X-ray standing wave determines Al occupancy in zeolite

Zeolites are microporous crystalline materials, and in the unit cell, the tetrahedrally coordinated Si and Al atoms occupy the so-called crystallographic T-sites. In addition to their pore size, Al's occupancy in the specific T-sites is extremely important in catalytic activity. So far, however, the distribution of Al has remained an unresolved problem. Recently, Professor J. A. van Bokhoven (ETH Zurich, Switzerland) and his colleagues employed the X-ray standing wave technique to study Al distribution in scolecite (CaAl₂Si₃O₁₀-3H₂O, hydrated calcium aluminum silicate). They measured the intensity of X-ray fluorescence, Al K, Si K and Ca Kα near the Bragg conditions of (040), (002) and (-402) reflections. The experiments were done at beamline ID32, ESRF. For more information, see the paper, "Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves", J. A. van Bokhoven et al., Nature Materials, 7, 551-555 (2008).