Coprecipitated CuO-MnOx catalysts for low-temperature CO-NO and CO-NO-O-2 reactions

The activity of the mixed copper-manganese oxides CuO-MnOx (1.5 < x < 2), o btained by coprecipitation and activated at 300 degrees C, has been studied for CO-NO and CO-NO-O-2 reactions. As shown by magnetic susceptibility dat a, X-ray diffraction, FTIR spectra, and catalytic tests, an interaction bet ween CuO and MnOx with formation of a disordered mixed oxide with a spinel- like structure is the cause of the high activity of CuO-MnOx samples. At ambient temperature (25 degrees C) both adsorption and interaction of CO and NO become more intense with increasing atomic fraction of copper conte nt Cu/Cu + Mn up to 0.53 (catalyst C5M5). For the most active sample C5M5, the degree of NO conversion to N-2 attained with a CO + NO + O-2 + Ar mixtu re is almost the same as that obtained with a CO + NO + Ar mixture. A Langm uir-Hinshelwood mechanism is proposed for both (CO-NO and CO-NO2) interacti ons at ambient temperature. With increasing temperature under the conditions of a CO + NO + Ar mixture, reduction of the catalyst surface starts. This leads in turn to depression of the CO-NO reaction at temperatures up to 130 degrees C (low-temperature region) and to progressive acceleration of the CO-NO reaction at temperatu res above 130 degrees C (middle-temperature region). In the presence of oxy gen (a CO + NO + O-2 + Ar mixture), CuO-MnOx catalysts have an even higher activity over a wide temperature range (75-300 degrees C). (C) 1999 Academi c Press.