The salient fact here is that all of the exhaust gas has to contact with the palladium, or the gas would not be catalyzed (cleaned up). So you have gas with 80% of the heat from the burned gasoline coming in contact with ~3 g of Pd or Pt.
Here is another way to estimate maximum thermal output from an automobile engine: An automobile engine can produce 150 hp but they only do that when you accelerate. As far as I know, most cars traveling ~80 miles an hour burn ~4 gallons of gasoline per hour. That produces raw heat: 132 MJ * 4 = 422 MJ/hr. Divide by 3600 s/hr that equals power of around 147 kW. If only 20% is delivered as vehicle propulsion that would be 29 kW which seems excessively low to me. Anyway, it is on the order of 118 kW of hot gas passing through some amount of Pd, 2 to 7 g. The amount of Pd per converter ranges from 2 to 7 g because some catalytic converters are bigger than others, for bigger cars. A car that can produce 150 hp is big. Huge. My 3 cylinder Geo Metro delivers 55 HP (41 kW). It has a small catalytic converter. Assuming it is 2 g, that comes to ~82 kW/g. Assuming there is 7 g in converter for a monster 150 HP motor, that would come to ~64 kW/g. - Jed
