(558av) Ionic Liquids Confined with Mesoporous Silica for Boosting Catalytic Conversion of CO2 into Cyclic Carbonates

Ionic
Liquids Confined with Mesoporous Silica for Boosting Catalytic Conversion of CO₂
into Cyclic Carbonates

Qian Su, Wei-Guo Cheng and Suo-Jiang Zhang

Key
Laboratory of Green Process and Engineering, Institute of Process Engineering,
Chinese Academy of Sciences, P.O. Box 353, Beijing, 100190, China

*Corresponding author:
sjzhang@home.ipe.ac.cn

As an
important approach for efficient utilization of CO₂, the synthesis
of carbonates from fixation of CO₂ and high-energy epoxides opens up
a technologically innovative direction for alleviating energy shortages and
environmental concerns. In recent years, numerous
catalysts have been developed for catalytic fixation of CO₂ with
epoxides (Scheme 1), such as metal-based catalysts, organic bases, modified
molecular sieves and ionic liquids (ILs)^1-4. ILs are thought to be most
promising due to high stability and great catalytic performance. However, the high energy
consumption and economic cost caused by using homogeneous ILs become barriers to
industrial application. On the basis of economic and energy-saving criteria,
new forms of heterogenous ILs catalysts should be explored for reducing the
usage of ILs while maintaining their intrinsic properties.

Scheme 1 Fixation of CO₂
and epoxides into cyclic carbonates

  Confinement method
provides possibility for this exploration⁵. In this work, mesoporous
silica (mSiO₂) was adopted as a kind of confined space for
investigation about the minimum effective dosage of ILs. By
one-step assembly of different ILs with mSiO₂,
a series of confined ILs were prepared. Through
experiment and molecular simulation, the adjusting law of ILs content and structure
on confined ILs was revealed. To
begin with, the materials owning high dispersity and stability tend to be
obtained under low ILs concentration. Compared with bulk phase owning similar
activity, nearly 40% of ILs was saved. The high dispersity of active sites and
the strong confining effect of mSiO₂ skeleton might be the main
factors facilitating the catalytic performance. Furthermore, the ILs with short
carbon chain (carbon number £¼ 8) were found to be more
suitable for confined catalysis, and the symmetric ILs with four carbon chains functioned
best both in stability and recyclability, mainly due to a propping effect in
four directions, both to ensure stability and create more space for mobility of
active anions. This study not only optimizes the ILs structure and amount which
is needed for efficient CO₂ conversion, but also provides an
efficient way to investigate nano- and micro-scale catalytic mechanism, which
means a lot both in academia and industrial areas.

Keywords: ionic liquids, CO₂, cyclic
carbonate, mesoporous silica, confined ILs

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