Effects of CeO₂ Addition on Improved NO Oxidation Activities of Pt/SiO₂-Al₂O₃ Diesel Oxidation Catalysts

Abstract

The catalytic activities for NO oxidation achieved by different amounts of CeO2-modified Pt/SiO2-Al2O3 catalysts Pt/SiO2-Al2O3-wCeO2 (the mass fraction w being 0%, 5%, 10%, 15%, 30%), prepared using step-wise impregnation, were investigated in the presence and absence of CO and C3H6. The results showed that the NO oxidation activity could be efficiently improved by modification of CeO2, No.6 HUANG Yu-Fen et al.: Effects of CeO 2 Addition on Improved NO Oxidation Activities of Pt/SiO 2-Al 2 O 3 DOCs 1243 wherein the 15%-CeO2-modified catalyst exhibited the maximum NO conversion of 61% even in the presence of CO and C3H6, which were proved to inhibit NO2 formation in this study. A series of characterization methods were performed over the as-prepared samples to correlate their surface and structural characteristics with their enhanced NO oxidation activities. CO-chemisorption illustrated that appropriate CeO2-loading was effective for enhancing Pt dispersion, thus enhancing Pt surface-to-volume ratio, confirmed by transmission electron microscope (TEM) images. X-Ray Diffraction (XRD) further suggested that ceria addition could suppress the growth of the Pt crystal, resulting in higher surface Pt atomic ratio. Further, H2 temperature-programmed reduction (H2-TPR), together with TEM results, implied that the presence of ceria could enhance the interaction between metal and supports, thus facilitating reducibility of both active platinum and ceria. Hence, this study displays that ceria could act as a dispersion promoter and a reducibility booster, both of which are beneficial to NO oxidation activity. The improved NO oxidation activity is significant for the efficient purification of diesel integrated catalytic system.

New Insights into Excellent Catalytic Performance of the Ce-Modified Catalyst for NO Oxidation

“…7 The peak II located at 174 °C was ascribed to the reduction of Pt oxides weakly interacting with alumina surface. 15 Besides, the peak III at 270 °C belonged to the reduction of bulk PtO x such as PtO and PtO 2 species. 7 For Pt/CeSA and Pt/CeO 2 catalysts, the area of all reduction peaks was larger than that of Pt/SA, indicating that not only Pt oxides but also the surface oxygen of ceria were reduced.…”

“…This result was consistent with TEM measurement in our previous work, which showed that the mean sizes of Pt particles in Pt/SA and Pt/15CeSA catalysts were 26.5 and 6.3 nm, respectively. 15 However, no diffraction peaks of Pt were observed in XRD patterns for Pt/ CeO 2 , demonstrating that the dispersion of Pt over Pt/CeO 2 was higher than that over Pt/15CeSA. Nevertheless, shown by the results of the activity test, the catalytic performance of Pt/ CeO 2 was greatly lower than that of Pt/15CeSA, because the catalytic activity of the catalyst was simultaneously influenced by multifarious factors.…”

“…We prepared SiO 2 −Al 2 O 3 materials with a loading content (mass fraction) of 15 wt % Ce by the incipient wet-impregnation method according to a previously reported method. 15 Meanwhile, pure CeO 2 supports were obtained by calcining Ce(NO 3 ) 3 •6H 2 O at 550 °C for 3 h in flowing air. Then 1 wt % Pt was loaded respectively on SiO 2 −Al 2 O 3 , Ce-modified SiO 2 −Al 2 O 3 , and CeO 2 supports by the same impregnation method.…”

“…5 In addition to this, we reported that CeO 2 -modified Pt/SiO 2 −Al 2 O 3 catalysts prepared by step-impregnation method had high catalytic performance, and relevant experiments revealed that the dispersion of Pt particles increased after the addition of ceria. 15 It is noteworthy that the influences of CeO 2 -based materials on the catalytic performance are as follows: First, metal particles maintain a high dispersion on CeO 2 support even after high temperature calcination, which corresponds to the strong Pt−support interaction. 16 presented outstanding stability resulting from anchoring Pt on CeO 2 .…”

“…39 Besides, the interface of noble metal oxide could be optimized by designing a core−shell structure to enhance activity. 15 Therefore, in this work, various characterization methods were carried out, including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), N 2 adsorption−desorption, H 2 temperature-programmed reduction (H 2 -TPR), highresolution transmission electron microscopy (HRTEM), Raman spectroscopy, and Fourier transform infrared spectrometry (FTIR), to further explore the effect of metal oxide interface and active oxygen species on catalytic performance.…”