There are many things in the fuel system that can damage a catalytic converter or increase HC (Hydrocarbon) emissions.
Perform a fuel pressure and leak-down test. Fuel pressure should be within the manufacturer's specifications and hold steady after the pump is shut off.
A rapid drop in pressure may indicate that fuel injectors are leaking, or that a problem exists with the fuel pressure regulator, or the supply check valve.
Fuel pressure which is slightly shy of the normal working range can result in significant emissions issues, and can also result in excessive cranking time when cold. Both conditions can cause rapid converter failure.
The fuel filter should be replaced per the manufacturer's recommended maintenance schedule. Finally, check for water contamination in the fuel tank, and air trapped in the fuel rails, which can cause cylinder misfires.