Microscopic insight into catalytic HCN removal over the CuO surface in chemical looping combustion

Hydrogen cyanide (HCN) is well-accepted as a main nitrogen-containing precursor from fuel nitrogen to nitrogen oxides. When using coal as fuel with a CuO-based oxygen carrier in chemical looping combustion (CLC), complex heterogeneous reactions exist among the system of HCN, O 2 , NO, H 2 O, and CuO particles. This work performs density functional theory (DFT) calculations to systematically probe the microscopic HCN heterogeneous reactions over the CuO particle surface. The results indicate that HCN is chemisorbed on the CuO surface, and the third dissociation step within the consecutive three-step HCN dissociations (HCN*→CN*→NCO*→N*) is the rate-determining step. Namely, the CN*/NCO* radicals can be deemed as an indicator of the performance of HCN removal due to their quite higher dissociation energies. With the existence of O 2 , H 2 O, and NO, the reaction mechanism of HCN conversion becomes extremely complex. Both DFT calculations and kinetic analyses determine that O 2 , NO, and H 2 O all significantly accelerate the consumption of CN*/NCO* radicals to produce various N-containing species (NOx or NH 3 ) to different extents. Finally, a skeletal reaction network in a system of O 2 /NO/H 2 O/HCN is concluded, which clearly elucidates that CuO exhibits excellent catalytic activity toward HCN removal.