For the catalytic reduction of nitrogen oxides with methane in oxygen rich exhaust gases zeolite catalysts are used. During a catalyst screening the beta-zeolite (BEA) which was modified with Indium has been chosen for kinetic measurements in a fixed bed reactor. Therefore zeolite pellets were prepared. The influence of the residence time, temperature and gas composition at the inlet of the reactor were investigated by experiments and simulations, An isothermic process model was developed which is based on a balance scheme.