Produce Propylene Carbonate Research Articles

Unveiling the complementary mechanism in the one-pot synthesis of glycerol carbonate from CO2 and glycerol

The chemical conversion of inert carbon dioxide (CO2) into high value-added chemicals is a continuing challenge. In this work, an experimental and theoretical mechanism study is presented for one-pot synthesis of glycerol carbonate (GC) from CO2, glycerol (Gly), and propylene epoxide (PO) catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-enenium iodide (HDBUI) ionic liquid. 92% GC yield was obtained in the one-pot reaction through cycloaddition of CO2 with PO to produce propylene carbonate (PC), followed by transesterification of Gly with PC to yield targeted products. Density functional theory (DFT) calculations were used to unveil the HDBUI-mediated catalytic mechanism and key catalytic species. It was revealed that the HDBUI-catalyzed cycloaddition was assisted by the hydrogen bond donor Gly, the transesterification reactant, by promoting the ring-opening of PO and the insertion of CO2. By activating Gly hydroxyl group, alkaline HDBUI-bonded propan-1-ylium-2-yl carbonate, an intermediate in cycloaddition, catalyzed transesterification. The complementary mechanism of cycloaddition and transesterification in the one-pot provides a feasible method for utilizing inert CO2.

Solvent-catalyst optimization of ionic liquid-based CO2 conversion to propylene carbonate: Laboratory validation and techno-economic analysis

Ionic liquids (ILs) have been widely suggested as efficient catalysts to produce propylene carbonate (PC) from CO2 and propylene oxide (PO). Recently, the use of liquid-liquid extraction (LLE) has been proposed to efficiently separate ILs from PC since it reduces energy consumption, with fatty alcohols when selecting hydrophobic ILs. However, the study of this reaction-separation system at experimental level is scarce. In addition, the solvent-catalyst system design to improve the global process performance is a current challenge. This work develops an integrated experimental-computational multiscale approach to improve the PC production process by CO2 cycloaddition to PO using the IL [P66614][Br] as catalyst. Reaction yield and liquid-liquid equilibrium measurements were carried out for the experimental validation of the proposed catalytic/separation systems using different solvents (fatty alcohol and water). Process modelling and techno-economic analysis were performed using Aspen Plus for solvent-catalyst optimization, proceeding with an integrated iterative experimental-computational approach to decrease energy requirements and operating costs. It was found that the presence of solvents in the reaction affects conversion and selectivity of the reaction, with fatty alcohols increasing PC yield and enabling IL/PC separation, while water reduces PC selectivity. On the other hand, the presence of water in the process allows reducing electricity demands as well as vacuum requirements. It was possible to modulate fatty alcohol and water dosages to minimize energy consumption, vacuum requirements and utility costs. Optimal configurations have an energy consumption of approximately 0.6 kWh/kgPC and utility costs of 6.6 $/tPC.

Toward Sustainable and Cost‐Effective CO2 Conversion Processes to Propylene Carbonate Based on Ionic Liquids

AbstractThe use of ionic liquids (ILs) for CO2 capture and utilization into a valuable product is attracting interest even though literature evaluating their sustainability is scarce. A liquid–liquid extraction (LLE)‐based separation is recently proposed as an alternative to the high energy‐consuming distillation‐based reference approach to produce propylene carbonate (PC). In this work, the environmental impacts associated to the distillation‐based reference and two proposed LLE‐based approaches to produce PC are evaluated by means of process modeling and life cycle impact assessment tools. Simulations prove that tuning operating variables in terms of environmental benefits also improves the cost‐effectiveness of the process. In addition, sustainability of the processes is nearly not altered by the IL selection when an effective recovery is designed. The emissions associated to the proposed approaches vary between 0.12 and 0.22 kg CO2 equiv. per kgPC, while the operational costs range from 3 to 8 $ per tPC. The water‐mediated LLE‐based approach imposes the best environmental, capital expenditures, and operating expenses performance.

