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Synergistic effect of methylene and carboxyl group in pyrazolium ionic liquids on the cycloaddition of CO2. • A series of carboxyl functionalized pyrazolium ionic liquids are firstly synthesized. • They are efficient catalyst for cycloaddition of CO 2 even under 70 °C. • Ethyl group is assurance for activity of carboxyl functionalized ionic liquids. The carboxyl functionalized ionic liquids normally show better catalytic activity than the corresponding ionic liquids without functional group for the coupling reaction of carbon dioxide and epoxides. However, a long alkyl chain, at least propyl, is required as bridge between carboxyl group and N atom of aromatic heterocycle to ensure the catalytic activity. Inclusion of long alkyl chain indicates the low synthetic yield and harsh synthetic conditions. It is rarely reported that the carboxyl functionalized ionic liquid with methyl would present the high catalytic activity. With the help of ethyl substituted on the other N atom of pyrazolium ring, the carboxylmethyl pyrazolium ionic liquid (CMEPzBr) would present the excellent catalytic activity (yield >99%). Moreover, the product yield still keeps larger than 90% even under 70 °C and 1.0 MPa CO 2 initial pressure. The role of methylene appeared on the near N atom is elucidated by density functional theory. The catalytic activity of carboxylmethyl imidazolium ionic liquid is not refined greatly when methylene is substituted on the other N atom of imidazolium ring. The optimal reaction conditions are investigated along with the recyclability and reusability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Double-IL and Cluster-IL model models are employed to study the catalyzed CO 2 fixation. • The Cluster-IL model is firstly employed in this work. • Solvent effect of ionic liquids is studied by combination of ONIOM and MD. • Double-IL model has the best compromise between computational cost and result. Abstract Although the mechanism of coupling reaction of carbon dioxide with propylene oxide catalyzed by 1-(2-hydroxyl-ethyl)-3-methylimidazolium chloride (HEMIMC) ionic liquids has been elucidated previously, there are two major drawbacks. One is that the solvent effect is treated by the existed solvent model rather than the real HEMIMC ionic liquids. The other one is that the influence of interactions between ionic liquids on the catalysis is not considered, which has been testified to be important in the catalytic process. So the mechanism is explored by Double-IL model and Cluster-IL model again to fully consider the interactions among ionic liquids. The Cluster-IL model is firstly employed in this work. Then, the HEMIMC are incorporated in Double-IL model and Cluster-IL model as the solvent, respectively, although it is very expensive for the computational cost. Our central aim we aimed to compare the difference among different catalytic models, to consider the solvent effect aroused by ionic liquids, and to improve the reliability of theoretical prediction. [ABSTRACT FROM AUTHOR]

A series of low-cost and easily prepared benzyl substituted imidazolium ionic liquids are firstly synthesized and employed as catalyst for the cycloaddition of carbon dioxide with epoxides without any solvent and co-catalyst. The synthesized imidazolium ionic liquids are characterized by 1 H NMR, HRMS, and MS. The influence of different substituted groups in cation and reaction parameters on catalytic activity is investigated. The highest conversion yield of cyclic carbonate (94.89%) could be achieved with slight amount of catalyst (0.25 mol%) under 130 °C and 2.0 MPa during 4 h. Meanwhile, the mechanisms of cycloaddition of carbon dioxide with epoxides catalyzed by four benzyl substituted ionic liquids with different substituted groups are investigated by theoretical calculations. The role of hydrogen bond and other noncovalent interactions played in catalytic process is further uncovered to deeply understand the difference of various catalysts from atomistic level. [ABSTRACT FROM AUTHOR]

Numerous binary catalysts of IL/Lewis acid have been developed for the coupling reaction of carbon dioxide and epoxides to form cyclic carbonates with high catalytic activity under benign environment. However, the mechanism is still obscure for most of catalysts. The catalytic mechanism of the binary catalysts hexaalkylguanidinium bromide/ZnBr 2 is elucidated by theoretical method in this work to obtain the reason of their high catalytic activity. Owing to the complicated of the binary catalysts, there are lots of possible attack forms. Finally, it is confirmed that the electrophilic attack from the Zn complex and the nucleophilic attack from the Br − anion are the essential factors to promote the ring opening of PO. Following the most favorable route, the catalytic activity of different binary catalysts, including the ILs/ZnBr 2 and NBu 4 Br/Zn(salphen), is compared. Moreover, the influence of the bulk of hexaalkylguanidinium salt on the catalytic activity is studied. The catalytic activity is enhanced with the increased bulk of the hexaalkylguanidinium salt. It is expected that our theoretical study would provide valuable clues to further refine the binary catalysts. [ABSTRACT FROM AUTHOR]

