The invention includes a process for reducing the amount of HCN discharged to atmosphere from a FCC unit, having a regenerator and a means for collecting and supporting catalyst particles. The process comprises adding a catalyst to the regenerator flue gas prior to entering the collecting means and precipitating the catalyst in the collecting means to form a catalyst bed. Ammonia or ammonia precursor is optionally added to the flue gas. The flue gas HCN is reacted in the presence of water and oxygen in the flue gas, and optional ammonia or ammonia precursor, at 200° C. to 800° C. in the presence of the catalyst bed to reduce the HCN amount, and the flue gas containing a reduced amount of HCN is discharged to atmosphere. The catalyst is one or more supported transition or lanthanide metal catalysts. The process can also be utilized in any combustion process.