Selective catalytic combustion of hydrogen cyanide over metal modified zeolite catalysts: From experiment to theory

A series of metal modified zeolite including Cu-(Beta, FER, MCM-22, MCM-49, MOR) and M-(M = Cu, Co, Fe, Mn, Ni)-ZSM-5 was prepared by impregnation method and characterized by BET, XRD, and H-2-TPR. HCN-SCC (selective catalytic combustion) activity measurement results suggest that Cu-ZSM-5 exhibiting excellent HCN conversion activity (T-90= 350 degrees C) and N-2 yield (> 95% at T > 350 degrees C) constitutes one kind of promising candidate for HCN catalytic abatement. The HCN-SCC mechanism was further investigated by density functional theory (DFT) over constructed 20T-Cu-ZSM-5 models, which suggests that: (i) the 20T-Cu-ZSM-5 containing double active [Cu](+) site was much more favorable than that of 20T-Cu-ZSM-5 with single active [Cu](+) site during NCO generation step, being mainly related to the cooperation effect of double active [Cu](+) site; (ii) NCO + NO -> N-2+ CO2 was confirmed to the one kind of probable reaction pathway for N-2 and CO2 generations, wherein the NO could be produced through oxidation of NCO; (iii) the DFT energy calculation results as well as the microkinetic analyses suggested that the NCO formation step possessing the highest energy barrier (10.4 kcal mol(-1)) was proposed to be the rate determining step of the whole catalytic cycle.