Zengjing Guo

Hydrophobic Mesoporous Poly(ionic liquid)s towards Highly Efficient and Contamination‐Resistant Solid‐Base Catalysts

Mesoporous poly(ionic liquid)s were synthesized by radical copolymerization of the ionic liquid 1‐aminoethyl‐3‐vinylimidazolium bromide with divinylbenzene plus the ion exchange of bromide anions with hydroxyls. Characterizations revealed the high ionic liquid content, large surface area, and hydrophobicity for the sample prepared with equimolar amounts of ionic liquid and divinylbenzene, with good accessibility to organic compounds and resistance to CO2/H2O contamination. The mesoporous copolymer behaved as a superior and recyclable solid‐base catalyst for solvent‐free Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate, giving the much higher turnover frequency of 304 h−1 (yield 99 %, 0.5 h) than those of the nonporous analogues, commercial strong basic resins, and even homogeneous NaOH. The high activity was confirmed by Knoevenagel condensation with various substrates and Claisen–Schmidt condensation. A possible synergistic Lewis–Brønsted dual‐base‐center mechanism is proposed for understanding the catalytic behavior.

Hydroxyl-Exchanged Nanoporous Ionic Copolymer toward Low-Temperature Cycloaddition of Atmospheric Carbon Dioxide into Carbonates

An ionic copolymer catalyst with nanopores, large surface area, high ionic density, and superior basicity was prepared via the radical copolymerization of amino-functionalized ionic liquid bromide and divinylbenzene, followed with a hydroxyl exchange for removing bromonium. Evaluated in chemical fixation of CO2 with epoxides into cyclic carbonates in the absence of any solvent and basic additive, the nanoporous copolymer catalyst showed high and stable activity, superior to various control catalysts including the halogen-containing analogue. Further, high yields were obtained over a wide scope of substrates including aliphatic long carbon-chain alkyl epoxides and internal epoxide, even under atmospheric pressure and less than 100 °C for the majority of the substrates. On the basis of in situ Fourier transform infrared (FT-IR) investigation and density functional theory (DFT) calculation for the reaction intermediates, we proposed a possible reaction mechanism accounting for the superior catalytic activity of the ionic copolymer. The specifically prepared ionic copolymer material of this work features highly stable, noncorrosive, and sustainable catalysis and, thus, may be a new possibility for efficient chemical fixation of CO2 since it is an environmentally friendly, metal-free solid catalyst.

Pore structure controllable synthesis of mesoporous poly(ionic liquid)s by copolymerization of alkylvinylimidazolium salts and divinylbenzene

By chain radical copolymerizations of imidazolium-type ionic liquids and divinylbenzene, mesoporous poly(ionic liquid)s with tunable pore structures were synthesized. The pore size and copolymer composition involving the ionic liquid and divinylbenzene can be controlled through varying the solvents. A series of 3-alkyl-1-vinylimidazolium bromide ionic liquids with different carbon chain lengths of 4, 6, 8, 12 and 16 in the alkyl groups were used in the synthesis, which is significant for the formation of pore structures. The obtained poly(ionic liquid)s were characterized by BET, CHN elemental analysis, FT-IR and UV-vis spectra. The results indicated that poly(ionic liquid)s with varied mesopores and compositions can be facilely achieved in this system. CO2 sorption capability and sorption–desorption cycling were tested, showing superior adsorption capability for CO2 and durable sorption properties.

Imidazolinium based porous hypercrosslinked ionic polymers for efficient CO2 capture and fixation with epoxides

The efficient capture and chemical conversion of carbon dioxide (CO2) requires a solid simultaneously with a large surface area and highly effective active sites. Herein, imidazolinium based porous hypercrosslinked ionic polymers (HIPs) with a high surface area, rich micro/mesoporosity and abundant ionic sites were constructed via the hypercrosslinkage of 2-phenylimidazoline and benzyl halides, in which quaternization and Friedel–Crafts alkylation happened simultaneously to afford ionic polymeric networks. The obtained HIPs were efficient in the selective capture of CO2 and cycloaddition of CO2 with epoxides. High yield, stable reusability and good substrate compatibility were achieved under mild conditions (down to ambient conditions), dramatically outperforming the homogeneous ionic liquid monomer and post-modified analogues. The synergistic adsorption and conversion enabled the efficient low-temperature conversion of diluted CO2 (0.15 bar CO2 and 0.85 bar nitrogen, the simulation of flue gas) catalyzed by HIPs in the presence of co-catalyst ZnBr2. The in situ formed ionic sites with a high leaving ability being homogeneously embedded in the hypercrosslinked polymeric skeleton responded to the high adsorption and catalysis performance. This work highlights the functional HIPs as a versatile platform to reach efficient CO2 capture and conversion under mild conditions.

Nanobelt α-CuV2O6 with hydrophilic mesoporous poly(ionic liquid): a binary catalyst for synthesis of 2,5-diformylfuran from fructose

Direct transformation of renewable biomass-derived carbohydrates into value-added chemicals usually involves a tandem reaction, and therefore demands catalysts with different versatile isolated active sites that can independently take action in each step. In this work, the task-specific binary catalyst nanobelt α-CuV2O6 with the mesoporous poly(ionic liquid) (MPIL) derived solid acid P(EVPI-Br) was constructed for the direct synthesis of 2,5-diformylfuran (DFF) from fructose. α-CuV2O6 gave a >99.9% DFF yield in the aerobic oxidation of 5-hydroxymethyl furfural (HMF) under atmospheric O2 (130 °C, 3 h). The binary catalyst α-CuV2O6 with P(EVPI-Br) afforded a 63.1% DFF yield in the one-pot and one-step conversion of fructose into DFF (O2, 135 °C, 3.5 h). Stepwise addition of the two catalyst units further increased the DFF yield to 76.1%. The hydrophilic surface of P(EVPI-Br) enabled the preferential adsorption of fructose on the acid sites whereas α-CuV2O6 showed strong adsorption of HMF but weak affinity to fructose. Such surface wettability-controlled adsorption features inhibited the oxidation of fructose and facilitated the transfer of HMF to the oxidative sites on α-CuV2O6 and its timely conversion into the final product, thanks to the high activity of α-CuV2O6. Moreover, facile catalyst recovery and good reusability were observed in the synthesis of DFF from both HMF and fructose. This work highlights the potential of manipulating the surface wettability of a binary catalyst towards an efficient multifunctional catalysis system for biomass-related tandem reactions.

Amphiphilic Mesoporous Poly(Ionic Liquid) Immobilized Heteropolyanions Towards the Efficient Heterogeneous Epoxidation of Alkenes with Stoichiometric Hydrogen Peroxide

New mesoporous poly(ionic liquid)s (MPILs) that feature a pure polycationic framework and tunable hydrophobicity were synthesized through the free‐radical polymerization of alkyl‐functionalized ionic liquids (ILs) and bisvinylimidazolium salt. Phosphotungstic (PW) anions were immobilized firmly on these MPILs with a high dispersion and density. The obtained catalyst was effective in the epoxidation of cis‐cyclooctene with stoichiometric hydrogen peroxide (H2O2) to give a high yield (>98 %) and a remarkable H2O2 efficiency (>98 %). The maximum turnover number and turnover frequency was 2375 and 685 h−1, respectively. The catalyst can be recovered easily by filtration and reused with stable activity. Other alkenes can be converted with high yields. The extraordinary performance was attributed to the pure ionic porous framework with an enhanced hydrophobicity that not only provides strong cation–anion interactions towards the stable immobilized PW anions with a high dispersion but also enables the strong affinity of the catalyst with both the substrate and oxidant.