The Reduction of Nitric Oxide in Automobile Emissions—Stabilisation of catalysts containing ruthenium

Catalysts containing ruthenium are used to reduce nitric oxide in auto-mobile exhaust emissions but volatile oxides formed under transient oxidising conditions during operation can severely aJfect them. However, basic oxides such as alkaline earths or rare earths can stabilise the ruthenium by forming ruthenates, which have little tendency to volatilise. The ruthenates are synthesised either before the catalyst is made or in position on the catalyst support, which may be monolithic or pelleted. In the development of catalysts for the reduction of nitric oxide in the purification of automotive exhaust emissions one of the desired attributes of a catalyst is its ability to promote selectively the reduction of nitric oxide NO to molecular nitrogen (and not to ammonia as happens over a large majority of catalysts), in the presence of hydrogen