Synergistic effect of vanadium and zirconium oxides in the Pd-only three-way catalysts synthesized by sol–gel method Original Research Article

Various Pd-only three-way catalysts containing vanadium and zirconium oxides were prepared by the sol–gel method and investigated with XRD, XPS, 51V NMR, 27Al MAS NMR, Raman spectrometry, BET analysis and three-way catalytic reaction. In the Pd-only three-way catalyst prepared by the sol–gel method, vanadium and zirconium were good promoters to improve the resistance against SO2 poisoning and to enhance the thermal stability, respectively. Excellent properties such as high activity at low-temperature, improved durability against SO2 gas and enhanced thermal stability at high temperature were found only on the catalyst containing the specific mole ratio of V/Zr=0.36, Pd (1 wt.%)-V (2 wt.%)-Zr (10 wt.%)-Al2O3 catalyst, which was ascribed to some synergism between V and Zr like a formation of V–O–Zr bonds. Because of the synergism on the catalyst, the advantageous textural forms such as highly dispersed Pd clusters, Zr–O–X bond (X=V and Al), γ-Al2O3 and amorphous tetrahedrally coordinated (M–O)3VO were not deteriorated significantly to the disadvantageous textural forms such as large crystalline Pd clusters, monoclinic ZrO2, κ-Al2O3 and θ-Al2O3, and microcrystalline octahedrally coordinated V2O5 species, in spite of thermal aging at 1000°C.