Chemists in Japan have developed an oxygen storage system with almost ten times more capacity than the conventional materials used in automotive catalysts.

Masato Machida, who discovered the new system with colleagues at Kumamoto University, explained that oxygen storage materials (OSMs) are important in emission-control catalysts because they store or release oxygen to achieve the ideal air-to-fuel ratio needed for complete fuel combustion. The combustion process also creates noxious pollutants and OSMs are able to convert these pollutants to less harmful compounds by oxidation and reduction.

Machida investigated the OSM praseodymium oxysulfate (Pr₂O₂SO₄) because it works at low temperatures. He modified the Pr₂O₂SO₄ structure to increase the surface area and reduce its operating temperature. 'Getting our OSM to work at low temperatures is important,' said Machida, 'because at low temperatures both the surface reaction and the oxygen storage processes become so slow that conversion of the noxious gases is difficult.'

Machida made the Pr₂O₂SO₄ with a porous layered structure, which accelerates the solid-gas reaction for both oxygen release and storage to almost stoichiometric values that are unaltered at higher temperatures. 'It is important that OSMs can store and release oxygen over a wide temperature range because automobile exhaust temperatures vary depending on driving conditions,' said Machida.

Paolo Fornasiero at the University of Trieste, Italy, said 'the work may be revolutionary because most of the requirements needed for large scale application - very high storage capacity, good thermal stability and low working temperatures - are present in the Pr₂O₂SO₄ OSM system'.

Fornasiero recommended 'that Pr₂O₂SO₄ is further investigated as a potential replacement for widely used ceria-zirconia materials', although he cautioned that 'the cost of OSMs is important for commercial applications'.

Janet Crombie