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

摘要

The 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/CeO2 catalysts. It is found that the reducing ability of H2 is more predominant than that of CO and C3H6 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, H2 regenerated Ba storage sites more effectively than did CO and C3H6, and Ba(NO3)2 could be easier reduced than Ce(NO3)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 C3H6 was due to its lowest activation ability by the catalysts. Furthermore, water addition had a positive effect on CO reduction ability at 200 ℃ but little influence at elevated temperatures. It was assumed that H2O improved the low temperature NO_x reduction process by alleviating CO poisoning of Pt.