NO reduction by CO over gold based on ceria, doped by rare earth metals

The reduction of NO by CO over gold catalysts supported on ceria doped by rare earth metals (Y, La, Sm and Gd) was studied. The mixed oxide supports, containing 10 wt% of the dopant, were prepared by co-precipitation and then 2 wt% gold was loaded by deposition–precipitation method. Gold catalysts, supported on lanthanides doped ceria showed a high activity and stability. The conversions both of NO and CO at 250 °C were close to 100% using Sm, La or Gd as dopants. Below 250 °C the Au catalyst on Sm doped ceria exhibited a little higher activity. The lowest catalytic activity was observed using Y as a modifier. The lattice parameter a of ceria and the average size of ceria crystallites were evaluated by XRD. The defective structure of ceria, including oxygen vacancies, caused by the introduction of Me3+ dopant, was estimated by Raman spectroscopy data. The redox behaviour of fresh gold samples as well as after their reoxidation at 220 °C was established by TPR technique. The low temperature reducibility of the reoxidized gold catalysts supported on doped CeO2 showed a good correlation with the catalytic properties. It was established that the addition of water to the gas feed improved the catalysts’ selectivity to N2.