Oxygen effect in NO direct decomposition over K/Co-Mg-Mn-Al mixed oxide catalyst - Temperature programmed desorption study

Abstract

Co-Mg-Mn-Al mixed oxide with or without K was prepared and characterized by XPS, TPR H-2, TPD NO, TPD O-2 and TPD NO+O-2. NO decomposition was performed over catalyst activated in different atmosphere (N-2, He, O-2). Presence of oxygen during activation changed the course of surface stabilization but did not affect NO conversion achieved at steady state. O-2 desorbed as a reaction product does not affect the reaction rate for NO inlet con-centration of 400-8000 ppm, but presence of O-2 in inlet gas mixture (0.05 -3 mol.%) has significant inhibiting effect. Transition metals in octahedral coordination represent sites for NO chemisorption, while potassium en -sures NO oxidation to surface nitrites, which are indispensable reactive species. Oxygen desorption was the slowest reaction step, while N-2 desorption was fast. Oxygen inhibition was ascribed to oxidation of NO* species on the octahedral Co3+ and Mn3+ to more stable surface nitrates making NO* species as limiting reactant.