I. V. Mishin

A study of the concentration and mobility of the hydroxyl-group hydrogen in zeolite catalysts by heteromolecular isotopic hydrogen exchange. 6. Dealuminized type-y zeolites and mordenite

Conclusions1.Dealuminization reduces the mobility and concentration of the surface hydrogen in mordenite and type-Y zeolites.2.The hydroxyl groups of dealuminized zeolites are kinetically uniform with respect to the H-D exchange.3.The hydroxyl covering on the mordenites is more stable than the covering on the faujasites.

Effect of heat treatment on the catalytic activity and selectivity of action of high-silica zeolites in transformations of xylenes

Conclusions1.In studying the isomerization and disproportionation of xylenes, the temperature range of the formation and destruction of active centers in zeolites of the pentasil and mordenite type was established. Active centers resistant to heat treatment at 973–1073 K are present on the surface of zeolites prepared by direct synthesis.2.After treatment of zeolite of the pentasil type with air at 1073–1273 K, the selectivity with respect to formation of p-xylene increased significantly, and the reaction of disproportionation of the xylenes with a decrease in the total catalytic activity was inhibited.

Amination of butanol on Na forms of zeolites

Conclusions1.The capacity of zeolites in the Na form to conduct the reaction of amination of 1-butanol by ammonia was demonstrated. The activity and selectivity of the zeolites increase in the order Na-mordenite <NaA<NaHSZ<NaY<NaX.2.Nonlocalized sodium cations are the carriers of the catalytic activity in the reaction of amination on Na forms of zeolites.

Role of structural factors and acidity in conversions of alkylaromatic hydrocarbons on high-silica zeolites

Conclusions1.On high-silica zeolites of the pentasil family, xylenes are converted to isomerization products with high selectivity. In the presence of wider-pore zeolites, the isomerization is accompanied with a considerable degree of disproportionation, the contribution of which increases with increasing diameter of the zeolite pores.2.The hydroxyl cover in the pentasils has a far higher thermal stability than in the mordenites; and as a consequence, the pentasils retain high catalytic activities even when heat-treated at 700°C.3The acidic centers of zeolites of the pentasil and mordenite types are similar in heats of ammonia adsorption and in their specific activity in xylene conversion.

Dehydration of methylbutanols on mordenites

Conclusions1.Dehydration of 2-methyl-2-butanol takes place on weak and strong acid sites, while 3-methyl-2-butanol is primarily dehydrated on the strong acid sites of the catalyst.2.Dehydration of 2-methyl-2-butanol on mordenites takes place only according to the mechanism of Β-elimination, while 3-methyl-2-butanol is dehydrated according to the mechanism of both Β- and γ-elimination, and an increase in the acidity of the catalyst causes γ-elimination.

Conversion of xylenes in the presence of high SiO2/Al2O3 zeolites 2. Catalytic activity of dealuminated mordenites

Conclusions1.Mordenite catalysts dealuminated by 50% show the highest activity for the isomerization of o-xylene.2.At low degree of conversion, the ratio of the disproportionation and isomerization rates of o-xylene is independent of the aluminum content of the mordenite framework, and the closer one approaches equilibrium, the more the disproportionation contribution increases with increasing degree of dealumination.

Surface composition of dealuminized mordenites and their catalytic activity in xylene conversions

Conclusions1.In the acid treatment of mordenite, the aluminum removal takes place first in the surface layer, and as a result, a nonuniform distribution of Al is observed in the dealuminized samples.2.The catalytic conversion of alkylaromatic compounds take place in the large channels of the mordenite, close to the surface.3.In mordenites with a low content of aluminum, molecular-sieve selectivity is manifested in the primary formation of unsymmetrical trimethylbenzenes in the products from the disproportionation of o-xylene.

Study of the catalytic activity of decationized L zeolites in transformations of o-xylene

Conclusions1.L zeolite exhibits weak selectivity for NH4+ cations which decreases as the degree of ion exchange increases in substitution of potassium cations with ammonia ions.2.Only L zeolites with a degree of decationization above 50% exhibit catalytic activity in transformation of o-xylene.3.Isomerization of xylenes on L zeolites primarily takes place by means of intramolecular transformations.

Conversion of xylenes in the presence of zeolites with a high SiO2/Al2O3 ratio

Conclusions1.A study has been made of the conversion of m− and o-xylenes in the presence of an ultra-high silica zeolite in the initial and decationized forms and in the presence of decationized and dealuminated mordenite at 150–550°C, atmospheric pressure, and a space velocity of 180 h−1.2.The Na- and H-forms of the ultrahigh-silica zeolite lead mainly to the isomerization of xylenes, while the isomerization and disproportionation of xylenes take place on the mordenites.3.In the presence of the Na- and H-forms of the ultrahigh-silica zeolite, which possesses a high stability in comparison with the decationized mordenite, the isomerization of m- and o-xylenes is characterized by an enhanced selectivity with respect to the formation of pxylene.

Dehydration of 3-methyl-2-butanol on zeolites

Conclusions1.Dehydration of 3-methyl-2-butanol on zeolites Y, mordenite, and entasil in the sodium and hydrogen forms and on dealuminated mordenites was studied. The hydrogen forms of zeolites from the pentasil family and dealuminated mordenite with a SiO2/Al8O3 ratio of 14 exhibit the highest activity.2.3-Methyl-2-butanol is dehydrated on the zeolites not only according to the mechanism of β-elimination, but also according to the mechanism of γ-eliminatton to a significant degree.