Abstract: The present invention is directed to a catalytic combustion system having a gas turbine engine recuperator and an annular catalytic combustor. The annular catalytic combustor includes a pre-burner/pre-mixer which functions as a pre-burner during startup and as a pre-mixer for the fuel and air during catalytic operation. This pre-burner/pre-mixer includes a plurality of primary tangential air-fuel venturis each having a fuel injector, and a plurality of secondary tangential air dilution holes. The pre-burner/pre-mixer is joined to the annular in-line catalytic canister by a transition section which includes a plurality of tertiary air dilution holes which introduce air radially into the transition section from the inner liner thereof. The in-line annular catalyst canister includes a large plurality of microlith catalyst elements positioned between support tings and held at the open end thereof by a plurality of support spokes.