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Study of N 2 O Formation over Rh- and Pt-Based LNT Catalysts

机译：Rh和Pt基LNT催化剂上N 2 O形成的研究

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In this paper, mechanistic aspects involved in the formation of N 2 O over Pt-BaO/Al 2 O 3 and Rh-BaO/Al 2 O 3 model NO x Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by using H 2 and NH 3 as reductants. It was found that N 2 O formation involves the presence of gas-phase NO, since no N 2 O is observed upon the reduction of nitrates stored over both Pt- and Rh-BaO/Al 2 O 3 catalyst samples. In particular, N 2 O formation involves the coupling of undissociated NO molecules with N-adspecies formed upon NO dissociation onto reduced Platinum-Group-Metal (PGM) sites. Accordingly, N 2 O formation is observed at low temperatures, when PGM sites start to be reduced, and disappears at high temperatures where PGM sites are fully reduced and complete NO dissociation takes place. Besides, N 2 O formation is observed at lower temperatures with H 2 than with NH 3 in view of the higher reactivity of hydrogen in the reduction of the PGM sites and onto Pt-containing catalyst due to the higher reducibility of Pt vs. Rh.
机译：本文讨论了在Pt-BaO / Al 2 O 3和Rh-BaO / Al 2 O 3模型NOx储存还原（NSR）催化剂上形成N 2 O的机理。使用H 2和NH 3作为还原剂，研究了气相NO和储存的硝酸盐的反应性。已经发现N 2 O的形成涉及气相NO的存在，因为在Pt-和Rh-BaO / Al 2 O 3催化剂样品上储存的硝酸盐还原时都没有观察到N 2O。特别地，N 2 O的形成涉及未解离的NO分子与在NO解离时形成的N-种物质偶联到还原的铂族金属（PGM）位点上。因此，当PGM位点开始被还原时，在低温下观察到N 2 O的形成，而在PGM位点被完全还原且发生完全的NO离解的高温下，N 2 O的形成消失。此外，由于Pt相对于Rh的较高还原性，在PGM位点的还原中以及在含Pt的催化剂上氢具有较高的反应性，因此在H 2处比在NH 3处在较低的温度下观察到N 2 O形成。

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