The fixation of carbon dioxide with epoxide catalysed by a series of carboxylic acidic functionalised ionic liquids (ILs) catalysts is investigated by density functional theory method. Except for the catalysts reported by the experiment, the catalytic activity of a new designed catalyst (4c see Scheme 1) is also explored. These ILs are categorised into four groups according to the different cation structures and number of functional groups. The effects of different chain length, anion, and cation structure on the catalytic activity are explored. The elongation of alkyl chain length in cation will increase the product yield, while increasing the chain bulk has almost negligible effect on the enhancement of catalytic activity. Utilisation of imidazole group as the cation is better than pyridine group. And the cation with two functional groups will have a better catalytic activity than that with one functional group. [ABSTRACT FROM PUBLISHER]

Utilization of CO 2 (carbon dioxide) to synthesize useful organic compounds has attracted much attentions from the academia and industry. Recently, the fixation of CO 2 catalyzed by using four hydroxyl-functionalized ionic liquids (ILs) has been successfully achieved. However, the detailed mechanism is still ambiguous. We performed a theoretical study on the mechanism of the fixation of CO 2 catalyzed by 2-hydroxyl-ethyl-triethylammonium bromide (HETEAB) using the DFT method. The structural and energetic information for each possible route were obtained. Furthermore, the similarities and differences of two different catalysts, HETEAB and 2-hydroxyl-ethyl-tributylammonium bromide (HETBAB), were discussed in detail. In addition, the result shows that the OH functional group is one essential factor to improve the catalyst ability. Except that, including active H atom in the IL is the other major factor to refine the catalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mg-Ni dual atomic catalysts are constructed for eCO 2 RR to produce syngas. • Faradaic efficiency is close to ∼100 % exhibiting the excellent selectivity. • The controllable H 2 /CO ratio is achieved by tuning Ni content. • Synergistic effect to win instead of each species doing its own job by DFT calculations. Electrochemical carbon dioxide reduction reaction (eCO 2 RR) to generate syngas is an appealing strategy for CO 2 net reduction. However, it suffers from the inferior faradaic efficiency (FE), selectivity, and difficult modulation of hydrogen/carbon monoxide (H 2 /CO) ratio. To address these issues, a series of magnesium-nickel (Mg-Ni) dual atomic catalysts with different Ni contents are fabricated on the nitrogen-doped carbon matrix (MgNi X -NC DACs) by one-step pyrolysis. MgNi 5 -NC electrocatalyst generates 0.51–0.79 H 2 /CO ratios in a potential range of −0.6 to −1.0 V vs. reversible hydrogen electrode (RHE) and the total FE reaches 100 % with good stability. While a wider range of H 2 /CO (0.95–4.34) is achieved for MgNi 3 -NC electrocatalyst in the same overpotential range, which is suitable for typical downstream thermochemical reactions. Introduction of Ni species accelerates the generation of CO, however, there is much less influence on the H 2 production as compared with Mg-based single atomic electrocatalyst. According to the experimental results and density functional theory (DFT) calculations, the synergistic effect between Mg and Ni achieves the satisfied results rather than each one fulfill its own duty for selective producing H 2 and CO, respectively. This work introduces a feasible approach to develop atomic catalysts on main group metal for more controllable CO 2 RR. [ABSTRACT FROM AUTHOR]

