The adsorption and activation of triplet O2 on the surface of nitrogen-doped carbon nanotube (NCNT) with different diameter and length were investigated. It was found that, rather than the unfavorable adsorption on normal carbon nanotube (CNT), the adsorption of O2 on NCNT was obviously exothermic and the electron transition of O2 happened in the adsorption process. The oxygen adsorbed on NCNT showed an interesting electron configuration which was similar to the active oxygen anion. The spin density, charge, and bond length of O2 changed with the size of NCNT. In combination with the recent results reported by Dai et al. (Science, 2009, 323, 760), it is reasonable to believe that these NCNTs should be a potential metal-free catalyst. The results presented here should be useful for designing and developing effective catalyst based on NCNT.

The influence of ionic liquid (IL) modification on the reactivity of metalloporphyrins was carefully investigated to design a recoverable and highly effective metalloporphyrin catalyst. On the basis of the research, which included a total of 34 different catalysts, the following modification methods make metalloporphyrins more powerful: (1) increasing the spin density (SDO), charge (QO), or isotropic fermi contact couplings (IFCCO) of the O atom in the Fe═O part and (2) decreasing the spin density carried by the Fe atom (SDFe) or the HOMO–LUMO gap between a catalyst and reactant (LUMOC–HOMOR). The order of the correlation between the structure parameters and the reactivity is SDo > Qo > IFCCO ≈ SDFe ≈ LUMOC–HOMOR. Compared with changing the cation of metalloporphyrins, changing the anion is a more effective way to increase the reactivity. The order is AlBr4– > AlCl4– > BCl4– > PF6– > AsF6– > SbF6– > BF4– > Tf2N– > AlF4– > HSO4– > CF3SO3– > CF3CO2– > Cl–. However, the long distance between the IL part and the catalytic active center or electron-donating substituent on the N atom weaken the influence induced by the IL modification. These structure–reactivity relationships could be used in designing a catalyst.

The catalyst-free N-formylation of amines using CO2 as the C1 source and BH3NH3 as the reductant has been developed for the first time. The corresponding formylated products of both primary and secondary amines are obtained in good to excellent yields (up to 96% of isolated yield) under mild conditions.

•Permeation of H2S and CO2 in SILMs with neutral and basic ILs were investigated.•[bmim][Ac] shows high gas permeability and superior permselectivity of H2S/CO2.•The facilitated transport of H2S in SILMs is reported.•The facilitated transport mechanism of H2S and CO2 in [bmim][Ac] were analyzed.Supported ionic liquid membranes (SILMs) are considered as promising media for the upgrading of natural gas. However, most research has focused on the selective separation of CO2 and CH4, paying little attention to the selective separation of H2S and CH4 or H2S and CO2 in SILMs. In this work, the permeability of CH4, CO2, and H2S in two different categories of ionic liquids (neutral and basic ionic liquids) were systemically investigated under dry conditions. The ideal selectivity of CO2/CH4, H2S/CH4, and H2S/CO2 were calculated. The effect of anion species, transmembrane pressure difference, and temperature on the permeability of single gas and ideal selectivity of gas pairs were studied. It is found that neutral ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium trifluoromethanesulfonate) show high permeability of CO2 and H2S, and competitive permselectivity of CO2/CH4 and H2S/CH4, and thus can be used for the simultaneous removal of H2S and CO2 from natural gas. Basic ionic liquids (1-butyl-3-methylimidazolium acetate) show not only high permeability of CO2 and H2S, but also superior permselectivity of CO2/CH4, H2S/CH4 and H2S/CO2, and thus can be potentially used for selective removal of H2S from natural gas. Moreover, facilitated transport of H2S and CO2 were observed in 1-butyl-3-methylimidazolium acetate. To the best of our knowledge, this is the first time that the facilitated transport of H2S in SILMs is reported.

Copper catalysts with an imidazole salt tag ([Cu-Imace-R-H][X], X− = F−, Cl−, Br−, I−, CF3CO2−, HSO4−, NO3−, PF6− or BF4−; R = H or CH3) show quite high reactivity for the oxidation of non-aromatic olefins with good selectivity for epoxides. The reactions perform well with a part per million (ppm) catalyst loading at mild temperature and ambient pressure. The highest turnover frequency (TOF) reaches up to 900 000 h−1. The catalytic activity is easy to control by changing the anion of [Cu-Imace-R-H][X]. This catalyst is effective for a series of substrates, including internal and terminal olefins, tri- and tetra-substituted olefins and aromatic olefins. In addition, the copper catalyst can be conveniently separated from the reaction system and reused for at least six cycles without any obvious loss of catalytic activity.

