displacement a test cycle approved by the epa was performed and then the lean burn operation curve shown in fig1 was plotted for this purpose different exhaust gas compositions lambda values are generated by changing carburetor settings at a constant rpm at each of these points the hydrocarbon content of the exhaust gas is measured before and after the catalytic converter this gives the conversion rate which is recorded in fig1 versus the lambda values in a glass cylinder 491 2 g of a la stabilized aluminum oxide having a bet of 120 g m 2 is suspended in water then 8 8 g of a 10 palladium chloride solution is added and adsorbed on the aluminum oxide all other steps are carried out analogously to comparative catalytic converter 2 above this example is carried out analogously to catalytic converter 3 above except a noble metal solution zirconium nitrate is added so that a weight ratio of pd to zr of 1 1 results all other steps are carried out analogously to catalytic converter 2 above the results of the engine tests can be seen in fig1 the hc conversion rates of the described catalytic converters were recorded versus the lambda values clear differences in the conversion behavior can be recognized at different lambda values while the hc conversion rate of the comparative examples catalytic converter 1 and catalytic converter 2 fall significantly at lambda values lt 0 9 thus in the rich mixture range the catalytic converters according to the invention surprisingly exhibit constant hc conversion rates over the entire lambda range this.