Consecutive interlayer disassembly-reassembly during alumination of UOV zeolites: insight into the mechanism

Investigation of the kinetics of UOV germanosilicate alumination by X-ray diffraction, Al-27 and Si-29 MAS NMR, ICP/OES and FTIR spectroscopy showed the multi-stage mechanism of the process. The first step consists of degermanation and partial disassembly followed by Al incorporation into the UOV germanosilicate framework in the second step. The Al atoms stabilize the UOV framework by healing the defects formed after rapid hydrolysis of Ge-O-Si bonds, which was evidenced by comparison with the reference treatment of initial UOV samples with HNO3 (pH = 2). Post-synthesis alumination of UOV leads to the generation of strong Bronsted and Lewis acid sites; their ratio in aluminated UOV derivatives can be adjusted by the variation of treatment conditions. The intrinsic properties of parent UOV germanosilicates determine the textural properties of aluminated derivatives.