Pd–MeO_x/Al₂O₃ (Me = Co, La, Ce) catalysts for methane combustion

Abstract

Two series of Pd–MeO_x/Al₂O₃ (Me = Co, La, Ce) catalysts were prepared and tested in reaction of methane combustion. The first series comprises the samples obtained by impregnation of γ-Al₂O₃ with the corresponding salts of La and Ce and additionally modified with Co. For the second series the LaCeAl₂O₃ SG and LaAl₂O₃ SG supports were prepared by the sol–gel method and the cobalt was not included as a modifying element. The aim was to obtain catalysts with comparable activities to that of the Co-containing samples, however the using of cobalt being subject of exclusion due to its high toxicity. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Temperature programmed reduction and Fourier transform infrared spectroscopy. The modification of alumina with lanthanum and cerium by impregnation, before the cobalt introduction, decreases interaction between the PdO and the support leading to the easy transformation of PdO into the less active Pd, when the catalyst is treated at high temperatures. The cobalt-free samples prepared by sol–gel method exhibit activity and stability comparable with those of the impregnated cobalt containing Pd + Co/LaAl₂O₃ catalyst. The observed high activity is explained by the formation of stable PdO particles, however the needed Pd-content to achieve the same activity as Co-containing samples is remarkably higher.