Gas Solubility in Ionic Liquids

Gas Solubility in Ionic Liquid

Predictive Thermodynamic Models for Ionic Liquid–SO₂ Systems

Two types of predictive thermodynamic models, i.e., the UNIFAC model and GCLF EOS (group contribution lattice fluid equation of state), were applied to predict the solubility of SO₂ in ionic liquids (ILs). The group interaction parameters were estimated by correlating the solubility data of SO₂ in ILs exhaustively collected from the articles published until July 2015. It was verified that both the UNIFAC model and GCLF EOS could be used for predicting the solubility of SO₂ in ILs, but the UNIFAC model gives results that are better than those of GCLF EOS. The UNIFAC model then was used to identify the structure–property relation for SO₂ solubility and selectivity of CO₂ to SO₂, whereas GCLF EOS was used to investigate the volume expansivity of ILs upon the addition of SO₂. The results showed that volume expansivity is independent of the different combinations of cations and anions and exhibits a linear relationship with SO₂ solubility in ILs

Local Electric Field Effect of TMI (Fe, Co, Cu)-BEA on N₂O Direct Dissociation

Zeolite catalyst consists of an infinite network of TO₄ tetrahedra (T = Si, Al, etc.) having various physic-chemical properties, among which the electric field effect (EFE) constituting one of the most important properties plays a major role in the heterogeneously catalytic reactions. However, up to now few works have been devoted to establishing the relationship between EFE and related catalytic behavior for the zeolite catalyst. In light of that, the present work systematically investigated the local electric field effect of the transition-metal-ion modified β zeolites [TMI (Fe, Co, Cu)-BEA] during N₂O direct decomposition based on Mulliken charge transfer (CT) analysis, frontier molecular orbital analysis (FMO), and diffuse reflectance infrared Fourier transform spectra (DRIFTS). For the O₂ formation mechanism, the EFEs of TMI-BEA and formed αO greatly influenced adsorption and further activation of N₂O through the CT, which was quantitatively determined by the FMO gaps between TMI-BEA and N₂O. For the NO_<i>x</i> formation mechanism, the weak EFEs of Fe-BEA and formed αO during N₂O adsorption through its N end gave a clue of low NO selectivity of Fe-BEA. The EFE investigation of zeolite catalyst facilitates the deeper understanding of the reaction mechanism and clarifies the principle for catalyst design

Pd–Co Coating onto Cordierite Monoliths as Structured Catalysts for Methane Catalytic Combustion

Alumina-supported mono- and bimetallic cobalt (Co) and palladium (Pd) monolithic catalysts were prepared and tested for methane catalytic combustion. The activity test showed that the catalyst containing 0.1 wt % Pd and 0.25 wt % Co was the most promising, with a high activity that did not decline with time on stream. With the aim to explain the relationship between activity–stability and structure, the catalysts were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed oxidation (TPO) techniques. The high stability displayed by the bimetallic catalysts is attributed to the influence of Co upon hindering the decomposition of PdO into metallic palladium, as a consequence of the increase in oxygen mobility in the spinel phase of cobalt oxides. The intrinsic kinetics of the methane oxidation reaction over various Pd–Co mono- and bimetallic catalysts has been measured in a fixed-bed reactor in the absence of internal and external diffusions, and the 0.1% Pd–0.25% Co/γ-Al₂O₃ catalyst exhibited the lowest activation energy. This work combines the advantages of the Pd–Co bimetallic catalyst with the monolithic structure

Extractive Distillation with a Mixture of Organic Solvent and Ionic Liquid as Entrainer

