Comment by scythe
5 years ago
Catalytic converters don't reduce greenhouse gases. Their function is to reduce poisonous gases: NO, NO2, O3, CO, HO2, and sometimes HCN and H2CO. The good news is that all of these compounds are thermodynamically unstable so a catalyst can destroy them.
I don't know where you got the 14.7:1 number but I am certain that NOx are unstable at any concentration (at or near STP) and will always be depleted by a catalyst.
Another commenter is unsure whether the NOx or some GHGs should be reduced preferentially. To clarify: CO2 can't be removed, it is stable; only CH4, N2O and O3 can be removed, and they are not present at relevant levels (except ozone which is poisonous) anyway. The poisonous gases are far more important — NOx pollution alone kills thousands of people every year (statistically, considering excess deaths as correlated to air pollution).
The increased price of catalytic converters is partially related to the supply of palladium, which experienced a glut following the collapse of the USSR. The Soviet palladium ran out in 2012:
https://www.mining.com/russias-stockpiles-said-to-be-deplete...
>I don't know where you got the 14.7:1 number
The cat has to be hot to catalyze. The engine is run rich so unburnt fuel makes it to the cat and is combusted there, warming it up enough to also kill the undesirable gases. This is wasted heat... unless you mount a turbocharger after the cat, which has its own set of weird tradeoffs. (I've never heard of a factory car with a rear turbo)