Novel MOF catalysts based on calix[4]arene for the synthesis of propylene carbonate from propylene oxide and CO2

In this study, novel composite materials based on calix[4]arene with hydroxyl groups in the arene “bowl” (K-OH) and the aluminum(III) 2-aminoterephthalate metal organic framework (NH2-MIL-101(Al), MIL) have been synthesized according to in situ or “bottle around ship” strategy. The effect of the synthesis method, i.e., MW-assisted technique (MW) and the solvothermal procedure (Solv), on the structural, morphological, textural and catalytic properties of MIL/K-OH composites was demonstrated. Catalytic performance of the MIL/K-OH(MW) and MIL/K-OH(Solv) composites was studied in solvent-free coupling of CO2 and propylene oxide (PO) to produce propylene carbonate (PC) at 0.8 MPa of CO2 and 80 °C. The activity of the MIL/K-OH(Solv) catalyst was higher in comparison with MIL/K-OH(MW) material as a result of the differences in the textural properties. The binary system MIL/K-OH(MW)/[n-Bu4N]Br was demonstrated to be a promising catalyst for cycloaddition of CO2 to PO. In its presence, the conversion of PO was 77 % with 99 % selectivity towards PC at 1.2 MPa of CO2, 50 °C for 24 h.

Synthesis of highly effective [Emim]IM applied in one-step CO2 conversion to dimethyl carbonate

Ionic liquid 1-ethyl-3-methylimidazolium ([Emim]IM) with high thermal stability and strong basicity was successfully synthesized. Using [Emim]IM as catalyst, dimethyl carbonate (DMC) was directly synthesized from epoxy propane (PO), CO2, and methanol under mild reaction conditions. A continuous two-stage DMC synthesis process was developed. The cycloaddition of CO2 and PO was first conducted to produce propylene carbonate (PC), and then methanol was introduced into the system to synthesize DMC. During the cycloaddition process, 97.40% PO conversion and 97.40% PC yield were achieved with TON of 99.49. In the subsequent transesterification stage, DMC yield attained 83.63% with selectivity higher than 99% and TON of 70.15. [Emim]IM was reused for seven times without obvious deactivation, exhibiting good stability. The effects of reaction temperature, reaction time, the initial pressure of CO2, and catalyst weight on cycloaddition and transesterification reactions were systematically investigated. The kinetic study showed that the activation energies (Ea) of cycloaddition and transesterification reactions were 28.02 and 38.53 KJ·mol−1, respectively, much lower than those of catalysts reported in the literatures. In addition, [Emim]IM displayed superior catalytic activity for the cycloaddition of CO2 with various epoxy compounds.

Universal and low energy-demanding platform to produce propylene carbonate from CO2 using hydrophilic ionic liquids

Ionic liquids (ILs) have been extensively proposed as efficient catalysts to promote CO2 cycloaddition reaction to epoxides for producing cyclic carbonates. Recently, liquid-liquid extraction with water as an enhancer approach to regenerate ILs and to purify the product was proposed, since it reduces energy consumption and enhances the neat catalytic activity of the IL due to hydroxyl groups of water. In this work, a comprehensive sample of homogeneous IL catalysts proposed in the literature is experimentally evaluated both in the catalytic step and in its separation by liquid-liquid extraction with water, to demonstrate the universality of the proposed reaction-separation proposal for hydrophilic ILs. Then the complete processes for CO2 conversion to propylene carbonate were modelled using Aspen Plus to compare the catalyst/product separation efficiency and the specific energy consumption using liquid-liquid extraction and distillation-based platforms. The energy consumption is significantly lower using liquid-liquid platform (1.1–1.3 kWh/kgPC) than distillation one (2.4–3.1 kWh/kgPC). It is concluded that hydrophilic ionic liquids, as those formed by [EtOHmim] cation and halide anions, are promising catalysts since they allow: (i) reducing the process energy consumption due to their high catalytic activity and (ii) full catalyst recovering, even at high catalyst loadings, by improving the water extractive properties for IL separation from PC.

