Direct Synthetic Processes for Cyclic Carbonates from Olefins and CO<Subscript>2</Subscript>

This short review presents the recent developments in the direct synthesis of cyclic carbonates from olefins and CO₂. The straightforward synthesis of cyclic carbonates from olefins instead of epoxides, also called one-pot “oxidative carboxylation” of olefins, can be viewed as the coupling of two sequential reactions of epoxidation of olefins and CO₂ cycloaddition to epoxides formed. The facile synthetic approach would make carbonate synthesis simpler and even cheaper with industrial potential from environmental and economic points of view. Some progresses have been made on this direct synthetic reaction for cyclic carbonates with homogeneous and heterogeneous catalysts, however, this reaction system is still at a preliminary stage. Among the catalysts reported, only a few can be considered as effective for the direct oxidative carboxylation of olefins to cyclic carbonates. Thus active and selective catalysts should be explored to put the direct synthesis of cyclic carbonates into practical applications.     

Basic ionic liquids promoted chemical transformation of CO<Subscript>2</Subscript> to organic carbonates

Ionic liquids (ILs), especially basic ILs with unique physicochemical properties, have wide application in catalysis. Using basic ILs as catalysts for the conversion of cheap, abundant, nontoxic, and renewable CO₂ into value-added organic carbonates is highly significant in view of environmental and economic issues. This review aims at giving a detailed overview on the recent advances on basic ILs promoted chemical transformation of CO₂ to cyclic and linear carbonates. The structures of various basic ILs, as well as the basic ILs promoted reactions for the transformation of CO₂ to organic carbonates are discussed in detail, including the reaction conditions, the yields of target products, the catalytic activities of basic ILs and the reaction mechanism.     

Fast CO<Subscript>2</Subscript> sequestration by aerogel composites

The increasingly evident impact of anthropogenic CO₂ emissions on climate change and associated environmental effects is stimulating the search for viable methods to remove this gas. One of the most promising strategies is the long-term storage of CO₂ in inert, insoluble and thermodynamically-stable materials. This strategy mimics the natural reactions that transform silicates into carbonates regulating the cycle of CO₂ on the surface of the Earth, operating on a geological time-scale. Consequently, the aim is to accelerate these reactions to be applicable on the timescale of human lives. We present the various technologies developed or proposed to date, based on this particular approach. The principal limiting factor is that high pressures and temperatures are required to produce appropriate materials capable of CO₂ sequestration and storage. Nevertheless, the synthetic materials known as aerogels can be modified in shape, size and chemical functionality so as to catalyse the process of CO₂ elimination through silicates (of Ca or Mg), considerably reducing the reaction time and working at atmospheric pressure and temperature.     

Metal-organic frameworks MOF-808-X as highly efficient catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol

A series of metal-organic frameworks MOF-808-X (6-connected) were synthesized by regulating the ZrOCl₂·8H₂O/1,3,5-benzenetricarboxylic acid (BTC) molar ratio (X) and tested for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH with 1,1,1-trimethoxymethane (TMM) as a dehydrating agent. The effect of the ZrOCl₂·8H₂O/BTC molar ratio on the physicochemical properties and catalytic performance of MOF-808-X was investigated. Results showed that a proper ZrOCl₂·8H₂O/BTC molar ratio during MOF-808-X synthesis was fairly important to reduce the redundant BTC or zirconium clusters trapped in the micropores of MOF-808-X. MOF-808-4, with almost no redundant BTC or zirconium clusters trapped in the micropores, exhibited the largest surface area, micropore size, and the number of acidic-basic sites, and consequently showed the best activity among all MOF-808-X, with the highest DMC yield of 21.5% under the optimal reaction conditions. Moreover, benefiting from the larger micropore size, MOF-808-4 outperformed our previously reported UiO-66-24 (12-connected), which had even more acidic-basic sites and larger surface area than MOF-808-4, mainly because the larger micropore size of MOF-808-4 provided higher accessibility for the reactant to the active sites located in the micropores. Furthermore, a possible reaction mechanism over MOF-808-4 was proposed based on the in situ FT-IR results. The effects of different reaction parameters on DMC formation and the reusability of MOF-808-X were also studied.     

