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 t emperature of decomposition-oxidation of these groups in inert atmosph ere or in air. This reduction effect is enhanced with the incorporatio n of Pt into the sulfate-promoted zirconia (the so-called ''Pt-to-sulf ate'' effect), resulting in the loss of the sulfate groups at a signif icantly lower temperature. Such an enhanced reduction activity of hydr ogen can be explained by the well known activation action of Pt on mol ecular hydrogen at relatively high temperatures. Moreover, this also r esults in the production of some surface zirconium sulfide.