Encapsulated Lewis acidic ionic liquids by halloysite using as efficient catalyst for CO2 conversion

A type of clay-supported catalysts were developed for conversion of CO2 by encapsulating ZnBr2-based Lewis acidic ionic liquids (ZnBr2/IL) in halloysite (Hal) via a one-step strategy. The Lewis acidic ionic liquid was loaded within enlarged lumens of Hal via acid treatment, and the mesoporous structure was found to benefit for CO2 storage/conversion. The composite ZnBr2/IL@P-Hal was found to have an adsorption capacity (6.43 cm3/g) of CO2 via adsorption/desorption isotherm measurements. The composite ZnBr2/IL@P-Hal showed excellent catalytic performance (TOF value was 1747.7 h−1) for coupling of CO2 with epoxides to produce propylene carbonate under the lack of any cocatalyst. Kinetic investigations indicated the reaction followed an order of one, with respect to catalyst ZnBr2/IL@P-Hal. The overall pathway of CO2 cycloaddition was theoretically validated via DFT calculations. These experimental and computational efforts deepen comprehension of the rational design of clay-based catalysts for CO2 cycloaddition, further elucidated halloysite was a promising support.

Fatty alcohol/water reaction-separation platform to produce propylene carbonate from captured CO2 using a hydrophobic ionic liquid

• A novel and sustainable biphasic platform to CO 2 conversion and catalyst regeneration is created. • COSMO-RS predicted a biphasic system (fatty alcohol/water) to separate propylene carbonate and catalyst. • Fatty alcohol media synergistically improves catalytic activity enhancing CO 2 conversion from 68 to 86%. • Five consecutive reaction + separation cycles validate the stability of the catalytic/separation system. • Open possibilities to integrate chemical capture and conversion with a bifunctional chemical absorbent-catalyst. The combined use of a hydrophobic ionic liquid catalyst and a fatty alcohol is presented to synergistically improve cycloaddition reaction of CO 2 to epoxides producing cyclic carbonates and envision catalyst recovery by cyclic carbonate removal using water as extracting solvent. This approach is described for the production of propylene carbonate using trihexyl(tetradecyl)phosphonium 2-cyanopyrrolide catalyst -which chemically captures CO 2 reactant- and 1-decanol/water mixture as extracting solvent. The novel use of fatty alcohols on CO 2 cycloaddition reaction not only permits the effective separation of the catalyst and the product purification, but also improves the CO 2 conversion in the reactor, and opens the challenge of process intensification by integrated CO 2 capture and conversion.

Effect of MAF-6 Crystal Size on Its Physicochemical and Catalytic Properties in the Cycloaddition of CO2 to Propylene Oxide

Zeolitic imidazolate frameworks MAF-5 and MAF-6 based on Zn2+ and 2-ethylimidazole were demonstrated to be efficient heterogeneous catalysts in solvent-free coupling of CO2 and propylene oxide (PO) to produce propylene carbonate (PC) at 0.8 MPa of CO2 and 80 °C. Activity of MAF-5 was lower in comparison with MAF-6 due to the difference in their structural and textural characteristics. MAF-6 samples with particle size of 190 ± 20, 360 ± 30, and 810 ± 30 nm were prepared at room temperature from [Zn(NH3)4](OH)2 and 2-ethylimidazole. Control of particle size was achieved by variation of type of alcohol in alcohol/cyclohexane media for the preparation of MAF-6. According to this comprehensive study, the yield of PC was found to decrease with increasing crystal size of the MAF-6 material, which was related to the change in textural properties and the number and localization of active sites. The combination of MAF-6 with particle size of with particle size of 190 ± 20 nm and tetrabutylammonium bromide ([n-Bu4N]Br) as co-catalyst led to an approximately 4-fold enhancement in the yield of PC (80.5%). Compared with reported ZIFs catalysts, the efficiencies of MAF-5/[n-Bu4N]Br and MAF-6/[n-Bu4N]Br binary systems were comparable and higher under similar reaction conditions.

