COMPARISON OF CATALYTIC ACTIVITIES BOTH FOR SELECTIVE OXIDATION AND DECOMPOSITION OF AMMONIA OVER Fe/HZβ CATALYST

Ammonia is one of the syngas contaminants that must be removed before using the syngas downstream applications. The most promising hot-gas clean-up techniques of ammonia are selective catalytic oxidation (SCO) and catalytic decomposition. In this study, the catalytic activities over Zeolite Hβ supported iron catalyst (Fe/HZβ) were compared both for the two catalytic routes. For SCO experiments; temperature (300-550 °C), O 2 (2000-6000 ppmv) and (0-10%) H 2 concentrations were investigated with the presence of 800 ppm NH 3 in each of the final gas mixture. In the second route, catalytic ammonia decomposition experiments were carried out with H 2 in balance N 2 (0-30%) containing 800 ppm NH 3 at 700°C and 800°C. In the SCO, NH 3 conversions were increased with increasing reaction temperatures with the absence of H 2 in the reaction mixture. With 10% H 2 , it was shown that NH 3 conversions increased with decreasing the reaction temperature. This was interpreted as the competing H 2 and NH 3 oxidations over the catalyst. On the other hand, in the catalytic decomposition, thermodynamic equilibrium conversion of almost 100% was attained at both 700 and 800 °C. Upon H 2 addition, all conversions decreased. The decrease in conversion seemed to be linear with inlet hydrogen concentration. Hydrogen was seen to inhibit ammonia decomposition reaction. It was shown that Fe/HZβ catalyst is better to use for catalytic decomposition of NH 3 in syngas rather than SCO of NH 3 in spite of higher reaction temperatures needed in the decomposition reaction.