LAUSR

Abstract A dealuminated Y-zeolite with a nSi/nAl ratio of 130 is treated in pure water and aqueous solutions of NaCl at different pH values between 3 and 7 at 100 °C for up to 3 weeks. The change of specific micropore volume, the specific external surface, and the mesopore size distribution are monitored by N2-adsorption (77 K). The decrease of micropore volume proceeds due to a zero order kinetics. The zeolite loses no mass, but according to an XRD analysis the loss of micropore volume is paralleled by the formation of mainly amorphous material. The amorphization is assumed to start at the outer surface of the zeolite crystals leading to a core-shell distribution of amorphous and zeolitic material. The amorphization is coupled with the formation of mesopores and an increasing external surface area. The evolution of mesopores mainly occurs at diameters near the lower boundary region of the pore size analysis by N2 sorption (3 nm). The degradation is catalyzed by hydroxide ions present in bulk water. Both the exchange of the acidic protons with Na+-ions and the presence of NaCl in the water phase accelerate the degradation at pH 7. The zeolite is decomposed in 1 M NaCl at pH 7 and 100 °C within 40 min. However, when the pH is lowered to 3, it is stable in 1 M NaCl for more than 10 days. The protonated form in pure water is about half as stable as the Na+-form in 1 M NaCl at pH 3.