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 Cu2 +(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.