Surfactant-controlled synthesis of Pd/Ce0.6Zr0.4O2 catalyst for NO reduction by CO with excess oxygen

For the first time, this work reports a surfactant-controlled synthetic method to obtain a nanophase of mesoporous ceria-zirconia solid solution containing cationic defects in the crystalline structure. The incorporation of a cationic surfactant (myristyltrimethylammonium bromide) into the ceria-zirconia solid network not only controlled the pore diameter distribution but also induced creation of the lattice defect. Ceria-zirconia solid solution showed crystal microstrain and structural distortion that varied with the calcination temperature. Compared to pure ceria, the addition of zirconium to the ceria promoted the bulk oxygen reducibility and enhanced the thermal stability of the solid. Hydrogen could be stored into or released from the PdO/Ce0.6Zr0.4O2 catalyst during the TPR procedure, which is associated to the formation/decomposition of a PdHx phase, due to the hydrogen dissociation catalyzed by metallic Pd. At cool start of reaction, NO reduction by CO with excess oxygen over the Pd/Ce0.6Zr0.4O2 catalyst showed selectivity around 100% to N2. A competition between NO reduction by CO and CO oxidation by O2 was observed: at reaction temperatures below 200 deg. C, NO inhibited CO oxidation activity; however, at reaction temperatures above 200 deg. C, high activity of CO oxidation resulted in an inhibition effect on NO reduction