Article

Direct synthesis of formic acid from carbon dioxide and hydrogen: A thermodynamic and experimental study using poly-urea encapsulated catalysts

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Abstract

The present work is concerned with direct hydrogenation of CO2 to formic acid which takes into account thermodynamic feasibility and experimental studies. Poly-urea encapsulated catalysts were explored and the effect of ionic liquids under supercritical conditions was examined. The monometallic and bimetallic catalysts were prepared, characterized, screened for the hydrogenation of CO2 and also compared with a commercially available poly-urea-Pd catalyst. The effect of reaction temperature, type of the catalyst, promoter, pressure and molar ratio of the feed (H2/CO2) on the yield of formic acid has been studied and discussed in order to maximize the formation of formic acid. The highest yield of formic acid obtained in terms of turn-over frequency (TOF) was 11900 h-1 at a total pressure of 144 bar, temperature of 70 °C, mole ratio (H2/CO2) of 1, catalyst (poly urea encapsulated Ru) loading of 0.04 g/cm3 and 3.12×10-5 mol/cm3 of ionic liquid (trihexyl (tetradecyl) phosphonium chloride).

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... CCS and CCU technologies must be employed on the commercially viable large-scale (Markewitz et al. 2012). Catalytic technologies will have a great future and thus the design of active catalysts for CO 2 conversion to valuable bulk chemical products such as formic acid, methanol, dimethyl ether and dimethyl carbonate (DMC), and a host of chemicals through Fischer-Tropsch Chemistry will find many applications in the future (Wang et al. 2011;Najafabadi 2013;Saavalainen et al. 2015;Kabra et al. 2016). Other CO 2 -based chemicals on lesser scale could also be produced which is the subject of this work. ...
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... Motokura et al. (2012) used the hydrosilanes and water as feedstock to produce HCOOH with Cu(OAc) 2 ‧H 2 O catalyst at 100 C and 1 atm, acquiring high yield (95%) and TON value (8,100) of HCOOH. Kabra et al. (2016) gained an extreme high turnover frequency (TOF ¼ 11,900 h À1 ) using the as-synthesized poly-urea encapsulated catalyst (EnCap Ru) for CO 2 /H 2 conversion at 144 bar (P H 2 /CO 2 ¼ 72/72 bar) and 70 C with trihexyl (tetradecyl) phosphonium chloride (IL) as a promoter. Nevertheless, most high efficient homogeneous catalysts are nonrecyclable that is impractical for industrial large-scale production. ...
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... 3shows the assumed process flowsheet that was used to make all assumptions. Please note that, in this flow sheet, some simplifications have been made in order to be able to conduct the full assessment.Direct hydrogenation of CO 2 to formic acid is a method of producing formic acid that encourages recovery and utilization of CO 2 but it is still in the laboratory scale, mainly due to unfavorable thermodynamics (Kabra et al., 2016).In this experimental reaction route, the starting materials are H 2 and CO 2. The synthesis of formic acid occurs at a temperature and pressure of 50 C and 150 bar, respectively. ...
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This article reviews the progress made in CO2 capture, storage, and utilization in Chinese Academy of Sciences (CAS). New concepts such as adsorption using dry regenerable solid sorbents as well as functional ionic liquids (ILs) for CO2 capture are thoroughly discussed. Carbon sequestration, such as geological sequestration, mineral carbonation and ocean storage are also covered. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers which offers a way to mitigate the increasing CO2 buildup is introduced.
Article
2-Phenyl ethanol (2-PEA) is an important chemical which finds several applications in perfumes, deodorants, soaps and detergents. It is prepared by different polluting and dangerous routes. The current work is concerned with production of 2-PEA by hydrogenation of styrene oxide using polyurea encapsulated catalysts (EnCat) in methanol and supercritical carbon dioxide (scCO2). Bimetallic Pd–Cu catalyst encapsulated with polyurea, Pd–Cu EnCat, is the best catalyst. The epoxide ring in styrene oxide is selectively hydrogenated to give 2-PEA in scCO2 without formation of any isomerization or deoxygenated products, which are formed in methanol. A complete conversion of styrene oxide with 100% selectivity to 2-PEA was obtained without addition of any promoter. Effects of various parameters were studied and a bifunctional site Langmuir–Hinshelwood–Hougen–Watson kinetic model was found to be in good agreement with the experimental data. The process is clean and green.
