The highly active catalysts of nanometric CeO2-supported cobalt oxides for soot combustion

摘要

Nanometric CeO2-supported cobalt oxide materials with variable Co/Ce atomic ratios were prepared by the method of ultrasonic-assisted incipient-wetness impregnation. The catalytic behaviors of a series of CoO_xmCeO2 catalysts have been studied for soot combustion. XRD, XPS, Raman, UV-vis DRS and FT-IR spectroscopy characterization results indicated that CoO or cobalt-cerium solid solutions were formed in the samples with the low Co loading amount, while Co3O4 was formed in the samples with high Co loading amount. CoO_xmCeO2 catalysts can further promote soot combustion in contrast to nanometric CeO2. This improvement is related to the increase in the redox properties of the catalysts brought about by loading cobalt oxide on nanometric CeO2. The TPR experiment results under hydrogen atmosphere indicated that the presence of Co decreases the reduction temperature of catalyst from 555 °C (nanometric CeO2) to 286 °C (Co_(20)mCeO2). On the other hand, attributing to nanopartide effect and NO2 formation, Co_mmCeO2 oxide catalysts prepared in this study have very high activity for soot combustion. The best catalytic activity was obtained over Co_(20)mCeO2 catalyst that T_(10), T_(50), T_(90) were 286 °C, 368 °C, 418 °C, respectively, and S_(CO2)~m was 98.8%. Compared with the blank case (i.e., without catalyst) for soot combustion, T_(50) decreased by more than 200 °C and S_(CO2)~m increased by 40% point. And this catalytic activity for the combustion of soot particle is as good as supported Pt catalysts, which is the best catalyst system so far reported for soot combustion under loose contact conditions. This temperature of soot combustion can ensure immediate activation of the catalyst on the filter under the conditions of diesel engine emissions.