Catalytic converter

Do not use leaded gas. Lead in gas will collect in the converter and plug it up over time. There is nothing you can do about that other than to replace it. What makes you think it needs to be cleaned?

As Doc says, there is nott a real way to "clean" a converter other than to prevent it from being damaged in the first place. Most converter failures are the result of misfires and burning oil. The rest are mechanical failure and age.

The misfires and oil both dump a fuel source into the converter that causes it to burn hotter than it is designed for, that actually melts the honeycomb structure inside and destroys the converter. When it does not melt it down the oil/fuel creates a coating on the internal catalyst structure and prevents it from operating, that coating is baked onto the substrate at a very high temperature and nothing that you can use to remove it will not also damage the ceramic under it.

Mechanical failure is from age and use, the interior of the unit breaks up and comes apart and plugs the system, or the converter takes an impact that physically damages it and breaks the internal structure.