Acidic property of YNU-5 zeolite influenced by its unique micropore system

YNU-5 zeolite has the YFI-type framework with a 12-12-8-ring system (2-dimensional 12-oxygen membered ring pores 3-dimensionally connected by twin 8-ring channels), and isolated channels separated from thin (mono-atomic silicate) wall. In this study, acidic property of was analyzed mainly means ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method. addition, accessibility acid sites evaluated through adsorption pyridine. The number Brønsted approximately agreed Al atoms, amount Lewis negligible, indicating that most have nature bridging Si(OH)Al group in YFI framework. Most OH groups on zeolites (including dealuminated samples) reacted pyridine vapor at 343 K to form pyridinium cations, are highly accessible system. Enthalpy desorption site, which can be an index strength or reactivity site basic reactant, following order: FAU < MOR (12-ring) ≈ *BEA MFI MWW (8-ring), markedly large enthalpy compared other 12-ring zeolites. DFT calculations suggest protons especially high located but side. dealumination temperature under reflux conditions nitric resulted preferential removal low enthalpy, probably presence reactive 8-ring, them system, reasonably consistent previously reported catalytic properties for dimethyl ether-to-olefin reaction.