Transformation of CO 2 to cyclic carbonate catalyzed efficiently by ionic liquids with multiple active centers under mild conditions without any solvent or co-catalyst. [Display omitted] • A novel ionic liquid with multiple active centers is synthesized. • Capture of CO 2 plays a critical role in the reaction system. • The 98.5 % CPC yield could be achieved under 50 °C and 1 bar CO 2 during 6 h. • A new reaction mechanism is proposed by DFT and 13C NMR. The ideal catalyst for the coupling reaction of CO 2 with epoxides is expected to have comprehensive advantages. An appealing ionic liquid, C[CMImBrTMG] 2 , with multiple active centers is synthesized to accomplish several goals in a single-component catalyst to adsorb CO 2 and afford the robust electrophilic and nucleophilic groups. The 98.5 % yield of chloropropylene carbonate (CPC) is achieved at 50 °C under 1 bar CO 2 pressure during 6 h. Moreover, C[CMImBrTMG] 2 is easy to be simply separated from the catalytic system by washing with ethyl acetate. A new reaction mechanism is constructed by the density functional theory (DFT) along with the 13C NMR confirmation. The contribution of critical groups in C[CMImBrTMG] 2 to the catalytic performance is further elucidated by the electrostatic potential (ESP), atoms in molecule (AIM), and electron localization function (ELF). [ABSTRACT FROM AUTHOR]

The mechanism for the cycloaddition of carbon dioxide and epoxides catalyzed by ionic liquids has been elucidated in lots of theoretical literature. It is well known that the calculated barrier height could not be compared with the activation energy. However, it is expected that the sequence of activity estimated by barrier height could be consistent with the experimental result. Actually, the calculated results are not accurate enough to be reliable. One of possible reasons is attributed to the improper treatment for the solvent effect. The solvent effect induced by ionic liquids is not carefully considered or neglected at all in most of previous theoretical studies. In this work, ionic liquids are really included in the catalytic system to consider the solvent effect by the ONIOM method along with the molecular dynamics simulations. When the solvent effect is considered, the theoretical reliability is greatly improved. More important, this model is suitable not only for non-protic ionic liquids but also for protic ones and not only for imidazolium ionic liquids but also for pyrazolium ionic liquids. The solvent effect aroused by epoxides is also considered by the same model. Unlabelled Image • The solvent effect is considered by ONIOM model. • ONIOM model is reliable for both imidazolium and pyrazolium ionic liquids. • OINOM model is suitable for both non-protic and protic ionic liquids. [ABSTRACT FROM AUTHOR]

The cycloaddtion reaction of CO 2 and PO catalyzed by amino-functionalized pyrazolium ionic liquids with good balance among various conditions. [Display omitted] • A series of amino-functionalized pyrazolium ionic liquids are firstly synthesized. • They are efficient homogeneous catalysts for cycloaddition of CO2 with PO. • The preparation of ionic liquid is simple with product yield over 94%. • Catalytic reaction conditions are more benign than other ionic liquids. • The reaction mechanism is elucidated by DFT calculation. Numerous ionic liquids have been developed to catalyze the coupling reaction of carbon dioxide with epoxides without co-catalyst and organic solvent. Although the catalytic activity is satisfied with cyclic carbonate yield over 90%, the reaction condition is still not regarded as benign enough, especially for reaction temperature and carbon dioxide initial pressure. Four new amino-functionalized pyrazolium ionic liquids, AEMPzBr, APMPzBr, AEEPzBr, and APEPzBr, have been firstly synthesized in simple reaction steps with cheap raw materials. Moreover, they would catalyze the coupling reaction of carbon dioxide with propyleneoxide under the optimal reaction conditions, 110 °C, 1.5 MPa carbon dioxide initial pressure as well as 1.0 mol% catalyst amount for 4.0 h, with propylene carbonate yield over 94%. The reaction temperature is decreased by 10–20 °C as compared with other single-component ionic liquids. At the same time, the carbon dioxide initial pressure is not increased to keep 1.5 MPa, which is also superior to lots of other ionic liquids, such as imidazolium, pyrazolium, and guanidinium ionic liquids. The recyclability and suitability of amino-functionalized pyrazolium ionic liquids are also explored. Finally, the catalytic mechanism is investigated by the density functional theory. Moreover, the influence of weak interactions on the reaction is analyzed by atoms in molecules and non-covalent interactions. As compared with other reported ionic liquids, the reaction condition catalyzed by APEPzBr is more benign with comparable product yield. More importantly, there is good balance among various reaction conditions without sacrificing one to ensure others. Amino-functionalized pyrazolium ionic liquids would be a new kind of powerful catalysts for the carbon dioxide fixation. [ABSTRACT FROM AUTHOR]

