Imidazolium-based silica microreactors for the efficient conversion of carbon dioxide

Abstract

5Imidazolium based silica microreactors were synthesized in a one-pot procedure. A straightforward synthesis approach was achieved through self-organization/polymerization of the amphipathic organic salts that behave as template for the construction of silica architecture and as catalytic active sites. The porous silica shell allowed the diffusion of reactants and products to/from the active sites and conferred stability to the polymeric matrix. The solid was extensively characterised by transmission and scanning electron microscopy, N 2 adsorption/desorption, X-ray diffraction, 29 Si solid state MAS-NMR and combustion chemical analysis. The material 10 was tested as catalyst for the reaction of carbon dioxide with various epoxides to produce cyclic carbonates. The organic-inorganic hybrid microreactors displayed excellent performances in terms of both, yield and selectivity. Moreover it can be used in multiple catalytic cycles.

A polyhedral oligomeric silsesquioxane-based catalyst for the efficient synthesis of cyclic carbonates

“…37 In the literature, difference in chemical shift of 10 ppm can be found only for POSS with T 8 R 7 R' structures where the R and R' have a very different nature (e.g. It is known 21,22 that without "co-activation", good conversions at temperatures lower than 100 °C are difficult to achieve. In the present case the POSS-Imi is mainly a hepta-substituted silsesquioxane with similar R and R' functionalities, however the ionic nature and the aromatic character of the imidazolium moieties should not be underestimated.…”

“…[2][3][4][5] One of the most studied reactions involving the use of CO 2 is represented by its fixation onto epoxides to produce cyclic carbonates and/or polycarbonates. [20][21][22] It is worth to be mentioned that, as highlighted by Sakakura, 3 a temperature of 150 °C does not represent necessarily a drawback in industrial applications. 2, 6-10 Among the possible active species able to catalyze the synthesis of cyclic carbonates, 6 imidazolium ionic liquids have shown excellent performances acting as catalysts or co-catalysts, for the latter usually in combination with organometallic complexes with Lewis acid properties.…”

“…2, 6-10 Among the possible active species able to catalyze the synthesis of cyclic carbonates, 6 imidazolium ionic liquids have shown excellent performances acting as catalysts or co-catalysts, for the latter usually in combination with organometallic complexes with Lewis acid properties. 21,25,26 Due to their excellent performances various imidazolium based catalysts working under both homogeneous and heterogeneous conditions have been proposed. [20][21][22] It is worth to be mentioned that, as highlighted by Sakakura, 3 a temperature of 150 °C does not represent necessarily a drawback in industrial applications.…”

Bi-functional heterogeneous catalysts for carbon dioxide conversion: enhanced performances at low temperature

“…10,16 For comparison, the activity of the all-silica MCM-41 solid functionalized with imidazolium moiety (XS-MCM-41-Imi) was studied as well (see entry 1 in Table 2). Moreover, before starting the investigation in the presence of the bifunctional catalysts an additional catalytic test adding a small amount of ZnCl 2 (corresponding approximatively to the quantity inserted in the silica framework) to the reaction mixture was performed in order to evaluate the positive contribution of a salt with Lewis acid properties under homogeneous conditions.…”

“…8 To achieve an easy recovery from the reaction mixture and reuse of the catalyst for multiple cycles, most of these salts were also heterogenized 9 on different supports. Silica-based porous materials, 10,11 polymers, 12,13 single as well as multi-walled carbon nanotubes, [14][15][16] and more recently carbon nanohorns 17 among others were already selected for this purpose. The mechanism of the reaction is well known and was already reported in various publications.…”