A mixture of organic solvent and ionic liquid (IL) was proposed as entrainer for the ethanol/water separation by extractive distillation. The vapor–liquid equilibrium (VLE) experimental results showed that the relative volatility of ethanol to water is significantly enhanced using the ethylene glycol (EG) and [EMIM]⁺[Ac]⁻ mixed entrainers when compared to that of the benchmark solvent EG. The nonrandom-two-liquid model parameters were correlated using the measured ternary and quaternary experimental VLE data. On this basis, process simulation was carried out to evaluate the improvement of the proposed mixed entrainers. It was found that for the ethanol/water separation using the mixed entrainers, the overall heat duties on reboilers in the processes without and with heat integration (HI) decrease 11.53% and 10.34%, respectively, when compared to the conventional benchmark solvent EG. Moreover, the presented process intensification method is easily achieved in practice by substituting the proposed mixed entrainers for the conventional solvent without changing the whole flowsheet

New Aspects on the Mechanism of C₃H₆ Selective Catalytic Reduction of NO in the Presence of O₂ over LaFe_1–<i>x</i>(Cu, Pd)_<i>x</i>O_3−δ Perovskites

A series of LaFe_1–<i>x</i>(Cu, Pd)_<i>x</i>O_3−δ perovskites was fully characterized and tested for the selective catalytic reduction (SCR) of NO by C₃H₆ in the presence of O₂. The adsorbed species and surface reactions were investigated for mechanistic study by means of NO-temperature-programmed desorption (TPD), C₃H₆/O₂-TPD, and in situ diffuse reflectance Fourier transform spectroscopy, in order to discriminate the effects of copper and palladium partial substitutions. With respect to LaFeO₃, Cu²⁺ incorporation obviously improved SCR performance, due to its properties for C₃H₆ activation with an easy generation of partially oxidized active surface C_<i>x</i>H_<i>y</i>O_<i>z</i> species. The excellent catalytic activity at the low temperatures over LaFe_0.94Pd_0.06O₃ was attributed to the formation of reactive nitrites/nitrates, leading to a rapid reaction between adNO_<i>x</i> and C_<i>x</i>H_<i>y</i>O_<i>z</i> species, as well as a decreased occupation of the active sites by the inactive ionic nitrates. A mechanism was herein proposed with the formation of nitrite/nitrate and C_<i>x</i>H_<i>y</i>O_<i>z</i> surface species and the further organo nitrogen compounds (ONCs)/–CN/–NCO as important intermediates. Moreover, the acceleration of both formation of inactive ionic nitrate and deep oxidation of C₃H₆ contributed to a negative effect of O₂ excess for NO reduction, while Pd substitution significantly increased the O₂ tolerance ability

Extension of the UNIFAC Model for Ionic Liquids

The UNIFAC model has recently become very popular for ionic liquids (ILs) because of its applicability for prediction of thermodynamic properties. This work is a continuation of our studies on the extension of group parameters of the UNIFAC model to systems with ILs. The new IL groups for 33 main groups and 53 subgroups were added into the current UNIFAC parameter matrix. The parameters of group surface area and volume for ILs were obtained by the COSMO calculation, while the group binary interaction parameters, <i>a</i>_nm and <i>a</i>_mn, were obtained by means of correlating the activity coefficients of solutes at infinite dilution in ILs at different temperatures exhaustively collected from literature by the end of 2011. The predicted results of UNIFAC model are more accurate than those of the COSMO-RS model so that it can be used for identifying the general relationship between molecular structure of ILs and separation performance for the separation of liquid mixtures with ILs

Theoretical Investigation of the Structural Stabilities of Ceria Surfaces and Supported Metal Nanocluster in Vapor and Aqueous Phases

