What a catalytic converter actually does
Look down the inlet of a used can and the pipe does not keep going. A ceramic face is sitting in there — thousands of square cells, a pale brick stuffed in a rusty shell. Exhaust has to crawl through that maze. That is the catalytic converter. It is not the muffler.
The wash on those walls is the metal. Platinum, palladium, rhodium. Once the brick is hot, a three-way catalyst does three jobs on the same surface: it strips oxygen off NOx, and it burns leftover carbon monoxide and unburned fuel. Cold, the washcoat is just ceramic. Light-off is the whole point. A lot of cars put a first brick right off the manifold, where the gas still has the heat, and a second brick under the floor. Two bricks. One can, or two.
The muffler is a can too. Baffles and wool. It kills sound. It does not care what molecules leave. People hear a rasp and blame the cat. People smell rotten eggs and blame the muffler. The sulfur is the brick working a rich mix. A hollow rattle is the honeycomb broken loose in the shell.
On the stands, look forward of the resonator. Oval steel, a heat shield, a flex joint just ahead of the bulge. That is the chemistry can. The last can before the tip is the muffler.