Novel insights on the Pd speciation in Pd/SSZ-13 and on the role of HO in the Pd reduction by CO.

Pd speciation induced by the combined effect of CO and water on Pd/SSZ-13 samples prepared by both impregnation and ion exchange was examined by FT-IR spectroscopy of CO adsorbed at room temperature and at liquid nitrogen temperature on anhydrous and hydrated samples. Starting from the literature findings related to the CO reducing effect on Pd cations, the present work gives precise spectroscopic evidences on how water is necessary in this process not only for compensating with H the zeolite exchange sites set free by Pd reduction, but also for mobilizing isolated Pd/Pd cations and making possible the reduction reactions. The aggregation of some Pd sites, just formed by the reduction and mobilized by the hydration, gives rise to the formation of PdO particles.