Study On The Supported Noble Metal Free Nox Storage And Reduction Catalyst CuO/K₂CO₃/TiO₂

Conventional NO_x storage and reduction?NSR? catalysts often employ noble metals as active phases, increasing the catalyst cost. In this work, a series of TiO₂ supported base metal Cu-based NSR catalysts were prepared, using copper oxides to replace the noble metal Pt totally. Their performance for NSR was evaluated; their structures and NSR mechanisms were also investigated carefully.A series of non-platinic lean NO_x trap catalyst Cu O-K2CO3/TiO₂ with different Cu loadings were prepared by sequential impregnation, which exhibited rather good performance for lean NO_x storage and reduction. The catalyst containing 8% CuO displayed not only the largest NO_x storage capacity of 1.559 mmol/g·cat at lean condition but also the highest NO_x reduction percentage of 99% in cyclic lean/rich atmospheres; besides, zero selectivity of NO_x to N2 O was found during NO_x reduction over this catalyst. Multiple techniques including XRD, HR-TEM, CO₂-TPD, EXAFS, H2-TPR and in-situ DRIFTS were employed for catalyst characterization. The results conformably indicated that the highly dispersed CuO was the main active phase for NO to NO₂ oxidation and NO_x to N2 reduction. Strong interaction between K2CO3 and CuO was revealed, which favored the adsorption of NO_x. The appearance of negative bands around 1436 and 1563 cm-1 corresponding to –CO₂ asymmetric stretch in bicarbonates and-C=O stretch in bidentate carbonates suggested the involvement of carbonates in NO_x storage. After used for 15 cycles of NO_x storage and reduction at alternative lean/rich atmospheres, the CuO species in the catalysts changed very little, showing high catalytic stability. Based upon the results of in-situ DRIFTS and other characterizations, a model describing NO_x storage routes and the distribution of CuO and K2CO3 species was proposed.A series of CuO /TiO₂ catalysts precursor were calcined at different temperatures?350, 450, 550, 650 and 750 oC?. Their catalytic performance for NO_x storage and reduction was evaluated. Multiple techniques including BET, XRD, HR-TEM, H2-TPR and in-situ DRIFTS were employed for catalyst characterization. The results conformably indicated that in the catalysts calcined at different temperatures, the main copper species were CuO. The catalyst calcined at 450 oC, displayed not only the largest NO_x storage capacity of 1.808 mmol/g at lean condition but also the highest NO_x reduction percentage of 99.8% in cyclic lean/rich atmospheres; moreover, after used for 22 cycles of NO_x storage and reduction at alternative lean/rich atmospheres, the catalytic activity changed very little, showing high catalytic stability. When the calcination temperature was increased to 750 oC, the specific surface areas of the catalysts declined evidently, which was unfavorable to the dispersion of K and CuO species, leading to the formation of more bulk K2CO3 and CuO species, as a result, the catalytic performance declined.