•Supported PIL membranes used for separation of CO2 are firstly investigated.•The highest CO2/N2 and CO2/CH4 permselectivities are 151 and 72.•New mechanism of facilitated transport separation of CO2 is explained.In this work, four diamine-monocarboxylate-based protic ionic liquids (PILs) were firstly introduced to prepare supported ionic liquid membranes (SILMs) and the selective separation of CO2/N2 and CO2/CH4 gas pairs in these SILMs under humidified condition were investigated. The effects of transmembrane pressure and temperature on the permeablity of CO2 and the permselectivity of CO2/N2 and CO2/CH4 gas pairs were also studied. It is found that the supported PILs with 15 wt% water exhibit much higher CO2 permeabilities under humidified conditon than those pure PILs under dry condition. The permeability increases with the decreasing transmembrane pressure, indicating a typical feature of facilitated transport membrane. The permeability of CO2 increases with the increasing temperature whereas the permselectivity of CO2/N2 and CO2/CH4 decreases at the same time. The highest CO2/N2 selectivities obtained is 151, and the highest CO2/CH4 selectivities is 72. These PILs is found to be tunable and selective carriers of CO2 in the presence of water, and the supported protic-ionic liquid membranes exhibit competitive permeability and higher permselectivity in comparison with the supported aprotic- ionic- liquid membranes.

•Solubility of CO2 in aqueous [DMAPAH][F] was 3.62 mol/kg.•Dissolution enthalpy ΔHSOL was − 35 to − 43 kJ·mol− 1.•Aqueous PIL had high regeneration efficiency (over 94%) for five absorption-desorption cycles.Solubilities of CO2 in a series of aqueous 3-(dimethylamino)-1-propylamine (DMAPA) cation-based protic ionic liquids (PILs) with different anions were determined at 308.2 K and pressure up to 3.5 bar. Impressively, the solubility of CO2 in the [DMAPAH][F] aqueous solution reached up to 3.62 mol/kg at 1 bar and 308.2 K, which was much superior to the traditional amine solutions and other ILs reported in the literature. A novel absorption mechanism is proposed and verified by 13C NMR and 19F NMR spectra. Based on this, CO2 absorption behaviors on pressure, temperature and concentrations of [DMAPAH][F] in aqueous solutions were studied. Meanwhile, the relevant parameters, such as the apparent absorption rate constant k, the absorption activation energy Ea, the dissolution enthalpy change ΔHSOL and the entropy change ΔSSOL were also calculated from the dynamic and thermodynamic data. Regeneration under the condition of 353.2 K and 15 kPa for 1 h showed that aqueous [DMAPAH][F] solution had good regeneration efficiency (over 94%). The absorption capacity (3.62 mol/kg), the ΔHSOL (− 35 to − 43 kJ·mol− 1), as well as the good recyclability indicate that the aqueous [DMAPAH][F] is a kind of promising absorbent for the separation of CO2 and believed to have potential use in gas decarburization.

Ionic liquids (ILs) were demonstrated to be highly efficient media for the liquid-phase Claus reaction. The reaction of H2S with SO2 in ILs proceeds very fast and almost completely to result in solid sulfur (S8) under mild conditions without the addition of any catalysts. Various ILs with different cations and anions were investigated and a simple IL 1-hexyl-3-methylimidazolium chloride ([hmim][Cl]) was found to be the most effective for the capture and conversion of H2S. It enables the transformation of H2S to S8 with a conversion ratio as high as >96% within 3 min. This finding opens up a promising method for the capture and conversion of H2S from gas streams.

The solubility of SO2 and CO2 in four cyano-containing protic ionic liquids (PILs) was experimentally measured at temperatures from 303.2 to 333.2 K and pressures up to 3.0 bar. Their physical properties, such as density, viscosity, and decomposition temperature, were also determined. It is found that [DMPANH][MOAc] and [DMAPNH][EOAc] have the best selective absorption of SO2 from CO2 at 303.2 K and 1.0 bar among the investigated PILs, and the ideal selectivities (119 and 107, respectively) of SO2/CO2 are significantly higher than those reported in literature for other ILs. The temperature-dependent Krichevsky–Kasarnovsky (K–K equation) and PR-NRTL equations are used to calculate the solubility data of SO2 and CO2, and the interactions between PILs and acid gases are analyzed thermodynamically. Quantum chemical calculations are also done to obtain the interaction configurations and energies. It is shown from the themodynamic analysis and the quantum chemical calculations that the interaction between SO2 and PILs is more energy favorable than that between CO2 and PILs, primarily due to the existence of the cyano group on the cation of PILs. The protic ionic liquids were reused for five absorption–desorption cycles without obvious loss in the absorption capacity, showing their potential as selective absorbents of SO2.

