Hydrogen plays a crucial role in various catalytic reactions, serving as an energy vector and a reactant in chemical refineries. Ammonia decomposition is a key reaction in the context of hydrogen storage, transport, and release. We combined density functional theory (DFT) calculations with microkinetic modeling to address the promotion mechanism of Ba species for ammonia decomposition on Co catalysts. Challenges of modeling the ammonia decomposition reaction were addressed and the effect of hydrogen coverage on the adsorption of NH3 was investigated. The modified adsorption properties of Co upon the addition of metallic Ba or BaO suggest that the promoters play a role in alleviating the competitive adsorption of H. The superiority of the BaO-promoted catalyst is attributed to a lower energy for the transition state of the rate-determining step, coupled with a reduced impact of the hydrogen coverage on weakening the ammonia adsorption. The kinetic analysis implies that Ba on the Co surface is likely to be in an oxide form under reaction conditions.Water impurities in the feedstock of the ammonia decomposition reaction lead to the adsorption of oxygen species which blocks the active sites on the catalyst surface. We explored the oxygen poisoning effect on promoted and unpromoted Co surfaces. We found that Co-BaO was more resistant to oxygen poisoning and more sensitive to H2 pressure than Co.
Hydrogen can also transform unsaturated hydrocarbons into valuable products through hydrogenation processes. DFT-based reaction profiles and microkinetic simulations were used to describe the catalytic selective hydrogenation of acetylene on Ni, Ni3In, NiIn, and Ni2In3 model intermetallic surfaces. Among the NixIny intermetallic catalysts, NiIn showed the highest ethylene yield. Microkinetic simulations using free energy values calculated at high acetylene coverage showed that the presence of In on the catalytic surface decreased the rate of acetylene consumption with a trade-off relation between activity and selectivity. We confirmed that ethylene hydrogenation and acetylene C−C coupling were the primary sources for ethane and oligomer formation, respectively.
The unique properties of hydrogen make it an indispensable element in the development of sustainable energy solutions and the production of essential chemicals.
