Sergey V. Bubennov

Objectives. The work set out to compare the catalytic properties of microporous H–Y zeolite and granulated hierarchical (micro-, meso-, and macroporous) H–Y _h zeolite in the synthesis of benzimidazoles via the reaction of o-phenylenediamine with aromatic ( p -chlorobenzaldehyde) and aliphatic (hexanal) aldehydes. Methods. Granulated hierarchical zeolite was synthesized by hydrothermal crystallization of pellets containing microporous H–Y zeolite and amorphous aluminosilicate. The physicochemical properties of the catalyst samples were studied using standard zeolite characterization methods. After synthesizing the benzimidazoles in stirred flasks, the reaction was carried out in an oxidizing (air) or inert (nitrogen) atmosphere. The reaction mixture was analyzed using high-performance liquid chromatography. The structure of the compounds was determined using chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. Results. It is established that the hierarchical H–Y _h zeolite, which possesses a well-developed system of meso- and macropores, provides higher selectivity for the formation of target benzimidazoles than its microporous analog. The reaction atmosphere was shown to have a decisive influence on the product composition. While monosubstituted benzimidazoles are selectively formed (up to 83–86%) in an oxidizing environment (air), in an inert atmosphere (nitrogen), the fraction of intermediate Schiff base or disubstituted products increases. Synthesis conditions for benzimidazoles offering the highest yields were identified. Conclusions. The hierarchical H–Y _h zeolite, which offers improved transport characteristics and increased accessibility of acid sites, provides higher selectivity for the target products than its microporous analog. In order to promote the selective formation of monosubstituted benzimidazoles, the reaction was carried out in an oxidizing medium. Under optimal conditions, their yields reach the following values: 2-(4-chlorophenyl)-1 H -benzimidazole, 81%; 1-(4-chlorobenzyl)-2-(4-chlorophenyl)-benzimidazole, 73%; and 2-pentyl-1 H -benzimidazole, 80%.

This study investigates how the synthesis method for hierarchical H-ZSM-5 zeolites affects their catalytic activity and product selectivity in the condensation of o-phenylenediamine with ketones (acetone, methyl ethyl ketone, 2,4-pentanedione, and acetophenone). Samples with enhanced porosity were prepared using two different procedures: (1) treatment of a microporous ZSM-5 zeolite with alkali (H-ZSM-5a) followed by acid (H-ZSM-5aa); and (2) direct synthesis of a granulated ZSM-5 zeolite (H-ZSM-5_h). The H-ZSM-5_h granular zeolite exhibited superior catalytic performance in the reaction of 1,2-phenylenediamine with acetone, achieving 94% conversion and 83% selectivity. This is attributable to its extensive meso/macroporosity, high total acidity (740 μmol/g), and optimal proportion of strong acid sites (43%)—properties that favor rapid diffusion and prevent the accumulation of intermediates. Under the conditions studied, the reaction proceeded via an imine route rather that an aldol route (through mesityl oxide). Acetone afforded the highest target product yield (87%).

A new approach to the synthesis of a nanosized and hierarchical titanosilicate, TS-1, is presented. Instead of using specific solid or additional mesoporous templates or individual additives to slow down the hydrolysis of titanium alkoxides, it is proposed that the titanosilicate TS-1 can be obtained from gels synthesized with hydrolysis catalysts (HNO₃ and tetrapropylammonium hydroxide). When nitric acid catalyzes tetraethyl orthosilicate (TEOS) hydrolysis, the resulting crystalline TS-1 that can be obtained has uniform particle sizes (150–180 nm), is anatase-free, and contains up to 46–67% of mesopores. When a base catalyst is applied, the obtained material’s features are opposite. Moreover, acid-promoted TS-1 samples catalyze cyclohexene H₂O₂-oxidation via a heterolytic route to the cyclohexane epoxide with 67% selectivity, which is non-typical.