Titanocene dichloride/KI: an efficient catalytic system for synthesis of cyclic carbonates from epoxides and CO2

Titanocene dichloride (Cp₂TiCl₂)/KI was developed to be an efficient catalytic system for the cycloaddition of CO₂ to epoxides to synthesize relevant cyclic carbonates from epoxides and CO₂. Various influencing factors on the coupling reaction, such as co‐catalyst, temperature, CO₂ pressure and reaction time, were investigated. The optimal reaction conditions were KI as co‐catalyst, 150 °C reaction temperature, 12 atm CO₂ pressure and 4 h reaction time using THF as solvent for the synthesis of propylene carbonate in 98% yield. Copyright © 2013 John Wiley & Sons, Ltd.     

No-Glycerol rapid heterogeneous biodiesel production on K<Subscript>2</Subscript>CO<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by coupling process

Biodiesel containing almost no glycerol has been produced by coupling reaction carried out over K₂CO₃ supported by calcium oxide as solid base catalysts. The solid base catalysts synthesized by wet impregnation exhibit an exceedingly high activity in biodiesel production. It was found that the reaction time required for the highest yield of biodiesel, 99.2%, can be shortened to 30 min over K₂CO₃/Al₂O₃ under the optimum reaction conditions: 8: 1: 1 molar ratio of methanol/DMC/oil, 30 wt % K₂CO₃/Al₂O₃ catalyst, and 65°C reaction temperature. Solid basic catalysts examined in the study were characterized by BET surface area, XRD, CO₂-TPD, and SEM techniques. The strong interaction between K₂CO₃ and the support yields a new basic active site, which can be probably responsible for the high activity of K₂CO₃/Al₂O₃.     

Hybrid catalytic effects of K<Subscript>2</Subscript>CO<Subscript>3</Subscript> on the synthesis of salicylic acid from carboxylation of phenol with CO<Subscript>2</Subscript>

As a base-promoted Kolbe–Schmitt carboxylation reaction, the mechanism of synthesis of salicylic acid derivatives from phenols with CO₂ in the industry is still unclear, even up to now. In this paper, synthesis of 3,6-dichloro salicylic acid (3,6-DCSA) from 2,5-dichloro phenoxide and CO₂ was investigated in the presence of K₂CO₃. We show the reaction can proceed by itself, but it goes at a slower rate as well as a lower yield, compared to the case with the addition of K₂CO₃. However, the yield of 3,6-DCSA is only minorly affected by the size of K₂CO₃, which cannot be explained from the view of catalytic effect. Therefore, K₂CO₃ may on one hand act as a catalyst for the activation of CO₂ so that the reaction can be accelerated, while on the other hand, it also acts as a co-reactant in deprotonating the phenol formed by the side reaction to phenoxide, which is further converted to salicylate.     

Preparation and characterization of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/ZrO<Subscript>2</Subscript> catalyst for carbonation of methanol into dimethyl carbonate

A H₃PW₁₂O₄₀/ZrO₂ catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO₃ or H₂WO₄, enhanced the catalytic performances of the supported ZrO₂. The mesoporous structure of H₃PW₁₂O₄₀/ZrO₂ was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m²/g. The strong acidity of H₃PW₁₂O₄₀/ZrO₂ was confirmed by the desorption peak observed at 415 °C in NH₃ temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO₂/N₂ volumetric flow rate ratios (CO₂/N₂?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO₂/N₂?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10^?3 min^?1) and activation energy (E_a?=?15.54 kJ/mol) at 170 °C with CO₂/N₂?=?1/7 which were favorable for DMC formation.     

