The effects of active component (Ru, Rh, Pt, Pd, Ni, Fe) and support (CNTs, AC, Al2O3, MgO, ZrO2, TiO2) On the catalysis of ammonia decomposition were studied for the generation of COx-free hydrogen. It was shown that the Ru catalyst using CNTs as support exhibits the highest conversion of NH3. The performance can be further improved by modifying CNTs with KOH. According to the results of XRD, TEM, and chemisorption (CO and H-2 as adsorbates) investigations, Ru dispersion is the highest on CNTs. In the range of 2-5 nm, the particle size of Ru on CNTs is the smallest among the supported Ru catalysts; the Ru particles on the metal oxides are in the 3-16 nm range. It seems that larger Ru particles are more active for NH3 decomposition in terms of TOE Further investigation on the relationship between support basicity and catalytic activity disclosed that a support material of strong basicity is essential for high catalytic performance. In the N-2-TPD studies of supported Ru catalysts, desorption was promoted over catalysts of strong basicity, suggesting that N-2 desorption is the rate-determining step in ammonia decomposition. These results implied that it is possible to develop a highly efficient Ru catalyst for NH3 decomposition by using electron-conductive materials of strong basicity as support. (C) 2004 Elsevier Inc. All rights reserved.