The Preparation And Characterization Of Precious Metal Catalyst On Diesel Oxidation Converter (DOC)

Diesel vehicles has become more and more popular in the worldwide for its good fuel economy, excellent power performance and lower carbon dioxide emissions. However, diesel engines run in the condition of lean-burn, and would exhaust high concentration oxygen. Therefore, the traditional three-way catalysts are not able to used in adatement diesel exhaust. Among the variety of techniques, diesel oxidation converter (DOC) technology is one of most important technology to eliminate the CO and HC pollution. Diesel oxidation converter(DOC) can significantly reduce the emissions of CO, HC, SOF (soluble organic matter), and also have some effect on the removal of NO. Due to the low temperature of the exhaust of diesel exhaust, high sulfur content, which requires the catalyst has good catalytic properties and sulfur resistance.Firstly, the loading process of the DOC catalyst noble metal, by dipping, rotary evaporation and combined process, were compared of the activity of the catalyst. The result showed that the Pt/CeO2-XJ catalyst activity obtained by combined process reached the maximum, which of CO and C3H6 light-off temperature (T50) were reduced to 190℃ and 180℃, Through impregnated filtrate analysis, ultrasonic immersion method alone will result in the loss of 34% of Pt, and rotary evaporation process did not produce a filtrate, to avoid wastage of precious metals. The CO-TPD analysis showed that the ultrasonic dipping can enhance the degree of dispersion of Pt on the CeO2 surface of the carrier, the degree of its dispersion value is equivalent to 1.2 times of the rotary evaporation method.Secondly, the paper examines the activity of the catalyst variation of the different active ingredient with the carrier. Precious metals are the main factors that control the activity of the catalyst changes, the carrier is a relatively small impact on the catalytic activity. The amount of the noble metal load strongly influence the catalytic activity of the catalyst, when the load increases from 0.5% to 4%, the catalyst from the combustion temperature dropped about 100℃. The type of precious metals is a relatively small impact on the catalytic activity of Pd catalyst for the conversion of CO and C3H6 slightly higher than that of Pt catalyst. Pt-Pd noble metal catalyst can improve the conversion rate of CO and C3H6 wherein Pt0.2Pd0.8/CeO2 catalyst showed the highest activity. The carrier of the catalyst of the different core-shell structure, and its activity showed some differences, wherein CeO2 as the core of the catalyst exhibits higher CO and C3H6 conversion activity. Incorporation of rare earth Y in the shell obtained ZrO2+YO2@ CeO2 catalyst, it’s activity is highest.Finally, the DOC catalyst poisoning and sulfur resistance mechanism are studied. Poisoning of the catalyst is found by sulfate accumulated on the catalyst surface, thereby covering caused by the active site Has the best low temperature (<180℃) reductive Pt0.8Pd0.2/Ce02 catalyst showed better anti-sulfur performance. The high proportion of Pt/Pd catalyst having more surface active oxygen, the relative values have a good relation with the catalyst sulfur resistance when under the condition of sulfate poisoning. The amount of noble metal catalyst having a high surface active oxygen which benefite catalytic reactions.