AUTOMOTIVE EXHAUST CATALYSIS UNDER PERIODIC OPERATION

Catalytic converters in automobiles now number in the millions. All of these devices are periodically forced about the stoichiometric air-fu el ratio at a frequency of about 1 Hz and a small amplitude. Experimen ts show that this periodic forcing suppresses rather than enhances con versions under normal operating conditions, even though many publicati ons demonstrate that large rate and conversion improvements do occur f or the converter reactions over the individual noble metals used in th e three-way catalysts. This review concludes that improvements are not found because enhancement becomes very small in the 400-600 degrees C temperature range and forcing at about 1 Hz is sub-optimal.