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

Various Pd-only three-way catalysts containing vanadium and zirconium oxide s were prepared by the sol-gel method and investigated with XRD, XPS, V-51 NMR, Al-27 MAS NMR, Raman spectrometry, BET analysis and three-way catalyti c reaction. In the Pd-only three-way catalyst prepared by the sol-gel metho d, vanadium and zirconium were good promoters to improve the resistance aga inst SO2 poisoning and to enhance the thermal stability, respectively. Exce llent properties such as high activity at low-temperature, improved durabil ity 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 h ighly dispersed Pd clusters, Zr-O-X bond (X=V and Al), gamma -Al2O3 and amo rphous tetrahedrally coordinated (M-O)(3)V=O were not deteriorated signific antly to the disadvantageous textural forms such as large crystalline Pd cl usters, monoclinic ZrO2, kappa -Al2O3 and theta -Al2O3, and microcrystallin e octahedrally coordinated V2O5 species, in spite of thermal aging at 1000 degreesC. (C) 2001 Elsevier Science B.V. All rights reserved.