Steady-state isotopic transient kinetic analysis of the H2/D2 exchange reaction as a tool for characterising the metal phase in supported platinum catalysts Original Research Article

The steady-state isotopic transient kinetic analysis (SSITKA) technique has been applied to the characterisation of the metal phase in Pt/CeO2 and Pt/SiO2 catalysts by studying the H2/D2 exchange process. The time scale of the exchange process is close to the delay in the transport of the gases through the reactor. The behaviour of the reactor has been studied by analysing the curves corresponding to blank experiments and it can be satisfactorily modelled with the mathematical equation corresponding to two continuous stirred-tank reactors (CSTRs) in series. The curves in the presence of catalyst can be modelled with a simple mathematical equation that yields the values of the total number of sites active in the isotopic exchange and the apparent first order rate constant for the H2/D2 exchange process. The results so derived are in good agreement with those obtained from the analysis of the TPD experiments following the ITK runs. Although the results suggest a normal equilibrium isotope effect and an inverse kinetic isotope effect, the measured isotope effects are moderate in both cases and include possible contributions from the uncertainties in the calibration of the HD signal.