FT-IR study on CO<Subscript>2</Subscript> adsorbed species of CO<Subscript>2</Subscript> sorbents

The stability of amine-functionalized silica sorbents prepared through the incipient wetness technique with primary, secondary, and tertiary amino organosilanes was investigated. The prepared sorbents were exposed to different gaseous streams including CO₂/N₂, dry CO₂/air with varying concentration, and humid CO₂/air mixtures to demonstrate the effect of the gas conditions on the CO₂ adsorption capacity and the stability of the different amine structures. The primary and secondary amine-functionalized adsorbents exhibited CO₂ sorption capacity, while tertiary amine adsorbent hardly adsorbed any CO₂. The secondary amine adsorbent showed better stability than the primary amine sorbent in all the gas conditions, especially dry conditions. Deactivation species were evaluated using FT-IR spectra, and the presence of urea was confirmed to be the main deactivation product of the primary amine adsorbent under dry condition. Furthermore, it was found that the CO₂ concentration can affect the CO₂ sorption capacity as well as the extent of degradation of sorbents.     

Adsorption of CO<Subscript>2</Subscript>-containing gas mixtures over amine-bearing pore-expanded MCM-41 silica: application for CO<Subscript>2</Subscript> separation

Adsorption of CO₂, N₂, CH₄ and H₂ on triamine-grafted pore-expanded MCM-41 mesoporous silica (TRI-PE-MCM-41) was investigated at room temperature in a wide range of pressure (up to 25 bar) using gravimetric measurements. The material was found to exhibit high affinity toward CO₂ in comparison to the other species over the whole range of pressure. Column-breakthrough dynamic measurements of CO₂-containing mixtures showed very high selectivity toward CO₂ over N₂, CH₄ and H₂ at CO₂ concentrations within the range of 5 to 50%. These conditions are suitable for effective removal of CO₂ at room temperature from syngas, flue gas and biogas using temperature swing (TS) or temperature-pressure swing (TPS) regeneration mode. Moreover, TRI-PE-MCM-41 was found to be highly stable over hundreds of adsorption-desorption cycles using TPS as regeneration mode.     

Preparation and performance of potassium-based sorbent using SnO<Subscript>2</Subscript> for post-combustion CO<Subscript>2</Subscript> capture

Potassium-based sorbents using γ-Al₂O₃ or TiO₂ as a support or an additive material have disadvantages in terms of their thermal stability and cyclic CO₂ capture. To overcome the shortcomings of these sorbents, a novel potassium-based sorbent (KSnI30) using SnO₂ was developed in this study. The KSnI30 sorbent formed only K₂CO₃ and SnO₂ phases without any inactive alloy species even after calcination at high temperatures (500–700 °C), indicating the good thermal stability of the KSnI30 sorbent regardless of the calcination temperature. Furthermore, the KSnI30 sorbent has an excellent regeneration property (above 98 %), as well as high CO₂ capture capacities (89–94 mg CO₂/g sorbent). Its excellent regeneration property is due to the formation of a KHCO₃ phase without by-products during CO₂ sorption. These results of the present study demonstrate that the SnO₂ shows promise as a new support or an additive material to replace TiO₂ and γ-Al₂O₃ in the preparation of a regenerable potassium-based sorbent for post-combustion CO₂ capture with good thermal stability and excellent regeneration property.     

CO<Subscript>2</Subscript> and SO<Subscript>2</Subscript> uptake by oil shale ashes

In the present research, CO₂ and SO₂ binding ability of different oil shale ashes and the effect of pre-treatment (grinding, preceding calcination) of these ashes on their binding properties and kinetics was studied using thermogravimetric, SEM, X-ray, and energy dispersive X-ray analysis methods. It was shown that at 700 °C, 0.03–0.28 mmol of CO₂ or 0.16–0.47 mmol of SO₂ was bound by 100 mg of ash in 30 min. Pre-treatment conditions influenced remarkably binding parameters. Grinding decreased CO₂ binding capacities, but enhanced SO₂ binding in the case of fluidized bed ashes. Grinding of pulverized firing ashes increased binding parameters with both gases. Calcination at higher temperatures decreased binding parameters of both types of ashes with both gases studied. Clarification of this phenomenon was given. Kinetic analysis of the binding process was carried out, mechanism of the reactions and respective kinetic constants were determined. It was shown that the binding process with both gases was controlled by diffusion. Activation energies in the temperature interval of 500–700 °C for CO₂ binding with circulating fluidized bed combustion ashes were in the range of 48–82 kJ mol⁻¹, for SO₂ binding 43–107 kJ mol⁻¹. The effect of pre-treatment on the kinetic parameters was estimated.     

