Evolution of Platinum Particles Dispersed on Zeolite upon Oxidation Catalysis and Ageing

Colloid impregnation and ion-exchange methods for the preparation of platinum-containing zeolites offer two distinct types of catalysts. The former leads to the stabilization of platinum nanoparticles on the outer surface of the zeolite, while the latter introduces Pt inside the micropores. The active sites are consequently confined in two different locations, as shown by two-dimensional pressure jump of adsorbed species infrared (2D-PJAS-IR) spectroscopy, and the activity in CO oxidation is found to be lower when Pt is in the pores. After ageing in air, both catalysts undergo a partial oxidative redispersion and Pt atoms are then found both on the external surface and in the pores. The presence of electron-deficient Pt species entrapped in the micropores is also evidenced by operando FTIR spectroscopy, through adsorbed dicarbonyl complexes, and chemometrics. Such particular species vanished at 475 K during the CO oxidation reaction and gave rise to metallic nanoparticles located in the pores.