Gold is used as a catalyst to oxidize carbon Monoxide to Carbon Dioxide. It's already in use in breathing apparatus for people working in an otherwise hazardous CO environment.
The new converters have sensors to adjust the exhaust gas composition so that the various catalysts convert the exhaust into the least possible hazardous mixture.
Some day, it will be very difficult to commit suicide be using exhaust from your car, it will be so clean. I guess you could suffocate from Carbon Dioxide while getting high on Nitrous Oxide.