▎ 摘　　要

NOVELTY - Method for removing residual chlorine from inorganic substances comprises heat treating an inorganic material in which residual chlorine is present for a predetermined time under ammonia atmosphere. USE - The method is useful for removing residual chlorine from inorganic substances for nitrogen oxide reduction catalyst (claimed). ADVANTAGE - The method: utilizes economical raw material; has excellent nitrogen oxide conversion even at low temperatures and removal efficiency. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for (1) preparing a catalyst for selective reduction of nitrogen oxide, comprising (i) supporting metal salts of ruthenium and iridium on a support, (ii) drying and heat treating the supported support and (iii) heat-treating the heat treated support under ammonia atmosphere; (2) catalyst for selectively reducing nitrogen oxide; (3) method for selective reduction of nitrogen oxide, comprising utilizing the catalyst; and (4) selective reduction system of nitrogen oxides, comprising nitrogen oxide reduction catalyst as the catalyst.