Abstract: Ultrafine zeolite NaYwas hydrothermally synthesized with silica sol and Al₂(SO₄)₃ as silica and alumina sources, respectively, by adding complexing agent such as citrate, acetate or editate to synthesis batch. The effect of the amount of citrate on the crystallization rate, SiO₂/Al₂O₃ ratio and crystal size of as synthesized zeolite NaYwas investigated. When the relatively lower amount of citrate[ n (citrate): n (Al₂O₃) ≤2:1] was added, both the crystallization rate and the SiO₂/Al₂O₃ ratio increased while the crystal size reduced obviously comparing with that in the absence of citrate. This indicates that the nucleation and crystallization of zeolite NaYwas promoted by complexing agent. When the relatively higher amount of citrate[ n (citrate): n (Al₂O₃)>2:1] was added, the above promotion effect diminished. The crystallization rate was found to reduce comparing with that in the absence of citrate, although the crystal size was still smaller than that in the later case. The optimum amount of citrate added to batch appears to be at the citrate:Al₂O₃ molar ratio of 1.5:1. The similar promotion effect was also observed both for the addition of editate and acetate with the molar ratio of editate:Al₂O₃ and acetate:Al₂O₃ equal to 1.5, respectively. The promotion effect of complexing agents to the nucleation and crystallization of zeolite NaYwas related with their complexing ability to aluminum.

Key words: Ultrafine zeolite, NaY, Synthesis, Crystal size, Complexing agent