A spin promotion effect in catalytic ammonia synthesis

The need for efficient ammonia synthesis is as urgent as ever. Over the past two decades, many attempts to find new catalysts for ammonia synthesis at mild conditions have been reported and, in particular, many new promoters of the catalytic rate have been introduced beyond the traditional K and Cs oxides. Herein, we provide an overview of recent experimental results for non-traditional promoters and develop a comprehensive model to explain how they work. The model has two components. First, we establish what is the most likely structure of the active sites in the presence of the different promoters. We then show that there are two effects dictating the catalytic activity. One is an electrostatic interaction between the adsorbed promoter and the N-N dissociation transition state. In addition, we identify a new promoter effect for magnetic catalysts giving rise to an anomalously large lowering of the activation energy opening the possibility of finding new ammonia synthesis catalysts. Catalytic ammonia synthesis continues to attract significant interest. Here, the authors develop a model to explain a large body of recent experimental data on new promoters. They find new promotion mechanism mediated by coupling between adsorption and spin polarization on the surface atoms of magnetic catalysts.

Automated summary

This article provides an overview of recent experimental results on new promoters for ammonia synthesis and develops a model to explain their working principles. The authors identify a new promotion mechanism mediated by the coupling between adsorption and spin polarization on the surface atoms of magnetic catalysts, resulting in a lowering of activation energy.