420Present day development of promising novel pro cesses for the petrochemical and petroleum refining industry is largely associated with progress in zeolite catalysis. Research in the field of designing next gen eration zeolite systems having a high activity in the cracking, dehydrogenation, isomerization, and arom atization reactions opens a sound possibility of involv ing in catalytic processing of light hydrocarbons to produce valuable chemicals. Aromatization of gaseous hydrocarbons occurs in the presence of various cata lytic systems, of which high silica zeolites of the pen tasil family are considered the most effective [1][2][3][4][5]. These are ZSM 5, ZSM 8, and ZSM 11 zeolites and their domestic analogs, such as zeolites of the TsVK, TsVM, TsVN, and other brands [6,7]. Among poten tial catalysts for aromatization of light hydrocarbons, metal-zeolite systems command the major attention as they exhibit higher activity and selectivity compared with the unmodified zeolite supports. In this case, the initial zeolite structure affects the activity of a catalytic system. Therefore, studying the structural features of various zeolites and revealing their influence on the catalytic properties of modified zeolite forms are of considerable scientific interest and practical impor tance.The objective of this work is to examine the influ ence of zeolite framework type on the catalytic activity of zinc containing catalysts prepared from these zeo lites in the aromatization reaction of ethane, which is a component of both natural has and associated petro leum gas. EXPERIMENTALFor investigation, zeolites of the ZSM 5, ZSM 8, and ZSM 11 framework types having SiO 2 /Al 2 O 3 molar ratios of 70, 80, and 90, respectively, were pre pared from alkaline alumina-silica gels by hydrother mal synthesis under laboratory conditions. The ZSM 12 type zeolite was the commercial product manufac tured by the Angarsk Catalyst and Organic Synthesis Plant (molar ratio of SiO 2 /Al 2 O 3 = 83). Zinc contain ing zeolite systems were prepared by impregnating the zeolites with a zinc nitrate (Zn(NO 3 ) 2 · 6H 2 O) solution. The zinc concentration in the system were 3.0 wt % (on metal basis). The parameters of the zeo lites synthesized were monitored by means of IR spec troscopy and X ray diffraction analysis. The IR spec tra of the test samples were recorded on a Nicolet 5700 Fourier transform IR spectrometer within the range of 2000-400 cm -1 in KBr disks (1.2 mg of zeolite per 300 mg of KBr) in air. The phase composition of zeo lites was determined by X ray diffractometry on a DRON 3M diffractometer using Сu α radiation and a Ni filter.The acid properties of the zeolite catalysts were tested using the ammonia temperature programmed desorption (TPD) technique. The choice of ammonia as an adsorbate is due to a small size of its molecule, simplicity of dosage, and high basicity, allowing deter mination not only strong, but also weak acid sites. The concentration of acid sites in the test specimens was determined from the amount of ammonia deso...

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<p>Crystalline galloalumino- and gallosilicates with pentasil structure were synthesised under hydrother-mal conditions. The influence of gallium concentration and binder amount both on physicochemical and catalytic properties of a zeolite in the process of C₂-C₄ light alkanes aromatization and on catalyst deacti-vation due to carbidization has been studied. Acidic properties of gallium-containing pentasils with differ-ent composition were studied using the method of thermoprogrammed ammonia desorption. The forma-tion of strong aproton acidic sites whose composition includes gallium ions was found. It has been shown that isomorphic aluminium replacement by gallium in the pentasil lattice leads to a significant increase in aromatizing activity and period of stable catalyst operation. A decrease in intensity of coking and the formation of less condensed coke deposits with a wide distribution by the structure are observed with the increase in gallium concentration. The introduction of a binder to galloaluminosilicate results in a signifi-cant increase in mechanical strength of a catalyst. It was established that the most efficient catalyst of the above process is a zeolite containing 2.2% of gallium oxide and 1.3% of aluminium oxide and mixed with 20% of the pseudobeumite. The selectivity of the formation of aromatic hydrocarbons reaches 55-60%, the period of stable operation exceeds 350 h. In accordance with the data obtained suggested are the principles of the selection of efficient catalysts of light alkanes aromatization and optimum conditions of the process.</p>

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