Preparation And Performance Of Monolithic Pd-only Three-way Catalysts For Automobile Exhaust Control

Catalytic converters are widely used to reduce the amounts of nitrogen oxides, carbon monoxide and unburned hydrocarbons in automotive emissions. During vehicle use, the converter is exposed to heat. As a result, catalyst activity deteriorates. In recent years, the problem has been exacerbated by the trend to install catalytic converters closer to the engine, which ensures immediate activation of the catalyst on engine start-up, but also places demanding requirements on the catalyst's heat resistance.In this paper, the aim is to develop TWC catalysts with high catalytic performance and good thermal stability. Great efforts were taken to improve the Pd-only TWC catalyst performance at high temperature by adjustment of preparation method and surfactant addition. After comparing with the performances of catalysts prepared by several different methods, the best preparation method was selected and then adding surfactants in the preparation of catalyst to improve the thermal stability of the catalyst. Thermogravimetric (TG), X-ray diffraction (XRD), low-temperature N2 adsorption, X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H2-TPR) were used to investigate the effects of raw-materials, preparation method and adding surfactants on the performance and heat resistance of the Pd-only TWC catalyst. The results show that, the heat resistance of catalyst prepared by one-step method is superior to that prepared by equal volume impregnation method and rotary evaporation method; the presence of surfactants in preparing catalyst can improve the performance of the catalysts by the interaction between surfactants and active metal mainly; the amount of adding surfactants (Tween-80, Span-20, PEG-200) should be appropriate in order to promote catalytic performance of the Pd-only TWC catalyst.