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Title: Characteristics of Desulfation Behavior for Presulfated Pt-BaO/CeO2 Lean NOx Trap Catalyst: The Role of the CeO2 Support

Abstract

The desulfation of presulfated Pt-BaO/CeO{sub 2} lean NOx trap catalyst was investigated by H{sub 2} TPRX (temperature programmed reaction), in situ TR-XRD (time-resolved X-ray diffraction), and in situ S K-edge XANES (X-ray absorption near edge spectroscopy) techniques. Compared with Pt-BaO/Al{sub 2}O{sub 3} materials, a reductive treatment in H{sub 2} for the CeO{sub 2}-supported sample up to 1073 K removes, at most, only a very small amount of sulfur species. However, the results of in situ TR-XRD measurements demonstrate that the quantity of a BaS phase formed on Pt-BaO/CeO{sub 2} is much smaller than that on Pt-BaO/Al{sub 2}O{sub 3}, implying that the formation of BaS crystallites, which occurs during the reduction from sulfate (SO{sub 4}{sup 2-}) to sulfide (S{sup 2-}), is significantly suppressed in the CeO{sub 2}-supported catalyst. As the desulfation temperature increases under reducing conditions (in H{sub 2}), in situ S XANES spectra show that, compared with alumina-supported samples, the reduction temperature for sulfates (S{sup 6+}) decreases by about 150 K. Concomitantly, the formation of sulfur species with lower oxidation states (S{sup 2}-S{sup 4+}) is enhanced. The absolute intensities of S XANES spectra before and after desulfation are very similar, implying that the amount of sulfur-containing species removed during themore » reductive treatment is negligible, in agreement with the results of H{sub 2} TPRX. These results suggest that H{sub 2}S produced by the reduction of BaSO{sub 4} is readily readsorbed on the ceria support to form ceria-sulfur complexes (e.g., Ce{sub 2}O{sub 2}S). The high affinity of ceria for H{sub 2}S, combined with the ease of reducibility of the ceria support material gives rise to various oxidation states of sulfur after high-temperature H{sub 2} treatments. Thus, the results of this study clearly show that the ceria support strongly affects the overall desulfation mechanism. The intrinsic role of the ceria support during desulfation and its effect on the overall NOx storage processes are discussed on the basis of the characterization results obtained here.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
DOE - OFFICE OF SCIENCE
OSTI Identifier:
1020145
Report Number(s):
BNL-95995-2011-JA
Journal ID: ISSN 1932-7447; TRN: US201116%%126
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry C
Additional Journal Information:
Journal Volume: 113; Journal Issue: 50; Journal ID: ISSN 1932-7447
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; AFFINITY; CATALYSTS; DIFFRACTION; SPECTRA; SPECTROSCOPY; STORAGE; SULFATES; SULFIDES; SULFUR; VALENCE; national synchrotron light source

Citation Formats

Kim, D, Kwak, J, Szanyi, J, Wang, X, Li, G, Hanson, J, and Peden, C. Characteristics of Desulfation Behavior for Presulfated Pt-BaO/CeO2 Lean NOx Trap Catalyst: The Role of the CeO2 Support. United States: N. p., 2009. Web. doi:10.1021/jp9062548.
Kim, D, Kwak, J, Szanyi, J, Wang, X, Li, G, Hanson, J, & Peden, C. Characteristics of Desulfation Behavior for Presulfated Pt-BaO/CeO2 Lean NOx Trap Catalyst: The Role of the CeO2 Support. United States. doi:10.1021/jp9062548.
Kim, D, Kwak, J, Szanyi, J, Wang, X, Li, G, Hanson, J, and Peden, C. Thu . "Characteristics of Desulfation Behavior for Presulfated Pt-BaO/CeO2 Lean NOx Trap Catalyst: The Role of the CeO2 Support". United States. doi:10.1021/jp9062548.
@article{osti_1020145,
title = {Characteristics of Desulfation Behavior for Presulfated Pt-BaO/CeO2 Lean NOx Trap Catalyst: The Role of the CeO2 Support},
author = {Kim, D and Kwak, J and Szanyi, J and Wang, X and Li, G and Hanson, J and Peden, C},
abstractNote = {The desulfation of presulfated Pt-BaO/CeO{sub 2} lean NOx trap catalyst was investigated by H{sub 2} TPRX (temperature programmed reaction), in situ TR-XRD (time-resolved X-ray diffraction), and in situ S K-edge XANES (X-ray absorption near edge spectroscopy) techniques. Compared with Pt-BaO/Al{sub 2}O{sub 3} materials, a reductive treatment in H{sub 2} for the CeO{sub 2}-supported sample up to 1073 K removes, at most, only a very small amount of sulfur species. However, the results of in situ TR-XRD measurements demonstrate that the quantity of a BaS phase formed on Pt-BaO/CeO{sub 2} is much smaller than that on Pt-BaO/Al{sub 2}O{sub 3}, implying that the formation of BaS crystallites, which occurs during the reduction from sulfate (SO{sub 4}{sup 2-}) to sulfide (S{sup 2-}), is significantly suppressed in the CeO{sub 2}-supported catalyst. As the desulfation temperature increases under reducing conditions (in H{sub 2}), in situ S XANES spectra show that, compared with alumina-supported samples, the reduction temperature for sulfates (S{sup 6+}) decreases by about 150 K. Concomitantly, the formation of sulfur species with lower oxidation states (S{sup 2}-S{sup 4+}) is enhanced. The absolute intensities of S XANES spectra before and after desulfation are very similar, implying that the amount of sulfur-containing species removed during the reductive treatment is negligible, in agreement with the results of H{sub 2} TPRX. These results suggest that H{sub 2}S produced by the reduction of BaSO{sub 4} is readily readsorbed on the ceria support to form ceria-sulfur complexes (e.g., Ce{sub 2}O{sub 2}S). The high affinity of ceria for H{sub 2}S, combined with the ease of reducibility of the ceria support material gives rise to various oxidation states of sulfur after high-temperature H{sub 2} treatments. Thus, the results of this study clearly show that the ceria support strongly affects the overall desulfation mechanism. The intrinsic role of the ceria support during desulfation and its effect on the overall NOx storage processes are discussed on the basis of the characterization results obtained here.},
doi = {10.1021/jp9062548},
journal = {Journal of Physical Chemistry C},
issn = {1932-7447},
number = 50,
volume = 113,
place = {United States},
year = {2009},
month = {1}
}