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 NH₃ in each of the final gas mixture. In the second route, catalytic ammonia decomposition experiments were carried out with H₂ in balance N₂ (0-30%) containing 800 ppm 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 ammonia decomposition reaction. 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.

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