Mechanism on the role of support and promoter

There is no consistent understanding on the role of mechanism of alkali metals and alkaline earth metals on ruthenium catalysts and their state under the operating conditions. The current studies show that the dynamics of the ammonia synthesis reaction are different using the alkali metals and alkaline earth metals as the promoters, respectively. Therefore, using combination of promoters is more favorable to increase the catalytic activity. 

The easily reduced noble metals usually are supported on metal oxides which cannot be reduced. The noble metal oxides are first reduced to form metal particles and the surfaces of these small grains have different crystal faces and different properties. The size of metal particles are also influenced by the chemical—physical property of supports, enrichment and agglomeration of metals, the reduction temperature and the formation process of metals grain. There is electronic interaction between the support, promoters and metal particles, and so can affect the activity. 

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