Three pyrazolium ionic liquids, 1,2-diethylpyrazolium bromide (DEPzBr), 1,2-diethyl-3-methylpyrazolium bromide (DEMPzBr), and 1,2-diethyl-3,5-dimethylpyrazolium bromide (DEDMPzBr), are firstly applied as catalysts for coupling reaction of carbon dioxide (CO 2 ) and propylene oxide (PO) with the propylene carbonate (PC) yields in a range of 82.7%–88.7% under a benign condition, 120 °C, 2.0 MPa initial CO 2 pressure and 4 h with 0.5 mol% catalysts loading. The relationship between structure and catalytic activity of pyrazolium ionic liquids are investigated by two different theoretical models, which indicates that both electrostatic interaction and hydrogen bond promote the ring-opening of PO. Both the theoretical and experimental results present that the catalytic activity decreases in the sequence of DEPzBr > DEDMPzBr > DEMPzBr. Pyrazolium ionic liquids would be employed as a novel efficient single-component catalyst without solvent and co-catalyst. It is expected that we would open an express pathway to develop new catalysts with the desired properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solvent effect of ionic liquids on the fixation of CO 2 is studied by ONIOM and MD. • Critical hydrogen bond and C-Br interaction are analyzed by NCI and AIM. • ONIOM model displays the more reasonable result than PCM model. • Which one is more important, nucleophilic or electrophilic activation? The solvent effect of ionic liquids on CO 2 fixation catalyzed by hydroxyl-functionalized quaternary ammonium-based ionic liquids is thoroughly investigated by ONIOM method associated with the molecular dynamics simulation. As compared with the catalytic activity determined in experiment, the catalytic activity estimated by ONIOM model is more credible than previous result calculated by the polarized continuum model. The critical hydrogen bond and C-Br interaction are analyzed by non-covalent interaction and the atoms in molecules methods. The analysis indicates that the electrophilic activation aroused by hydrogen bond provides more contribution than nucleophilic activation aroused by C-Br interaction in reaction catalyzed by trihydroxyethylethyl ammonium bromide. In contrast, the nucleophilic activation is more important in reactions catalyzed by other three ionic liquids. Choice of the suitable model is possible to obtain the reliable catalytic activity, which would be comparable with the experimental result. [ABSTRACT FROM AUTHOR]

The efficient fixation of CO 2 without co-catalyst and solvent under metal-free condition is still an urgent topic in sustainable chemistry. In this work, a series of dialkylpyrazolium ionic liquids are employed to promote the cycloaddition of CO 2 and PO to produce PC. They would be easily synthesized by a simple one-pot reaction. The effect of alkyl chain length in cation and different anion is explored. Diethylpyrazolium iodide presents the excellent catalytic activity with the product yield of 96% and selectivity of 99% in a benign condition. Moreover, the catalyst could be reused for at least five times without significant loss of catalytic activity. An intensive structure-activity research testifies that the cycloaddition of CO 2 with PO is activated by a synergistic effect from both cation and anion of ILs. To confirm it, the detailed mechanism is investigated by density functional theory associated with the non-covalent interactions and atoms in molecule analysis. Besides the electrostatic interaction between cation of ionic liquid and PO, the noncovalent interaction, especially for hydrogen bond, plays a vital role in promoting the reaction. [ABSTRACT FROM AUTHOR]

An effective strategy to immobilize Ni-Pc molecules on the fruit-peel-derived carbon framework surface, which showed outstanding selectivity, catalytic activity, and stability in the electrocatalytic reduction CO 2 to CO. [Display omitted] • A mass of defects and mesopores can be observed in the Fruit-peel-derived CF surface. • The stabled, dispersed Ni-Pc molecules catalyst was immobilized on the CF surface. • The obtained Ni-Pc/CF catalyst exhibits excellent selectivity and catalytic activity for CO 2 -to-CO conversion. • The Ni-Pc/CF catalyst possesses outstanding electrochemical durability. Developing a robust catalyst for CO 2 reduction reaction (CO 2 RR) is critical to achieving a closed carbon cycle. Yet, the process of CO 2 RR still faces enormous challenges, in part because of the lack of highly active, stable, as well as cost-effective electrocatalysts. In this work, we reported an effective and sample strategy to immobilize nickel phthalocyanine (Ni-Pc) molecules on the fruit-peel-derived carbon framework surface (denoted as Ni-Pc/CF and carbon framework denoted as CF) with exceptional CO production performances. Dispersed Ni-Pc molecules on the carbon materials are verified by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman measurements. The obtained Ni-Pc/CF catalyst shows that the high faradaic efficiency (FE) exceeds 95.0 % over a potential of −0.7 to −0.9 V (vs reversible hydrogen electrode (RHE), V RHE), the maximum FE (99.1 %) can close to 100 % at −0.8 V, and the excellent stability over a 10 h reaction period. This work offers valuable insights into the immobilization of stabilized, highly dispersed molecule catalysts on carbon materials surfaces for selective reduction of CO 2 to CO. [ABSTRACT FROM AUTHOR]

