A process for catalytic oxidation of ammonia gas by way of an oxygen-containing gas in a presence of a noble metal-containing catalyst may be employed to give nitrogen monoxide. A temperature of an ammonia/air mixed gas may be optimized in respect of nitrogen monoxide selectivity of the reaction before contact with the catalyst. Examination of catalytic NH3 oxidation according to 4NH3+5O2→4NO+6H2O revealed that an optimum mode of operation of an NH3 burner in an HNO3 plant is not to be achieved by maintenance of a constant gauze temperature of the catalyst gauze by automatic setting of the NH3:air ratio. Rather, there is an optimum temperature for each process condition that should be set not by changing the NH3:air ratio but instead by altering the temperature of the NH3/air mixed gas before contact with the catalyst gauzes.