In Situ Studies of Zeotype Materials Under Operating Conditions

Abstract

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. Furthermore, some of the framework-incorporated divalent ions such as Co2+ or Mn2+ are known to exhibit oxidation-reduction properties thereby introducing a new dimension to the catalytic performance. Although only relatively small amounts of these heterovalent substituents have been achieved (of the older of 2 wt%), they nevertheless produce highly active catalytic centres. Understanding the overall framework structure of these microporous solid acid catalysts on the one hand, and the local structure around the hetero atoms on the other, allows the precise description of these shape selective catalysts. It was demonstrated earlier that the combined use of the XRD/XAS techniques enhances our understanding of the structure of various active catalysts[2-5]. In addition, insights into their stability (retention of microporous structure) and oxidation-reduction properties[6,7] are also gained. Here we show how the combined XRD/XAS permits us to characterise zeotype materials under operating conditions either during hydrothermal synthesis or during the activation of the solid acid catalysts.