An effective method using gold(I) isocyanide complexes as catalysts for the transformation of various alkynes to the corresponding ketones is successfully developed. The hydration process proceeds smoothly at room temperature with quite high yield (up to 99%). The catalytic center is the isocyanide-Au(I)+ cation. Further theoretical research reveals a direct hydration mechanism by H2O, and the rate-determining step has an energy barrier of 23.7 kcal mol−1. These results show a good example to reduce unnecessary steps and achieve milder reaction conditions at the same time for the hydration of alkynes.

A series of chiral Mn(III) catalysts [salen–Mn(III)][X] (X− = Cl−, OAc−, NO3−, BF4−, CF3SO3−, OCH2CH3−) were synthesized by ion exchange. The influence of the axial anion on both the electronic structure and steric configuration of [salen–Mn(III)][X] were carefully investigated. Besides, the reactivity and enantioselectivity of these catalysts were explored in the asymmetric epoxidation of olefins. The obtained results indicate that the axial anions have influences on both electronic structure and steric configuration of the chiral Mn(III) salen complexes. Controlling the reactivity and enantioselectivity of these chiral Mn(III) salen complexes can be achieved by changing the axial anions.

•A water-soluble palladium-salen catalyst modified by pyridinium salt was synthesized.•This catalyst can efficiently catalyze the Heck reactions.•This catalyst is not only recyclable, but also show higher reactivity compared with the un-modified one.A novel and water-soluble palladium-salen catalyst modified by pyridinium salt was synthesized and characterized by NMR, HRMS, FT-IR, ICP, elemental analysis and UV–vis spectroscopy. The catalyst can efficiently catalyze the Heck reaction between aryl halides and olefins. The reaction using 0.5 mol% catalyst can achieve 98.3% conversion with 99% selectivity. The catalytic activity of catalyst modified by pyridinium salt is higher than that of un-modified one. Furthermore, the catalyst can be easily separated from reaction system by water wash and subsequently recycled for six runs without significant loss of activity and selectivity.

•Facilitated separation of CO2 and SO2 in SILMs was realized by using carboxylate-based ILs.•Very high permeability of acidic gases and selectivity of gas pairs were obtained under mild conditions.•Dicarboxylate-based ILs were found to be tunable carriers in the selective separation of CO2 and SO2 through SILMs.•Facilitated transport mechanism of CO2 and SO2 in carboxylate-based ILs was proposed and discussed.The facilitated separation of CO2 and SO2 in a series of supported ionic liquid membranes (SILMs) impregnated with carboxylate-based ILs (including monocarboxylates and dicarboxylates) was investigated systematically under humidified condition. The effects of transmembrane pressure difference and temperature on the permeability of acidic gases and permselectivity of gas pairs were studied. It is found that dicarboxylate-based ILs are a class of tunable media for the selective separation of acidic gases. When the anions of dicarboxylate-based ILs are fully deprotonated, they could be used as effective carriers for the selective separation of CO2. The permeabilities of CO2 in triethylbutylammonium malonate ([N2224]2[malonate]) and triethylbutylammonium maleate ([N2224]2[maleate]) under the partial pressure of 0.1 bar range from 2147 to 2840 barrers and the permselectivities of CO2/N2 and CO2/CH4 in them approach to 178–265 and 98–221, respectively. However, when the anions of dicarboxylate-based ILs are half deprotonated, they are efficient solvents for the selective separation of SO2. Triethylbutylammonium dimalonate ([N2224][dimalonate]) could facilitate the permeation of SO2 with a permeability of 7208 barrers under the transmembrane pressure difference of 0.05 bar, and the permselectivities of SO2/N2, SO2/CH4 and SO2/CO2 are 585, 271 and 18, respectively. The mechanism of facilitated separation is explained successfully from the reversible reactions of CO2 and SO2 with different forms of dicarboxylate-based ILs.

