An ammonia converter system and method are disclosed. The reactor can alter the conversion of ammonia by controlling the reaction temperature of the exothermic reaction along the length of the reactor to parallel the equilibrium curve for the desired product. The reactor 100 can comprise a shell 101 and internal catalyst tubes 109. The feed gas stream enters the reactor, flows through the shell 101, and is heated by indirect heat exchange with the catalyst tubes 109. The catalyst tubes 109 comprise reactive zones 122 having catalyst and reaction limited zones 124 that can comprise inert devices that function to both separate the reactive zones, increase heat transfer area, and reduce the temperature of the reaction mixture as the effluent passes through the catalyst tube 109.