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RESEARCH PRODUCT

Catalytic combustion of ethane over high surface area Ln1−xKxMnO3 (Ln = La, Nd) perovskites: The effect of potassium substitution

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Publisher Summary As a general trend, the substitution of the rare earth cation by potassium decreased the intrinsic activity, reduced the reaction order in oxygen, and, for the more substituted samples (x>0.10), it increased the selectivity to ethene. Supported platinum or palladium catalysts have so far been used almost exclusively, because of their excellent activity. However, their high price, tendency to be poisoned, and volatility in some applications have estimulated the search for suitable substitutes. LaCoO3, as a potential auto exhaust catalyst, starting a wide interest in the catalytic properties of perovskites. Their specific application as catalysts in flameless combustion has been investigated only since 1980. The most active catalysts were Co and Mn perovskites. Researchers investigated the catalytic activity of various transition-metal perovskites for methane combustion. In every case, carbon monoxide or partial oxidation products were scarcely detected during oxidation. The activities of LaCoO3, LaMnO3, and LaFeO3 were quite close to that of a Pt/alumina catalyst. While the catalytic activity for n-butane oxidation was affected both by the transition-metal substitution and rare earth substitution, the catalytic activity for methane oxidation was only influenced by the rare earth ion substitution. It is known that the use of alternative synthetic pathways produces high purity, homogeneous powders, and requires low temperatures to obtain the phases, thus, leading to products with smaller particles and high specific surface area (SSA). Besides these advantages, these alternative methods play an essential role in the preparation of potassium containing materials, because of the volatility of potassium oxide at high temperatures. In the alternative method, involving freeze-drying, all the cations are mixed at the atomic scale in the solution and this facilitates the incorporation of potassium to the perovskite lattice, because it occurs at the initial stage of the preparative procedure.