Electroplating sludge-derived spinel catalysts for NO removal via NH3 selective catalysis reduction

The hazardous electroplating sludge (ES) waste can be converted to metal oxide catalysts for pollution reduction. Combining the computational study with experimental verification, we converted the ES containing Ni, Cu, and Cr to spinel oxide catalysts for NO removal via selective catalysis reduction with NH3 (NH3-SCR), yielding > 96% NO removal at 200-300 degrees C. Then we investigated computationally the mechanisms of NH3-SCR for the two Cr-spinel oxides, showing the reaction barrier for CuCr2O4 is lower than NiCr2O4. Subsequent experiments supported the computation results: CuCr2O4 yielded 88% and NiCr2O4 achieved 60% NO removal at 225 degrees C. Compared with the two studied Cr-spinel oxides, the ES after calcination had a better removal effect and wider operating temperature window. This study provides atomistic insights into the catalytic mechanism of Cr-spinel oxides in NH3-SCR reactions, promoting the design of spinel oxide catalysts and the resource utilization of ES as a high value-added product from an environment engineering point of view.