A theoretical model describing the diffusion and adsorption on bidisperse porous catalyst during a pulse experiment in a CSTR is presented. The analytical solution for dual and single resistance and their long-time solutions are developed. The first moment and the long-time solution of the response curve are used to estimate the parameters and thus avoiding the use of inaccurate higher moments. The effect of external surface adsorption is discussed. Response curves of propane are measured over HZSM-5 extrudates and previously reported curves of propane/butane on 5A pellets are analysed.