Control of the size of Pd nanoparticles by pre-precipitation for anti-sintering three-way catalysts

Restricting the Pd sintering during aging is crucial for the three-way catalysts (TWCs). Herein, following the Ostwald-ripening mechanism, Pd sintering in the commercial TWCs was greatly suppressed by increasing the initial size of the Pd NPs, through a pre-precipitation method. Our catalysts showed initially larger Pd NPs after calcination at 550 ℃ (3.3 vs. 1.8 nm) while smaller ones after aging at 1000 ℃ (35.0 vs. 70.1 nm) than the counterpart made by impregnation. The optimal aged catalyst showed much better performance than the counterpart: T50 was decreased by 40, 13 and 14 ℃ for CO, NO and C3H6 over the powder samples, and a higher oxygen storage capacity was observed (248 > 178 mg/L) over the monolith converters. The decreased size of the Pd NPs and the improved reducibility as well as the more concentrated adsorbed oxygen species for the optimal aged catalyst were responsible for the improved performance.