Abstract: Apparatus for high temperature catalytic conversion of gases is disclosed in which the first part of the heating is done with a heating gas and the final most difficult part is done with electric heaters. The heating gas is passed between spaced layers of catalyst, out of contact and crosswise and countercurrent to the flow of gases to be converted. The gases are first subjected to preheating with heating gas, then heating as the gases contact catalyst, and then superheating, i.e. heating to a final high temperature, with electric heaters in the absence of heating gas.