The effect of non-framework aluminum on the stability and activity of REY zeolite

The influence of a routine step, washing, following the preparation of calcined rare earth exchanged Y zeolite (REY), on its hydrothermal stability, was studied. The amount and the chemical type of the acidic media used for washing could significantly influence the content of remaining non-framework aluminum (NFA) and consequently further affect the hydrothermal stability of the washed REY products. The content of remaining NFA in REY-A series zeolite played a key role in the hydrothermal stability of the zeolite samples. The crystallinity retention was obviously very closely related to the removal of NFA species. In other words, the less NFA species remained in zeolite samples, the higher crystallinity retention of REY could be achieved. The removal of NFA by different leaching media decreased in the order: REY-B-3 > REY-B-1 > REY-B-4 > REY-B-2. For industrial practice, the leaching medium ammonium sulfate + ammonia water is recommended for the NFA removal.