Regenerative selective catalytic reduction (RSCR) systems and process are provided whereby NO.sub.x levels in gases are reduced by mixing the gas with a reactant and then introducing the gas into an RSCR apparatus for treatment that entails heating the gas, causing the gas to undergo one or more catalytic reactions, and then directing the gas through a heat transfer area, to which the gas provides heat for use in connection with successive cycles of the RSCR process.