Hydrogen Cyanide Emissions from Three-Way Catalyst Prototypes under Malfunctioning Conditions

Measurements have been made of the emissions from a prototype three-way catalyst automobile, during normal and simulated malfunction driving conditions. Four ceramic-supported catalyst compositions were investigated, ranging from Rh through two mixtures of Rh-Pt to Pt. Driving conditions included cyclic and cruise modes. Under normal operating conditions no HCN was detected. Under rich malfunction conditions, HCN was generally observed, even in the absence of a catalyst. In some cases, catalysts appeared to remove HCN from the exhaust gas; in others they increased its level. The highest emission rate for HCN was observed for the Rh catalyst, about 40 mg/km at 64 kph cruise.