Cyanide species played a role in the selective reduction of NO by isobutane over Cu-MFI. Cyanogen was a significant product under partial conversion conditions and the deposits that accumulated during deactivation liberated HCN when heated in the absence of oxidant. HCN was oxidized much more readily by NO/O2 mixtures than by O2 alone. Cyanogen could be a significant product of both reactions, being produced during the course of continual deactivation with HCN/O2 at < 300°C and in high yields under steady-state conditions at 200°C with HCN/NO/O2. Completion conversion to N2 and CO2 occurred during the latter reaction at 270°C. The much higher reactivity of HCN in the presence of NO was ascribed to oxidation of NO to NO2, which maintained activity through catalyst reoxidation and/or removal of adsorbed cyanide and ammonia. Deactivation during isobutane-SCR at similar temperatures might be carried out because NO2 concentrations were kept low via back conversion to NO as a consequence of reaction with carbonaceous deposits.
- Hydrogen cyanide
- NO + isobutane