Study Of Pt-Ir Three-way Catalysts

With the increase of vehicles, vehicle exhaust pollution is becoming more and more serious today. One of the most effective measures to control the vehicle exhaust emission is installing purifiers on vehicles. The three-way catalyst(TWC) is a comprehensive technology in cleanning the exhaust. Till now, the main active components of the three-way catalysts(TWCs) are Pt, Rh and Pd. In this paper, two kinds of commercial three-way catalysts(TWCs) of foreign companies installed in vehicles were analyzed meticulously. The washcoat compositions of the catalysts were analysed by X-ray fluorescence(XRF). And their physical and chemical properties were characterized by X-ray diffraction(XRD), Transmission electron microscope(TEM), X-ray photoelectron spectroscope(XPS), Temperature programmed reduction(TPR) methods. The results showed that the Pd and Rh metals of the three-way catalysts manufactured by company A were loaded on γ-A12O3 and Ce0.35Zr0.65O2 carrier materials, respectively. However, for the other catalyst produced by company B, the Pd and Rh components were loaded on the mixture carriers of Ce0.35Zr0.65O2 and γ-A12O3. The Pd/Rh system is the main active component of the catalysts of the two companies. In the market, Pd-Rh and Pt-Rh are the precious metal component of three-way catalysts, but the price of Pd continues to rise.. The amount of 40% of Pt was used in three way catalyst on cleanning vehicle exhaust. Considering the price of Ir is cheaper than Pt and Pd, we prepared the Pt-Ir bimetallic catalyst to reduce the amount of Pt and the cost of three-way catalyst.In this paper, bimetallic Pt-Ir nanoparticles in different structures(alloy and coreshell structure) were prepared by using the solution chemical reduction to decrease the particle size. Using H2PtCl6·6H2O and H2IrCl6·6H2O as metal precursor, CTAB as protective agent, Na BH4 as reducing agent, Pt-Ir nanoparticles in alloy structure were prepared by co-reduction process. The water and ethylene glycol were used as the solvents, respectively. The regular morphology nanoparticles in alloy structure were prepared by using ethylene glycol as the solvent. The bimetallic Ir@Pt nanoparticles in core-shell structure were prepared by using successive reduction method. Under the premise of H2IrCl6·6H2O was metal precursors, Ir nanoparticles were prepared in different consumption of protective agent CTAB, reducing agent NaBH4, and solvent. The Ir nanoparticles was dispersed in the water and added amount of H2PtCl6 and AA solution was added. The Ir@Pt core-shell particles were prepared from Ir cores with different thickness of Pt shell. The sizes of Ir@Pt NPs were 2.2, 2.8, 4.5 and 6.5 nm while the Ir and Pt molar ratio were 2/1, 1/1, 1/2 and 1/4, resulting in different thickness of Pt shell.The catalysts were prepared by nanoparticles loaded onto the γ-A12O3 and SiO2 carriers respectively. The performance of the catalysts were investigated. It showed that the Ir@Pt/SiO2 catalysts with the Ir and Pt molar ratio of 1/1 exhibited better three-way catalytic activity than the Pt/SiO2 catalyst in reducing the NO content, and the air-to-fuel(λ) work window was widened. More studies showed the H2 O and SO2 rarely affect the activity of the Ir@Pt(1/1)/SiO2 catalyst, while the nitrogen selectivity was increased.