Surface reactivity of non-hydrolytic silicophosphate xerogels: a simple method to create Bronsted or Lewis acid sites on porous supports

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Authors

STÝSKALÍK Aleš ŠKODA David MORAVEC Zdeněk BARNES Craig E. PINKAS Jiří

Year of publication 2016
Type Article in Periodical
Magazine / Source New Journal of Chemistry
MU Faculty or unit

Central European Institute of Technology

Citation
Web http://pubs.rsc.org/en/Content/ArticleLanding/2016/NJ/C5NJ02928G#!divAbstract
Doi http://dx.doi.org/10.1039/c5nj02928g
Field Inorganic chemistry
Keywords Non-hydrolytic; sol-gel; silicon acetate; silicophosphate; xerogel; heterogeneous; catalysis; Lewis acid; Bronsted acid
Description Non-hydrolytic sol-gel reactions of silicon acetates with trimethylsilyl (TMS) esters of phosphoric and phosphonic acids produce cross-linked matrices containing homogeneous dispersions of silicate and phosphoryl groups connected together by networks of Si-O-P(QO) linkages. The condensation degrees reach 80 to 90%. Residual organic groups (10 to 20%) were reacted with a variety of compounds (H2O, Me3SiOSiMe3, POCl3, SiCl4, AlMe3, Al(NMe2)(3), and AlCl3) in order to enrich the surface of these porous matrices with Bronsted (RP-OH) and Lewis (tetracoordinated Al) acid functional groups. The differences in the reactivity of RSi-OAc and RP-OSiMe3 groups were utilized for the selective modification at the silicon and phosphorus atoms. The reaction procedures were optimized and significantly porous silicophosphate materials with a high content of either hydroxyl groups or four-coordinated aluminium species were obtained. The activity and selectivity of prepared samples as catalysts for the dimerization of a-methylstyrene were tested. Excellent activities and moderate to very high selectivities were achieved suggesting the potential use of silicophosphate xerogels in heterogeneous catalysis.
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