Effect of H/N ratio control in a multibed ammonia synthesis system with Ru-based catalysts

Ammonia has recently attracted attention as a hydrogen carrier and fuel, based on the power-to-fuel concept. This concept can be realized using Ru-supported rare-earth oxides for the synthesis of ammonia from hydrogen and nitrogen (3H2 + N2 - 2NH3) under mild conditions. However, at a high H/N ratio, Ru catalysts exhibit hydrogen poisoning, which reduces their activity for ammonia synthesis. This study investigates the effect of the H/N ratio on the ammonia synthesis activity of the developed Ru catalyst Ru(5 wt%)/Ce0.5La0.4Si0.1O1.8 under isothermal conditions (350-500 degrees C). The optimal H/N ratio for achieving the highest catalytic activity decreases as the temperature is lowered (H/N = 0.5 at 350 degrees C; H/N = 2.0-2.5 at 450 degrees C). In a multibed reactor, adjusting the H/N ratio to a lower value in the downstream catalyst beds-where the temperature decreases along the gas flow path-can enhance the overall rate of ammonia production by optimizing the reaction conditions in these cooler stages. We propose a system to control the H/N ratio for each catalyst bed in a multibed reactor and demonstrate an increase in the rate of ammonia production when using a double-bed reactor containing the Ru/ Ce0.5La0.4Si0.1O1.8 catalyst. The proposed system offers various opportunities to accelerate the use of ammonia as a hydrogen carrier and fuel.