Apparatus for the production of ammonia synthesis gas by the catalytic cracking of coke oven gas in the presence of water vapor and air is disclosed. The apparatus includes concentric inner and outer pipes, a first annular reaction zone between the pipes and a second reaction zone inside the inner pipe, both zones containing a catalyst. The purified coke oven gas along with air and water vapor is introduced into the interior of the outer pipe, i.e., into the first reaction zone at one end. The gas flows along the length of the pipes and then into the inner pipe, i.e., the second reaction zone, through a number of openings in the end of the inner pipe opposite the end of the outer pipe where the coke oven gas was initially introduced. The gas then flows along the length of the inner pipe to the opposite end where the cracked gas is removed.