[Display omitted] • Machine learning was used to predict the yields of ionic liquids catalyzed CO 2 cyclization reaction for the first time. • Density function theory calculations were conducted to obtain reaction descriptors with high-precision. • The strategy of refining the database quality improves the predictive ability of RF model significantly. • The ML model was interpreted well by the shapely additive explanation method. Ionic liquids are one of the excellent catalysts for the CO 2 cycloaddition reaction, which is an effective means to realize CO 2 utilization and alleviate environmental problems. However, the design of ionic liquids catalysts has great blindness due to the diversity of their anion and cation structures. Herein, we collected a database of 866 samples for CO 2 cyclization with ionic liquids as catalysts and established the yield prediction model with various machine learning regression algorithms. Together with density function theory (DFT) calculated molecular electronic properties and the experimental conditions as the input descriptors, random forest (RF) model has better prediction accuracy than support vector regression (SVR) and multilayer perceptron (MLP) for the whole data. When the dataset was subdivided into different subsets based on substrates and ionic liquids, the prediction accuracy of the model was also improved. For the imidazole subset with no additional solvent or additive added, the RF model achieves good accuracy with the R2 of 0.80 for the test data. Moreover, the shapely additive explanation (SHAP) method was used to interpret the ML models. The strategy of refining the descriptors and dataset used in our work provides guidance for establishing highly reliable machine learning models in the chemistry reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Suitable transition metals are selected for CO 2 RR on the defective g-C 3 N 4. • Machine learning builds a bridge between catalytic activity and various features. • Selected transition metals are coordinated on other carbon supporter. • The 25% doped amount of uncoordinated N is suitable. Electrocatalysis of CO 2 reduction reaction (CO 2 RR) has attracted elevated attentions since it is favorable to prompt the carbon cycle in a sustainable pathway. However, the applications of this technology is obstructed by the low activity and selectivity due to the inert of CO 2 and favored hydrogen evolution reaction. Development of robust catalysts is the most feasible method to decrease the overpotential and suppress the competitive side reaction. Single-atom-catalysts (SACs) is one of the most promising catalysts with the satisfied activity. However, the clear and popular rules are still absence to explore the SACs with the desired properties due to the complicated items related with the overall performance. The suitable transition metals (TMs) are screened out based on the defective g-C 3 N 4 (V N -C 3 N 4) supporter by the first principle. Among 24 screened transition metals, the Ni-V N -C 3 N 4 exhibits the better performance as compared to others. Later, the machine learning (ML) algorithm builds a bridge between catalytic activity and intrinsic structural and atomic features. Then, the same coordination environment is constructed on the graphene to explore the possibility to replace the V N -C 3 N 4 with other carbon substrate. When the doped amount of uncoordinated N reaches 25 wt%, the catalytic activity of Ni N C SAC based on the graphene is close to that based on the V N -C 3 N 4. This work introduces a method to construct the SACs by regulating the N -doped amount on the supporter. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalyzed mechanism of propargylic alcohol and H 2 O is investigated. • CO 2 could be absorbed by the [Bu 4 P+] cation to form [Bu 4 P -H -CO 2 ] complex. • A novel mechanism is proposed with the [Bu 4 P -H -CO 2 ][Im +H ] complex employed as the actual catalytic species. Hydration of propargylic alcohols is one of the most important pathways to synthesize α-hydroxy ketones. However, its mechanism is still obscure in the presence of multiple catalytic species. The mechanism of catalysis for the hydration of propargylic alcohols in the presence of [Bu 4 P+][Im-] is investigated along with the carbon dioxide (CO 2) as the co-catalyst by the density functional theory (DFT) with the aim to elucidate the role of [Bu 4 P+] cation and [Im-] anion. The CO 2 could be absorbed by the [Bu 4 P+] cation to form [Bu 4 P -H -CO 2 ] complex after the hydrogen atom in [Bu 4 P+] cation transfers to the [Im-] anion. Then, both [Bu 4 P -H -CO 2 ] and [Im +H ] are employed as the actual catalytic species to construct a new pathway. It is the more favorable as compared with the previously reported pathways. In previous reported pathway, the [Im-] anion is regarded as the real catalytic species, while [Bu 4 P+] cation plays the auxiliary role to stabilize the substrate by the hydrogen bond. The mechanism of the same reaction catalyzed by other four different ionic liquids is also investigated to further testify the contribution of [Bu 4 P+] cation and [Im-] anion in the catalysis. This work not only provides a new insight into the cation-regulated pathway for the hydration of propargylic alcohols but also points out a new strategy to design the ionic liquids achieving the improved catalytic efficiency. [ABSTRACT FROM AUTHOR]

