Methane combustion on perovskites-based structured catalysts

LaMnO3 perovskites supported on La stabilised gamma-Al2O3 and MgO have been prepared and characterised as methane combustion catalysts. XRD analysis, BET surface area results and H-2 TPR measurements have all revealed the presence of significant interaction between the perovskite and the alumina based support, which becomes very strong upon thermal treatment at 1100 degrees C. On the other hand, MgO supported samples undergo only sintering processes with reduction of surface area upon treatment at 1100 degrees C. Catalytic activity measurements in methane combustion have been performed both in fixed bed and in monolithic reactor. The results on powders have shown that the dispersion on both supports is effective to enhance the catalytic performances of the catalysts treated at 800 degrees C. A very strong deactivation is observed for the La/lAl(2)O(3) supported catalyst when pre-treated at 1100 degrees C, while LaMnO3/MgO shows a promising high thermal stability. The chemical nature of the active sites changes by dispersing LaMnO3 on both supports, even if to a different extent, as revealed by the estimated values of apparent activation energy and reaction orders for methane and oxygen. Structured combustion catalysts have been prepared following well established procedures to washcoat commercial cordierite monoliths with lanthanum stabilised alumina. The subsequent deposition of precursors on the coated monolith has been obtained by deposition precipitation method. Comparison between monolith and corresponding powder sample shows a higher catalytic activity of the former, likely to be attributed to the better dispersion obtained with repeated deposition cycles of active phase on the thin washcoat layer. Moreover, a lower deactivation has been observed on monolith after ageing under reaction at 1050 degrees C for 2 h, suggesting promising developments of this technique to produce catalytic combustion systems for high temperature applications. (C) 2000 Elsevier Science B.V, All rights reserved.