High-Efficient Conversion of CO<Subscript>2</Subscript> in AC-Pulsed Tornado Gliding Arc Plasma

An AC-pulsed tornado gliding arc plasma was employed for CO₂ conversion via CO₂ decomposition and dry reforming reactions. A stable and high-efficient constant arc length discharge mode was obtained in this plasma reactor. And then, CO₂ conversion was studied under this discharge mode. In the case of CH₄/CO₂ = 0, CO₂ was converted to CO and O₂ via the CO₂ decomposition reaction. Energy efficiency of 29 % was attained at CO₂ conversion of 6 %. With strong reducing agent CH₄ added into CO₂, the main contributor of CO₂ conversion changed from CO₂ decomposition to dry reforming of CH₄. Conversions of CH₄ and CO₂, energy efficiency and energy cost changed sharply at CO₂/CH₄ ratios lower than 1/4, while they changed slowly at CH₄/CO₂ ratios above 1/4. In the case of CH₄/CO₂ = 2/3, energy efficiency of 68 % and syngas energy cost of 1.6 eV/mole were achieved at CH₄ conversion of 29 % and CO₂ conversion of 22 %.     

Ternary reciprocal systems Na,K||BO<Subscript>2</Subscript>,CO<Subscript>3</Subscript> and Na,K||BO<Subscript>2</Subscript>,Cl

The phase diagrams of the ternary reciprocal systems Na,K||BO₂,CO₃ and Na,K||BO₂,Cl were studied for the first time by a calculation-experimental method and by differential thermal analysis. Analytical models of phase equilibrium states were derived, and the coordinates of eutectics were found to be (680°C, 32 mol % NaBO₂, 68 mol % KCl) and (648°C, 9 mol % NaBO₂, 45.5 mol % NaCl, 45.5 mol % KCl). Binary solid solutions based on metaborates and carbonates of sodium and potassium were shown to be stable. The possibility of synthesizing tungsten oxide bronzes in a eutectic melt in the ternary system NaBO₂–NaCl–КCl was revealed.     

Dry Potassium-Based Sorbents for CO<Subscript>2</Subscript> Capture

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, CaO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property of various sorbents were measured in the presence of H₂O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO₂ absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO₃)₂(OH)₂, K₂Ca(CO₃)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely convert to the original K₂CO₃ phase at temperatures below 200 °C, during the CO₂ absorption process in the presence of 9 vol.% H₂O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO₃ crystal structure was formed during CO₂ absorption. The formation of active species, K₂CO₃·1.5H₂O, by the pretreatment with water vapor and the formation of the KHCO₃ crystal structure after CO₂ absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (87 mg CO₂/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO₂ capture capacity of KMgI30 (178.6 mg CO₂/g sorbent) than that of the theoretical value (95 mg CO₂/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO₂ capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO₂ absorption, and the role of water vapor and its effects on CO₂ absorption.     

Thermal behavior of LDH 2CuAl.CO<Subscript>3</Subscript> and 2CuAl.CO<Subscript>3</Subscript>/Pd

Cu/Al layered double hydroxide (LDH) can be used as a catalyst for important processes such as cross-coupling reactions. This property may be improved by adding palladium by either impregnation or intercalation. Therefore, the LDH matrix and its composites with Pd⁰ or [PdCl₄]^2? have been prepared. By powder X-ray diffraction, FT-infrared spectroscopy, thermogravimetric and elemental analysis it was determined the LDH formula Cu₄Al₂(OH)₁₂CO₃.4H₂O, with malachite as the second phase. The LDH thermal decomposition occurs between 120 and 600 °C, having as intermediates the double oxi-hydroxide and the mixed oxide phases. At 800 °C the residue is composed of CuO and CuAl₂O₄. The composites were obtained employing [PdCl₄]^2? and Pd₂(dba)₃ as precursors, and the solvent choice for this process was shown to be of significant importance: the materials obtained using DMF had Pd impregnated in the surface, while the usage of water promoted the intercalation of [PdCl₄]^2? in the LDH matrix. The thermogravimetric analysis was able to distinguish the mode of supporting palladium between the composites being a reliable characterization for such task.     