Investigation of Using Multi-Hydroxyl Ionic Liquid Polymer as Catalyst to Produce Propylene Carbonate

Ionic liquid with a single hydroxyl group, 1-(2-hydroxyl-ethyl)-3-methylimidazolium bromide (HEMIMB), was prepared. It was found that HEMIMB could be an efficient catalyst for CO2 cycloaddition to propylene oxide to produce propylene carbonate (PC). An ionic liquid polymer with multi-hydroxyl groups poly(1-2-hydroxyl-ethyl)-3-vinylimidazolium bromide (PHEVIMB) was also prepared. In this study, both catalytic reaction performances of HEMIMB and PHEVIMB were investigated. Results showed that product separation and catalyst recycles in the process of PHEVIMB catalytic reaction system was much more efficient with a yield of 55.5%, even after three consecutive catalyst reuses. Meanwhile, the separation was less time-efficient for homogeneous catalytic system of HEMIMB molecules with a single hydroxyl group despite of a yield of 92.4%. When it comes to practical industrial process design, the single component with multifunctional ionic liquid polymer, as catalyst, may be considered effective and friendly process.

Understanding the CO2 valorization to propylene carbonate catalyzed by 1-butyl-3-methylimidazolium amino acid ionic liquids

Nowadays, CO2 emission impacts on our life standards, revealing itself as one of the major environmental challenges of present century. One main strategy is to develop new technologies within integrated Carbon Capture and Utilization (CCU), to obtain valuable chemical products. The design of new systems able to efficiently retain CO2 and convert it at mild operating conditions is an important challenge. Ionic liquids (ILs) were demonstrated as multitask absorbents-catalysts in processes involving CO2 capture and cycloaddition reaction to obtain cyclic carbonates. In this work, the use of amino acid based ionic liquids (aa-ILs) is proposed to promote a sustainable catalytic process for CO2 valorization using propylene oxide (PO) to produce propylene carbonate (PC). Three aa-ILs were proposed in the study: 1-butyl-3-methylimidazolium glycinate ([bmim][GLY]), 1-butyl-3-methylimidazolium methioninate ([bmim][MET]), and 1-butyl-3-methylimidazolium prolinate ([bmim][PRO]). Computational calculations by DFT method reveals that the reaction firstly occurs through the PO ring opening by aa-IL catalyst, followed by CO2 nucleophilic addition, rather than direct CO2 activation. The carbonate formation using aa-IL catalysts was experimentally demonstrated by ATR-FTIR experiments at mild conditions (4 bar of initial pressure and 80–120 °C), obtaining PC yields ordered as [bmim][MET] > [bmim][GLY] > [bmim][PRO], same trend than their CO2 chemical absorption capacity. Further stirred tank reactor experiments were carried out to scale-up the process, confirming the suitability of aa-ILs as homogeneous catalyst for CO2 conversion to cyclic carbonates, with extremely low consumption (0.5% m/m).

One‐pot Fixation of CO2 into Glycerol Carbonate using Ion‐Exchanged Amberlite Resin Beads as Efficient Metal‐free Heterogeneous Catalysts

