摘要
Ce/BEA has great potential as a passive NO_(x)absorber(PNA)to reduce the NO_(x)emissions during the cold start phase especially in diesel engine for its high resistance to CO and suitable NO_(x)desorption temperature range.However,as a novel material,its physical and chemical properties still remain unknown.In this work,Ce/BEA was synthesized by ion-exchange method to identify the active species in NO_(x)adsorption,compared with aggregated Ce species in Ce/SiAlO_(x) prepared by impregnation method.X-ray diffraction(XRD),high resolution-transmission electron microscopy(HR-TEM)and aberration-corrected-scanning transmission electron microscopy(AC-STEM)were performed to confirm the isolated single atom formation of Ce species in Ce/BEA.UV-vis diffraction reflection spectra(DRS)and X-ray photoelectron spectroscopy(XPS)were conducted to find the difference of chemical environment between the isolated Ce species and aggregated ones.PNA performance evaluation and temperature programmed reduction of hydrogen(H_(2)-TPR)results show the high NO_(x)storage capacity and active oxygen species quantity in Ce/BEA.It is also found that the main NO_(x)adsorption species are Ce^(4+)-O^(∗)rather than Ce^(3+).NO_(x)-diffuse reflectance infrared Fourier transform spectroscopy(NO_(x)-DRIFTS)confirms that the bidentate nitrite species are the critical NO_(x)adsorption intermediates and the conception of NO_(x)adsorption and desorption processes is proposed.
基金
Project supported by the National Key R&D Program of China(2021YFB3503200)
the Innovative Research Groups of the National Natural Science Foundation of China(51921004)
Young Elite Scientists Sponsorship Program by CAST(2021QNRC001)
the Key R&D project of Shandong Province(2021CXGC010703,2022CXGC020311)。
