I need advise onp0420 code

I have a 2004 honda accord ex 4cylinder. P0420 poped up
4 months ago.cleared the code with device. One month
later it came on. Found a broken air intake hose replaced
it.cleared the code once again then 73 days later check
engine light came on with the same p0420.im starting to
think it's not the catalytic converter. Because the light
would of came on sooner. Do you think it's the bank 1
sensor is faulty? I'm in California so they say if it's the
catalyst converter I'd need dealer only because of the car
family. I need some advice.