Ammonia synthesis is one of the most important chemical reactions. Due to thermodynamic restrictions and the reaction requirements of the current commercial iron catalysts, it is also one of the worst reactions for carbon dioxide emissions and energy usage. Ruthenium-based catalysts can substantially improve the environmental impact as they operate at lower pressures and temperatures. In this work, we provide a screening of more than 40 metals as possible promoter options based on a Ru/Pr₂O₃ catalyst. Cesium was the best alkali promoter and was held constant for the series of double-promoted catalysts. Ten formulations outperformed the Ru-Cs/PrO_x benchmark, with barium being the best second promoter studied and the most cost-effective option. Designs of experiments were utilized to optimize both the pretreatment conditions and the promoter weight loadings of the doubly promoted catalyst. As a result, optimization led to a more than five-fold increase in activity compared to the unpromoted catalyst, therefore creating the possibility for low-ruthenium ammonia synthesis catalysts to be used at scale. Further, we have explored the roles of promoters using kinetic analysis, X-ray Photoelectron Spectroscopy (XPS), and in situ infrared spectroscopy. Here, we have shown that the role of barium is to act as a hydrogen scavenger and donor, which may permit new active sites for the catalyst, and have demonstrated that the associative reaction mechanism is likely used for the unpromoted Ru/PrO_x catalyst with hydrogenation of the triple bond of the dinitrogen occurring before any dinitrogen bond breakage.

Ammonia synthesis is one of the most important chemical reactions. Due to thermodynamic restrictions and the reaction requirements of the current commercial iron catalysts, it is also one of the worst reactions for carbon dioxide emissions and energy usage. Ruthenium-based catalysts can substantially improve the environmental impact as they operate at lower pressures and temperatures. In this work, we provide a screening of more than 40 metals as possible promoter options based on a Ru/Pr2O3 catalyst. Cesium was the best alkali promoter and was held constant for the series of double-promoted catalysts. Ten formulations outperformed the Ru-Cs/PrOx benchmark, with barium being the best second promoter studied and the most cost-effective option. Designs of experiments were utilized to optimize both the pretreatment conditions and the promoter weight loadings of the doubly promoted catalyst. As a result, optimization led to more than a five-fold increase in activity compared to the unpromoted catalyst, therefore creating a possibility for low ruthenium ammonia synthesis catalysts to be used at scale. Further, we have explored the roles of promoters using kinetic analysis, XPS, and in situ infrared spectroscopy. Here, we have shown that the role of barium is to act as a hydrogen scavenger and donor, which may permit new active sites for the catalyst, and have demonstrated that the associative reaction mechanism is likely used for the unpromoted Ru/PrOx catalyst with hydrogenation of the triple bond of the dinitrogen occurring first before any dinitrogen bond breakage.

Utilizing a permeation membrane that in situ removes the hydrogen from the reactor improves the performance and allows for the catalysis to be more efficient and achieve near quantitative conversion of ammonia.

Currently, there is a push to reduce reliance on hydrocarbon fuels for energy storage by using hydrogen carriers. One solution is ammonia; however, for use in the hydrogen economy, advances must be made for both ammonia synthesis and decomposition. We have studied several dysprosium‐doped praseodymium oxide supports, which were impregnated with ruthenium and tested for ammonia decomposition and ammonia synthesis activities. Some of these dysprosium‐praseodymium oxide supports significantly increased the rate of ammonia decomposition, while improving the stability of the catalyst when compared with the non‐doped samples. Moreover, an optimum was found close to 20 wt.% Dy ₂ O ₃ in the support, leading to a near tripling in activity for ammonia synthesis. Further, we have used X‐ray diffraction, Raman, UV–vis spectroscopy, temperature programed reduction, CO ₂ ‐TPD, and CO‐diffuse reflectance infrared fourier‐transform spectroscopy to understand the leading causes of this improved activity. With this, we highlight the benefit of mixed‐phase supports for ammonia decomposition catalysts, which is not required for ammonia synthesis.