Catalytic properties that mesoporous amorphous titanosilicate catalysts differing in physicochemical characteristics exhibit in cyclohexene oxidation with hydrogen peroxide to a mixture consisting mainly of alcohol and ketone were studied. The cyclohexene conversion and selectivity of formation of oxidation products depend both on the physicochemical properties of the titanosilicates studied (nature of active sites, porosity, etc.) and on the reaction conditions. The total selectivity with respect to the enol + enone fraction of 94% at the maximal cyclohexene conversion of 55% was reached in the presence of TSMa titanosilicate (Si/Ti = 40).

Amorphous mesoporous materials are promising as catalysts for processes involving or forming bulk molecules. In a reaction such as acetone condensation to form mesitylene, an effective catalyst should not only have a developed porous structure but also have active centers of acidic and basic types. The sol–gel approach allows one to obtain titanosilicates with such characteristics. This work demonstrates the possibility of controlling their properties by varying the conditions for the synthesis of titanosilicate gels. It has been established that controlling hydrolysis allows one to increase the activity of amorphous mesoporous titanosilicates by 10 times: from acetone conversion of 6% to 60%. It has been shown that the use of titanium acetylacetonate complexes in the synthesis of gels leads to an increase in the content of tetracoordinated Ti in the structure and contributes to an increase in the acidity of titanosilicates. During the condensation of acetone on the obtained mesoporous titanosilicates, high acetone conversion (60–79%) and mesitylene selectivity of up to 83% were achieved.

The physicochemical properties of a series of catalysts based on granulated Na-Yh zeolite with the hierarchic (micro–meso–macro) pore structure (Na-Yh, HNa-Yh, MgO/Na-Yh, La₂O₃/Na-Yh, TiO₂/Na-Yh) and the activity and selectivity of these catalysts in isophorone aromatization were studied. MgO/Na-Yh and La₂O₃/Na-Yh zeolites with high content of basic sites and low content of Brønsted acid sites are the most effective in the synthesis of 3,5-dimethylphenol: The 3,5-dimethylphenol formation selectivity reaches 63–69% at 87–94% isophorone conversion. In the presence of Na-Yh zeolite containing both acid and base sites, the prevalent reactions are isophorone isomerization and synthesis of trimethylbenzenes. The modification of Na-Yh with titanium oxide leads to an increase in the content of acid sites on the TiO₂/Na-Yh surface and to the prevalence of the aromatization to form trimethylbenzenes. In the presence of HNa-Yh containing a set of the strongest Brønsted and Lewis acid sites, isophorone transforms into a mixture of polymethylbenzenes.

The study investigates the catalytic performance of microporous and granular micro–meso–macroporous zeolites (H-ZSM-5 and H-ZSM-5h, respectively) in synthesis of quinolines by the reaction of 2-aminoacetophenone with diketones (2,4-pentanedione or dimedone), known as the Friedländer synthesis. In the presence of H-ZSM-5h, 1-(2,4-dimethylquinolin-3-yl)ethanone ( 1a ) and 3,4-dihydro-3,3,9-trimethyl-1(2 H )-acridinone ( 1b ) were produced in 82 and 93% yields, respectively.

The study investigates the catalytic performance of hierarchical granular Na–Y_h zeolites promoted with metal oxides (designated as ZnO/Na–Y_h, NiO/Na–Y_h, Co₃O₄/Na–Y_h, and CuO/Na–Y_h) in the synthesis of quinolines from aniline and n-propanol. The highest aniline conversion and highest total quinoline selectivity (49 and 63%, respectively) were achieved in the presence of the ZnO/Na–Y_h sample. The samples promoted with Ni, Co, and Cu oxides reached a twofold lower aniline conversion (20–26%) with quinoline selectivity of 42–51%.

The study investigates the catalytic performance of microporous (H–Y) and micro–meso–macroporous (H–Y_h, Fe₂O₃/H–Y_h, PbO/H–Y_h, and La–H–Y_h ) FAU-type zeolites in the condensation of acetone with ammonia. In the presence of H–Y_h, Fe₂O₃/H–Y_h, and La–H–Y_h, 2,4,6-trimethylpyridine was synthesized with selectivity of 54%, 58%, and 24%, respectively. In the presence of H–Y and PbO/H–Y_h, the predominant reaction was acetone condensation, with the reaction products mostly consisting of diacetone alcohol and mesityl oxide.