IN-SITU STUDIES OF ZEOTYPE MATERIALS UNDER OPERATING-CONDITIONS

Heterovalent ions substituted aluminophosphates (divalent in place of Al3+ or tetravalent for P5+) or trivalent (for eg.Al3+ or Fe3+ or Ga3 in place of Si4+) ions in substituted zeolites[1] have been shown to be efficient catalysts for Bronsted acid catalysed reactions. Furtherm ore, some of the framework-incorporated divalent ions such as Co2+ or Mn2+ are known to exhibit oxidation-reduction properties thereby intro ducing a new dimension to the catalytic performance. Although only rel atively small amounts of these heterovalent substituents have been ach ieved (of the older of 2 wt%), they nevertheless produce highly active catalytic centres. Understanding the overall framework structure of t hese microporous solid acid catalysts on the one hand, and the local s tructure around the hetero atoms on the other, allows the precise desc ription of these shape selective catalysts. It was demonstrated earlie r that the combined use of the XRD/XAS techniques enhances our underst anding of the structure of various active catalysts[2-5]. In addition, insights into their stability (retention of microporous structure) an d oxidation-reduction properties[6,7] are also gained. Here we show ho w the combined XRD/XAS permits us to characterise zeotype materials un der operating conditions either during hydrothermal synthesis or durin g the activation of the solid acid catalysts.