Physicochemical and catalytic properties of a new type of as-synthesized aluminium-deficient Y zeolite

Abstract

Physicochemical (IR spectroscopy, 27Al and 29Si MAS NMR spectroscopy, XRD, adsorption measurements) and catalytic properties of a new type of low-alumina Y zeolite (LAY) prepared by direct synthesis (SiO 2/Al 2O 3 molar ratios 5.5–7.2) without using any templating agents or post-synthesis dealumination procedures were studied in comparison with the conventional or dealuminated Y zeolites. The low-alumina NaH-LAY zeolites are characterized by the higher thermal stability of acidic OH groups as compared with dealuminated Y zeolite. The unit cell parameter measured by XRD remains virtually unchanged and close to 2.463 nm for Na-LAY zeolite with SiO 2/Al 2O 3 ratios of 5.85–7.2. Extraframework aluminium was not found in decationized LAY zeolite samples by 27Al MAS NMR until the residual Na 2O content reached values below 1 wt.%. In addition, it is possible to tune the activity in the catalytic cracking of n-hexane by varying the extent of decationization. The content of isomer products increases with a growth of the residual Na 2O content in LAY zeolite. Introduction of this new zeolite into the cracking catalysts provides the maximum yield of gasoline at lower catalyst/feed ratios, compared to catalysts containing dealuminated Y zeolites. The case of the commercial use of the NaH-LAY zeolite is discussed.