S. V. Konnov

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 %.

Nanocrystalline zeolites beta: Features of synthesis and properties

The effect of synthesis conditions for BEA zeolite nanocrystals (BEA-ZNC) on the combination of their morphological, textural, and acidic properties has been studied. BEA-ZNC have been synthesized by the hydrothermal or vapor-phase crystallization of reaction mixtures with a high template concentration using the following variable synthesis parameters: the SiO2/Al2O3 ratio the presence of mineralizing additives, the SiO2 source and template type, and the synthesis pH. It has been found that an increase in the aluminum content in BEA-ZNC from 2.7 to 7.8 Al atoms per unit cell is accompanied by a decrease in the size of the ZNC from 250–350 to 100 nm, an increase in the acid site concentration, and an increase in the fraction of weak acid sites in the acidity range of the samples. It has been shown that the specific feature of the synthesis of BEA-ZNC is a low degree of inclusion of silica and the template into the zeolite composition, which is 28–62 and 3.4–5.5%, respectively, of the amounts initially introduced into the reaction mixture. It has been proposed that silica gel should be used as the most promising SiO2 source for the preparation of BEA-ZNC; the use of silica gel provides formation of a material in the form of isolated nanocrystals with a size of 150–300 nm, a developed pore structure, and a high concentration of acid sites. It has been shown that the BEA-ZNC synthesized by vapor-phase crystallization are inferior to the samples prepared by conventional hydrothermal crystallization with respect to the pore structure characteristics and acidic properties.

Effect of the degree of zeolite recrystallization into micro–mesoporous materials on their catalytic properties in petroleum refining and petroleum chemistry processes

It has been shown that by varying the degree of recrystallization of zeolites, it is possible to obtain mesostructured zeolites (RZEO-1), micro–mesoporous nanocomposites (RZEO-2), and mesoporous materials with zeolite fragments (RZEO-3). The main features of the effect of recrystallization degree of MOR, BEA, and FER zeolites on their catalytic properties in the processes of cracking of 1,3,5-triisopropylbenzene, skeletal isomerization of butene-1, hydroisomerization of n-alkanes, alkylation of benzene with dodecene-1, alkylation of naphthalene with cyclohexene, and disproportionation of cumene have been revealed. It has been found that each type of catalytic reaction requires a micro–mesoporous catalyst with an optimal degree of recrystallization. Zeolites RZEO-1 are the most efficient in the reactions that require strong acidity; zeolites RZEO-2 are the most promising in consecutive reactions and reactions that proceed in pore mouths; and RZEO-3 are optimal for transformations of bulky molecules.

Methanol to lower olefins conversion in a slurry reactor: Effects of acidity and crystal size of silicoaluminophosphate catalysts

Effects of the crystal size and acidity of silicoaluminophosphates on their catalytic behavior in the methanol to lower olefins conversion in a slurry reactor have been studied. It has been found that an increase in the crystal size of silicoaluminophosphate causes a reduction in its catalytic activity, which is due to an increase in diffusion limitations for both reagents and reaction products. An increase in the number of acid sites and their localization on the outer catalyst layer improve the time stability of silicoaluminophosphate performance and the selectivity of methanol conversion to lower olefins.

Dimethyl ether conversion to olefins in a slurry reactor: the effect of MFI zeolite catalyst acidity and selectivity control

The textural, acidic and catalytic properties of nanosized samples of commercial MFI zeolites with SiO2/Al2O3 molar ratios of 30, 50 and 80 supplied by Zeolyst Co. and some synthesized nanocrystallites of MFI zeolites with a SiO2/Al2O3 molar ratio of 55 and 80 were compared. It was shown that the SiO2/Al2O3 ratio had no impact on catalyst deactivation in the slurry reactor as in the conventional fixed-bed reactor. Irreversible deactivation was observed only for the samples with an extremely high external surface Brønsted acidity indicating that near-surface secondary processes are responsible in catalyst deactivation. It was shown that the reaction temperature influenced the product selectivity due to change in the contribution of both hydrogen transfer reaction and arene/alkene circles and can be considered to be an efficient tool of selectivity control for DME conversion in the slurry reactor.

