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1.
Chemistry ; 19(30): 9849-58, 2013 Jul 22.
Artículo en Inglés | MEDLINE | ID: mdl-23780864

RESUMEN

TiCl4 grafted to dehydrated silica is an industrially applied catalyst for the epoxidation of propylene. As with many heterogeneous catalysts, the precise nature of the surface species is not yet fully known, prohibiting reliable structure-activity correlations. In this study, the speciation and restructuring of site-isolated Ti(IV) Lewis acid centers was carefully investigated by using a variety of techniques. The initially formed ≡SiOTiCl3 species were found to restructure upon heating through the transfer of Cl ligands to the silica surface, eventually leading to tripodal (≡SiO)3 TiCl species. The superior activity and stability of such tripodal species is demonstrated for catalytic olefin epoxidation under continuous flow conditions.

2.
Chimia (Aarau) ; 64(4): 225-30, 2010.
Artículo en Inglés | MEDLINE | ID: mdl-21138187

RESUMEN

Functionalizing organic molecules is an important value-creating step throughout the entire chemical value-chain. Oxyfunctionalization of e.g. C-H or C=C bonds is one of the most important functionalization technologies used industrially. The major challenge in this field is the prevention of side reactions and/or the consecutive over-oxidation of the desired products. Despite its importance, a fundamental understanding of the intrinsic chemistry, and the subsequent design of a tailored engineering environment, is often missing. Industrial oxidation processes are indeed to a large extent based on empirical know-how. In this mini-review, we summarize some of our previous work to help to bridge this knowledge gap and elaborate on our ongoing research.

3.
Dalton Trans ; 48(9): 2886-2890, 2019 Feb 26.
Artículo en Inglés | MEDLINE | ID: mdl-30734797

RESUMEN

Thiolate-coordinated ruthenium alkylidene complexes can give high Z-selectivity and stereoretentivity in olefin metathesis. To investigate their applicability as heterogeneous catalysts, we have successfully developed a methodology to easily immobilize prototype ruthenium alkylidenes onto hybrid mesostructured silica via a thiolate tether. In contrast, the preparation of the corresponding molecular complexes appeared very challenging in solution. These prototype supported complexes contain small thiolates but still, they are slightly more Z-selective than their molecular analogues. These results open the door to more active and selective heterogeneous catalysts by supporting more advanced thiolate Ru-complexes.

4.
Dalton Trans ; 42(35): 12725-32, 2013 Sep 21.
Artículo en Inglés | MEDLINE | ID: mdl-23752559

RESUMEN

The volatile molecular precursors CrO2Cl2 and VOCl3 were grafted to thermally dehydrated silica in order to obtain site-isolated, monopodal ≡SiO-MO(x)Cl(y-1) species (M = V, Cr). Thermal restructuring under dynamic vacuum was investigated up to 450 °C with different spectroscopic techniques (viz., NMR, UV-Vis, IR, Raman and XPS). During this thermal restructuring, VOCl3 or CrO2Cl2 is partially eliminated from the surface, whilst the remaining surface species become multiply bound to the silica surface. This restructuring increases both the chemical and thermal stability of these materials, and has significant consequences for their performance as heterogeneous catalysts.

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