Effects of temperature and reductant type on the process of NOx storage reduction over Pt/Ba/CeO2 catalysts

Abstract

a b s t r a c tThe influences of temperature and reductant type on NO x storage and reduction behavior were studied by transient lean/rich cycles and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments over Pt/Ba/CeO 2 catalysts. It is found that the reducing ability of H 2 is more predominant than that of CO and C 3 H 6 especially at low temperatures. DRIFTS results showed that NO x can be stored as nitrates on both Ba and Ce sites by replacing carbonates species during the lean phase. During the rich phase, however, H 2 regenerated Ba storage sites more effectively than did CO and C 3 H 6 , and Ba(NO 3 ) 2 could be easier reduced than Ce(NO 3 ) 4 . The relatively low reduction performance of CO was attributed to Pt sites being poisoned by CO, which affected low temperature performance, and by carbonates formation, which affected high temperature conversions. The least reactivity of C 3 H 6 was due to its lowest activation ability by the catalysts. Furthermore, water addition had a positive effect on CO reduction ability at 200• C but little influence at elevated temperatures. It was assumed that H 2 O improved the low temperature NO x reduction process by alleviating CO poisoning of Pt.

Pt/Ce Pr1−O2 (x= 1 or 0.9) NO storage–reduction (NSR) catalysts

“…Ceria can act as a support material and is particularly effective at stabilizing high Pt dispersions [3], in addition to BaO [4]. Moreover, ceria is able to store NOx at low to moderate temperatures [5][6][7][8][9][10], thereby improving NSR NOx storage capacity. This makes ceria-containing catalysts particularly attractive for relatively low temperature applications, given that BaObased formulations typically perform poorly at temperatures below 250ºC [9].…”

Synergistic catalysis effect of Mn-promoted BaAl2O4 catalysts on catalytic performance for soot combustion

“…With increasing temperature, the band at 1228cm -1 gradually decreased, while the bands at 1535 and 1345cm -1 increased, and bidentate nitrite at 1265cm -1 emerged at 300°C [6]. Additionally, the bands at 1733, 944cm -1 ascribed to bulk nitrate, 1400cm -1 assigned to ionic nitrate, and 1037cm -1 due to monodentate nitrate showed up after 200°C [19,20]. This demonstrates the good performance of NOx storage owning to BA.…”

“…Linear baric nitrite at 1223cm -1 was identified as the main adsorbed species over B 0.2 M 0.8 A at 150°C in Fig.4c while minor bidentate nitrate on the Ba site at 1304cm -1 and bidentate nitrate on the Ba and Mn sites at 1537cm -1 were also formed [19]. As temperature rose, the adsorbed nitrite gradually transformed into bidentate nitrate at 1304cm -1 and ionic nitrate at 1398cm -1 , accompanied with some relatively weak species such as bulk nitrate at 1728, 974 and 890cm -1 , ionic nitrate at 1125cm -1 , and monodentate nitrate at 1035cm -1 [19,20].…”

“…As temperature rose, the adsorbed nitrite gradually transformed into bidentate nitrate at 1304cm -1 and ionic nitrate at 1398cm -1 , accompanied with some relatively weak species such as bulk nitrate at 1728, 974 and 890cm -1 , ionic nitrate at 1125cm -1 , and monodentate nitrate at 1035cm -1 [19,20]. All the nitrites had turned into nitrate species at 300°C, implying that the co-existence of Ba and Mn resulted in a more facile formation of nitrate species from nitrites.…”

Application and Improvement of NOx Storage and Reduction Technology to Meet Real Driving Emissions

“…In the early stage of development, the key function of NSR was considered to be the NO x storage function to reduce large amount of NO x , therefore, the desulfation performance and technologies to suppress PGM sintering were the main focus points. However, following the detailed clarification of the NO x reduction reaction under a reducing atmosphere [3,4], the research on NSR technology evolved into finding new ways to make additional reductants for further NO x purification. These are made from stored NO x and fuel based reductants, as represented by p-SCR and DiAir (Fig.…”