A STUDY OF THE CATALYTIC PROPERTIES OF PEROVSKITE-TYPE OXIDES LAMNYCO1-YO3 .2. THE INTERACTION BETWEEN TRANSITION-METAL IONS AND THEIR CATALYTIC PROPERTY IN AMMONIA OXIDATION

It has been found that the interaction between the two transition metal Mn, Co ions on B-site and their Redox property an the important factors influencing the NO-selectivity in ammonia oxidation. The NO-selectivity is related to the redox ability of Mn3+ --> Mn4+ or Co2+, Co3+, which could be promoted by doping a small amount of foreign transition metal ions on B-site of matrix samples, but not for the sample with the composition of y = 0.5. In Mn-rich region (y > 0.5), the magnetic property and NO-selectivity are controlled by the ferromagnetic superexchange of Mn3+-O2--Mn4+. The main factor influencing the NO-selectivity of Co-rich samples (y < 0.5) is the concentration of Co2+ and Co-III ions, The strong ferromagnetism of the sample with the composition of y = 0.5 may be due to its crystal structure, and the redox between Mn3+ and Co3+ is unfavorable for the producing of NO. There exists a close relationship between the NO-selectivity and the valence, d-electron configuration, electron transmission rate and the interaction between the electrons.