Abstract
Diffuse reflection infrared Fourier transform (DRIFT) spectra have been quantitatively evaluated to determine unknown extinction coefficients as well as the number of active surface centers and the amount of adsorbed species. Sulfated zirconia with n-butane as probe gas was used as model system. For quantitative evaluation of n-butane adsorption at 323 K, the sulfate band S=O at 1400 cm−1 was chosen. During adsorption, this band is red-shifted to lower wavenumbers accompanied by a structural change of the band indicating isomerization reaction. By analyzing difference spectra and determining the areas of the selected band, the extinction coefficients as well as the number of active centers and the amount of chemisorbed n-butane were calculated. The quantitative evaluation results in a mean internal decadic extinction coefficient of 60 cm−1 µmol−1, an average amount of n-butane adsorbed to the sulfated zirconia of about 4 μmol, and a number of active centers of around 21 μmol/g. These results correspond very well with values from the literature obtained by microcalorimetry. Thus, this method is suggested to be transferred also to unknown systems of interest.
Highlights
The calculation of extinction coefficients via measured IR spectra is discussed in the literature in many ways, and there are a number of different approaches to determine quantitative data from the measured spectra
The quantitative evaluation results in a mean internal decadic extinction coefficient of 60 cm−1 μmol−1, an average amount of n-butane adsorbed to the sulfated zirconia of about 4 μmol, and a number of active centers of around 21 μmol/g
He investigated the adsorption of pyridine on Si/Al-based catalysts and defined an integrated molar extinction coefficient (IMEC) characteristic for one special absorption band with the assumption that the IMEC does not depend on the catalyst or the strength of the acid site
Summary
The calculation of extinction coefficients via measured IR spectra is discussed in the literature in many ways, and there are a number of different approaches to determine quantitative data from the measured spectra. What all of these approaches have in common is that the measurements were performed using transmission IR-spectroscopy. He investigated the adsorption of pyridine on Si/Al-based catalysts and defined an integrated molar extinction coefficient (IMEC) characteristic for one special absorption band with the assumption that the IMEC does not depend on the catalyst or the strength of the acid site. The calculated IMEC values were 1.67 cm/μmol for the Brønsted acid site at 1545 cm−1 and 2.22 cm/μmol for the Lewis acid site at 1455 cm−1
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