Abstract
Zr-based oxoclusters MxOy(OR)w(OOR’)z are promising catalysts for the activation of hydrogen peroxide. However, they need to be integrated into suitable matrices to increase their hydrolytic stability and allow for their recovery after use. Polymeric materials can be successfully employed for this aim, since they modify the properties of the resulting hybrid materials, in terms of polarity and chemical affinity for the substrates, improving the catalytic activity. Herein, we report the synthesis of different acrylic polymers based on various co-monomers (methyl methacrylate (MMA), 2,2,2-trifluoroethylmethacrylate (TFMA) and 3-methacryloxypropyltrimethoxylsilane (MAPTMS)) covalently cross-linked by a Zr4-based oxocluster, whose composition was tuned to optimise the catalytic oxidation of methyl p-tolyl sulphide. To assess their properties and stability, the materials were characterised via Fourier Transform Infrared (FT-IR) and Raman spectroscopies, Thermogravimetric Analysis (TGA), Solid-State NMR (SS-NMR) and X-Ray Absorption Spectroscopies XAS, before and after catalytic turnover.
Highlights
The preparation of hybrid materials integrating catalytic units represents a promising possibility to design heterogeneous catalysts [1]
Zirconium butoxide (Zr(OBu)4, 80% wt. in n-butanol), and methacrylic acid were employed for the synthesis of the oxocluster and were purchased from Sigma-Aldrich, while methyl methacrylate (MMA, 99% wt.), 2,2,2-trifluoroethylmethacrylate (TFMA, 99% wt.), 3-methacryloxypropyltrimethoxysilane (MAPTMS), benzoyl peroxide (≥97% wt.) and toluene, purchased from Sigma-Aldrich, were used for the synthesis of the hybrid materials
By a combination of different investigation tools, based on Fourier Transform Infrared (FT-IR), Raman measurements and 13 C Solid-State NMR (SS-NMR) spectroscopies, it was possible to determine the structure of the hybrids, revealing unreacted carbon double bonds eventually present
Summary
The preparation of hybrid materials integrating catalytic units represents a promising possibility to design heterogeneous catalysts [1]. Class II hybrid materials in particular are made of organic and inorganic components, held together by covalent bonds [2]. Among the available inorganic nanofillers, different authors reported the use of polyhedral oligomeric silsesquioxanes (POSS) [3,4], polyoxometalates (POM) [5,6,7] or oxoclusters of early transition metals [8]. Oxoclusters, with a general formula of My Ox (OH)w (O(O)CR)z , are a versatile class of polynuclear compounds including early transition metal ions M, such as TiIV , ZrIV , HfIV or NbV , linked by oxygen bridges and coordinated by organic ligands bearing bidentate, typically carboxylic, moieties [9,10]. When the organic components of the hybrids are organic polymers/co-polymers, oxoclusters decorated with polymerisable groups can act as multi-functional cross-linking agents. Several covalent bonds endow the final material with enhanced stability, preventing phase separation and leaching [12]
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