Promotion effect of rare-earth elements on the catalytic decomposition of ammonia over Ni/Al2O3 catalyst

Abstract

Ammonia decomposition has attracted much attention as an efficient method for the on-site generation of hydrogen. In this study, alumina-supported nickel catalysts (Ni/Al2O3) modified by rare-earth elements were prepared by the impregnation method and their catalytic activity for the ammonia decomposition was investigated. The addition of rare-earth elements promoted the decomposition reaction over catalysts and the La-modified catalyst achieved the highest ammonia conversion in this work. For the modified catalysts, the adsorbed hydrogen, which is known to be an inhibitive species for the ammonia decomposition, desorbed at lower temperature compared to the unmodified one. Therefore, the effective alleviation of hydrogen inhibition would be responsible for the activity enhancement for the modified catalysts. The reaction kinetics study also supported this proposed mechanism. For the La-modified catalyst, the optimal pretreatment condition was investigated to enhance the catalytic activity. The catalyst calcined at 400°C followed by reduction at 600°C exhibited the highest ammonia conversion of 94% at 550°C.