Expansion the Temperature Window of Catalytic Action via “Lattice Tuning” of Ceria
The interaction of palladium and ceria with formation of ionic palladium species is considered to be a main reason of high activity of Pd/CeO2 catalysts in CO and methane oxidation at low-temperatures [1-3]. The formation of the solid solution PdxCe1-xO2-x-δ in Pd/CeO2 catalysts have been proposed in literature, and the near-square-planar local environment of Pd2+ ion in ceria lattice was established experimentally in our work . The bulk Pd2+ ions, serving as a dopants, increase the O2- ions non-stoichiometry in parent ceria phase and decrease the size of ceria particles which results in thermostability enhancement . Nickel which is analog of palladium is able to similar interaction with a ceria lattice with formation of the bulk NixCe1-xO2-x-δ solid solutions. The same near-square-planar environment of Ni2+ in ceria was demonstrated using resonance Raman spectroscopy. Ni2+ incorporation in ceria lattice leads to it contraction in contrast with it expansion while Pd2+ is incorporated in ceria. We have shown that tuning of lattice period of ceria is possible via variation of Pd2+/Ni2+ ratio which results in substantial enhancement of the stability of such doped ceria to sintering. Obtained (PdNi)xCe1-xO2-x-δ catalyst show unique wide window of catalytic action: high activity at below-ambient temperatures (for CO) and below 300oC (for methane) and stability up to 900oC.