In the last years, the PTK (periodic transient kinetics) method has been introduced as a new dynamic investigation method in heterogeneous catalysis . The method uses a periodic change in the composition of the inflowing reactive gas and analyses the system's response in the transient phases. With a sufficiently long period duration, the system reaches a stationary operating point . After sufficient switching periods the so-called limit cycle is established, which is characterised by the fact that all dynamic processes in the system are reversible .