Surface properties and catalytic performance for ethane combustion of La1-xKxMnO3+delta perovskites

The influence of K substitution in LaMnO3 perovskite on the surface propert ies and catalytic oxidation of ethane has been studied. La1-xKxMnO3+delta p erovskites (x=0.05, 0.10, 0.15, 0.20 and 0.25) with BET surface area of 20- 26 m(2) g(-1) have been prepared by the freeze-drying method and characteri zed by X-ray diffraction patterns (XRD), TPR, TPD and XPS. The XRD analyses showed the presence of a single crystalline phase (x less than or equal to 0.15,) with the linear increase of the lattice parameter corroborating the incorporation of potassium in the perovskite structure. The XPS studies rev ealed an enrichment of the perovskite surface with potassium accompanied by an increase in the surface Mn4+/Mn3+ ratio. The TPR and chemical analyses suggested the presence of an oxygen non-stoichiometry (delta) of +0.15 for LaMnO3 which decreases to -0.04 for La0.85K0.15MnO3. Oxygen temperature pro grammed desorption experiments showed similar results with the amount of be ta oxygen desorption decreasing in the presence of potassium in the perovsk ite structure. The catalytic activity for the total oxidation of ethane dec reased for K containing perovskite and was closely related to the oxygen no n-stoichiometry (delta). The effect of oxygen partial pressure and temperat ure suggests the predominance of an intrafacial mechanism at higher tempera ture with a possible contribution of the suprafacial reaction at lower temp eratures. (C) 2001 Elsevier Science B.V. All rights reserved.