Improved version of oxygen-storage material boosts engine-emission cleanup

A simple heat treatment can alter the structure and thermal stability of a cerium-zirconium material, thereby improving its ability to strip pollutants from automobile engine emissions (Appl. Catal., B 2020, DOI: 10.1016/j.apcatb.2020.119450). Catalytic converters on gasoline-powered vehicles scrub toxic combustion products in the exhaust stream with three-way catalysts (TWCs). The name reflects the catalysts’ ability to oxidize carbon monoxide and hydrocarbons and reduce smog-forming nitrogen oxides. The key to TWCs’ knack for mediating oxidations and reductions—chemically opposed reactions—is a rhodium-doped cerium oxide–zirconium oxide (CZO) oxygen-storage material. CZO intermittently stores oxygen during reduction steps and releases it during oxidations. Today’s TWCs use the tetragonal form, t-CZO. Recent studies suggest that the pyrochlore form, pyr-CZO, which has a different lattice structure, could outperform t-CZO. But pyr-CZO morphs into t-CZO at high temperatures, and it has low surface area, rendering it ineffective catalytically. A research team including Jason Wu of Ford Motor and Joerg R. Jinschek of the Ohio State University has shown that treating commercial CZO with hydrogen at 1,200 °C followed by a simple cooling procedure leads to high-surface-area pyr-CZO, which retains its structure after aging at 910 °C. And it outperforms t-CZO in converting nitric oxide and hydrocarbons.