Effects of Steam on Ni/Al₂O₃ Catalysts for Ammonia Decomposition

Abstract

Decomposition of gaseous NH 3 from ammonia (NH 3 )-containing wastewater was explored using Ni-loading Al 2 O 3 catalysts. The thermochemical decomposition of an NH 3 /steam mixture (wet-NH 3 ) with different steam contents at 873, 923, and 973 K using a fixed-bed reactor under ambient pressure. The present results indicated that the catalysts can be deactivated by the formation of NiAl 2 O 4 , which can be thermodynamically generated, and confirmed that the extent of deactivation was greatly affected by the partial pressure of the steam (P H 2 O ). The catalytic activities at 873 K decreased with increasing P H 2 O , whereas the activity was constant above P H 2 O of 25 kPa. However, the NH 3 conversion was almost independent of the NH 3 flow rate and temperature, and ∼30% of the NH 3 was decomposed at each temperature. This study indicated that, even in the presence of steam, this catalyst could decompose NH 3 from NH 4 + -containing water.

Comparative Study of Ammonia‐fueled Solid Oxide Fuel Cell Systems

“…One is that the reaction rate of the NH 3 decomposition is slower than that of the electrochemical reactions over the electrodes in the higher current region. The inhibition of the NH 3 decomposition by the water produced in the cells can be also considered as the reason . The stack performance for the autothermally cracked NH 3 ‐fueled system achieved 234 W at 36 A, which was superior to that for the direct NH 3 ‐fueled one (232 W at 36 A).…”

Review of the Decomposition of Ammonia to Generate Hydrogen

“…The decomposition of ammonia is one of the slowest stages in the supercritical oxidation process of sludge. The decomposition of ammonia into N 2 and H 2 in the presence of water vapor was studied using Ni-based catalysts supported on alumina; , water vapor inhibited the conversion of ammonia and initially deactivated the catalyst until a constant conversion was reached.…”

Higher Activity of Ni/γ-Al2O3 over Fe/γ-Al2O3 and Ru/γ-Al2O3 for Catalytic Ammonia Synthesis in Nonthermal Atmospheric-Pressure Plasma of N2 and H2

“…Various nickel-containing materials have been reported to be active for the catalytic decomposition of ammonia [40][41][42][43][44][45][46]. Since the ammonia decomposition reaction is an equilibrium reaction at a middle temperature range, these earlier works might suggest the possibility of the nickel-containing materials working as active catalysts for ammonia synthesis.…”