AbstractThe one‐pot synthesis of glycerol carbonate from carbon dioxide and glycerol was achieved using ion‐exchanged Amberlite resin beads as metal‐free heterogeneous catalysts. Two commercially available Amberlite resin beads consisting of polystyrene cross‐linked with divinylbenzene and functionalized with either trimethyl ammonium chloride (IRA‐900) or dimethyl ethanol ammonium chloride (IRA‐910) groups were used as starting materials to prepare the catalysts. These polymeric beads were transformed into their iodide (Amb‐900‐I, Amb‐OH‐910‐I) or hydroxide (Amb‐900‐OH and Amb‐OH‐910‐OH) counterparts through straightforward ion‐exchange reactions. First, the two resin bead catalysts in hydroxide form were tested in the base‐catalyzed transcarbonation reaction of glycerol with propylene carbonate. Both resin bead catalysts were more active compared to benchmark basic catalysts as hydrotalcites and attained 80 % yield of glycerol carbonate over Amb‐OH‐910‐OH after 2 h at 115 °C, employing a 4 : 1 ratio between propylene carbonate and glycerol. Then, the one‐pot reaction of CO2, glycerol and propylene oxide to produce propylene carbonate, glycerol carbonate and propylene glycol was investigated as the main target of this study. The reaction involves two steps: the reaction of propylene oxide with CO2 yielding propylene carbonate, and the transcarbonation of the formed cyclic carbonate with glycerol. Amb‐900‐I, Amb‐OH‐910‐I, Amb‐OH‐910‐OH and combinations of the latter two were employed as catalysts. Although Amb‐OH‐910‐I alone is poorly active in the transcarbonation reaction, it showed the highest catalytic activity in the one‐pot cascade reaction, surprisingly surpassing the performance of the Amb‐OH‐910‐I/Amb‐OH‐910‐OH mixtures and reaching high yields of glycerol carbonate (81 %, 115 °C, 4 h). These findings led to proposing a mechanism for the one‐pot reaction using the Amb‐OH‐910‐I catalyst. The bead format led to easy recovery of the catalyst, which displayed good reusability in consecutive runs.

Catalytic conversion of CO2 to propylene carbonate over Pt-decorated Mg-substituted metal organic framework

Porous coordination polymers of Mg (II) dihyroxyterephtalate (Mg-MOF-74) at various Ptx loadings (x = 0–10 wt%) were synthesized, characterized and tested for the catalytic cycloaddition reaction between CO2 and propylene oxide (PO). The reaction was studied over a range of temperatures between (100–170 °C), pressures (9.1–19.5 bar) and reaction times (4–15 hours) to produce propylene carbonate (PC). The results show that the Pt loading on the catalyst surface improves the selectivity toward PC in the presence of dimethylformamide (DMF) and dichloromethane (DCM) which serve as solvents and promoters for the reaction. Pt loading is shown to be concomitantly related to the number of uncoordinated MgO defect sites produced during synthesis. As Pt loading increases, the number of uncoordinated MgO sites in the Mg-MOF-74 framework structure also increases. During reaction, PO conversion and PC selectivity were shown to systematically increase with Pt loading and the number of uncoordinated MgO defect sites. A synergistic effect is observed where the combined use of Ptx/Mg-MOF-74, DMF and DCM exhibit performance benefits beyond their use individually. The catalysts we characterized before and after reaction using XRD, EDX, ICP, BET, SEM and TGA. The catalysts show a relatively high stability and reusability as confirmed by reaction studies, XRD and FE-SEM.

CO2 cycloaddition with propylene oxide to form propylene carbonate on a copper metal-organic framework: A density functional theory study

Metal-organic frameworks (MOFs) have emerged as unique catalysts for CO2 conversion, but the catalytic mechanism remains elusive. In this study, a density functional theory (DFT) study is reported on CO2 cycloaddition with propylene oxide (PO) to produce propylene carbonate (PC), catalyzed by a Cu-MOF (NTU-180) in the presence of tetrabutylammonium bromide (TBAB). This reaction was experimentally observed to have a remarkably high efficiency. We compute the electronic and Gibbs energies of the reactants, intermediates, transition states and products for two alternative reaction pathways. On NTU-180/TBAB, the three-member ring opening of PO is revealed to possess a higher activation barrier than the five-member ring closure of PC, and thus it is the rate-determining step. Pathway I is kinetically more favorable as its ring opening has a lower barrier than in Pathway II. Moreover, the activation barriers of ring opening and ring closure steps on NTU-180/TBAB are substantially lower than those in the gas phase, and also lower than those on TBAB alone and on a Cu2 paddle-wheel/TBAB complex. At a molecular level, these results unambiguously highlight the important roles of the Cu sites and the confinement effect of NTU-180 in enhancing the stabilities of reaction intermediates and transition states, and promoting the catalytic cycloaddition of CO2 with PO. In addition, the sensitivities of the DFT calculation results to the choice of functional and basis set are critically analyzed. While the electronic and Gibbs energies vary substantially with functional, the activation barriers in the rate-determining step are affected only slightly by the functional and marginally by the basis set. This theoretical study provides microscopic and quantitative insights into the high catalytic activity observed experimentally for CO2 cycloaddition on NTU-180/TBAB, and might facilitate the development of new catalysts for efficient CO2 conversion.