Article
Due to their negligible volatility, reasonable thermal stability, strong dissolubility, wide liquid range and tunability of structure and property, ionic liquids have been regarded as emerging candidate reagents for CO2 capture from industries gases. In this review, the research progresses in CO2 capture using conventional ionic liquids, functionalized ionic liquids, supported ionic-liquids membranes, polymerized ionic liquids and mixtures of ionic liquids with some molecular solvents were investigated and reviewed. Discussion of relevant research fields was presented and the future developments were suggested.
Article
The kinetics and mechanism of formate synthesis by hydrogenation of CO2 (CO2 + 1/2H2 → HCOOa) and the formate decomposition into CO2 and H2 (HCOOa → CO2 + 1/2H2) over Cu(111) and Cu(110) surfaces were studied by in-situ infrared reflection−absorption spectroscopy (IRAS) using a high-pressure reactor (1 atm). The reaction rates and the apparent activation energy of the formate synthesis were measured for Cu(111) and Cu(110), indicating that the formate synthesis on Cu was found to be structure-insensitive. The pressure dependence of CO2 and H2 on the initial formation rate of formate suggested an Eley−Rideal type mechanism, in which a gaseous CO2 molecule directly reacts with an adsorbed hydrogen atom on Cu. This is analogous to the well-known mechanism of formate synthesis by organometallic catalysts, in which CO2 is inserted into a Cu−hydride bond. The reaction rates and the activation energy of the decomposition were measured for Cu(111) and Cu(110). It was found that the formate decomposition on Cu was structure-sensitive in contrast to the formate synthesis. The promotional effect of coexisting H2 upon the rate of formate decomposition by 17 times at maximum was incidentally found only on Cu(111). Interestingly, the increase in the decomposition rate was due to an increase in the preexponential factor of the rate constant for the formate decomposition with the activation energy being constant. Furthermore, the decomposition kinetics of the formate prepared by adsorption of formic acid on O/Cu(111) was identical with the H2-promoted decomposition kinetics of the synthesized formate. The difference in the decomposition kinetics was ascribed to the ordered structure of formate based on the previous STM results, in which a chainlike structure of formate was observed for the synthesized formate, whereas no formate chain was observed for the formate prepared by adsorption of formic acid on O/Cu(111). The unique character of both the decomposition kinetics and the structure of formate observed only for Cu(111) was discussed from the viewpoint of the mass transport of copper atoms creating added formate chains.
Article
Rapid, selective, and high-yield hydrogenation of CO2 can be achieved if the CO2 is in the supercritical state (scCO2). Dissolving H2, a tertiary amine, a catalyst precursor such as RuH2[P(CH3)3]4 or RuCl2[P(CH3)3]4, and a promoting additive such as water, CH3OH, or DMSO in scCO2 at 50 °C leads to the generation of formic acid with turnover frequencies up to or exceeding 4000 h-1. In general, experiments in which a second phase was formed by one or more reagents or additives had lower rates of reaction. The high rate of reaction is attributed to rapid diffusion, weak catalyst solvation, and the high miscibility of H2 in scCO2. The formic acid synthesis can be coupled with subsequent reactions of formic acid, for example, with alcohols or primary or secondary amines, to give highly efficient routes to formate esters or formamides. With NH(CH3)2, for example 420 000 mol of dimethylformamide/mol of Ru catalyst was obtained at 100 °C. The demonstrated solubility and catalytic activity of complexes of tertiary phosphines in scCO2 suggest that scCO2 could be an excellent medium for homogeneous catalysis and that many phosphine-containing homogeneous catalysts could be adopted for use in supercritical media.
Article
This paper considers the problem of reducing CO2 emissions from a power grid consisting of a variety of power-generating plants:  coal, natural gas, nuclear, hydroelectric, and alternative energy. The problem is formulated as a mixed integer linear program (MILP) and implemented in GAMS (General Algebraic Modeling System). Preprocessing and variable elimination strategies are used to reduce the size of the model. The model is applied to an existing Ontario Power Generation (OPG) fleet analyzed under three different operating modes:  (1) economic mode, (2) environmental mode, and (3) integrated mode. The integrated mode combines the objectives of both the economic and environmental modes through the use of an external pollution index as a conversion factor from pollution to cost. Two carbon dioxide mitigation options are considered in this study:  fuel balancing and fuel switching. In addition, four planning scenarios are studied:  (1) a base-load demand, (2) a 0.1% growth rate in demand, (3) a 0.5% growth rate in demand, and (4) a 1.0% growth rate in demand. A sensitivity analysis study is carried out to investigate the effect of parameter uncertainties such as uncertainties in natural gas price, coal price, and retrofit costs on the optimal solution. The optimization results show that fuel balancing can contribute to the reduction of the amount of CO2 emissions by up to 3%. Beyond 3% reductions, more stringent measures that include fuel switching and plant retrofitting have to be employed. The sensitivity analysis results indicate that fluctuations in gas price and retrofit costs can lead to similar fuel-switching considerations. The optimal carbon dioxide mitigation decisions are found, however, to be highly sensitive to coal price.
