Characteristics of desulfation behavior for presulfated Pt-BaO/CeO 2 lean NOx trap catalyst: The role of the CeO2 support

Do Heui Kim; Ja Hun Kwak; Janos Szanyi; Xianqin Wang; Guosheng Li; Jonathan C. Hanson; Charles H.F. Peden

doi:10.1021/jp9062548

Characteristics of desulfation behavior for presulfated Pt-BaO/CeO ₂ lean NOx trap catalyst: The role of the CeO₂ support

Do Heui Kim, Ja Hun Kwak, Janos Szanyi, Xianqin Wang, Guosheng Li, Jonathan C. Hanson, Charles H.F. Peden

Chemical and Materials Engineering

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Abstract

The desulfation of presulfated Pt-BaO/CeO₂ lean NOx trap catalyst was investigated by H₂ 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/Al₂O₃ materials, a reductive treatment in H ₂ for the CeO₂-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/CeO₂ is much smaller than that on Pt-BaO/Al₂O ₃, implying that the formation of BaS crystallites, which occurs during the reduction from sulfate (SO₄2-) to sulfide (S2-), is significantly suppressed in the CeO₂-supported catalyst. As the desulfation temperature increases under reducing conditions (in H₂), in situ S XANES spectra show that, compared with alumina-supported samples, the reduction temperature for sulfates (S6+) decreases by about 150 K. Concomitantly, the formation of sulfur species with lower oxidation states (S2--S4+) 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 H₂ TPRX. These results suggest that H₂S produced by the reduction of BaSO₄ is readily readsorbed on the ceria support to form ceria-sulfur complexes (e.g., Ce ₂O₂S). The high affinity of ceria for H₂S, combined with the ease of reducibility of the ceria support material gives rise to various oxidation states of sulfur after high-temperature H₂ 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.

Original language	English (US)
Pages (from-to)	21123-21129
Number of pages	7
Journal	Journal of Physical Chemistry C
Volume	113
Issue number	50
DOIs	https://doi.org/10.1021/jp9062548
State	Published - 2009

All Science Journal Classification (ASJC) codes

Electronic, Optical and Magnetic Materials
General Energy
Physical and Theoretical Chemistry
Surfaces, Coatings and Films

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@article{aa19126db656487192c151c19e2d433f,

title = "Characteristics of desulfation behavior for presulfated Pt-BaO/CeO 2 lean NOx trap catalyst: The role of the CeO2 support",

abstract = "The desulfation of presulfated Pt-BaO/CeO2 lean NOx trap catalyst was investigated by H2 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/Al2O3 materials, a reductive treatment in H 2 for the CeO2-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/CeO2 is much smaller than that on Pt-BaO/Al2O 3, implying that the formation of BaS crystallites, which occurs during the reduction from sulfate (SO42-) to sulfide (S2-), is significantly suppressed in the CeO2-supported catalyst. As the desulfation temperature increases under reducing conditions (in H2), in situ S XANES spectra show that, compared with alumina-supported samples, the reduction temperature for sulfates (S6+) decreases by about 150 K. Concomitantly, the formation of sulfur species with lower oxidation states (S2--S4+) 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 H2 TPRX. These results suggest that H2S produced by the reduction of BaSO4 is readily readsorbed on the ceria support to form ceria-sulfur complexes (e.g., Ce 2O2S). The high affinity of ceria for H2S, combined with the ease of reducibility of the ceria support material gives rise to various oxidation states of sulfur after high-temperature H2 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.",

author = "Kim, {Do Heui} and Kwak, {Ja Hun} and Janos Szanyi and Xianqin Wang and Guosheng Li and Hanson, {Jonathan C.} and Peden, {Charles H.F.}",

year = "2009",

doi = "10.1021/jp9062548",

language = "English (US)",

volume = "113",

pages = "21123--21129",

journal = "Journal of Physical Chemistry C",

issn = "1932-7447",

publisher = "American Chemical Society",

number = "50",

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TY - JOUR

T1 - Characteristics of desulfation behavior for presulfated Pt-BaO/CeO 2 lean NOx trap catalyst

T2 - The role of the CeO2 support

AU - Kim, Do Heui

AU - Kwak, Ja Hun

AU - Szanyi, Janos

AU - Wang, Xianqin

AU - Li, Guosheng

AU - Hanson, Jonathan C.

AU - Peden, Charles H.F.

PY - 2009

Y1 - 2009

N2 - The desulfation of presulfated Pt-BaO/CeO2 lean NOx trap catalyst was investigated by H2 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/Al2O3 materials, a reductive treatment in H 2 for the CeO2-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/CeO2 is much smaller than that on Pt-BaO/Al2O 3, implying that the formation of BaS crystallites, which occurs during the reduction from sulfate (SO42-) to sulfide (S2-), is significantly suppressed in the CeO2-supported catalyst. As the desulfation temperature increases under reducing conditions (in H2), in situ S XANES spectra show that, compared with alumina-supported samples, the reduction temperature for sulfates (S6+) decreases by about 150 K. Concomitantly, the formation of sulfur species with lower oxidation states (S2--S4+) 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 H2 TPRX. These results suggest that H2S produced by the reduction of BaSO4 is readily readsorbed on the ceria support to form ceria-sulfur complexes (e.g., Ce 2O2S). The high affinity of ceria for H2S, combined with the ease of reducibility of the ceria support material gives rise to various oxidation states of sulfur after high-temperature H2 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.

AB - The desulfation of presulfated Pt-BaO/CeO2 lean NOx trap catalyst was investigated by H2 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/Al2O3 materials, a reductive treatment in H 2 for the CeO2-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/CeO2 is much smaller than that on Pt-BaO/Al2O 3, implying that the formation of BaS crystallites, which occurs during the reduction from sulfate (SO42-) to sulfide (S2-), is significantly suppressed in the CeO2-supported catalyst. As the desulfation temperature increases under reducing conditions (in H2), in situ S XANES spectra show that, compared with alumina-supported samples, the reduction temperature for sulfates (S6+) decreases by about 150 K. Concomitantly, the formation of sulfur species with lower oxidation states (S2--S4+) 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 H2 TPRX. These results suggest that H2S produced by the reduction of BaSO4 is readily readsorbed on the ceria support to form ceria-sulfur complexes (e.g., Ce 2O2S). The high affinity of ceria for H2S, combined with the ease of reducibility of the ceria support material gives rise to various oxidation states of sulfur after high-temperature H2 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.

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Characteristics of desulfation behavior for presulfated Pt-BaO/CeO ₂ lean NOx trap catalyst: The role of the CeO₂ support

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