock dilution with benzene (C6H6: C3H6O = 9: 1) facilitate increasing of the yield of cumene as a main product.

One-step synthesis of N-methylaniline by hydroalkylation of nitrobenzene over oxide catalysts

The reaction of nitrobenzene hydroalkylation with methanol forming N-methylaniline as the main product has been studied. Alumina modified with copper and chromium compounds deposited by incipient wetness impregnation has been examined as the catalyst. It has been shown that the reductive alkylation of nitrobenzene with methanol is preferable to conduct at a temperature of 250°C, a feed weight hourly space velocity of 1 to 2 h−1, a methanol: nitrobenzene molar ratio of 3 to 4, and hydrogen: nitrobenzene molar ratio of 3–6. It has been found that promotion of the copper-containing catalyst with chromium leads to enhancement of the catalyst activity and facilitates an increase in selectivity for N-methylaniline.

Physicochemical and catalytic properties of micro-mesoporous zeolite materials

Micro-mesoporous zeolite materials differing in their content of micro- and mesopores are obtained by the recrystallization of modernite zeolite. Using physicochemical methods such as scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction analysis, small-angle X-ray scattering analysis, low-temperature adsorption of nitrogen, temperature-programmed desorption of NH3, and IR spectroscopy, it is shown that recrystallization leads first to the formation of mesopores with sizes of 20–30 Å in zeolite crystals, then to the appearance of zeolite/MCM-41 nanocomposite, and finally to the complete conversion of zeolite into mesoporous MCM-41. During this process, the concentration of strong Brønsted acid sites accessible to pyridine bases first increases then drops. The catalytic properties of the synthesized materials are studied in the reaction of alkylation of benzene by dodecene-1. It is shown that the creation of transport pores and the increase in the accessibility of acid sites due to recrystallization under soft conditions facilitate the alkylation reaction.