Article
Interfacial polycondensation is an important polymerization technique that encapsulates a variety of active principles. Mechanisms governing the reaction and interplay of physical and chemical rate processes need to be understood for both rational design of reaction equipment and the process control to produce capsules with desired characteristics. A theoretical and experimental study of the process is reported here. Kinetic data were obtained over a range of concentrations, monomer mole ratios and polymer film thicknesses, using a technique that relies on the on-line measurement of pH as a function of time. To understand the mechanisms the reaction was slowed down by reducing the interfacial area. A minimum thickness of the polymer was observed to be necessary so that capsules preserve their integrity and do not break up. The theoretical model developed considers ionic equilibria in the aqueous phase and the resistance due to external mass transfer, diffusion through the polymer, and interfacial reaction. Under the conditions chosen, the resistance due to the chemical reaction is generally more dominant. Values of rate parameters were determined by fitting the model to the experimental data. Observed variations in the diffusivity between different experiments were rationalized through a study of the crystalline structure of polymers.
Article
Innovative off-the-shelf CO2 capture approaches are burgeoning in the literature, among which, ionic liquids seem to have been omitted in the recent Intergovernmental Panel on Climate Change (IPCC) survey. Ionic liquids (ILs), because of their tunable properties, wide liquid range, reasonable thermal stability, and negligible vapor pressure, are emerging as promising candidates rivaling with conventional amine scrubbing. Due to substantial solubility, room-temperature ionic liquids (RTILs) are quite useful for CO2 separation from flue gases. Their absorption capacity can be greatly enhanced by functionalization with an amine moiety but with concurrent increase in viscosity making process handling difficult. However this downside can be overcome by making use of supported ionic-liquid membranes (SILMs), especially where high pressures and temperatures are involved. Moreover, due to negligible loss of ionic liquids during recycling, these technologies will also decrease the CO2 capture cost to a reasonable extent when employed on industrial scale. There is also need to look deeply into the noxious behavior of these unique species. Nevertheless, the flexibility in synthetic structure of ionic liquids may make them opportunistic in CO2 capture scenarios.
Article
The water-soluble Ru(II)–phosphine complex, [{RuCl2(mTPPMS)2}2] was found a suitable catalyst for the hydrogenation of NaHCO3 to NaHCO2 in aqueous solution under mild conditions with catalyst turnover frequencies (TOFs) in the range of 35–50 h−1 at 50 °C and 10 bar total pressure. The suggested reaction mechanism involves the formation of Ru(II)-hydrides of the general formula [RuHX(mTPPMS)4] where X=H−, HCO3− or HCO2−. At 80 °C and 95 bar total pressure, the reduction of NaHCO3 proceeded with high reaction rate (9600 h−1) hitherto unobserved in purely aqueous solutions. The reactions do not require the presence of organic amine additives, however, the addition of quinoline increased the rate considerably. Aqueous suspensions of calcium carbonate could also be hydrogenated with CO2/H2 gas mixtures.
Article
AUROlite, consisting of gold supported on titania (picture shows extrudates in a steel net cage), is a robust catalyst for the production of catalyst-free HCOOH/NEt(3) adducts from H(2), CO(2), and neat NEt(3). Pure HCOOH is freed from the adducts by amine exchange.
Article
The combination of techniques including switching experiments, temperature programed reduction and in situ neutron scattering-conductivity are used to investigate the sensing mechanism of 1% Pd/SnO2 toward hydrogen-containing gas mixtures. In particular, the use of the in situ neutron scattering-conductivity for the first time allows the simultaneous monitoring of electrical conductivity and inelastic neutron scattering spectra of the sensor material. Direct evidence is obtained on a reversible migration of hydrogenic species from and to the metal and the underlying tin oxide surface, i.e., reversible hydrogen spillover. As a result of this spillover, a dramatic change in electrical conductivity of the Pd doped tin oxide material is observed. We confirm, in accordance with the known mechanism, that the change of conductivity is based upon the creation or destruction of negatively charged adsorbed oxygen species on the sensor surface. In addition, we report a new but important sensing mechanism, the spillover hydrogen species behaving like a shallow donor to the semiconductor oxide as the direct source of conductivity occurs concurrently with the known mechanism.
