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 pre sence of significant interaction between the perovskite and the alumina bas ed support, which becomes very strong upon thermal treatment at 1100 degree s C. On the other hand, MgO supported samples undergo only sintering proces ses with reduction of surface area upon treatment at 1100 degrees C. Cataly tic activity measurements in methane combustion have been performed both in fixed bed and in monolithic reactor. The results on powders have shown tha t the dispersion on both supports is effective to enhance the catalytic per formances of the catalysts treated at 800 degrees C. A very strong deactiva tion 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 stabilit y. 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 ox ygen. Structured combustion catalysts have been prepared following well establish ed procedures to washcoat commercial cordierite monoliths with lanthanum st abilised alumina. The subsequent deposition of precursors on the coated mon olith has been obtained by deposition precipitation method. Comparison betw een monolith and corresponding powder sample shows a higher catalytic activ ity of the former, likely to be attributed to the better dispersion obtaine d with repeated deposition cycles of active phase on the thin washcoat laye r. Moreover, a lower deactivation has been observed on monolith after agein g under reaction at 1050 degrees C for 2 h, suggesting promising developmen ts of this technique to produce catalytic combustion systems for high tempe rature applications. (C) 2000 Elsevier Science B.V, All rights reserved.