PROBING SILICON SUBSTITUTION IN MOLECULAR-SIEVES BY PLASMA DESORPTIONMASS-SPECTROMETRY

Plasma desorption was used to produce secondary ion mass spectra from samples of unsubstituted and substituted aluminum phosphate materials. The yield of fingerprint ions representative of silicon oxide solids indicates that the incorporation of silicon into the material during s ynthesis and following calcination occurs via the formation of silicon -rich islands. Complementary Xray photoelectron data provide supportin g evidence that the surface of the substituted aluminum phosphate mate rial becomes silicon rich and phosphorus depleted. No changes in the u nsubstituted and substituted material with respect to composition and phase were detected using powder X-ray diffraction. (C) 1998 Elsevier Science B.V. All rights reserved.