Catalytic converters have to convert a tiny part of the output, and they convert them into more stable forms.

The problem with CO2 is that it's the most stable form.

Also, if you want to absorb the CO2, for 1 pound of fuel you get like 3 pounds of CO2. You can absorb it into a solid and the density is like 3 times the density of the fuel. So with a lot of approximations you need container that has the same volume than the fuel tank to store the CO2, or even bigger if you absorb it in a liquid or much much much bigger as a gas. And you must empty/exchange the container when you refuel. And then you realize that it's better to use an electric car.