Synthesis of pillared clays assisted by microwaves

Abstract

Microwave (MW) irradiation was used to synthesize aluminum-pillared clays (MW-Al-PILCs) by replacing the conventional calcination of Al-PILCs precursors (pre-Al-PILCs). X-ray diffraction (XRD) patterns and nitrogen adsorption/desorption isotherms showed that the MW-irradiated pre-Al-PILCs gave a series of MW-Al-PILC materials exhibiting some characteristics comparable to Al-PILCs obtained by conventional heating. However, differential thermal analysis (DTA), thermogravimetric analysis (TGA), impedance spectroscopy, 27Al MAS NMR, and intercalative adsorption of methylene blue (MB), indicated that the MW-Al-PILC samples were intermediate between Al-pre-PILCs and conventional Al-PILCs. The 27Al MAS NMR spectra showed that in MW-Al-PILCs obtained after 18 min of MW irradiation, the Al IV/Al VI ratio was 1/9, which is comparable to that in Al-pre-PILCs (8% Al IV; 92% Al VI) and significantly different from the typical values of conventional Al-PILCs (23% Al IV; 77% Al VI). It is assumed that the MW-induced calcination gives PILCs containing a fraction of residual, hydroxylated Al-polycations. The good thermal stability of the MW-Al-PILCs supports their possible use as acid catalysts.