Single-Phase PrO<i>_y</i>−ZrO₂ Materials and Their Oxygen Storage Capacity: A Comparison with Single-Phase CeO₂−ZrO₂, PrO<i>_y</i>−CeO₂, and PrO<i>_y</i>−CeO₂−ZrO₂ Materials

Abstract

High-surface-area PrOy−ZrO2 mixed oxide, crystallized in the cubic fluorite structure, is synthesized for the first time as a single-phase material over a wide range of composition by sol−gel processing. X-ray powder diffraction shows that the material remains single phase even after thermal treatment in air to 900 °C. The oxygen storage capacity of PrOy−ZrO2, where praseodymium undergoes Pr3+ ↔ Pr4+ interconversion, is assessed by temperature-programmed reduction with H2. The results show that there is little oxygen storage capacity unless the PrOy concentration exceeds 25 mol %. A comparison of oxygen storage capacity from similarly prepared single-phase CeO2−ZrO2, PrOy−CeO2, and PrOy−CeO2−ZrO2 materials is presented. Measurements of lattice parameter and reducibility suggest that there are preferred associations that lead to PrOy−ZrO2 and CeO2−ZrO2 rather than PrOy−CeO2 in the ternary mixed oxide. An evaluation of model Pd catalysts, using PrOy−ZrO2 and CeO2−ZrO2 as support materials, in functional tests approximating warmed-up, steady-state operation of an automotive catalyst, is also reported.