Citric acid modified Ni/La₃Ce₇O_x to achieve efficient ammonia decomposition for hydrogen production: Mechanism of modification with transition metals and deactivation

In order to develop efficient non-precious metal catalysts for hydrogen production by ammonia decomposition, the effects of transition metal （Co, Fe, Mn, Cu） doping and chelating agent （citric acid, triammonium citrate） modification on the structure and properties of Ni/La₃Ce₇O_x were investigated. The results reveal that transition metal doping led to structural degradation of the catalyst, as indicated by increased grain size, reduced specific surface area, and decreased oxygen vacancies, which in turn lead to weakened metal-support interactions. Citric acid modification significantly optimizes the catalyst structure, reducing grain size, enhancing low-temperature reducibility, and increasing oxygen defect concentration. Performance testing demonstrates that the Ni/La₃Ce₇O_x catalyst, prepared via citric acid addition, exhibits excellent catalytic activity and stability. Under conditions of a gas hourly space velocity of 60000 mL/（g·h） and a temperature of 550 °C, the ammonia decomposition conversion and hydrogen production rate reach 57.5% and 39 mmol/（g·min）, respectively. Moreover, the catalyst maintains stable activity over a 100 h cycling test. The above results provide valuable insights for the development of cost-effective and high-performance catalysts for ammonia decomposition to hydrogen production.