EFFECTS OF B3+ CONTENT OF B-ZSM-11 AND B-ZSM-5 ON ACIDITY AND CHEMICAL AND THERMAL-STABILITY

The geometrical environments of B3+ in sol-gel suspensions, dried gels, and resultant crystals of B-ZSM-5 and B-ZSM-11 zeolites have been probed with luminescence, luminescence lifetime, B-11 nuclear magnetic resonance (NMR), X-ray powder diffraction (XRD), and thermal methods. The concentration range of B3+ that can be monitored with luminescence is 0.1-0.5 wt % B3+ as evidenced by concentration quenching studies. Both trigonal and tetrahedral B3+ environments are observed by both luminescence and B-11 NMR methods. Contraction of unit cell volume has been observed with XRD methods. The thermal stabilities of B-ZSM-5 and B-ZSM-11 have been tracked with XRD and luminescence methods with structural loss occurring near 900-degrees-C with the formation of H3BO3 as identified by luminescence emission and an increase in surface [B3+] as detected by X-ray photoelectron spectroscopy (XPS). Treatment of B-ZSM-5 or B-ZSM-11 with HCl also leads to loss of B3+ from the framework. Infrared experiments have shown that both Bronsted and Lewis acid sites that are weak exist in these materials. B-ZSM-5 crystals have hexagonal morphologies, whereas B-ZSM-11 crystals are less well-formed. The lateral and depth uniformity of [B3+] in B-ZSM-5 crystals is suggested on the basis of scanning Auger microscopy and XPS. Thermal treatment to 900-degrees-C leads to migration of B3+ to the surface of ZSM-5 as shown by XPS.