The catalytic decomposition of ammoniaElectric field effect on the catalytic activity

The decomposition of ammonia over a Pt-Rh-Pd catalyst has been studied in an electric field. At a given temperature, the activity and resistance of the catalyst are significantly increased by the field. A negative potential on the catalyst causes a decrease in the temperature of the catalyst accompanied by a corresponding increase in the temperature near the anode. The increase in temperature is probably caused by recombination reactions of ions in the gas phase. The effect of the field is greatest the first 15–25 hr of the catalyst lifetime, decreasing continuously with time. A corresponding decrease in the ion current was observed but the decrease in ion current was about ten times faster than the decrease in catalytic activity. In this study, ions were observed in a system of H 2 and in a H 2 -N 2 mixture. However, for these systems, the electric field did not change the temperature of the catalyst and of the gas flow. These results indicate that the catalyst participates as an energy carrier to the gas volume, thus initiating reactions there. A two-stage mechanism is proposed for the catalytic decomposition of ammonia.