In order to estimate the effect of diffusion during the selective catalytic reduction of nitrogen oxides (NOx) using propane on Co-ion-exchanged ZSM-5, the catalytic activity was measured for catalysts prepared from zeolites having various crystal sizes, The conversion of NOx and propane on a catalyst having a large crystal size (1.3μm) was much less than that on a catalyst having a smaller crystal size (0.10μm). Based upon the experimental data and various assumptions, the effective intracrystalline diffusion coefficient of NO during reaction in the presence of water vapor at 673K was estimated to be 6 x 10-15 to 9 x 10-15m2/s.

Estimation of the Intracrystalline Diffusion Coefficient of the Reactant during Selective Catalytic Reduction of Nitrogen Oxide by Propane on Co-ZSM-5. T.Tabata, H.Ohtsuka: Catalysis Letters, 1997, 48[1-2], 203-11