A new type of periodic operation is investigated for a simple model of a heterogeneous catalytic continuous stirred tank reactor For the heterogeneous case, two scales of response times were derived slow for heat processes and fast for concentration processes. Periodic operation in intermediate mode between slow and fast processes is studied by manipulation of the feed flow rate. The new approach is designated as mediating operation, which demonstrates ability to control interaction between fast and slow reactor subsystems due to desired separation of dynamic responses for temperature and concentration processes by a single input variable. The conversion improvement at lower temperature can be achieved for lower and upper stable steady states. For the system analysis, analytical investigation of the slow manifolds is used as well as numerical study.