A new quantitative approach to in situ experiments is proposed based on consistent combination of modeling of the relevant processes in the catalyst pellet with realization of the multi-spectroscopic experiment under dynamic regimes. Using well defined Co- and Fe-FER samples the approach is illustrated by three case studies showing potential of the approach for detail analysis of the processes over metallo-zeolites, i.e. adsorption of NH3 on CoNa-FER, and reactions of selective catalytic reduction of NO by NH3, and N2O decomposition over Fe-FER. Combination of simultaneous in situ FTIR and UV-Vis spectroscopies under transient conditions and a single-pellet reactor model of the spectroscopic cell are used for obtaining some quantitative information on the transport, adsorption/desorption phenomena, and surface species transformation over transition metal ion/zeolite system under such conditions. (c) 2006 Elsevier B.V. All rights reserved.