The promotional effect of transition metals on the catalytic behavior of model Pd/Ce0.67Zr0.33O2 three-way catalyst

The behavior of Pd-only three-way catalysts supported on Ce0.67Zr0.33O2 mixed oxides (CZ) doped by transition metals (M = Cr, Mn, Fe, Co, Ni) (Pd/CZM) have been examined under stoichiometric CO + HC + NOx + O2 reaction conditions and characterized. Different characterization techniques reveal that transition metal ions have entered into the ceria lattice and atomically more homogeneous mixed oxides have formed on the order of CZFe ≈ CZCo > CZNi ≈ CZ > CZMn > CZCr. It is confirmed that the homogeneity of ternary solid solution clearly modifies the properties of the samples and the catalytic behavior of the corresponding catalysts. The introduction of transition metals especially doped Fe and Co improves the oxygen mobility and strongly enhances the oxygen storage capacity of CZ and the corresponding catalysts. Moreover, the addition of Fe and Co into CZ forms more homogeneous Ce–Zr–M–O ternary solid solution and simultaneously promotes the reduction of CZ and Pd noble metal, respectively. It is worthwhile to note that it has a strong interaction between transition metals and Pd noble metal. Furthermore, the presence of Fe and Co obviously decreases the light-off temperature and significantly enhances the catalytic activity of the catalysts. Simultaneously, the windows of activity over Pd/CZFe and Pd/CZCo catalysts become wider compared to that of Pd/CZ.