An investigation of the use of zirconia as a support for rhodium catalysts Original Research Article

The nature and properties of zirconia-supported rhodium catalysts after high temperature treatment in an oxidising atmosphere have been studied. No interaction between the metal and the support is seen even after calcination at 700°C, easily reduced rhodium oxide being the only Rh species present. Higher dispersion of this species can be achieved by using a higher surface area alumina-doped ZrO2 although it is necessary to pre-sinter the support to prevent encapsulation of the Rh. Rh/ZrO2 catalysts calcined at 500°C have remarkably high activity for methane combustion, similar to that of a Pd/Al2O3 catalyst calcined at the same temperature. Whilst the use of zirconia is preferable to alumina for combustion reactions, the activity of the zirconia-supported Rh in the selective reduction of NO with propene under lean-burn conditions is less than was found previously for Rh/Al2O3. This can be attributed to a lack of isolated Rh3+ ions in the Rh/ZrO2 catalysts.Attempts have been made to inhibit the deactivation reaction of rhodium oxide with Al2O3 by pretreatment of the Al2O3 with Zr-containing precursors. The extent to which the Zr modifies the surface properties of the support are discussed.