A thermal reactor for use during the abatement of a semiconductor manufacturing process is provided, including a thermal reaction unit having: an interior porous wall that defines a central chamber, the interior porous wall formed from a plurality of stacked porous sections; at least one gas inlet in fluid communication with the central chamber and adapted to introduce gaseous waste stream to the central chamber; a thermal mechanism positioned within the central chamber and adapted to decompose the gaseous waste stream within the central chamber, thereby forming reaction products; and a fluid delivery system adapted to provide a fluid to the central chamber through the interior porous wall at a sufficient force to reduce deposition of reaction products on an inner surface of the interior porous wall of the central chamber; wherein at least one of the porous sections has one or more of: a property that varies within the porous section; and a property that differs from a property of at least one other porous section of the interior porous wall.