Synthesis of neodymium modified CeO_2-ZrO_2-Al_2O_3 support materials and their application in Pd-only three-way catalysts

Ce-Zr-Al-Nd2O3 （CZAN） support materials were prepared by co-precipitation and impregnation methods, respectively. They were characterized by X-ray diffTaction （XRD）, low temperature nitrogen adsorption-desorption, oxygen pulsing technique, H2-temperamre programmed reduction （H2-TPR） and X-ray photoelectron spectroscopy （XPS）. The Pd-only three-way catalysts （Pd-TWC） supported on these materials were prepared by incipient wetness method and studied by activity tests. The results demonstrated that the CZAN supports obtained by the two methods showed better structural, textural and redox properties than the CZA without Nd2O3, and the addition of Nd203 improved the catalytic activity of TWC. Especially, the CZAN-i support prepared by impregnation method had better thermal stability and redox property. Meanwhile, the Pd/CZAN-i catalyst exhibited the best catalytic performance. XPS measurements indicated that the Nd-modified samples possessed more Ce3＋ and oxygen vacancies on the surface of samples, which led to a better redox property. The excellent redox property of support materials helped to improve the catalytic activity of TWC.

Realization approach of Pd-only three-way catalysts with high catalytic performance and thermal stability

Pd-only three-way catalyst （TWC）, Pd supported on washcoating （the mixture of alumina and Ce-Zr solid solution）/cordierite, was prepared and its catalytic performance and the operation window （2-value） at 450 ℃ were evaluated with the simulated automotive exhaust feed gas. Surfactants such as Tween-80 and Span-20 were added in the process of preparing the catalyst in order to improve the thermal stability and catalytic performance of Pd-only TWC. The fresh and aged catalysts at 1000 ℃ for 4 h were characterized by low-temperature N2 adsorption, XRD, XPS, and H2-TPR techniques. The results show that the presence of surfactants in the synthesis slurry could influence the physicochemical properties of the final Pd-only TWC. The FTS catalyst prepared with the mixed surfactant of Tween-80 and Span-20 exhibited excellent three-way catalytic performance. After being aged at 1000℃ for 4 h, the catalytic performances of Pd-only TWCs slightly decreased, but the FTS catalyst still demonstrated higher catalytic performance and better thermal stability compared with the Pd-only catalysts prepared with single surfactant or without any surfactant. And the FTS catalyst has a wider 2 value （operation window） than other catalysts, even after being aged at 1000℃.

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods,and characterized by X-ray powder diffraction （XRD）,N2 adsorption/desorption （Brunauer-Emmet-Teller method）,CO-chemisorption and X-ray photoelectron spectroscopy （XPS）.The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles.The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor.It was found that the effect of Co significantly depended on the preparation process.PdCo/La-Al2O3 catalyst prepared by co-impregnation exhibited better water-resistant performance.The results of XPS indicated that both CoAl2O4 and Co3O4 were present in the Pd catalysts modified by Co.For the catalyst prepared by sequential impregnation method,the ratio of CoAl2O4/Co3O4 was higher than that of the catalyst prepared by co-impregnation method.It could be concluded that Co3O4 played an important role in improving water-resistant performance.