Nickel perovskite catalysts for ammonia decomposition: DFT calculations and microreaction kinetics

Abstract

Combining policy guidance, catalyzing ammonia decomposition to produce hydrogen is a new concept for hydrogen energy supply. Alkaline carriers can effectively improve the ammonia decomposition activity on the catalyst by adjusting the dispersion of nickel (Ni) and controlling the size of Ni. However, the activity of Ni-based perovskite catalysts does not seem to be entirely affected by the above factors. Exploring the mechanism of Ni and perovskite alkaline carrier surfaces through theoretical calculations provides deeper theoretical guidance for ammonia (NH3) decomposition. This study uses periodic density functional theory calculation methods to investigate the reaction paths and energy distribution of monomeric ammonia and dimeric ammonia on a nickel-doped barium zirconate (Ni/BaZrO3) catalyst. Molecular dynamics simulations, Bader charge analysis, and density of states assist in understanding the adsorption states of NH3 and the catalytic decomposition mechanism. The energy barriers for N-H bond breaking and nitrogen generation reactions of Ni clusters loaded on the BaZrO3 surface (Ni4/BaZrO3) were compared and analyzed. The results show that Ni/BaZrO3 is more conducive to ammonia decomposition, with a maximum reaction barrier of 0.90 eV. The catalytic activity of the catalyst under oxygen vacancy conditions was further examined. By comparing the mechanisms of dimeric ammonia decomposition on the clean catalyst surface and the oxygen vacancy catalyst surface, it was found that the presence of oxygen vacancies facilitates ammonia decomposition, but Ni doping provides more effective assistance for N-H bond breaking. The rate constant for ammonia decomposition was calculated using transition state theory. This work not only provides theoretical references for the decomposition mechanism of NH3 in Ni-based perovskite materials but also provides kinetic data for the kinetic modeling of NH3 decomposition.