Four in-series reactors accommodating 1 kg Ni/C catalyst in a 1.2-m bed were used to reduce NO with a (64.84:33.5 v/ v) propane-butane in relation to contact time (3, 6, 9 or 12 s), temp. (200-400 degrees C at 50 degrees steps) and NO inlet concn. (200, 500, 1000 or 2000 ppm). The kinetics of reduction was described by Yang-Hougen kinetic model with the sufficient accuracy. The temperature of 300-400 degrees C and the contact time of 6-12 s are the optimum parameters of the process.