Catalytic combustor
A catalytic combustor is a ceramic or metal honeycomb coated with precious metals that lets smoke ignite at around 500 °F instead of over 1,000 °F. Routing exhaust through it re-burns smoke that would otherwise leave the chimney, cutting emissions and extracting more heat — especially at low, overnight burn rates.
Catalytic stoves have a bypass damper: the fire is started with the combustor bypassed, then engaged once flue temperature is high enough. Operating one is slightly more involved than a non-catalytic stove, and the combustor is a consumable that degrades over several heating seasons of use.
The payoff is clean low burns: a catalytic stove can hold a long smolder that would make a secondary-burn stove smoke, which is why catalytic and hybrid models dominate the longest-burn-time and lowest-emission listings.