Add time:08/08/2019         Source:sciencedirect.com

The structural evolution of Y zeolite (Si/Al=2.17) weakly dealuminated by hexafluorosilicate (Si/Al= 3.13), denoted YD, and exchanged with calcium (CaYD) or lanthanum (LaYD), has been studied after acid-base treatments at 80°C close to the cation exchange conditions. The stability of the samples is followed by X-ray diffraction and solid-state NMR of 29Si and 27Al; YD zeolite is completely destroyed by treatment with acid at pH 2.5 and suffers serious degradation on treatment with alkali at pH 11.8. The introduction of calcium or lanthanum improves the stability of the zeolite in acid and base. In acid it is not destroyed until pH 1. At pH 2, silicon and aluminium are extracted and an amorphous phase is formed in the case of the calcium-exchanged zeolite. Base treatment at pH 13 does not affect CaYD and leads to silicon extraction in the case of LaYD. The introduction of lanthanum into YD leads to the formation of a new phase which is eliminated by acid-base treatment.

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