Complete oxidation of hydrocarbons on YFeO3 and LaFeO3 catalysts

Perovskite catalysts (YFeO3 and LaFeO3, supported on alpha-Al2O3) were synthesized via sucrose assisted solution-combustion method. The phase composition as well as the surface morphology and catalyst evolution were studied before and after carrying out the reaction using different instrumental methods as XRD, XPS and TPR. Different hydrocarbons (methane, n-hexane and toluene) were tested in reaction of complete oxidation. Considering the case of toluene the kinetics calculations for both catalysts showed as most probable the Langmuir-Hinshelwood mechanisms, which include adsorption of the reagents (toluene and oxygen) on different types of sites and dissociative adsorption of oxygen. With YFeO3 the Mars-van Krevelen mechanism cannot yet be excluded. The presence of small size A-type cation like Upsilon in the perovskite structure leads to structure deformation and makes it relatively unstable and does not permit an intensive transformation of Fe ions into higher or lower oxidation state. On the contrary - the structure of LaFeO3 is very stable and can easily accommodate certain amount of cation and anion defects without structural changes, which promotes more intensive fluctuation between the oxidation states of Fe ions and provides more active sites on the catalyst surface for interaction between hydrocarbon and oxygen molecules. (C) 2013 Elsevier B.V. All rights reserved.