Imidazolium-based ionic liquid silica xerogel as catalyst to transform CO 2 into cyclic carbonate
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Imidazolium-based ionic liquid silica xerogel as catalyst to transform CO2 into cyclic carbonate Daniela M. Rodrigues1 · Leonardo M. dos Santos2 · Franciele L. Bernard2 · Ingrid S. Pinto2 · Rubia Zampiva3 · Gabriel Kaufmann3 · Sandra Einloft1,2 Received: 11 August 2020 / Accepted: 14 October 2020 © Springer Nature Switzerland AG 2020
Abstract In this work silica xerogel samples containing different imidazolium ILs (EMIM-CF3SO3, EMIM-MSO3, BMIM-Cl, MBMIMTF2N, BMIM-TF2N and EMIM-TF2N) were synthesized, characterized and used as catalyst in cyclic carbonate synthesis. ILs mass percentage was varied from 5% to 25%. The effect fostered by the ILs mass variation in the synthesis of silica xerogel was observed both in the materials characterization as well as in the performance of these materials as solid catalysts in the cyclic carbonate synthesis from the cycloaddition reaction of CO2 with propylene epoxide. The obtained silica xerogel samples (SXs) were characterized by FTIR, RAMAN, TGA, SEM and TEM. The selectivity of the cycloaddition reaction was analyzed by GC and 1H and 13C NMR. The best results were obtained for SX-EMIM MSO3 (20% of IL) and SXBMIM Cl (15% of IL) with propylene carbonate yields of 91.4% and 83.4% and selectivities >99% and 97.4% respectively. Keywords Xerogel silica · Ionic liquid · Catalyst · CO2 · Cyclic carbonates · Cycloaddition reaction
1 Introduction Carbon dioxide (CO2) is one of the main greenhouse gases being emitted in large quantities. The anthropogenic burning of fossil fuels in the last decades is responsible for more than 60% of global warming [1–4]. On the other hand, CO2 is also an interesting carbon source for synthesizing valuable chemicals and fuels [2, 5]. CO2 chemical transformation into cyclic carbonates is interesting from a green chemistry point of view providing waste reuse, using safe reagents besides being a process with 100% CO2 atom savings [6, 7]. Cyclic carbonates such as propylene carbonate (PC) find a wide application spectrum. PC can be used as intermediate in fine chemical production, pharmaceutical, and cosmetic industry, as secondary battery electrolytes, polar aprotic solvent as well starting material for polycarbonate production [6, 8, 9].
The disadvantage associated with using CO2 as a starting reagent is its high thermal and kinetic stability, making it essential to use catalysts in the CO2 chemical transformation reactions under milder reaction conditions [7, 10]. However, even using catalysts to overcome the high energy barriers for these reactions, high temperatures and CO2 pressures are still necessary for these reactions to happen, resulting in high energy costs [10–18]. So, catalysts development and catalytic systems that are capable of transforming CO2 into cyclic carbonates at temperatures below 100 °C and atmospheric C O2 pressure are crucial reducing synthesis energy costs. Although some catalysts have already shown promising results, they are still considered expensive and difficult to apply on an industrial scale, making it imp
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