Transport effects and chemical effects on NO removal by SCR with NH3 over iron-based catalyst in a magnetically fluidized bed

摘要

Selective catalytic reduction (SCR) of NO by NH3 on iron-based catalysts was investigated with a magnetically fluidized bed (MFB). Magnetic fields promoted the NO conversion. The optimal efficiency of 95 % was attained under a magnetic field of 0.01-0.015 T at 250 degrees C. Magnetic fields yielded transport effects and chemical effects on SCR of NO over Fe2O3 catalyst. The transport effects are reflected by the enhancement of physical transfer in a MFB. Magnetic fields can check and eliminate bubbles, increase gas-solid contact probabilities, and thereby improve heat and mass transfer characteristics in a MFB. The chemical effects can be summarized into three points. First, the magnetization of gamma-Fe2O3 by uniform magnetic fields gives rise to boundary effects, which results in Faraday force on paramagnetic NO molecules and yields NO movement to the catalyst surface, and hence increases NO chemisorption. Second, the synergy of magnetic fields and ferrimagnetic iron-based catalyst can boost the transformation of antimagnetic reactant into paramagnetic products, and accelerate electron transport in the reaction, which enhances the activation of NH3 on magnetic Fe (III) sites. Third, magnetic fields can alter the energy dispersal of a free radicals reaction system, and thereby promotes the free radicals reaction between NH2 center dot and NO center dot.