We are proposing 4 days of beamtime on GEM/Polaris to conduct the neutron powder diffraction experiments on PdRu alloy nanoparticles supported on CZ (CeO2-ZrO2) before and after the catalytic reactions at 400 °C with 3 different flow gases which are similar to actual exhaust gas of cars. PdRu alloy nanoparticles are expected to be high-performance and low-cost catalysts to remove CO and NOx in exhaust gas of cars. However, its endurance strongly depends the compositions of the gases (amount of CO for the stoichiometric reactions) and this mechanism must be clarified before practical use. The diffraction pattern and derived pair-distribution functions will provide direct information on the structural change caused by the reactions. The large difference between the neutron scattering cross sections of Pd and Ru and the high neutron intensity of GEM are keys in the present experiment.