Immobilized ionic liquids are one of the most popular catalysts for the cycloaddition of carbon dioxide (CO 2) and epoxides with some distinguished advantages. However, the harsh reaction condition, especially for the high reaction pressure, is still the obstacle for its large-scale application. A series of amino-functionalized pyrazolium ionic liquids are grafted on SBA-15 in this work. Among them, SBA-15-APMPzBr(20) exhibits the best catalytic activity achieving 97.6% product yield under 0.5 MPa CO 2 pressure at 100 °C by using 100 mg SBA-15-APMPzBr(20) for 10 h. No solvent is added in the catalytic system. Moreover, SBA-15-APMPzBr(20) exhibits the good recyclability and generality. Its excellent catalytic performance is attributed to the contribution from both immobilized ionic liquids and the SBA-15 supporter. Besides the mesoporous feature, the hydroxyl groups in SBA-15 promote the ring-opening of substrate, which is testified by the experimental measurements and density functional theory calculations. [Display omitted] • A series of amino-functionalized pyrazolium ionic liquids are grafted on SBA-15. • The 97.6% CPC yield could be achieved under 100 °C and 0.5 MPa CO 2 pressure. • SBA-15 and immobilized ionic liquids contribute to promote the ring-opening of ECH. • The mechanism is elucidated by the DFT calculations. [ABSTRACT FROM AUTHOR]

