Characteristics of Desulfation Behavior for Presulfated Pt-BaO/CeO2 Lean NOx Trap Catalyst: The Role of the CeO2 Support
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.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- DOE - OFFICE OF SCIENCE
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1020145
- Report Number(s):
- BNL-95995-2011-JA; TRN: US201116%%126
- Journal Information:
- Journal of Physical Chemistry C, Vol. 113, Issue 50; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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