Mahbod Bassir

Perovskite-type oxides synthesized by reactive grinding: Part IV. Catalytic properties of LaCo1−xFexO3 in methane oxidation

Abstract In this part of the present work, the catalytic properties in methane oxidation of perovskite-type mixed-oxides, LaCo 1− x Fe x O 3 prepared by reactive grinding of the component oxides were studied. A fine control of the nature and concentration of the various sites active in oxido-reduction catalysis was performed by applying the comprehensive picture of the effects of thermal pretreatment of the mixed-oxides generated by this technique, developed in part I of this contribution. These properties which were previously illustrated by the kinetics of complete oxidation of n -hexane over five nanocrystalline LaCo 1− x Fe x O 3 catalysts treated in parts II and III are now demonstrated by a kinetic study of methane oxidation over the same catalysts.

Perovskite-type oxides synthesised by reactive grinding: Part III. Kinetics of n-hexane oxidation over LaCo(1−x)FexO3

The catalytic properties in the n-hexane oxidation reaction of five nanocrystalline1 LaCo(1−x)FexO3 perovskites prepared by mechanosynthesis were studied. The characterisation of such samples was reported in Part I of this contribution. One of the advantages of this mechanosynthesis technique stems from the low preparation temperature, which allows to stabilise high surface area materials. In Part I, the unusual properties of these new materials were illustrated for LaCoO3 and LaCo(1−x)FexO3 perovskites [1]. It was shown that controlling the calcination conditions allows to tailor the surface properties of these materials. In Part II, a preliminary account of the catalytic behaviour of such catalysts in n-hexane oxidation was reported [2]. In the present contribution, the fine control of the nature and the concentration of the various sites active in redox catalysis is demonstrated through a kinetic study of the total oxidation of n-hexane by oxygen. The roles of two oxygen species O2− and O−, respectively, associated with α and β oxygens are discussed.

Optimization of Mixed Ag Catalysts for Catalytic Conversions of NO and C3H6

In order to adjust the redox properties of perovskite-based silver catalysts to satisfy the requirements for their application under overstoichiometric oxygen conditions (lean burn), three mixtures were prepared [Mixture (I): 10% La0.88Ag0.12FeO3 + 90% Al2O3; Mixture (II): 3% Ag/(10% La0.88Ag0.12FeO3 + 90% Al2O3); Mixture (III): 10% La0.88Ag0.12FeO3 + 90% (3%Ag/Al2O3)]. Mixture (I) with only a 10% La0.88Ag0.12FeO3 blend exhibited a NO reduction behavior similar to that of La0.88Ag0.12FeO3 alone at stoichiometric oxygen (1% O2). NO conversion of La0.88Ag0.12FeO3 under an excess of oxygen (10% O2) was however significantly improved by mixing with Al2O3 resulting in a value of ~ 30% at >400 °C in the case of Mixture (I). Ag impregnation facilitated the NO catalytic reduction, leading to a better deNOx performance for Mixture (II) and Mixture (III) than that of Mixture (I). It was also found that those silver atoms associated with Al2O3 are more effective for NO transformation. Therefore, the optimal mixed catalyst was Mixture (III), which shows satisfactory NO reduction and C3H6 oxidation at 500 °C under the whole range of O2 content from 1% to 10%.