HIGH-TEMPERATURE CATALYTIC REDUCTION OF NITROGEN MONOXIDE BY CARBON-MONOXIDE AND HYDROGEN OVER LA1-XSRXMO3 PEROVSKITES (M=FE, CO) DURING REDUCING AND OXIDIZING CONDITIONS

The catalytic activity of La1-xSrxMO3 perovskites (M = Fe or Co) was i nvestigated for the reduction of nitrogen monoxide. The catalytic acti vity for the NO + CO and the NO + H2 reaction was investigated in a fi xed bed reactor in the temperature interval 873-1223 K. The perovskite s showed high activity for the reduction of nitrogen monoxide in the a bsence of oxygen even at 873 K. Hydrogen was less active than carbon m onoxide as a reducing agent and the cobalt perovskites showed slightly higher activity than the iron perovskites in the lower temperature ra nge. The reduction of nitrogen monoxide was concluded to proceed throu gh the reduction of the surface by the reducing agent followed by adso rption and decomposition of nitrogen monoxide on the surface. The acti vated (reducing) perovskites were investigated by X-ray diffractometry . The cobalt perovskites were reduced to a compound of the K2NiF4 type , La2CoO4, while the iron perovskites retained their perovskite struct ure upon reduction. The perovskite structure of the cobalt perovskite was restored upon reoxidation of the La2CoO4 compound. The introductio n of excess oxygen into the gas mixture decreased the nitrogen monoxid e reduction level to zero. Nitrogen monoxide (1000 ppm) was completely reduced in a stoichiometriC CO + 02 MiXture (2% CO and 1% O2) over La 0.8Sr0.2CoO3 at 1173 K. LaCoO3 showed high thermal stability in a heli um atmosphere at 300-1223 K, while the perovskite was reduced to La2O3 and cobalt metal in a 10% CO + He atmosphere.