Simultaneous Removal Of Soot And NO_x With Three Noble Metal Catalysts In The Presence Of Rich Oxygen And SO₂as Well As H₂O

Concern on the hazards to the environment and human health caused by dieselexhaust is growing. Scholars have made a lot of research on the catalytic removal ofcarbon particles and NO_xexisted in emissions currently. But most of the studies havefocused on catalytic combustion of carbon particles or nitrogen reduction withexogenous reducing agent such as NH₃, H₂, hydrocarbons, alcohols, etc. Some otherresearches have made use of carbon particles existed in diesel emissions to realize theabatement of nitrogen oxides, but the catalysts are not effective for NO_xreduction onaccount of poor resistance of water and sulfur. Noble metals have better performancethan peroskite and alkali metals for the resistance of water and sulfur, and haveexcellent N₂selectivity. Our team has already finished the study of catalytic removal ofcarbon particles and nitrogen oxides simultaneously with Ru, Ir, Pt and Rh catalysts.Now the main subject of this research is to take the activity of Pd, Au and Ag catalizingremoval of carbon particles and nitrogen oxides simultaneously into account. Thecontents of our research are as follows:（1） We have investigated the activity of Pd, Au and Ag catalizing removal ofcarbon particles and nitrogen oxides simultaneously under two conditions: rich oxygenonly and SO₂and H₂O coexisted. The results confirm that carbon particles and nitricoxide are removed simultaneously in the role of the three noble metal catalysts. Thesimultaneous removal path is: NO is oxidized on catalyst to NO₂, then NO₂oxidizessoot and is reduced simultaneously.（2） And we also have investigated the influence of calcination temperature,calcination atmosphere, carrier and load amount to the catalytic activity. The preperationconditions have a great effect on the catalytic activity through affecting the grain size ofcatalysts, valence state of the active metal, the interaction between the active metal andthe carrier, etc. The best preperation conditions of the three precious metal catalysts areshowed as follows: the calcination temperature of Pd catalyst is800oC, the calcinationatmosphere is1.5%H₂/N₂, the load carrier is ZrO₂, the load amount is5%. Thecalcination temperature of Ag catalyst is850oC, the calcination atmosphere is N₂, theload carrier is ZrO₂, the load amount is5%. The calcination temperature of Au catalystis400oC, the calcination atmosphere is1.5%H₂/N₂, the load carrier is ZrO₂, the loadamount is1%.（3） At last we have investigated the influence of SO₂, H₂O on activities of the threecatalysts. SO₂has inhibited the oxidation of carbon particles, but can pormote theactivity of Pd/ZrO₂catalizing nitric oxide abatement. Especially when the volume concentration of SO₂is1ppm, a remarkable promotion has been ovserved on Pd/ZrO₂and Ag/ZrO₂catalysts. The existence of water vapor performs some promotion on theoxidation of carbon particles and NO abatement over Pd/ZrO₂. The coexistence of SO₂and H₂O has a synergic role on the catalytic activity.