Investigation on the catalysis of CO_x-free hydrogen generation from ammonia

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 CO _x-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 H₂ 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 TOF. 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 N₂-TPD studies of supported Ru catalysts, desorption was promoted over catalysts of strong basicity, suggesting that N₂ 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.