The mineral phase reconstruction of copper slag as Fenton-like catalysts for catalytic oxidation of NOx and SO2: Variation in active site and radical formation pathway

Herein, the copper slag through CaO-thermal treatment was used as a heterogeneous catalyst to activate H2O2 into free radicals to remove NOx and SO2. The NOx removal capacity of modified copper slag exhibited a volcano-type tendency with increased calcination temperatures. Because of the iron phase transformation and decrease in surface exposure Cu species by adjusting surface properties, the copper slag delivers a higher NOx capacity and H2O2 utilization rate than raw copper slag and bare H2O2. In addition, the interaction of multi-phases of modified copper slag was illustrated by simulation experiments. Moreover, the possible formation pathway of free radicals in the alkaline medium was proposed based on the electron paramagnetic resonance (EPR) as well as chemical quenching experiments. The surface-bound hydroxyl radical through equivalent to Fe3+ sites is decisive for free radical formation in alkaline conditions. Our findings shed new light on the feasibility of SO2 and NOx removal by metallurgical slag via mineral phase reconstruction as a novel heterogeneous catalyst.