Seems to me that to attenuate the sound you have to let the exhaust pulses escape thru the perforations. If you surround it with ceramic like that, its like plugging all those holes - you end up with the same result as a straight pipe.
On the other hand, if you used a few of those rings at intervals, you end up with something like a chambered muffler. Might sound pretty good.
Stainless or fiberglass wool is the usual packing material in those types of muffs. Or asbestos! Perforated motorcycle muffs without the packing are louder than the ones with it.
That's my initial response as well.
I wonder though
closed cell foam works just fine as sound deadening material so despite the stiffer cell walls could ceramic perform in the same way even if its attenuation is less?
I've never experimented with the various spray on sound deadening materials but one or two of them have a ceramic component iirc.