In the present work, the stabilities of three low-index ceria (CeO₂) surfaces, that is, (111), (110), and (100) in vapor and aqueous phases were studied using ab initio molecular dynamics (AIMD) simulations and density functional theory calculations. On the basis of the calculated Gibbs surface free energies, the morphology and exposed surface structures of the CeO₂ nanoparticle were predicted using the Wulff construction principle. It is found that the partially hydroxylated (111) and (100) are two major surface structures of the CeO₂ nanoparticle in the vapor phase at ambient temperature. As the temperature increases, the fully dehydrated (111) surface becomes the most dominant structure. However, in the aqueous phase, the exposed surface of the CeO₂ nanoparticle is dominated by the hydroxylated (110) structure. The morphology and stability of a cuboctahedron Pt₁₃ nanocluster supported on CeO₂ surfaces in both gas and aqueous phases were further investigated. Because of the strong metal–support interaction, AIMD simulations show that the supported Pt₁₃ nanocluster has the tendency to wet the CeO₂ surface in the gas phase. The calculated interaction energies suggest that the CeO₂(110) surface provides the best stability for the Pt₁₃ nanocluster. The CeO₂-supported Pt₁₃ nanoclusters are oxidized. The morphology of the CeO₂-supported Pt₁₃ nanocluster is less distorted because of the solvation effect in the aqueous phase. Compared with the gas phase, more electrons are transferred from the Pt₁₃ nanocluster to the CeO₂ support, implying the supported Pt₁₃ nanocluster is further oxidized in the aqueous phase

MOF-Derived Formation of Ni₂P–CoP Bimetallic Phosphides with Strong Interfacial Effect toward Electrocatalytic Water Splitting

Bimetallic phosphides have attracted research interest for their synergistic effect and superior electrocatalytic activities for electrocatalytic water splitting. Herein, a MOF-derived phosphorization approach was developed to produce Ni₂P–CoP bimetallic phosphides as bifunctional electrocatalysts for both hydrogen and oxygen evolution reactions (HER and OER). Ni₂P–CoP shows superior electrocatalytic activities to both pure Ni₂P and CoP toward HER and OER, revealing a strong synergistic effect. High-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy elemental mapping analysis show that, in the sample Ni₂P–CoP, the Ni₂P and CoP nanoparticles with an average particle size 10–20 nm were mixed closely on the nanoscale, creating numerous Ni₂P/CoP interfaces. By comparison with the sample Ni₂P+CoP, in which seldom Ni₂P/CoP interfaces exist, we documented that the Ni₂P/CoP interface is an essential prerequisite to realize the synergistic effect and to achieve the enhanced electrocatalytic activities in Ni₂P–CoP bimetallic phosphides. This finding is meaningful for designing and developing bicomponent and even multicomponent electrocatalysts

Hydrocarbon Extraction with Ionic Liquids

Separation and reaction processes are key components employed in the modern chemical industry, and the former accounts for the majority of the energy consumption therein. In particular, hydrocarbon separation and purification processes, such as aromatics extraction, desulfurization, and denitrification, are challenging in petroleum refinement, an industrial cornerstone that provides raw materials for products used in human activities. The major technical shortcomings in solvent extraction are volatile solvent loss, product entrainment leading to secondary pollution, low separation efficiency, and high regeneration energy consumption due to the use of traditional organic solvents with high boiling points as extraction agents. Ionic liquids (ILs), a class of designable functional solvents or materials, have been widely used in chemical separation processes to replace conventional organic solvents after nearly 30 years of rapid development. Herein, we provide a systematic and comprehensive review of the state-of-the-art progress in ILs in the field of extractive hydrocarbon separation (i.e., aromatics extraction, desulfurization, and denitrification) including (i) molecular thermodynamic models of IL systems that enable rapid large-scale screening of IL candidates and phase equilibrium prediction of extraction processes; (ii) structure–property relationships between anionic and cationic structures of ILs and their separation performance (i.e., selectivity and distribution coefficients); (iii) IL-related extractive separation mechanisms (e.g., the magnitude, strength, and sites of intermolecular interactions depending on the separation system and IL structure); and (iv) process simulation and design of IL-related extraction at the industrial scale based on validated thermodynamic models. In short, this Review provides an easy-to-read exhaustive reference on IL-related extractive separation of hydrocarbon mixtures from the multiscale perspective of molecules, thermodynamics, and processes. It also extends to progress in IL analogs, deep eutectic solvents (DESs) in this research area, and discusses the current challenges faced by ILs in related separation fields as well as future directions and opportunities