A comparative study on perovskite-type mixed oxide catalysts A$prime;xA1 $minus; xBO3 $minus; $lambda; (A$prime; = Ca, Sr, A = La, B = Mn, Fe, Co) for NH3 oxidation

摘要: Abstract Three series of samples having the stoichiometry A′xA1 − xBO3 λ (x = 0 1, B Mn, Fe, Co) were prepared and used as catalysts for NH3 oxidation. It was found that even at x or 1 compositions nonstoichiometric. The nonstoichiometric amount oxygen, λ, with which crystal structure, defects in solid, reactivity reactant catalytic activity could be correlated, a function x. A single-phase, solid solution exists composition range from to 0.4. miscibility gap appears about A′ 1(x 0.4) then an A′BO3 phase is . This two-phase region extends until appearance cubic 1.0. Doping lower valence cations (A′) case ABO3 results either increase oxidation state formation oxygen vacancies. In both concentration Mn4+ depend linearly upon x, but Co, due instability Co4+ toward reduction by O2−, only increases. Fe situated between above two. By ED, EM, Mossbauer investigation, vacancy-ordering ferrite system observed. XPS, TPD, EPR measurements gave suggesting possibility O−2 O−. adsorbing capacity catalyst surface depends closely on λ. A′xA1−xBO3−λ mixed oxides general attributed extent redox reaction 2 4+ + O 2− co ag Mn 3+ (g) Vo. Co systems are just two extreme cases. dependence Fecontaining their potential confirmed TPR 18O-isotopic exchange Study.