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.