Insight on asym-Pyrazolium Ionic Liquids for Chemical Fixation of CO2 and Propylene Epoxide into Propylene Carbonate without Organic Solvent and Metal

From the perspective of environmental protection and resource utilization, the fixation of carbon dioxide (CO2) is an interesting and meaningful topic. In this work, a series of asym-dialkylpyrazolium ionic liquids are synthesized by us to explore their catalytic activity for the cycloaddition of CO2 and propylene epoxide to produce propylene carbonate (PC). They could be easily synthesized by a simple reaction, which is the premise for the large-scale application. The effect of alkyl chain length in cation on catalytic performance is investigated. Although asym-pyrazolium ILs present less catalytic activity than sym-pyrazolium ILs, the product yield catalyzed by EPPzBr is as high as 85% with PC selectivity of 99%, which is better than most of nonfunctionalized ionic liquids. Moreover, the catalyst could be reused at least five times without significant loss of catalytic activity. To elucidate the structure–property relationship, the difference between asym-pyrazolium ILs and sym-pyrazolium ILs is discuss...

금속 함유 이온성 액체 촉매상에서의 프로필렌 카보네이트의 합성

본 연구에서는 세 가지 형태의 금속을 함유한 이온성 액체 촉매를 제조하고, 다양한 물리화학적 분석법으로 제조된 촉매의 특성분석을 실시하였다. 프로필렌 옥사이드(PO)와 이산화탄소의 부가반응을 통한 프로필렌 카보네이트(PC)의 합성반응에서 세 가지 촉매의 반응활성을 확인하였고 속도론적 연구를 통해 촉매들의 반응성 차이를 비교하였다. 세가지 금속이 다른 촉매에 대한 유사 반응속도 상수(<TEX>$K_{app}$</TEX>)는 <TEX>$(MeIm)_2ZnCl_2$</TEX>, > <TEX>$(MeIm)_2FeCl_2$</TEX> > <TEX>$(MeIm)_2CuCl_2$</TEX>의 순서이며, 이 것은 세 가지 촉매의 반응성이 <TEX>$(MeIm)_2ZnCl_2$</TEX> > <TEX>$(MeIm)_2FeCl_2$</TEX> > <TEX>$(MeIm)_2CuCl_2$</TEX>의 순서로 실험결과와 잘 일치하였다. In this study, three different metal-containing ionic liquid catalysts were prepared by metal insertion and characterized by various physicochemical analytic methods. The catalytic performance of the metal containing ionic liquids in the cycloaddition of <TEX>$CO_2$</TEX> with propylene oxide (PO) to produce propylene carbonate (PC) was investigated under the solvent free condition. The order of approximate rate constants (<TEX>$K_{app}$</TEX>) for the metal containing ionic liquid catalysts was <TEX>$(MeIm)_2ZnCl_2$</TEX>, > <TEX>$(MeIm)_2FeCl_2$</TEX> > <TEX>$(MeIm)_2CuCl_2$</TEX>. These results are in accord with the experimentally obtained activity order of the different metal containing ionic liquid catalysts.

