New route for dispersion of inorganic salts onto the channel surfaces of microporous crystals: high dispersion of CuCl2 in zeolites using a microwave technique

Abstract

A series of CuCl₂–zeolites with a weight ratio of CuCl₂·2H₂O:zeolites of 0.10–0.80 have been prepared. After the reaction of CuCl₂·2H₂O with zeolite in a microwave oven for 10–20 min at ambient temperature, the CuCl₂–zeolites (CuCl₂·2H₂O:NaZSM-5 = 0.10–0.50; CuCl₂·2H₂O:NaY = 0.1–0.60) showed only those X-ray peaks assigned to zeolites, the characteristic peaks of the CuCl₂·2H₂O having disappeared completely, which suggests that the CuCl₂ is highly dispersed in the channels of NaZSM-5 and NaY zeolites. Similar phenomena were observed for the samples of CuCl₂–silicalite-l, AuCl₃–NaY, AuCl₃–NaZSM-5, NiCl₂–NaZSM-5, RuCl₃–NaY, Li₂SO₄–AIPO₄-11. The n-hexane isotherms of CuCl₂–NaZSM-5 treated in a microwave oven exhibited a higher adsorption pressure to reach saturated adsorption of n-hexane, compared with those of NaZSM-5 and a mechanical mixture of NaZSM-5 and CuCl₂·2H₂O without treatment in a microwave oven. IR spectra of CO adsorbed on CuCl₂–NaZSM-5 treated in a microwave oven showed much stronger adsorption bands than those of CuZSM-5 ion-exchanged by CuCl₂ solution, which indicates that the concentration of Cu^{2 +}(CO) and Cu⁺(CO) on the CuCl₂–NaZSM-5 is larger than those on the CuZSM-5. Furthermore, CuCl₂·2H₂O–NaZSM-5 (weight ratio 0–0.50) exhibited no peak at the melting point of CuCl₂ in DTA curves, because the CuCl₂ was highly dispersed in the channels of NaZSM-5. However, increasing the CuCl₂·2H₂O loading in NaZSM-5 up to 0.60, beyond the high-dispersion capacity, the DTA curve exhibited peaks at 770 K assigned to the melting point of CuCl₂ due to residual crystalline CuCl₂.