Dimethyl ether to olefins conversion in a slurry reactor: Effects of the size of particles and the textural and acidic properties of the MFI-type zeolite

Effects of the particle size of a suspended zeolite catalyst based on the commercial MFI-type (high modulus zeolite, HMZ) zeolite on its physicochemical characteristics and catalytic properties in the conversion of dimethyl ether (DME) in a three-phase system with a slurry reactor are studied. In order to gain insight into the relationships between the physicochemical characteristics of MFI-type zeolites and their catalytic properties, the textural, acidic, and catalytic properties of HMZ zeolites and synthesized nanocrystallites of the zeolite with the MFI structure are compared. It was found that, in the conversion of DME in the slurry reactor, the catalytic properties of the MFI zeolite are strongly affected by the size of particles of the suspended catalyst: on passage to nanosized suspensions, the activity of the catalyst grows by several times. Reduction in the size of catalyst particles leads to an increase in the yield of hydrocarbons C5+ and a decrease in the yield of lower olefins. At the same dispersity of suspensions, the catalytic properties of suspended catalysts are considerably affected by the distribution of acid sites over strength in the studied zeolite sample and the fraction of amphoteric sites in them.

Effect of synthesis conditions on the properties of nanocrystalline faujasites

The effect of crystallization parameters on the properties of nanocrystalline zeolites Y has been studied to optimize the synthesis conditions. Zeolites Y are prepared by the three-stage hydrothermal crystallization with a gradual rise in synthesis temperature from room temperature to 60°C using the Na2O/SiO2 ratio in the reaction mixture and the number and duration of individual synthesis stages as variable synthesis parameters. It has been shown that an increase in the Na2O/SiO2 molar ratio in the reaction mixture above 9.6 leads to a change in the crystallization selectivity and causes formation of zeolite X with a crystal size of 200 nm as a crystalline product. An increase in the duration of the synthesis stage at 60°C is accompanied by increase in the crystal size and entails formation of an analcime impurity phase. A decrease in the duration of reaction mixture aging stages at 25 and 38°C leads to an increase in the zeolite Y nanocrystal sizes and a decrease in the crystalline product yield. It has been found that a pure zeolite Y phase with a nanocrystal size of 320–350 nm and a SiO2/Al2O3 ratio of 3.6–4.2 is formed during the three-stage synthesis from a (7.2–9.6)Na2O · Al2O3 · 14.4 SiO2 · 290 H2O reaction mixture with a yield of 0.60–0.88 g/g of reaction mixture.

Methanol to olefins conversion over silicoaluminophosphates with AEI structure: Effect of the active site type

Effect of the type of active site on the catalytic properties of microporous crystalline silicoaluminophosphates with AEI structure synthesized at 150, 170, and 190°C has been investigated. The state of the active site was changed by varying the catalyst synthesis conditions. It has been established that during the synthesis of silicoaluminophosphates with the AEI structure from the reaction mixture of the same composition, an increase in the temperature and crystallization time leads to an increase of the silicon content and crystal size growth. The observed changes in the physicochemical properties are accompanied by the change of the silicon state in the structure of silicoaluminophosphates with the predominant formation of silicon “islands” via the SM3 mechanism. According to 29Si NMR data, the formation of active sites of silicoaluminophosphates via the SM2 mechanism in the form of isolated silicon atoms in the structure is also observed for these materials. The presence of such sites, along with the morphological features of the crystals, determines the unusual catalytic properties of silicoaluminophosphate with AEI structure in MTO process, which are a high ethylene yield up to 41 wt % at an ethylene: propylene molar ratio of 1: 6.

Toluene disproportionation on recrystallized MFI zeolites

The textural, acidic, and catalytic properties of MFI zeolite-based micro–mesoporous materials synthesized by recrystallization have been studied. It has been shown that recrystallization does not affect the chemical composition of the samples, but it leads to a change of their porous structure and acid properties. All of the materials have exhibited stable activity in the toluene disproportionation reaction. In the presence of the micro–mesoporous materials obtained by recrystallization under mild conditions, the toluene conversion increases by more than three times compared with the parent MFI zeolite, reaching 33 wt %. Differences in the texture and acid properties of the samples do not affect the composition of the toluene disproportionation products. The enhancement of the catalytic activity of recrystallized MFI zeolites is assumed to be due to both the presence of through mesopores and the facilitation of access to strong acid sites.