Role of metal oxide supports in NH 3 decomposition over Ni catalysts

The decomposition of NH3 over Ni catalysts supported on various metal oxides (Y2O3, CeO2, MgO, La2O3, Al2O3, and ZrO2) was investigated, and the Ni/Y2O3 catalyst was found to show the highest activity. The rate of H2 formation per exposed Ni atom (turnover frequency) for the supported Ni catalysts depended strongly on the type of metal oxide support, indicating that the active sites for the Ni catalysts were not identical in nature. Investigation of the associative desorption of atomic nitrogen formed by NH3 decomposition over the Ni catalysts revealed that the N2 desorption temperature depended on the type of support. This result indicates that the NiN binding energy varied among the metal oxide supports, which would be attributable to the change of the Ni electronic state by the supports. The volcano-curve relationship was obtained between turnover frequency and N2 desorption temperature, indicating that the NH3 decomposition activity was dominated by the NiN binding energy. We considered that the metal oxide supports changed the rate-determining step for NH3 decomposition on Ni.