•Low-volatile and long-chain N-substituted imidazoles were investigated for the absorption of acidic gases.•The solubilities of SO2, H2S and CO2 under different temperatures and pressures were reported.•The solubility data were correlated with thermodynamic models to calculate thermodynamic parameters.•The absorption performance were compared with other organic solvents and ionic liquids.•The functionalization of organic solvents is another way to design efficient solvents for the selective separation of acidic gases.Exploring low volatile solvents for the capture of acidic gases is highly valued from the viewpoint of green chemistry. In this work, the solubilities of SO2, H2S and CO2 in two long-chain N-substituted imidazoles: N-dodecylimidazole (NDI) and 1,1′-[oxybis(2,1-ethanediyloxy-2,1-ethanediyl)]bis(imidazole) (Im2TEG) at different temperatures and pressures were determined systematically. It is shown that the absorption behaviour of SO2 in NDI and Im2TEG deviates strongly from the ideality. However, the absorption behaviour of H2S and CO2 in NDI and Im2TEG deviates only slightly from the ideality. Therefore, the solubility data of SO2 were correlated using the PR-NRTL model while the solubility data of H2S and CO2 were correlated with the Krichevsky–Ilinskara (K–I) equation. Thermodynamic parameters including the Henry's constants at infinitely dilute condition and the enthalpy of absorption were calculated from the thermodynamic modelling. The potential application of the two liquid solvents in the selective separation of acidic gases (i.e., SO2/CO2 and H2S/CO2) was evaluated by comprehensively considering the absorption capacity and ideal selectivity. The results were compared with other organic solvents and ionic liquids. It is revealed that NDI and Im2TEG are two promising solvents for the selective separation of acidic gases due to their high absorption capacity of SO2 and H2S and high selectivity of SO2/CO2 and H2S/CO2.

Solubilities of SO2 in five selected inexpensive organic solvents with low volatility were measured at temperatures from 303.2 K to 333.2 K and pressures up to 120 kPa. The solvents include sulfolane (SUF), ethylene glycol (EG), propylene carbonate (PC), N-methylimidazole (NMI) and N-methylpyrrolidone (NMP). The obtained results indicated that the solubilities of SO2 in the five organic solvents followed the sequence NMI > NMP > SUF > PC > EG. The absorption isotherms of SO2 in SUF, EG, and PC showed ideal profiles, while those in NMI and NMP showed nonideal types. The Henry’s law constants of SO2 in SUF, EG, and PC in terms of molality were calculated by drawing linear fit between SO2 solubilities and SO2 partial pressures. The interactions of SO2 with NMI and NMP were examined through density functional theory (DFT) calculations, and the solvent–solute complex formations were illustrated. The experimental solubilities of SO2 in NMI and NMP were successfully correlated by a reaction equilibrium thermodynamic model (RETM) proposed based on the DFT calculations. Subsequently, Henry’s law constants, reaction equilibrium constants, and heat of complex formation were also calculated to evaluate the potential of applying these organic solvents in SO2 absorption. The performance of SO2 absorption in these organic solvents were further compared with that in ILs and results illustrated that NMI and NMP were good alternatives to IL for applying in SO2 absorption.

Six acid salt ionic liquids (ASILs), triethylbutylammonium dicarboxylates, have been synthesized to act as green materials for SO2 capture. The experimental results reveal that the ASILs can trap SO2 reversibly and chemically with a large capacity of 0.112 up to 0.232 (mass ratio) at 15.5 kPa and of 0.374 to 0.456 (mass ratio) at 100 kPa and 40 °C. Two of these ASILs are interestingly found to have a low viscosity that enables the fast mass transfer of SO2. A reaction mechanism is proposed to explain the chemical absorption based on FTIR spectra and structural calculations using the density functional theory. Thermodynamic analysis indicates the enthalpy of the reaction of SO2 with the ASILs is low (−29.9 and −42.2 kJ mol−1 for [N2224][dimaleate] and [N2224][dimalonate], respectively). Additionally, the ASILs have a high thermal stability, which favors their potential application in flue gas desulfurization.

The reduction or elimination of noble metal used in carbon monoxide (CO) oxidation remains a challenge. Based on systematic research with methods using density functional theory, metal-free nitrogen-doped carbon nanotubes (NCNTs) are found to be effective catalysts for CO oxidation. The reaction route involves the direct oxidization of CO to CO2 by O2 adsorbed on the surface of NCNTs, as in CO + O2 → CO2 + O. The remaining O atom can further oxidize CO to CO2. The barrier heights of the rate-determining step range from 0.477 to 0.619 eV for different catalysts investigated in the present study. These values are quite close to those processes using noble metal catalysts. The catalytic ability of NCNTs is influenced by the tube length, diameter and number of doped N atoms. The barrier height for the rate-determining step slightly oscillates with increased tube length, and progressively increases with expanded tube diameter. The structure–reactivity relationships of NCNTs in CO oxidation are revealed. A lower negative charge of the doped N atom corresponds to more reactive NCNTs. NCNT–O2 with large spin densities on the O atom also show more powerful reactivity for CO oxidation. The present paper provides a way for the development of metal-free catalysts for CO oxidation.

