Electronic contribution of active site

Potassium is considered to be electron donor for the iron catalysts. For ruthenium catalysts, electronic effect of support and promoter is very important. According to the eletronegativity, the electronic effect of support and promoter are summarized and shown in Fig. 6.15 and Table 6.8.  

TOF of ammonia synthesis reaction and isotopic equilibrium rate of nitrogen molecule follow the order shown in Table 6.8. We can roughly estimate the performance of promoters from chemical property of element itself. The activity of ruthenium catalysts supported on AI2O3 is very low, while almost no activity is observed on activated carbon due to the acidicity of AI2O3 and absorption of electrons by activated carbon. 

Activity in the mass of unprocessed catalyst (RuCls 3H2O + support + promoter) as the base of calculating, except the mass of metal K can be neglected in the Ru-K/support catalyst. 

16 Effects of alkali metal on the rate of ammonia formation at N2 + H2 SOkPa on 2.5% Ru-AC (1.0g) at 588K95 

According to the promotion role of K on ammonia synthesis and nitrogen isotopic equilibrium over Ru/AC and pure ruthenium catalysts, it is found that with adding K at 673 K, the activity increases by 500 times on ruthenium catalyst, while the activity only increases by 25 times on Fe catalyst due to the inhibition of hydrogen. The inhibition of hydrogen is caused by the competitive adsorption of hydrogen which can inhibit the adsorption of nitrogen.  

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