Article
Amines to an end: The basic diamine-functionalized ionic liquid 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium trifluoromethanesulfonate was prepared and used in the hydrogenation of CO(2) to formic acid. One mole of the ionic liquid coordinates two moles of formic acid to promote the reaction. Both the ionic liquid and catalyst can be reused directly after their separation from the formic acid produced.
Article
A trace amount of alcohol cocatalyst and a stoichiometric amount of base are required during the hydrogenation of CO(2) to formic acid catalyzed by ruthenium trimethylphosphine complexes. Variation of the choice of alcohol and base causes wide variation in the rate of reaction. Acidic, nonbulky alcohols and triflic acid increase the rate of hydrogenation an order of magnitude above that which can be obtained with traditionally used methanol or water. Similarly, use of DBU rather than NEt(3) increases the rate of reaction by an order of magnitude. Turnover frequencies up to 95,000 h(-1) have now been obtained, and even higher rates should be possible using the cocatalyst and amine combinations identified herein. Preliminary in situ NMR spectroscopic observations are described, and the possible roles of the alcohol and base are discussed.
Article
Commercially available polystyrene supported amine and phosphine resins facilitate palladium-mediated Heck and Suzuki reactions in supercritical carbon dioxide (scCO2).
Article
Palladium(II) acetate microencapsulated in polyurea (MC-[Pd]) is an economical and versatile heterogeneous catalyst for a range of phosphine-free cross-coupling reactions in both conventional solvents and supercritical carbon dioxide (scCO2); the catalyst can be recovered by a simple filtration and recycled up to four times.
Article
An interfacial polymerisation approach is adopted to encapsulate palladium(II) acetate and palladium nanoparticles in polyurea microcapsules for use in catalysis.
Article
Immobilized catalysts have been reinvestigated from two aspects; as keys to environmentally benign chemical processes and high-throughput organic synthesis for combinatorial chemistry. While most known polymer-supported catalysts are less active than the corresponding original catalysts, new types of polymer-supported catalysts, microencapsulated catalysts, have been developed. The catalysts were immobilized on to polymers using physical envelopment by polymer backbones and interaction between pi electrons of benzene rings of the polystyrenes used as polymer backbones and vacant orbitals of the catalysts. Microencapsulated Sc, Os, Pd and Ru catalysts have been successfully prepared and high activities have been attained. In all cases, no leaching of the catalysts occurred, and the immobilized catalysts were recovered quantitatively by simple filtration and reused without loss of activity. It is noted that this method enables direct immobilization of metals onto polymers, and that normally unstable species such as Pd(0)(PPh3) can be kept stable by this immobilization technique. It is expected that other metal catalysts can be immobilized using this microencapsulation technique.
Article
The catalyst recycling in the conversion of CO2 into formate using the iridium complex with 4,7-dihydroxy-1,10-phenanthroline as a catalyst precursor is described. The catalyst precursor was dissolved in an aqueous KOH solution under CO2 pressure prior to the reaction, but was precipitated spontaneously at the end of the reaction. The acidification by the generation of formate caused the transformation from the water-soluble deprotonated form into the water-insoluble protonated form. When the reaction was carried out at 60 degrees C for 20 h using 0.1 M KOH solution under 6 MPa of H2:CO2 (1:1), the catalyst precursor was precipitated spontaneously and the added KOH was consumed completely. The catalyst was recovered by filtration, and the product was obtained by the evaporation of the filtrate. Iridium leaching into the filtrate was found to be 0.11 ppm (<2% of the loaded Ir). The recovered catalyst retained high catalytic activity for four cycles. Consequently, the CO2 conversion using the complex is an environmentally benign process, whose significant features are as follows: (i) catalyst recycling by self-precipitation/filtration, (ii) waste-free process, (iii) the easy isolation of the product, (iv) high efficiency under relatively mild conditions, and (v) aqueous catalysis without the use of organic materials. Furthermore, we have demonstrated the significant roles of the oxyanion generated from the acidic phenolic hydroxyl on the catalyst ligand, which are the catalyst recovery by acid-base equilibrium, as well as the water-solubility by its polarity and the catalyst activation by its electron-donating ability.
Article
(Chemical Equation Presented) A basic hydrogenation catalyst: The combination of a basic ionic liquid (IL) and a supported ruthenium complex catalyzes the hydrogenation of CO2 with satisfactory activity and selectivity (see scheme). The resulting formic acid is easily collected and the ionic liquid and catalyst can be reused directly after an easy separation step.
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