Alfira N. Khazipova

A series of catalysts were prepared from a granulated hierarchical (micro–meso–macroporous) NaY_h zeolite: NaY_h, H-NaY_h, H-Y_h, Li-NaY_h, K-NaY_h, Ca-NaY_h, Mg-NaY_h, and La-NaY_h. Their physicochemical properties were characterized, and their catalytic activity and product selectivity were investigated in the aromatization of isophorone. The highest performance in the synthesis of 3,5-dimethylphenol was achieved in the presence of K-NaY_h, the catalyst distinguished both by the highest basicity among the tested samples and by low concentrations of weak Brønsted acid sites and Lewis acid sites. This sample exhibited a 3,5-dimethylphenol selectivity of 78.6% at an isophorone conversion of 98.9%. H-Y_h, H-NaY_h, Ca-NaY_h, Mg-NaY_h, and La-NaY_h provided the highest possible isophorone conversion (up to 100.0% at 400°C and 1 h^–1), with the reaction products mainly consisting of dimethylbenzenes and trimethylbenzenes (their selectivity reached up to 72.9 wt %). In the presence of low-activity samples (NaY_h and Li-NaY_h), the predominant products were methylbenzenes (dimethylbenzenes and trimethylbenzenes, 26.6–30.9%) and isophorone derivatives (β-isophorone and dihydroisophorone, 30.5–33.0%).

The catalytic performance (activity and selectivity) of a FAU-type hierarchical NaY_h zeolite, as well as of a series of modified samples, was investigated in the homocondensation of acetone. The modified samples were prepared from NaY_h by ion exchange of Na⁺ for cations of alkali (Li⁺, K⁺), alkaline-earth (Ca²⁺, Mg²⁺), transition (Co²⁺, Ni²⁺), and rare-earth (La³⁺) metals, as well as by decationation (H-NaY_h, HY_h). The predominantly acidic zeolites (Ca-NaY_h, Mg-NaY_h, Co-NaY_h, Ni-NaY_h, La-NaY_h, H-NaY_h, and HY_h) promoted the formation of acetic acid and mesitylene even at 250°C. The zeolites that contained alkali metal cations (Na⁺, Li⁺, and K⁺) exhibited activity only when the temperature was elevated. Starting from 350°C, NaY_h and Li-NaY_h promoted the formation of acetic acid. In contrast, the performance of K-NaY_h under heating was characterized by the absence of acetic acid formation and a smooth increase in the selectivity towards isophorone (up to 23%) and mesitylene (up to 18%). Over the range of 400–450°C, in the presence of K-NaY_h, secondary isophorone transformations were intensified, resulting in the formation of 3,5-xylenol as the main product with a selectivity of 32%.

Using a combination of XRD, ²⁷Al and ³¹P MAS NMR, SEM, TEM, N₂ low-temperature adsorption–desorption, and IR spectroscopy of adsorbed pyridine, the effects of gel preparation conditions on the properties of the SAPO-11 molecular sieves crystallized from the gels were investigated. It was demonstrated that the crystal morphology and the characteristics of secondary pores of SAPO-11 molecular sieves can be controlled by adjusting the sequence in which the initial components are mixed during gel preparation. The synthesized micro–mesoporous SAPO-11 samples exhibited high selectivity in the hydroisomerization of n-hexadecane.

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 Ni-modified granular samples of hierarchical porous Y_h (FAU) zeolite, some of which were synthesized by ion exchange and others by impregnation. The samples were characterized by X-ray diffraction, X-ray fluorescence, low-temperature nitrogen adsorption/desorption (–196°C), scanning electron microscopy, hydrogen temperature-programmed reduction, and IR spectroscopy of adsorbed pyridine. The samples prepared by ion exchange of Na⁺ for Ni²⁺ exhibited high catalytic activity in oligomerization of pentene, specifically 98% monomer conversion and 67% yield of oligomers at 110°C and 10 wt % catalyst. In contrast, the catalysts prepared by impregnation (Ni/Na–Y_h) exhibited extremely low activity in pentene oligomerization. The Ni-modified Y_h samples showed lower stability in the oligomerization of pentene than H–Y_h.

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%.