Time resolved X-ray Powder Diffraction on a THree Way Catalyst at the GILDA beamline

Time resolved X-ray diffraction experiments carried out at the beamline BM08-GILDA of ESRF allowed to study the structural modifications taking place in a Pt/ceria-zirconia catalyst while the CO oxidation reaction was going on. The capillary tube in which the sample is stored acts effectively as a chemical microreactor that ensures homogeneity of the sample treatments and minimization of diffusion effects. During the flowing of the reactant CO/He mixture, the investigated catalyst undergoes a fast Ce(IV)-Ce(III) partial reduction, involving the release of one oxygen every two reduced Ce cations. Due to the larger ionic radius of Ce(III), the structural modification produces an increase of the lattice constant of the ceria-zirconia mixed oxide that is monitored by the translating imaging plate device implemented at GILDA. The CO2 resulting from the oxidation of the fluxed CO is monitored by a quadrupole mass spectrometer during the recording of the time resolved XRD pattern. The combined chemical and structural information allowed to show that the CO2 yield is nearly constant until the catalytic system can provide oxygen for the reaction, while the structural rearrangement of the catalyst is delayed with respect to the switching on of the CO/He flux. Only after this induction time, during which CO2 is produced with no structural modification of the catalyst, a fast increase of the lattice constant takes place.