Nickel–Silicon Catalysts for the OxidativeSteam Reforming of Renewable Natural Gas to Produce Hydrogen for Small-ScaleAmmonia Synthesis

The synthesis of ammonia is an energy-intensive process that consumes around 1.8% of global energy output each year and produces approximately 500 MMT of carbon dioxide. The production of hydrogen accounts for over 80% of the total energy required by the ammonia synthesis process. Haber-Bosch is the most widely used technology for ammonia production; however, it is only economically viable at a large scale. Oxidative steam reforming (OSR) is an alternative technology to produce synthesis gas for small-scale ammonia production. OSR combines the catalytic partial oxidation of methane (CPOM) and the steam reforming of methane (SMR) to efficiently generate a reformate with an H₂/N₂ molar ratio of 3, which is the stoichiometric value required for ammonia synthesis. One of the major challenges with OSR is the development of a catalytic material for CPOM that can show not only high activity and stability but also significant resilience to deactivation due to coke formation. In the present work, a novel and inexpensive nickel-based catalytic material has been synthesized using a facile sol–gel approach and tested for CPOM at temperatures below 500 °C. The prepared catalyst shows a remarkable activity comparable to that of catalysts based on noble metals and an outstanding resistance to the formation of carbon deposits. The catalytic activity is believed to result from the presence of carboxyl groups and oxygen-depleted regions, which led to an enhancement in the adsorption/activation of CH₄ and O₂, respectively. By using this catalytic material in the CPOM stage at 450 °C and an alumina-supported nickel catalyst in the SMR stage at 800 °C, we demonstrated the viability of an OSR reactor to produce a reformate with a suitable H₂/N₂ molar ratio for ammonia production.