Pseudo depth profiling by ESCA and X-ray microanalysis: An application to chemical dealumination of Y-zeolites

Abstract

A combination of electron spectroscopy for chemical analysis (ESCA) and scanning electron microscope X-ray microanalysis techniques is reported, which, when applied to Y zeolites, provides compositional depth profiles and a depth distribution of impurities in materials. The depth profile relies on the fact that ESCA samples down to ∼ 3 nm while variation of the incident electron-beam energy allows X-ray microanalysis to sample depths between ∼ 30 nm and ∼ 5 μm. The technique has been applied to Y zeolites dealuminated with (NH 4) 2SiF 6 and subsequently washed/ion exchanged in various ways. All the samples examined exhibit a decreasing Si Al ratio with increasing depth into the crystallites, showing that the dealumination process is diffusion controlled. Subsequent treatments alter the extent of the dealumination process; for example, washing with 0.1 m HNO 3 (aq) produced substantial further dealumination at all depths.