Studies On Selective Catalytic Reduction Of Nitrogen Oxides Over Cerium Based Catalyst

Selective catalytic reduction of nitrogen oxide with ammonia asreductant (NH3-SCR) is really an important exhaust gas after-treatmenttechnology of diesel to meet the increasingly strict exhaust gas regulations.It’s necessary to develop catalytic with great low temperature performanceand broad temperature window for diesel applying. Among a series of Ti-Ce-W mixed oxide catalysts prepared by SHS (self-propagating high-temperature synthesis) method, TiCe0.2W0.2Oxcatalyst (Ti/Ce/W molar ratiois1:0.2:0.2) shows100%NO removal efficiency and100%N2selectivitybetween200-420℃.The catalyst also has good performance when SO2wasadded into the gas mixture or under high GHSV(gas hourly space velocity).NO removal rate only decreases to80%in24h when SO2exits in250℃andrecovers to initial value quickly upon removing SO2. The performance ofTiC0.2W0.2Oxwas also tested under high GHSV of11400h-1and still showsabove80%NO removal efficiency and100%N2selectivity between200-450℃. In addition, the BET analysis indicates that catalyst activity isdirectly related to the specific surface area. The XRD tests shows that all theactive components of these catalysts are highly dispersed on the surface ofanatase TiO2as amorphous state. The SEM photographs reveal that there isabundant pore structure in microscopic surface of this series of cerium-basedcatalysts. Besides, coating process of depositing the catalyst directly on cordieritecarrier with SHS method was studied. The coating catalyst shows95%NOremoval efficiency and100%N2selectivity between250-450℃.The mechanisms of SCR process was investigated with in situ DRIFTStechnology. It was found that NH+4species stemming from ammoniaadsorbed on Br nsted acid sites play leading role in SCR process and bothgaseous phase NO and bridge nitrate participate in the process. So both Eley-Rideal and Langmuir-Hinshelwood reaction process takes placet in SCRprocess over TiCe0.2W0.2Ox.