Influences of Pd precursors and preparation method on the catalytic performances of Pd-only close-coupled catalysts

The properties and stabilities of Pd/Al2O3 close-coupled catalysts prepared with different methods and Pd precursors (PdCl2, Pd(NO3)2, and Pd(NH3)2(NO2)2) have been investigated, and characterized by N2 adsorption at low temperature, H2 chemical adsorption, X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM) and three-way catalytic activity testing. The results show that the catalyst prepared by a prefabricate method with Pd(NH3)2(NO2)2 precursor behaves higher catalytic activity and thermal stability for removing HC, CO and NOx, due to its higher BET surface area, higher Pd dispersion, smaller Pd particle sizes. And the prefabricate method can lead to stronger interaction between the Pd active species and the support by means of a strong electrostatic attraction and ion/ligand-exchange between the Pd complexes and the support surface, which restrict the remotion and sintering of Pd active particles at high temperature. Therefore, a prefabricate method is more suited to preparing close-coupled catalysts than a traditional impregnation method.