Catalytic combustion of methane over palladium alumina modified by niobia

Methane combustion was studied on Pd-x%Nb2O5/Al2O3, Pd/Al2O3 and Pd/Nb2O5 catalysts. The most active was Pd/Al2O3 catalyst and the less active was Pd/Nb2O5. DRS in situ and TPR results showed the presence of PdO and Pd-0, which have little interaction with the support or the niobium oxide coated on the alumina support. X-ray diffraction results did not show the existence of crystalline phases of niobium species over the alumina support and PdO particles. XPS results showed niobia dispersed over alumina surface and enrichment of niobium oxide at the surface. Results of methane oxidation showed that the Pd/Nb2O5/Al2O3 displayed intermediate activity with increasing temperature and hysteresis during descending temperature, thus enhancing the activity. It was attributed to the redox phenomena during the reaction, because niobia on alumina prevents segregation of NO and facilitate the formation of moieties during the reaction. On the contrary, the Pd/Al2O3 deactivates during descending temperature, due to the segregation of PdO particles. (c) 2005 Elsevier B.V. All rights reserved.