DMF and mesoporous Zn/SBA-15 as synergistic catalysts for the cycloaddition of CO2 to propylene oxide

A series of Zn/SBA-15 samples with Zn/Si molar ratios from 0.06 to 0.18 were prepared by one-pot synthesis method. XRD, N2 adsorption/desorption, TEM, FTIR and XPS techniques were used to determine the textual structures and physicochemical properties of Zn/SBA-15 samples. The mesoporous structure of SBA-15 was well preserved with Zn/Si molar ratio up to 0.18. Thereafter, Zn/SBA-15 was tested for the cycloaddition reaction of CO2 and propylene oxide to produce propylene carbonate in the presence of DMF. The catalytic results showed that Zn/SBA-15 and DMF synergistically catalyzed the cycloaddition of CO2 to propylene oxide. Moreover, the effects of various reaction factors, including different metal elements modified SBA-15, reaction temperature, CO2 pressure, reaction time and DMF amount were also discussed in detail. Propylene carbonate yield as high as 92.3% was achieved on Zn/SBA-15(0.15) catalyst at 160°C and 2MPa of CO2 pressure for 6h in the presence of DMF. In addition, the recycling property of Zn/SBA-15 catalyst was also investigated. A possible catalytic mechanism for the cycloaddition of CO2 to propylene oxide was proposed.

Catalytic synthesis of propylene carbonate from propylene oxide and carbon dioxide in the presence of rhodium complexes modified with organophosphorus ligands and chitosan

The reaction between CO2 and propylene oxide to produce propylene carbonate in the presence of rhodium complexes modified with organophosphorus ligands and chitosan has been studied. Highly effective catalysts mediating the reaction with almost a 100% yield and 100% selectivity have been prepared using rhodium compounds modified with triphenylphosphine and chitosan.

Effective synthesis of cyclic carbonates from CO2 and epoxides catalyzed by KI/cucurbit[6]uril

The development of efficient, inexpensive, and nontoxic catalysts for cycloaddition of CO2 with epoxides to produce five-membered cyclic carbonates is a very interesting topic. In this work, cycloaddition of CO2 with propylene oxide (PO) to produce propylene carbonate (PC) catalyzed by potassium halides (KCl, KBr, and KI) in the presence of cucurbit[6]uril (CB[6]) was studied at various conditions. It was discovered that the potassium halides and CB[6] had excellent synergetic effect in promoting the reaction, and the KI/CB[6] catalytic system was the most efficient among them. The decrease of the activity and selectivity of KI/CB[6] was negligible after the catalytic system was reused five times. Further study indicated that the KI/CB[6] catalytic system was also very active and selective for the cycloaddition of CO2 with other epoxides, such as glycidyl phenyl ether, epichlorohydrin, and styrene oxide. The mechanism for the synergetic effect of KI and CB[6] was also discussed.

MOF-5/n-Bu4NBr: an efficient catalyst system for the synthesis of cyclic carbonates from epoxides and CO2 under mild conditions

The development of efficient heterogeneous catalysts for the cycloaddition of CO2 with epoxides to produce five-membered cyclic carbonates under mild reaction conditions is of great importance. In this work, the coupling reaction of CO2 with propylene oxide (PO) to produce propylene carbonate (PC) catalyzed by MOF-5 (metal-organic frameworks) in the presence of quaternary ammonium salts (Me4NCl, Me4NBr, Et4NBr, n-Pr4NBr, n-Bu4NBr) was studied in different conditions. It was discovered that MOF-5 and quaternary ammonium salts had excellent synergetic effect in promoting the reaction, and the MOF-5/n-Bu4NBr catalytic system was the most efficient among them. The optimal temperature for the reaction was around 50 °C. The reaction could be completed in 6 h at low CO2 pressure with very high selectivity. A decrease of the yield of PC was not noticeable after MOF-5 was reused three times, indicating that the MOF-5 was stable. The MOF-5/n-Bu4NBr catalytic system was also very active and selective for the cycloaddition of CO2 with other epoxides, such as glycidyl phenyl ether, epichlorohydrin and styrene oxide. The mechanism for the coupling reaction is also discussed.