Abstract
CuxZnAlO mixed oxide catalysts for methane total oxidation have been obtained by thermal activa-tion of layered double hydroxides (LDHs) precursors. LDHs have been prepared following two differentroutes: (i) conventional coprecipitation (pH = 8 or 10) and (ii) hybridation achieved by intercalation ofCu-containing anionic complexes ([Cu-EDTA]2− and [Cu-citrate]−) into host ZnAl-LDH. The mixed oxidecatalysts showed only ZnO phase at Cu < 5 at.% and a mixture of ZnO and CuO phases at higher Cu con-tent. CuO particles differently interacting with the oxide supports were revealed by TPR analysis. Theywere reduced at lower temperature but with a lower H2 consumption in the mixed oxides derived fromthe hybrids suggesting lower accessibility. The activity of the catalysts in the total oxidation of methanestrongly depended on the method of preparation of the LDH precursors and on the Cu content. Cu10ZnAlO (10 at.% Cu) derived from a coprecipitated LDH showed the highest intrinsic activity and a good stabilitysuggesting an optimum dispersion of the copper-containing active species. Among the catalysts derivedfrom the hybrid precursors, the higher activity of the Cu(EDTA)-ZnAl ones may be due to their higher Cucontent. The lower intrinsic activities and higher activation energies of this series of catalysts comparedto the coprecipitated ones may be due to the lower accessibility to the CuO active sites.