Kinetics of selective catalytic reduction of NO with NH₃ on Fe-ZSM-5 catalyst

Fe-exchanged ZSM-5 has been found previously to be much more active than commercial vanadia-based catalysts for selective catalytic reduction (SCR) of NO with NH₃. The kinetics of the SCR reaction is studied in this work. The results show that the rate of NO conversion on Fe-ZSM-5 is first-order with respect to NO, zeroth-order w.r.t. NH₃ and nearly half-order w.r.t. O₂, at 260-300 °C. This is in good agreement with our previous FTIR result that the catalyst surface is nearly completely covered by ammonia adsorbed species (i.e. NH₄⁺ ions) under reaction conditions. The present results further support that the SCR mechanism on Fe-ZSM-5 involves NO₂ as an intermediate and the formation of NO₂ from NO oxidation (NO+(1/2)O₂→NO₂) is probably the rate-determining step. The apparent activation energy for the reaction is found to be 54 kJ/mol.