# Quantification of Silanol Species on Various Silicas by IR Spectroscopy

Jean Pierre Debs, Nicolas Malicki, Arnaud Travert, Pierre Ghesquières,

Frederic Thibault-Starzyk

► To cite this version:

Jean Pierre Debs, Nicolas Malicki, Arnaud Travert, Pierre Ghesquières, Frederic Thibault-Starzyk. Quantification of Silanol Species on Various Silicas by IR Spectroscopy. 2023 French/German Ad-sorption Conference, Oct 2023, Strasboug, France. hal-04477343

HAL Id: hal-04477343

https://hal.science/hal-04477343v1

Submitted on 27 Feb 2024

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# Quantification of Silanol Species on Various Silicas by IR Spectroscopy

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Jean Pierre Debs<sup>a,b*</sup>, A. Travert<sup>a</sup>, F. Thibault-Starzyk<sup>a</sup>, P. Ghesquière<sup>b</sup>, N. Malicki<sup>b</sup>

<sup>a</sup> Normandie Univ, ENSICAEN, UNICAEN, CNRS, LCS, 14000 Caen, France

<sup>b</sup> MFPMichelin, 23, Place des Carmes Dechaux, 63000 Clermont-Ferrand, France

*jean-pierre.debs@ensicaen.fr

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Silica plays a crucial role in the development of Michelin's 'green tyres', which are designed to be more fuel efficient, environmentally friendly, and durable. It is an essential component that reacts with silane, a coupling agent, to significantly improve the tyre's performance. The success of this reaction depends on a thorough understanding of the surface chemistry of silica, in particular the presence of silanol (Si-OH) groups. Silanol groups play an essential role in facilitating chemical bonds between silica, silane, and the tyre polymer matrix. In this study, we embark on a mission to explore the surface reactivity of five distinct silica using *in situ* Fourier transform infrared (FTIR) spectroscopy, following the methodology established by Gallas et al.<fnref n="1" /> Beyond qualitative insights, our effort involves quantitative analyses of the surface silanols as a whole, and then of each silanol groups individually. By understanding the reactivity, abundance, and spectral characteristics of these silanol groups, we aim to improve tyre performance by exploiting the full potential of silica-silane interactions.

## Silica and probes

* Four commercial silicas are studied using 5 different probes

<table><thead><tr><th>Silica</th><th>Zeosil® 1165MP 1<sup>st</sup></th><th>Zeosil® 1165MP 2<sup>nd</sup></th><th>Zeosil® Premium</th><th>ULTRASIL® 7000GR</th><th>ULTRASIL® 4000GR</th></tr></thead><tbody><tr><th>Sample code</th><td>160MP batch A</td><td>160MP batch B</td><td>P200</td><td>165G</td><td>80G</td></tr><tr><th>Specific surface area (m²/g)</th><td>154,4</td><td>154,4</td><td>212,4</td><td>173</td><td>93,9</td></tr></tbody></table>

<table><thead><tr><th>Probe molecule</th><th>Deuterium oxide</th><th>methanol</th><th>propan-2-ol</th><th>2-methyl-propan-2-ol</th><th>3-ethyl-pentan-3-ol</th></tr></thead><tbody><tr><th>Formula</th><td>D<sub>2</sub>O</td><td>CH<sub>4</sub>O</td><td>C<sub>3</sub>H<sub>8</sub>O</td><td>C<sub>4</sub>H<sub>10</sub>O</td><td>C<sub>7</sub>H<sub>16</sub>O</td></tr><tr><th>Structure</th><td>D-O-D</td><td>H-C-O-H<br>H</td><td>H<sub>3</sub>C(OH)<sub>3</sub>CH<sub>3</sub></td><td>HO</td><td>CH<sub>3</sub>OH</td></tr><tr><th>Molecular size (nm)</th><td>0,106</td><td>0,180</td><td>0,276</td><td>0,316</td><td>0,410</td></tr></tbody></table>

## A. Quantification of total number of silanols

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$$C_{OH} = \frac{A \cdot S}{\epsilon \cdot m}$$

C<sub>OH</sub>: Concentration of silanols (mol g<sup>-1</sup>)

A : area of the (ν + δ)(OH) band (cm<sup>-1</sup>)

S : pellet's geometrical surface (2.01 cm<sup>2</sup>)

ε : molar absorption coefficient (cm mol<sup>-1</sup>)

m : Pellet's mass (g)

<table><thead><tr><th></th><th>160MP batch A</th><th>160MP batch B</th><th>165G</th><th>80G</th><th>P200</th></tr></thead><tbody><tr><th>C<sub>OH</sub> (mmol/g)</th><td>3.6</td><td>3.0</td><td>3.3</td><td>3.2</td><td>3.0</td></tr></tbody></table>

## B. Assessement of silanols accessiblity

* *in situ* FTIR measures (under vacuum) qualitatively and quantitatively surface properties of catalysts by probe molecule

* H-D/O-D exchange and retro exchange

3. Retro-exchange with 4 alcohols from larger to smaller size.

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## D. Comparison of commercial silicas

Number silanols and accessibility to D₂O vs specific surface area

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## Distribution

%OH per group

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## Accessibility

Accessible C<sub>OH</sub> vs probe size

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## Conclusion

* No correlation of the total number of OH groups with BET or CTAB surface area

* Consistent absorption coefficients ε, correlated with the extent of hydrogen bonding

* No significant variation in the distribution of external, internal, and accessible silanol groups among the various silica samples.

* Slight changes in accessibility, only significant for two samples (160MP batch A vs. P200)

<footnote n="1">¹J.-P. Gallas, J.-M. Goupil, A. Vimont, J.-C. Lavalley, B. Gil, J.-P. Gilson and O. Miserque, Langmuir, 25, 5825–5834 (2009).</footnote>