The Study Of N₂O Formation Mechanism Using H₂as A Reductant In NSR Process

The N₂O formation mechanism was investigated over Pt-BaO/Al₂O₃modelcatalyst using H₂as a reductant.In the absence of H₂O, N₂O forms mainly at the initial phase of lean NOxtrapping; while in the presence of H₂O, N₂O appears mainly at the beginning of therich reduction phase. In the lean period, N₂O is formed by reacting the gaseous NO/O₂with the adsorbed NH3that is formed during the previous rich period. The N₂Oformation in the rich period is insignificant in the absence of H₂O but is greatlyenhanced by the presence of H₂O. The amount of N₂O formed is proportional to theH₂O level in the feed, and its formation is favored at low temperatures. Our FTIR datashow that H₂O enhances the rate of nitrite/nitrate reduction during the richregeneration, which increases the amount of released NOx, an oxygen source for N₂Oformation. Our temperature programmed experiments indicate that H₂O competeswith NH3for adsorption sites on Pt surface. This competitive adsorption may increasethe NH3desorption rate at low temperatures in the rich phase and make Pt surfacemore accessible to NO.In addition, this work also discussed the effect of the gas compositions of leanphase （NO/N₂, NO/O₂/N₂, NO₂/N₂） on the N₂O formation in rich phase. The amountof N₂O formation in rich phase is related to the gas compositions in lean phase, whichdecreases in the order of NO₂/N₂> NO/O₂/N₂> NO/N₂.