Abstract
The study of thermal decomposition mechanism of sulfates and the thermal stability of catalysts during heat treatments constitute a good approach for determination of sulfate mode bonds in sulfated zirconium pillared clay (ZrS-PILC) catalysts. The thermal stability of solids prepared with different SO42-/Zr have been investigated by means of TGA/DTG techniques, mass spectrometry (MS), 29Si MAS NMR, nitrogen adsorption-desorption at 77K and chemical analysis. The results indicate the presence of two modes of sulfate bonds. The first one, called Σ1, decomposes at low temperature to give SO2 and lets oxygen atoms to the matrix. This sulfate group probably links two tetrameric Zr entities present in the intercalation solution. Decomposition of the second type (referred as Σ2) which is probably low coordinated occurs with SO2 and O2 release. The coordination of sulfates Σ2 is equal to 2 and each one links most likely two zirconium octamers. For SO42-/Zr<0.125, the sulfates are linked with Σ1 mode bond and for higher ratio, the Σ2 mode takes place. However, the decomposition of each type of sulfates in two stages in the sample prepared with SO42-/Zr=0.175 could be explained by the presence of a high polymeric phase.