Reactions of Cr atoms with NO,N<Subscript>2</Subscript>O,CO<Subscript>2</Subscript>, NO<Subscript>2</Subscript>, and SO<Subscript>2</Subscript> molecules

Experimental results on the interaction of Cr atoms with various oxygen-containing molecules (NO, N₂O, CO₂, NO₂, and SO₂) at high temperatures (>1000 K) are presented. It is demonstrated that activation barrier for spin-forbidden reactions is higher, all other things being equal. For the reaction of Cr atoms with N₂O, an interpolated temperature dependence of the rate constant, based on the high-temperature measurements conducted in the present work and the published low-temperature data, is proposed.     

Time-Resolved CO<Subscript>2</Subscript> Dissociation in a Nanosecond Pulsed Discharge

Electrical discharges are increasingly used to dissociate CO₂ in CO and O₂. This reaction is the first step in the way for the synthesis of value-added compounds from CO₂ by using renewable electricity. If efficient, this technology might allow at the same time recycling CO₂ and storing renewable energy in chemical form. At present, while the dissociation degree is measured in the reactor exhaust, little is experimentally known about the dissociation kinetics in the discharge and post-discharge. This knowledge is however critical to increasing the overall efficiency of the plasma process. To estimate the time dependence of the CO₂ dissociation following a discharge event, we have coupled a LIF diagnostics to a nanosecond repetitively pulsed discharge in a mixture of CO₂ and H₂O. This paper discusses a procedure to obtain data on the time evolution of the CO₂ dissociation, its limits and future perspectives. In addition, the local gas temperature is measured as well. We find that a few microseconds after the discharge pulse, CO₂ is highly dissociated with a temperature around 2500 K. In about 100 µs, the temperature decreases at about 1500 K while the dissociation is reduced by about a factor of three.     

Synthesis,characterization, and biphasic ionic liquid media 1-hexene hydrogenation reaction of RuCl<Subscript>2</Subscript>(DMSO)<Subscript>2</Subscript>(NC<Subscript>5</Subscript>H<Subscript>4</Subscript>CO<Subscript>2</Subscript>Na-3)<Subscript>2</Subscript>

RuCl₂(DMSO)₂(NC₅H₄CO₂Na-3)₂ is very soluble in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium tetrafluoroborate, [(BMIM)BF₄]. The complex was prepared by reacting RuCl₂(DMSO)₄ with NC₅H₄CO₂Na-3, sodium nicotinate, in toluene, and was characterized by spectroscopic methods. The complex catalyzes the hydrogenation of 1-hexene (600 psi H₂, 100 °C) in a two-phase system consisting of cyclohexane/[(BMIM)BF₄] with 75% conversion in 24 h and modest substrate isomerization. The complex shows good stability and can be reused several times with little loss in activity.     

锂参与合成MOF-5用于CO2/CH4混合气体分离

利用溶剂热法合成了不同锂含量的MOF-5(xLi-MOF-5, x=0, 1, 3, 5).在MOF-5结晶过程中,锂离子被合并入其骨架结构中.实验表明,合并入骨架的锂能够改变MOF-5的结构和表面化学性质.不同的xLi-MOF-5能够不同程度降低骨架相互穿插的程度从而导致其吸附分离能力的大幅改变.其中,3Li-MOF-5具有最高的二氧化碳捕获能力(5.47 mmol·g^-1),对40% CO₂/60% CH₄混合气体具有最优吸附选择性.