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. 2024 Nov 21;29(23):5512.
doi: 10.3390/molecules29235512.

Generation of Acid Sites in Nanostructured KIT-6 Using Different Methods to Obtain Efficient Acidic Catalysts for Glycerol Acetalization to Solketal

Ewa Janiszewska  1 , Jolanta Kowalska-Kuś  1 , Justyna Wiktorowska  1 , Aldona Jankowska  1 , Agata Tabero  1 , Agnieszka Held  1 , Stanisław Kowalak  1
Affiliations

Generation of Acid Sites in Nanostructured KIT-6 Using Different Methods to Obtain Efficient Acidic Catalysts for Glycerol Acetalization to Solketal

Ewa Janiszewska et al. Molecules. .

Abstract

This study explored the preparation of pure silica KIT-6, as well as KIT-6 materials with an enhanced concentration of surface OH groups through aluminum incorporation or NH4F treatment. These materials with various contents of surface OH groups were subsequently modified via the post-synthesis grafting of sulfonic groups using 3-mercaptopropyltrimethoxysilane as a precursor, followed by oxidation to introduce acidic sites. The catalysts were thoroughly characterized using XRD, nitrogen adsorption/desorption, SEM-EDS, TEM, and FT-IR techniques to confirm their structural and chemical properties. The catalytic activity of acid-functionalized mesoporous silicas of the KIT-6 structure was further evaluated in the acetalization of glycerol to produce solketal. The results demonstrated a significant influence of the surface OH group concentration and acidic site density on catalytic performance, with KIT-6_F_SO3H showing the highest efficiency in glycerol-to-solketal conversion. This study provides valuable insights into the design of efficient catalytic systems for the valorization of biodiesel-derived glycerol into high-value chemicals, offering a sustainable approach to waste glycerol utilization.

Keywords: KIT-6 modification; KIT-6 synthesis; acidic active centers; glycerol acetalization; grafting of sulfonic groups; solketal.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Scheme of the enhancement of the number of OH groups through NH4F treatment.
Figure 2
Figure 2
Scheme of grafting of 3-mercaptopropyltrimethoxysilane (MPTMS) and its conversion to sulfonic groups.
Figure 3
Figure 3
Powder XRD patterns of indicated samples.
Figure 4
Figure 4
TEM images of KIT-6 (a), AlKIT-6 (b), and KIT-6_F (c).
Figure 5
Figure 5
Low-temperature nitrogen sorption isotherms (a) and pore size distributions (b) for the indicated KIT-6 type materials.
Figure 6
Figure 6
FT-IR spectra of unfunctionalized samples in the framework vibrations range.
Figure 7
Figure 7
FT-IR spectra of unfunctionalized and functionalized KIT-6_F materials with -SH and -SO3H groups.
Figure 8
Figure 8
XPS spectra in the S 2p core level region of sulfonated samples.
Figure 9
Figure 9
UV-Vis spectra of the indicated samples.
Figure 10
Figure 10
Catalytic activity expressed as glycerol conversion, selectivity to solketal, and yield of solketal for the initial and modified KIT-6 materials and their functionalized analogs in the glycerol acetalization reaction.
Figure 11
Figure 11
Dependence of glycerol conversion and solketal yield on the density of acidic centers in the glycerol acetalization reaction.
Figure 12
Figure 12
Glycerol conversion and product distribution in the KIT-6 materials before and after the functionalization procedure.
See this image and copyright information in PMC

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