Catalytic hydrolysis of HCN on ZSM-5 modified by Fe or Nb for HCN removal: surface species and performance

Abstract

The catalytic hydrolysis of HCN was systematically investigated using Fe/ZSM-5, Nb/ZSM-5 and Fe–Nb/ZSM-5 catalysts. Fe–Nb/ZSM-5 exhibited the highest HCN hydrolysis activity and the reaction products were NH₃ and CO. However, no NH₃ was detected due to the large ammonia storage capacity of the catalysts. The interaction between the Fe and Nb species resulted in increased amounts of isolated Fe³⁺, Nb⁵⁺, oligomeric Fe_xO_y and Nb_xO_y clusters, which could contribute to improving HCN hydrolysis. Furthermore, the excellent redox properties, favored pore structure and abundance of surface acid sites were responsible for the superior catalytic hydrolysis of HCN. Furthermore, the reaction pathway was speculated as follows: HCN and H₂O reacted to produce methanamide. Methanamide further reacted with H₂O to generate ammonium formate, which decomposed to formic acid and NH₃. Formic acid was then converted into CO and H₂O via pyrolysis.