Reduction of NO by CO over nanoscale LaCo1-xCuxO3 and LaMn1-xCuxO3 perovskites

Nanoscale perovskites with nominal formula of La(Co, Mn)(1-x)CuxO3 were generated by a novel method designated as reactive grinding and characterized by N-2 adsorption, X-ray diffraction (XRD), temperature programmed desorption (TPD) of O-2, NO, and CO, temperature programmed surface reduction (TPSR) of NO under CO/He flow. Activity tests of NO + CO reaction for those materials were also carried out in this study. A better catalytic performance (93% N-2 yield and 91 % CO conversion at 500 degrees C) was found over LaCoO3 compared to LaMnO3 (76% N2 yield and 76% CO conversion at 500 degrees C), with a reaction atmosphere of 3000 ppm NO and 3000 ppm CO in helium at a space velocity of 50,000 h(-1). The catalytic activity in NO + CO reaction for LaCoO3 can be considerably improved via 20% Cu substitution, leading to a 97% N-2 yield and nearly complete CO conversion at 450 degrees C. This improvement was ascribed to the ease of generation of anion vacancies after Cu incorporation, which plays a crucial role in NO adsorption and dissociation. In addition, the enhancement in lattice oxygen mobility of Cu substituted perovskites promotes the CO oxidation and anion vacancy recovery giving another clue for this improvement. N2O decomposition (68% N-2 yield at 500 degrees C) is much easier than NO decomposition (below 5% at T < 500 degrees C). Both NO and NO conversions are significantly improved by the reducing agent. A mechanism was proposed with dissociation of chemisorbed NO forming N-2 and/or N2O, and oxidized perovskite surface, with continuous reduction by CO with the production of CO2. O-2 has a strongly detrimental effect leading to the easy consumption of the reducing agent via CO oxidation. (c) 2006 Elsevier B.V. All rights reserved.