Raman spectroscopic studies on the sulfation of cerium oxide

Twu, Jen; Chuang, Chung Jen; Chang, Kuang I; Yang, Ching Hsiang; Chen, Kuei‐Hsien

doi:10.1016/s0926-3373(96)00085-9

Cited by 79 publications

(42 citation statements)

References 46 publications

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“…The maximum of the F 2g band is located at 462 cm −1 in all spectra, and this value is slightly lower to that reported for pure ceria (465 cm −1 [14,16]). This shift towards low values can be related to the partial substitution of Ce 4+ cations (0.097 nm) by Pr 3+ cations (0.113 nm), the latter being larger than the former.…”

Section: Characterization Of the Catalysts' Crystallinity By Raman Spcontrasting

confidence: 76%

Improved CO Oxidation Activity of 3DOM Pr-Doped Ceria Catalysts: Something Other Than an Ordered Macroporous Structure

et al. 2017

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Abstract:It is demonstrated that the synthesis procedure for preparing three-dimensionally ordered macroporous (3DOM) Pr-doped ceria catalysts using a polymethylmethacrylate (PMMA) template not only affects the porous structure, but also the chemistry of the ceria surface. The PMMA template does not affect the crystalline features (type of phases, crystallite size, and cell parameter) of Pr-doped ceria, Ce and Pr location into the particles, and the bulk reduction of the Ce-Pr mixed oxide catalysts. On the contrary, the utilization of the PMMA template improves both the porosity and surface redox properties. 3DOM Ce-Pr mixed oxide catalysts combine micro, meso, and macropores, the most area being in the macropore range, while a reference unshaped catalyst presents poor porosity in all ranges. However, the catalyzed CO oxidation rates do not correlate with the surface area of the catalysts (neither micro nor meso/macro). The Ce-Pr-3DOM catalyst also presents improved surface reducibility with regards to the counterpart reference material prepared without the template, and improved redox behavior under reaction conditions; that is, it has a higher area and this area is reduced and reoxidized more easily. X-ray photoelectron spectroscopy analysis evidences that this is mainly attributed to praseodymium cations, which accomplish redox cycles more easily than cerium cations.

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Section: Characterization Of the Catalysts' Crystallinity By Raman Spcontrasting

confidence: 76%

Improved CO Oxidation Activity of 3DOM Pr-Doped Ceria Catalysts: Something Other Than an Ordered Macroporous Structure

et al. 2017

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“…5 shows the visible Raman spectra of the CeO 2 , TiO 2 , and CeO 2 -TiO 2 catalysts. The pristine CeO 2 and TiO 2 samples showed typical Raman shifts attributed to CeO 2 (F 2g mode at 465 cm −1 ) [28,29] and TiO 2 (B 1g mode at 400 cm −1 , A 1g mode at 521 cm −1 and E g mode at 648 cm −1 ) [29,30], respectively. When the Ce species co-existed with the Ti species in the CeO 2 -TiO 2 catalyst, no peak assigned to CeO 2 was detected, and the typical peaks of TiO 2 in CeO 2 -TiO 2 were much weaker than those in pristine TiO 2 , which is in good agreement with the XRD results in Fig.…”

Section: Nh 3 -Scr Activity Of Ceo 2 -Tio 2 Monolith Catalystmentioning

confidence: 97%

An environmentally-benign CeO2-TiO2 catalyst for the selective catalytic reduction of NO with NH3 in simulated diesel exhaust

et al. 2012

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a b s t r a c tA Ce-Ti based (CeO 2 -TiO 2 ) catalyst prepared by an optimized homogeneous precipitation method showed excellent NH 3 -SCR activity, high N 2 selectivity, broad operation temperature window, and high resistance to space velocity (even under a high gas hourly space velocity (GHSV) of 500,000 h −1 ). Compared with V 2 O 5 -WO 3 /TiO 2 and Fe-ZSM-5 catalysts, the CeO 2 -TiO 2 catalyst showed better catalytic performance for NH 3 -SCR. Under a more realistic condition of simulated diesel engine exhaust, the monolith catalyst of CeO 2 -TiO 2 showed over 90% NO x conversion from 250 to 450• C under a GHSV of 20,000 h −1 in the presence of H 2 O, CO 2 , and C 3 H 6 . The high dispersion of active CeO 2 on TiO 2 in the process of homogenous precipitation and the synergistic effects between CeO 2 and TiO 2 in CeO 2 -TiO 2 are important reasons for the high NH 3 -SCR activity.

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“…During the nitration process, various nitrates and nitrites, including species in different chelation configurations such as uni-or bidentate geometry can be identified in the spectra. During the sulfation process, various oxy-sulfur species including sulfites, sulfates, bisulfates and pyrosulfates can be identified and discriminated (29)(30)(31)(32)(33)(34). The sensitivity of spectroscopic techniques provides information not only for the vibrational frequencies but also for rotational contours associated with the specific vibrational modes.…”

Section: Analytical and Experimental Methodsmentioning

confidence: 99%

A Fundamental Consideration on NOx Adsorber Technology for DI Diesel Application

Fang

Huang

et al. 2002

SAE Technical Paper Series

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Diesel engines are far more efficient than gasoline engines of comparable size, and emit less greenhouse gases that have been implicated in global warming. In 2000, the US EPA proposed very stringent emissions standards to be introduced in 2007 along with low sulfur (< 15 ppm) diesel fuel. The California Air Resource Board (CARB) has also established the principle that future diesel fueled vehicles should meet the same low emissions standards as gasoline fueled vehicles and the EPA followed suit with its Tier II emissions regulation. Achieving such low emissions cannot be done through engine development and fuel reformulation alone, and requires application of NOx and particulate matter (PM) aftertreatment control devices. There is a widespread consensus that NOx adsorbers and particulate filter are required in order for diesel engines to meet the 2007 emissions regulations for NOx and PM.In this paper, the key exhaust characteristics from an advanced diesel engine are reviewed. Development of the NOx adsorber technology is discussed. Spectroscopic techniques are applied to understand the underlying chemical reactions over the catalyst surface during NOx trapping and regeneration periods. In-situ surface probes are useful in providing not only thermodynamic and kinetics information required for model development but also a fundamental understanding of storage capacity and degradation mechanisms. The distribution of various nitration/sulfation species is related to surface basicity. Surface displacement reactions of carbonates also play roles in affecting the trapping capability of NOx adsorbers. When ultralow-S fuel is used as a reductant during the regeneration, sulfur induced performance degradation is still observed in an aged catalyst. Other possible sources related to catalyst deactivation include incomplete reduction of surface nitration, coke formation derived from incomplete hydrocarbon burning, and lubricant formulations. Sulfur management and the direction of future work for the successful implementation of such integrated engine and aftertreatment technology are discussed.

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Raman spectroscopic studies on the sulfation of cerium oxide

Cited by 79 publications

References 46 publications

Improved CO Oxidation Activity of 3DOM Pr-Doped Ceria Catalysts: Something Other Than an Ordered Macroporous Structure

Improved CO Oxidation Activity of 3DOM Pr-Doped Ceria Catalysts: Something Other Than an Ordered Macroporous Structure

An environmentally-benign CeO2-TiO2 catalyst for the selective catalytic reduction of NO with NH3 in simulated diesel exhaust

A Fundamental Consideration on NOx Adsorber Technology for DI Diesel Application

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