The mechanism of cycloaddition reactionbetween carbon dioxideand epoxide, catalyzed by HEMIMC (1-(2-hydroxyl-ethyl)-3-methylimidazoliumchloride), was investigated using the DFT (density functional theory)method. In the presence of HEMIMC, the reaction mechanism changedfrom single-step to multipath. Seven reaction pathways are reportedhere, including two steps, epoxide ring-opening and ring-closure ofcyclic carbonate, or three main steps, epoxide ring-opening, carbondioxide insertion, and ring-closure of cyclic carbonate. The catalyticactivity of HEMIMC was studied, and the catalytic mechanism was elucidated.The nucleophilic attack of anion and hydrogen bond are two of themost important factors to promote the cycloaddition reaction, especiallythe OH functional group in HEMIMC. Finally, the influence of differentanions on the catalytic activity was investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Structure-relationship for Ni single atom is studied for seventeen configurations. • Three elementary steps involved in CO 2 reduction are considered to make a comparison. • Ni-N3-V is potential active with the better equilibrium among various performance. • Contribution from C atoms around the Ni atom could not be neglected. The Ni single atom catalysts (SACs) are suggested to be efficient and popular for electrochemical CO 2 reduction reaction (CO 2 RR) with high Faradaic efficiency (FE). Although lots of studies have been performed to explore the structure–property relationship with the aim to develop the robust Ni SACs, there are conflict and totally inverse viewpoints about the influence of the Ni coordination environment on its catalytic performance. Moreover, the full systematical investigations for all possible structures are still lack, especially for the influence of vacancy defect and the comparison for the structures with and without vacancy defect. Seventeen Ni SACs on graphene have been built including the full coordinated structures and vacancy-defect structures as much as possible in this work. The free energies related with three steps to generate CO are all calculated by the first principle to explore the effect of coordination environment on the catalytic activity of Ni SACs. Moreover, the hydrogen evolution reaction (HER) is also considered to judge their selectivity. Inclusion of the vacancy-defect or decreasing the coordinated number of N atoms are favorable to promoting the formation of *COOH, however, the desorption of *CO step becomes more difficult. On the basis of above criteria, the structure with three coordinated N atoms and one vacancy-defect (Ni-N3-V) is a potential active catalyst standing out from other coordinated situations. According to the partial density of states (PDOSs) result, the activity of Ni-N3-V is affected by both the Ni atom and the C atoms around the Ni atom. The effect of support materials should be carefully considered to build the Ni SACs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel polystyrene-supported ionic liquid (PS-IMPCOOHTMGBr) is synthesized. • The 97.2% CPC yield could be achieved under 80 °C and 0.1 MPa CO 2 during 4 h. • Two possible reaction mechanisms are proposed. • There is no obvious decrease for the catalytic activity after 9 times. A novel polystyrene-supported ionic liquid (PS-IMPCOOHTMGBr) is synthesized and successfully applied to catalyze the cycloaddition of CO 2 and epichlorohydrin (ECH). The 97.2% product yield is achieved at 80 °C under atmospheric pressure. The high activity is attributed to the ability of CO 2 capture and multiple active centers of immobilized imidazolium ionic liquids. The catalytic activity is enhanced with the increasing amount of immobilized ionic liquids. Even after 9 runs, there is no obvious decrease for the catalytic activity of PS-IMPCOOHTMGBr. To further elucidate the catalyst structure and its catalytic feature, the PS-IMPCOOHTMGBr is characterized by elemental analysis, thermal gravimetric analysis, infrared spectroscopy, scanning electron microscopes, solid state NMR, and Brunauer-Emmett-Teller analysis. Two possible reaction mechanisms are proposed according to the characterized results and reported literature. The ionic liquids supported on the PS would have the comparable catalytic activity with those immobilized on the porous materials by judicious choice of ionic liquids. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of novel ionic liquids are synthesized. • Capture of CO 2 plays a critical role in the reaction system. • The 99.3 % CPC yield could be achieved under 50 °C and 1 bar CO 2 during 6 h. The efficient conversion of carbon dioxide (CO 2) to the valuable chemicals is of great significance but the development of robust catalyst is still an interesting and challenging issue. Four novel ionic liquids are facilely synthesized with the ability to adsorb carbon dioxide (CO 2). [BZTMA+][−O 2 EEPZ+][Br−] and [DBUH+][−O 2 EEPZ+][Br−] could catalyze the cycloaddition of CO 2 into cyclic carbonates under atmospheric pressure at 50 °C with 99.3 % and 97.5 % yields in the absence of co-catalyst and solvent. Moreover, the [DBUH+][−O 2 EEPZ+][Br−] could be reutilized by 11 times with a slightly decreased product yield. A new mechanism is proposed by the density functional theory (DFT). The excellent catalytic performance is mainly attributed to the ability of ionic liquids to adsorb CO 2. After the CO 2 is adsorbed, the formed intermediate would push the electrons towards the Br- anion leading to the stronger nucleophilic activation. This work introduces a new pathway to explore the ionic liquids for the chemical fixation of CO 2. [ABSTRACT FROM AUTHOR]

Amino-specified pyrazolium ionic liquid (APEPzBr) is synthesized by two steps. It is interesting that the product of the first step ([EPzPNH 3 Br 2) could also catalyze the coupling reaction of carbon dioxide (CO 2) and epoxides under 70 °C along with 0.5 MPa CO 2 pressure, which is even more benign than APEPzBr. It is attributed to the strong ability of [EPzPNH 3 Br 2 to absorb CO 2 along with robust electrophilic activation, which is testified by density functional theory and 13C NMR measurement. The difference between [EPzPNH 3 Br 2 and APEPzBr is further elucidated by electron localization function (ELF) and atoms in molecules (AIM). Unlabelled Image • [EPzPNH 3 Br 2 could be synthesized by only one step. • Coupling reaction of CO 2 is performed under 70 °C along with 0.5 MPa CO 2 pressure. • The mechanism is elucidated by DFT calculation along with 13C NMR data. [ABSTRACT FROM AUTHOR]

