2003 Peugeot 206 Misfire on Cylinder and Catalytic converte

Engine Mechanical problem
2003 Peugeot 206 6 cyl Manual

I have a peugeot 206 2.0 S and it showed me lately a misfire on cylinder. What would cause this misfire, and what should be done?
Also, every now and then, the car starts making sounds and it stops running as it was as if it is going to stop, and then on my screen it shows a Catalytic Converte Fault! What would cause this catalytic converter sudden fault? How can I fix it?

Thanks.