THERMAL-STABILITY OF THE PT BEARING SULFATE-PROMOTED ZIRCONIA IN THE PRESENCE OF HYDROGEN

Molecular hydrogen reduces the sulfate groups of the sulfate-promoted zirconia into volatile species, at a temperature much lower than the temperature of decomposition-oxidation of these groups in inert atmosphere or in air. This reduction effect is enhanced with the incorporation of Pt into the sulfate-promoted zirconia (the so-called ''Pt-to-sulfate'' effect), resulting in the loss of the sulfate groups at a significantly lower temperature. Such an enhanced reduction activity of hydrogen can be explained by the well known activation action of Pt on molecular hydrogen at relatively high temperatures. Moreover, this also results in the production of some surface zirconium sulfide.