Recent advances in Raman scattering studies of exhaust-gas catalysts

Willes H. Weber; Dairene Uy

doi:10.1117/12.447381

31 October 2001 Recent advances in Raman scattering studies of exhaust-gas catalysts

Willes H. Weber, Dairene Uy

Proceedings Volume 4469, Raman Spectroscopy and Light Scattering Technologies in Materials Science; (2001) https://doi.org/10.1117/12.447381
Event: International Symposium on Optical Science and Technology, 2001, San Diego, CA, United States

Abstract

Raman scattering is a powerful technique for studying catalysts used in the treatment of automotive exhaust gas. It has the sensitivity and chemical specificity needed to identify the oxide phases of many of the precious metals (Pt, Pd, Rh) used in these catalysts, even when they are highly dispersed on high-surface-area supports such as (gamma) -Al₂O₃. Moreover, this technique can be employed in situ under temperature (300 - 600 degree(s)C) and pressure (1 atm) conditions typically encountered in normal operation. Bulk Pd oxide (PdO) is readily detected with visible excitation, because of a strong resonance Raman enhancement, and its formation and decomposition on Pd/(gamma) -Al₂O₃ and Pd/ZrO₂ catalysts can be followed in real time. Pt does not oxidize as easily as Pd, but a layer of atomic O will form on Pt, and it produces a Raman signature that can be detected with UV excitation at 244 nm. Similarly, UV excitation enhances spectra from adsorbed NO_x and SO_x and hydroxyls on model Pt/(gamma) -Al₂O₃ catalysts. In situ UV Raman spectra of Ba-containing catalysts, being considered for use as NO_x traps, show adsorbed NO_x and SO_x and, thus, can be used to characterize the NO_x trapping, S poisoning, and regeneration of the trap. UV excitation has several advantages in addition to the eletronic resonance enhancment: the signal is increased because of the dependence of the Raman cross section on the fourth power of the frequency, the fluorescence is often Stokes shifted well beyond the range of the Raman lines, and the thermal background from a heated sample is negligible.

Citation Download Citation

Willes H. Weber and Dairene Uy "Recent advances in Raman scattering studies of exhaust-gas catalysts", Proc. SPIE 4469, Raman Spectroscopy and Light Scattering Technologies in Materials Science, (31 October 2001); https://doi.org/10.1117/12.447381

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