Ordered Heteroatom Siting Preserved by B/Al Exchange in Zeolites

The borosilicate zeolites SSZ-53, SSZ-55, SSZ-59, and SSZ-82 were converted to aluminosilicates by treating them with an aqueous Al(NO3)3 solution. The removal of boron atoms from the zeolite structures by acid leaching under comparable hydrothermal conditions was significantly inhibited. These findings reflect the complex post-synthesis chemistry of zeolites, where the Lewis acidic nature of Al3+ ions possibly plays a role. Density functional theory cluster calculations of 27Al chemical shifts and their comparison with experimental values were employed to determine the Al positions in the crystal structures. Al insertion takes place at the boron sites that had been previously established from X-ray diffraction data. The data suggest that making a detour via borosilicates can create aluminosilicate zeolite catalysts with ordered active sites for catalysis applications.