The study of catalyst behavior at pressure up to 12 bar during CH4, H2, CO and their mixtures combustion is the main purpose of this PhD thesis. Actually the interest towards catalytic combustion as an alternative route to produce electric power is renewed due to the use of Low-Btu fuels. Therefore the research activity was focused notably on CH4 but also on H2 and CO combustions and on the effect of their addition on methane combustion at variable pressure.