Ammonia is produced in a reactor 22, 24, 246, 248, 250 or 252, in which pseudoisothermal conditions can be approached by convective cooling of a reaction zone of the reactor by positioning at least a portion of the reaction zone in indirect contact with a flow of hot gas such as exhaust gas 18 or preheated air. The hot gas 18 may be supplied from a fired heater, a boiler 10, a reformer 202, a process air preheat furnace, a gas turbine, or the like. The reactor converts a feed stream of a purge gas 12 or syngas to ammonia. The method may be implemented in a primary synthesis loop (as at 246, 248, 250, 252) or in a purge gas loop 12 of a new ammonia plant, or by retrofitting an existing ammonia plant. Cooperatively installed with a primary ammonia synthesis loop, the reactor increases total ammonia production.