Never, ever take a hammer and rod to smash the honeycomb out. That turns your car into a gross polluter, makes it fail emissions tests, and is illegal in most places. It also makes your car louder, slower (due to lost backpressure), and smells like rotten eggs.
For a partially clogged converter you’ve already removed from the car: how to unblock a catalytic converter
A blocked catalytic converter can choke your engine’s performance, leading to sluggish acceleration, poor fuel economy, and failed emissions tests. While a severely melted converter must be replaced, mild clogs caused by carbon or oil soot can sometimes be cleared using specific DIY methods. Never, ever take a hammer and rod to smash the honeycomb out
The most common way to unblock a catalytic converter without removing it is by using specialized chemical cleaners added directly to your fuel tank. How to Unblock a Catalytic Converter - CarParts.com For a partially clogged converter you’ve already removed