Application of infrared photoacoustic spectroscopy in catalysis

Janusz Ryczkowski 

Abstract

Photoacoustic spectroscopy (PAS) measures a sample's absorbance spectrum directly with a controllable sampling depth and with almost no sample preparation. This technique is nondestructive, noncontact, applicable to macrosamples and microsamples, insensitive to surface morphology. In the contrary to the traditional transmission methods, PAS is carrying out the information from the surface of the measured sample. In the area of infrared PAS is a supplementary one to the other spectroscopic and classical physicochemical methods of the catalysts surface characterization. It is capable of measuring spectra of all types of solids without exposure to air or moisture. Photoacoustic spectroscopy is detecting a sample's IR spectrum by "listening" to the sound made when the sample absorbs infrared radiation. A highly sensitive microphone is used as a detector, and the spectrum is similar to absorbance spectra. One of the major advantages of PAS is its relative immunity to scattered light. Consequently, this methodology can provide absorption spectra of highly light-scattering materials such as powders (e.g. silica, alumina) or highly-absorbing materials (e.g. different type of carbonaceous adsorbents, materials, species, etc.). Several of the problems associated with the transmission techniques may be overcome utilizing photoacoustic detection (in particular, changes in the spectral region were inorganic supports are strong absorbers). Several practical and valuable examples will be presented covering various areas of catalysts investigations (catalysts preparation, adsorption, surface acidity, characterization of MCM-type materials, modified carbons, carbon deposits, etc.). Moreover, selected examples will be devoted to the comparison of data for the same studied material but obtained by the different techniques in the area of IR. Finally, there will be summarized advantages as well as the limits of the FT-IR/PAS.

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Presentation: Invited oral at E-MRS Fall Meeting 2006, Symposium B, by Janusz Ryczkowski
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-10 17:45
Revised:   2009-06-07 00:44
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