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

Abstract

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 SO 2 poisoning and to enhance the thermal stability, respectively. Excellent properties such as high activity at low-temperature, improved durability against SO 2 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.%)-Al 2O 3 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-Al 2O 3 and amorphous tetrahedrally coordinated (M–O) 3VO were not deteriorated significantly to the disadvantageous textural forms such as large crystalline Pd clusters, monoclinic ZrO 2, κ-Al 2O 3 and θ-Al 2O 3, and microcrystalline octahedrally coordinated V 2O 5 species, in spite of thermal aging at 1000°C.