Target modification of acid properties of ultrastable zeolite Y: Treatmentwith boron and phosphorus compounds

The effect of modification of ultrastable zeolite Y with phosphorus and bor on by treating with PCl3, B(OC2H5)(3), and water vapor on the crystal struc ture, nature and strength of acid sites and the elemental composition and s tate of zeolites was studied. Based on the data obtained by IR spectroscopy , temperature-programmed desorption of ammonia, IR spectroscopy of adsorbed ammonia, and X-ray photoelectron spectroscopy, it was shown that a modifyi ng agent is chemically bonded to the zeolite crystal framework upon these t reatments. Introduction of small quantities of phosphorus into the ultrasta ble zeolites decreases the total amount of acid sites, suppresses weak and strong acid sites, and, simultaneously, facilitates the revealing of sites that strongly retain ammonia. An increase in phosphorus content promotes th e formation of a more uniform spectrum of acid sites of primarily moderate strength. The boron-containing samples show the presence of rather strong a cid sites. Phosphorus occurs in two states in the samples, of which one cor responds to the coordination and the electronic state of phosphorus in NaH2 PO4 and the other reflects the possibility of formation of Al-O-P bonds. Th e combination of treatments with boron and phosphorus compounds leads to th e formation of the borophosphate structure. The modification results in fur ther dealumination of the zeolite framework because of interaction of the p roduced hydrogen chloride and water vapor with zeolite, and the number of P -O-Al bonds increases with increasing the phosphorus content. The boron mod ification results in a partial substitution of boron for the surface alumin um atoms, thus also increasing the Si/Al ratio.