Theoretical calculation is a powerful tool to uncover the reaction mechanism. Besides it, the theoretical calculation is expected to provide more helpful clues and play more important role for catalysis. Although the calculated barrier height could not be directly compared with the experimental measured activation energy, the range of barrier heights would be the same with that of experimental yields. It would be beneficial to estimating the experimental result and designing the efficient catalysts. For the coupling reaction of carbon dioxide with epoxides catalyzed by ionic liquids, both the interactions among ionic liquids and microenvironment of ionic liquids would affect the calculated barrier heights. They are considered by combination of density functional theory and molecular dynamics in this work. The reliability of calculated barrier heights is improved. More important, this method not only is suitable for the ionic liquids with the similar structures but also be applied to ionic liquids with different structures. Unlabelled Image • The method is suitable for three different kinds of ionic liquids. • Interaction among ionic liquids are included. • Influence of microenvironment of ionic liquids are considered. [ABSTRACT FROM AUTHOR]

Nine protic carboxyl imidazolium ionic liquids are synthesized. Then, they are employed to catalyze the chemical fixation of carbon dioxide (CO 2) and propylene oxide leading to propylene carbonate in the absence of co-catalyst and organic solvent. HCPImBr presents the best catalytic activity with the product yield of 92% under reaction temperature 120 °C, CO 2 initial pressure 1.5 MPa, catalyst amount 0.5 mol%, and reaction time 2.0 h. Even if the reaction temperature and CO 2 initial pressure are decreased to 80 °C and 1.0 MPa, respectively, the 85% of product yield would be kept with the 1.0% catalyst dosage along with 12.0 h. With the exception of the most optimal reaction conditions, generality, and recyclability of HCPImBr are also investigated. More importantly, the reaction mechanism is investigated by the density functional theory, which is the first time to report the mechanism for protic carboxyl imidazolium ionic liquids. The catalytic activity of ionic liquids would be further improved with the reasonable combination of cation and anion. Image 1 • Nine protic imidazolium ionic liquids with carboxyl group are synthesized. • They are firstly utilized to catalyze the fixation of CO 2. • Excellent yields could be achieved even under 80 °C and 1.0 MPa CO 2 initial pressure. • The reaction mechanism is investigated by the Double-IL model. [ABSTRACT FROM AUTHOR]

The reaction mechanism for the coupling reaction of carbon dioxide with epoxides catalyzed by single-component protic pyrazolium ionic liquids has been extensively elucidated. However, the calculated barrier heights are not accurate enough to predict the catalytic results for a series of ionic liquids with similar structures. The cluster of protic pyrazolium ionic liquids is regarded as catalyst to consider the effect of interactions among ionic liquids on the barrier heights. Moreover, the ionic liquids or epoxides would also affect the barrier heights as the environmental factors, which is also considered by ONIOM method. When the environmental influence is involved, the accuracy is greatly improved. The analysis of interactions between ionic liquid and reactant indicates that the electrophilic attacking plays the more critical role than nucleophilic attacking. Unlabelled Image • Number of ionic liquids is not the sole factor to determine the accuracy of results. • PO as solvent is more suitable than ionic liquids as solvent. • The electrophilic activation is more important than nucleophilic activation. [ABSTRACT FROM AUTHOR]

Lots of ionic liquids have been utilized as catalyst for the coupling reaction of carbon dioxide with epoxides, however, catalyzed conditions could not be regarded as benign, especially when no co-catalyst and/or organic solvent is involved. A series of hydroxyl-functionalized pyrazolium ionic liquids are firstly synthesized. They would efficiently catalyze the cycloaddition of carbon dioxide and propylene oxide under 110 °C and 1.0 MPa carbon dioxide initial pressure with 1 mol% catalyst during 4 h resulting in the product yield of 91.2%. The catalytic condition is greatly refined as compared with other single-component ionic liquids with simple anion. Simultaneously, the effect of reaction temperature, amount of catalyst, carbon dioxide initial pressure, and reaction time is explored along with the reusability of catalyst. For most of epoxides with terminal substituted group, HEEPzBr presents acceptable catalytic activity. The difference of HEMPzBr, HEEPzBr, and HPEPzBr is also explored by the density functional theory calculations. The chemical fixation of CO 2 with epoxides catalyzed by hydroxyl-functionalized pyrazolium ionic liquids. Unlabelled Image • Hydroxyl-functionazlized pyrozolium ionic liquids are firstly synthesized. • They are efficient homogeneous catalysts for cycloaddition of CO 2 with PO. • Excellent yields are achieved without solvent or co-catalyst. • The reaction mechanism is investigated by DFT calculation. • No solvent and co-catalyst are required. [ABSTRACT FROM AUTHOR]