Catalysts and Reactors for Selective Catalytic Reduction of NO

Mixing of ammonia with flue gas should be carried out with care because only a low slip (exit of unreacted ammonia) is allowed, typically less than Sppmv ammonia. 

During SCR, NH3 should react selectively with NO to N2 [Eqs. (6.18.8) and (6.18.9)]. If the temperature is too high, undesirable oxidation of ammonia to either NO or N2 may also occur  

The conversion of NO into N2 reaches a maximum at about 400 °C. At higher temperatures, the catalyst also produces a small but signiflcant amount of N2O, which is a very strong greenhouse gas with 310 times the global warming potential 0fC02. 

For the design of a SCR reactor, we need an appropriate reactor model, and the differential equations have to be solved based on the parameters of the intrinsic and effective kinetics. 

The SCR reactor can be regarded as almost isothermal. For a typical inlet content of NO of 1000 ppmv, we get a rather small value of the adiabatic rise in temperature (ATad) if we assume a heat capacity of the flue gas of 32Jmol and a reaction enthalpy of —406kJ mol [Eq. (6.18.8)], the heat balance leads to a relatively small value of ATad of 13 K  

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