The influence of adding H-2 in the feed during catalytic combustion of methane (CCM) on a Pd(2 wt.%)gamma-Al2O3 catalyst is studied. Various effects on the performances of the catalyst are observed, depending on the H-2 concentration. Activation is observed at low H-2 concentrations, but if too large concentrations of hydrogen are used (5 vol.% in this case), reduction of the surface of the palladium particles occurs and deactivation of the catalyst is therefore observed. A mechanistic interpretation is proposed, which explains the experimental observations. A comparison is also made with the characteristics of a Pt(2 wt.%)/gamma-Al2O3 catalyst. Both catalysts display different behavior towards the presence of H-2, which probably reflects different reaction pathways for CCM. (c) 2005 Elsevier B.V. All rights reserved.