Nature is reporting that a wash of citric acid can recharge catalytic converters. Catalytic converters are basically big arrays of platinum, which catalyzes the conversion of unburnt fuel and/or carbon monoxide to carbon dioxide. The problem is that other fuel components, like phosphorous and sulfur, eventually gum up the surface. And current cleaners are just too harsh, and pit the platinum surface. Is this sounding like a kitchen commercial yet?
So yes, citric acid seems to strip off the sulfur deposits and leave the platinum working like new. You have to cycle the exhaust line at 80 Celsius for a couple of hours.
Right now this is still more expensive for the average user than just replacing the thing.