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

Abstract

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), O2 (2000-6000 ppmv) and (0-10%) H2 concentrations were investigated with the presence of 800 ppm of NH3 in each final gas mixture. In the second route, catalytic ammonia decomposition experiments were carried out with H2 in balance N2 (0-30%) containing 800 ppm of NH3 at 700 °C and 800 °C. In the SCO, NH3 conversions were increased with increasing reaction temperatures with the absence of H2 in the reaction mixture. With 10% H2, it was shown that NH3 conversions increased with decreasing the reaction temperature. This was interpreted as the competing H2 and NH3 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 H2 addition, all conversions decreased. The decrease in conversion seemed to be linear with inlet hydrogen concentration. Hydrogen was seen to inhibit the decomposition of ammonia. It was shown that Fe/HZβ catalyst is better to use for catalytic decomposition of NH3 in syngas rather than SCO of NH3 in spite of higher reaction temperatures needed in the decomposition reaction.