Abstract: The extra-framework aluminum species on the acidity of HY molecular sieve has a major influence on the properties of modified molecular sieves. The effect of [AlO]+ and [Al(OH)]2+ extra-framework Al species on the acidity of Br?nsted acid in HY zeolites was studied by using the periodic Density Functional Theory. By analyzing the deprotonation energy and the ammonia adsorption energy, it was recognized that the [Al(OH)]2+ species can strengthen the Br?nsted acid more effectively than the [AlO]+ species. The attached ammonia molecule can grab the H atoms of Br?nsted acid and turn into NH4+ species, NH3 works as an electron donor to transfer part of the electrons to the active center of HY zeolite. The more strength of Br?nsted acid, the more electrons transferred. Through geometric and electronic analysis, it was found that the influence of extra-framework Al species on the structure of Br?nsted acid is insignificant, but affects the electron structure of the molecular sieve skeleton, thus affecting its acidity.

Key words: extra-framework aluminum, HY zeolite, Bronsted acid, Density Functional Theory