Novel Zn-MCM-41 mesoporous materials with particle diameters ranging from 20 to 120 nm were successfully prepared following a straightforward synthesis route. The structural and textural properties of the solids were characterized by N2-physisorption, X-ray diffraction, (29)Si MAS-NMR, TEM and EDX. These results allow evidencing the presence of an ordered mesoporous structure with a very high specific surface area. The insertion of zinc as single site species within the silica framework was investigated using XPS via the Auger parameter in a Wagner plot representation. This is the first time that an in-depth investigation of these types of solids using XPS techniques was performed. The presence of Brønsted and Lewis acidity was elucidated by following in the IR the interaction with ammonia and carbon monoxide. The materials were tested for the conversion of dihydroxyacetone into ethyl lactate with good results both in terms of yield and selectivity and the catalytic activity resulted in excellent agreement with IR and XPS analysis.
Novel heterogeneous bi-functional catalysts bearing tin or zinc inserted as single sites within the silica architecture acting as acid centres and decorated with imidazolium moieties as the nucleophile source were successfully synthesized. The materials were extensively characterized via various techniques including N 2 physisorption, solid state nuclear magnetic resonance, X-ray photoelectron spectroscopy, transmission electron microscopy and adsorption microcalorimetry. The solids were tested as catalysts for the conversion of carbon dioxide, selecting the synthesis of styrene carbonate as the target reaction.Both materials exhibited improved performances compared to the analogous solids functionalized with the sole imidazolium salt as well as to other materials reported in the literature. The Sn-based catalyst displayed excellent conversion also in the presence of various epoxides. In all experiments the bifunctional solid allowed reducing the reaction temperature below 150 C. In the presence of glycidol the temperature was decreased down to 30 C. The short synthesis protocol of the heterogeneous catalysts, together with the 100% atom economy of the target reaction and the low reaction temperature, make the entire process highly sustainable. Moreover, the Sn-based catalyst was stable under the selected reaction conditions and reusable for multiple catalytic cycles.
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