Peculiar kinetic properties of Cu-doped Pd/CexZr1-xO2 in water denitrification: Impact of Pd-Cu interaction vs structural properties of CexZr1-xO2

The performances of Pd-Cu bimetallic catalysts supported on ceria-zirconia were investigated in the reduction of nitrates by hydrogen. Particular attention was paid to the impact of structural heterogeneities in CexZr1-xO2 support materials on the catalytic properties of metallic Pd and Cu nano particles. The evaporation-induced self assembly preparation method afforded only the tetragonal structure. Co-precipitation led to a partial segregation of ceria and/or Ce-riched mixed oxide which orients differently the interactions between palladium and copper in agreement with XPS, ToF-SIMS, TEM and EDS analysis. Kinetic measurements in batch conditions led to a significant practical issue by obtaining high intrinsic rates at low Pd loading supported on Ce(x)Z(1-x)O(2) prepared by the self-assembly method. Ammonia as undesired by-product was usually detected. A sub-oxidation of ammonia to nitrites and nitrogen is observed with changes in the product distribution according to the preparation method of the support. Such changes have been discussed in terms intrinsic OSC properties of CexZr1-xO2 solid solution and the stability of Pd oxidation state in the course of the reaction. An optimal Pd-Cu interaction protecting Pd to extensive oxidation was observed on highly loaded Pd-Cu on CexZr1-xO2 prepared by the self assembly method suggesting that ensemble effects is able to monitor the structure sensitive production of ammonia.