Finite nitrogen-doped carbon nanotubes (NCNTs) with and without adsorbed O2 were systematically investigated using the B3LYP/6-31G* method. NCNTs with 10 different lengths and 9 different diameters were considered. The charge carried by the N atom and its circumjacent C atoms, the HOMO–LUMO gap, the O2 binding energy and the C–O bond length oscillate periodically as the tube length increases, whereas these values show a monotonic increase or decrease as the tube diameter is enlarged. All of the adsorbed oxygen investigated here is activated. Enlarging the tube diameter has a complicated influence on the catalytic ability of the NCNT. First, O2 adsorption becomes increasingly difficult on the surface of the NCNT, and the reactivity of the Oa atom becomes lower and lower as the tube diameter is enlarged, which reduces the reactivity of the NCNT. Second, enlarging the tube diameter creates more active centers for the adsorption and activation of oxygen, which will increase the reactivity of the NCNT.

New, simple, water-soluble copper catalysts with an imidazole salt tag [Cu-Imace-H][X] (X− = Cl−, Br−, HSO4−, NO3−, and BF4−) were synthesized via an organic solvent-free method. They were characterized by 1H NMR, 13C NMR, IR, UV–Vis, ESR, ESI-MS, elemental analysis, and melting point measurements. These catalysts are effective for phenol oxidation to dihydroxy derivates in water with H2O2 as oxidant. The anion evidently affects the appearance and electronic structure of the catalysts, as well as their catalytic reactivity. Both the phenol oxidation and catalyst syntheses were organic solvent-free to ensure a green process.Download full-size imageHighlights► New, simple and water-soluble copper catalysts were reported. ► These catalysts are effective for phenol oxidation in water. ► The anions evidently affect the properties of the catalysts.

The catalyst-free N-formylation of amines using CO2 as the C1 source and BH3NH3 as the reductant has been developed for the first time. The corresponding formylated products of both primary and secondary amines are obtained in good to excellent yields (up to 96% of isolated yield) under mild conditions.

The reduction or elimination of noble metal used in carbon monoxide (CO) oxidation remains a challenge. Based on systematic research with methods using density functional theory, metal-free nitrogen-doped carbon nanotubes (NCNTs) are found to be effective catalysts for CO oxidation. The reaction route involves the direct oxidization of CO to CO2 by O2 adsorbed on the surface of NCNTs, as in CO + O2 → CO2 + O. The remaining O atom can further oxidize CO to CO2. The barrier heights of the rate-determining step range from 0.477 to 0.619 eV for different catalysts investigated in the present study. These values are quite close to those processes using noble metal catalysts. The catalytic ability of NCNTs is influenced by the tube length, diameter and number of doped N atoms. The barrier height for the rate-determining step slightly oscillates with increased tube length, and progressively increases with expanded tube diameter. The structure–reactivity relationships of NCNTs in CO oxidation are revealed. A lower negative charge of the doped N atom corresponds to more reactive NCNTs. NCNT–O2 with large spin densities on the O atom also show more powerful reactivity for CO oxidation. The present paper provides a way for the development of metal-free catalysts for CO oxidation.

The influence of ionic liquid (IL) modification on the reactivity of metalloporphyrins was carefully investigated to design a recoverable and highly effective metalloporphyrin catalyst. On the basis of the research, which included a total of 34 different catalysts, the following modification methods make metalloporphyrins more powerful: (1) increasing the spin density (SDO), charge (QO), or isotropic fermi contact couplings (IFCCO) of the O atom in the Fe═O part and (2) decreasing the spin density carried by the Fe atom (SDFe) or the HOMO–LUMO gap between a catalyst and reactant (LUMOC–HOMOR). The order of the correlation between the structure parameters and the reactivity is SDo > Qo > IFCCO ≈ SDFe ≈ LUMOC–HOMOR. Compared with changing the cation of metalloporphyrins, changing the anion is a more effective way to increase the reactivity. The order is AlBr4– > AlCl4– > BCl4– > PF6– > AsF6– > SbF6– > BF4– > Tf2N– > AlF4– > HSO4– > CF3SO3– > CF3CO2– > Cl–. However, the long distance between the IL part and the catalytic active center or electron-donating substituent on the N atom weaken the influence induced by the IL modification. These structure–reactivity relationships could be used in designing a catalyst.