The present invention provides a catalyst
system for treating an
exhaust gas, the catalyst
system comprising: a first SCR catalyst comprising an iron (Fe)
ion exchanged
molecular sieve having a
ferrierite (FER) or MFI framework, where the first SCR catalyst is disposed on or within a substrate; and a second SCR catalyst, the second SCR catalyst comprising
vanadium, where the second SCR catalyst is disposed on or within the substrate; wherein the first catalyst and the second catalyst are arranged such that, in use,
exhaust gas first contacts the first SCR catalyst before contacting the second SCR catalyst. An exhaust
system, method, use, and vehicle comprising or utilizing such a catalyst system are also provided.