Effect of water impurities on promoted and unpromoted cobalt-catalysts during the ammonia decomposition reaction

Abstract

The feedstock of the ammonia decomposition reaction often contains water impurities. Water-induced Co oxidation leads to catalyst deactivation. DFT-based microkinetic simulations of ammonia decomposition and water dissociation reactions are used to understand oxygen poisoning on promoted and unpromoted Co surfaces. Simulations show that catalyst oxidation only occurs at low NH₃ conversion and, at higher conversion, the produced H₂ reduces the catalyst. Hence, in a typical flow reactor, catalyst oxidation is likely to occur only at the reactor inlet. However, the oxidized zone can slowly propagate along the reactor and impact the catalyst stability. The adsorption of oxygen was stronger on BaO-promoted Co in comparison to pristine Co. However, Co-BaO is more sensitive to H₂ pressure and needs a lower ammonia conversion to prevent oxygen poisoning on the surface. This indicates that the BaO promoter plays a role in making the catalyst more resistant to O-induced poisoning during the ammonia decomposition reaction.