Bobyk V. External acidity effect on catalytic properties of Pd-containing high-silica zeolites in n-hexane hydroisomerization

It is shown that as a result of decrease in external acidity owing to ion-exchange sorption of tetrabutylammonium cations on external surface of catalysts, n-hexane conversion is reduced at invariable high selectivity on hydroisomerization. Especially appreciable is a decrease in output of 2,2-dimetylbutane that testifies the formation of dibranched isomers mainly on an external surface of zeolite microcrystals. The method of quantitative determination of the external acid centers is offered by potentiometric titrations of zeolites suspensions by tetrabutylammonium hydroxide. It is established symbate dependence between amount of the external acid sites and an output 2,2-dimetylbutane in products of hydroisomerization. It is offered the method of increase of external surface and acidity by alkaline processing mordenite catalyst due to formation mesopores and reduction of Si to Al ratio in this zone. According to established symbate dependence it is shown that catalyst activity in hexane hydroisomerization and 2,2-dimetylbutane formation selectivity is increased. It is established that decrease in amount of the external acid sites due to acid dealumination on results in substantial growth of conversion and decrease in selectivity of catalyst PdHZSM-5 on hydroisomerization products. Decrease in selectivity is connected with the dimerization cracking mechanism owing to decrease in homogeneity of mutual distribution of hydrating/dehydrating and the acid sites.