Effect of pH in a sol-gel synthesis on the physicochemical properties of Pd-alumina three-way catalyst

The effect of pH during sol-gel synthesis on the structural and physicochemical properties of a Pd-Al₂O₃ three-way catalyst (TWC) prepared by the sol-gel method was investigated by using BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and solid state ²⁷Al MAS NMR. The Pd-Al₂O₃ catalyst prepared at pH=10 (Pd-Al₂O₃-B) showed a high activity in three-way catalytic reaction, a high dispersion of Pd, and large surface area and pore volume. A basic condition (pH=10) in the sol-gel process was essential for the preparation of highly dispersed palladium clusters on alumina gel. The formation of highly stable palladium oxide species in Pd-Al₂O₃-B that were not completely reduced at 423 K was ascribed to the strong interaction between Pd and oxygen in alumina texture, resulting in the formation of -Al-O-Pd bond. (C) 2000 Elsevier Science B.V.