Computational Study on Thermodynamic Properties of Fischer-Tropsch Synthesis Process

Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate thermodynamic data provide basic thermodynamic quantities for the actual chemical engineering process and are useful in analyzing product distribution because FTS demonstrates many features of an equilibrium-controlled system. Our results show that the number of thermodynamically allowed products to increase when lowering temperature, raising pressure, and raising H₂/CO ratio. At low temperature, high pressure and high H₂/CO ratio, many products are thermodynamically allowed and the selectivity of product has to be controlled by kinetic factors. On the other hand, high selectivity of lighter products can be realized in thermodynamics by raising temperature and lowering pressure. We found that the equilibrium product yield will reach a maximum and remain unchanged when lowering temperature, raising pressure, and raising H₂/CO ratio to some limits, implying that optimizing reaction conditions has no effect on equilibrium product yields beyond these limits. The thermodynamic analysis is also useful in designing and evaluating FTS reaction mechanisms. We found that reaction pathways through formaldehyde should be discarded because of its extremely low equilibrium yield. Recently, in the FTS process using metal-oxide-zeolite catalysts for the highly selective production of C₂-C₄ olefins and aromatic hydrocarbons, there are several guesses on the possible reaction intermediates entering the zeolite channel. Our results show that ketene, methanol, and dimethyl ether are three possible reaction intermediates.     

Calorimetric approach to metabolic carbon conversion efficiency in soils

Soil carbon is the largest reservoir of organic carbon on the planet and CO₂ production by soil thus has potentially large effects on atmospheric CO₂. Carbon sequestration in soil is determined by the metabolic efficiency (substrate carbon conversion efficiency) of soil micro-organisms. That could be measured by calorespirometric methodology (parallel measurement of metabolic heat rate and CO₂ production rate) and by theoretical thermodynamic models. Carbon conversion efficiency of the glucose degradation reaction in soil is calculated from both the calorespirometric ratio of heat rate to CO₂ rate and from energy and mass balance models combined with calorimetric heat rates. Results obtained, 0.77 and 0.75, are in good agreement.     

Efficient Disproportionation of Formic Acid to Methanol Using Molecular Ruthenium Catalysts

The disproportionation of formic acid to methanol was unveiled in 2013 using iridium catalysts. Although attractive, this transformation suffers from very low yields; methanol was produced in less than 2 % yield, because the competitive dehydrogenation of formic acid (to CO₂ and H₂) is favored. We report herein the efficient and selective conversion of HCOOH to methanol in 50 % yield, utilizing ruthenium(II) phosphine complexes under mild conditions. Experimental and theoretical (DFT) results show that different convergent pathways are involved in the production of methanol, depending on the nature of the catalyst. Reaction intermediates have been isolated and fully characterized and the reaction chemistry of the resulting ruthenium complexes has been studied.     

Theoretical Thermodynamic Efficiency Limit of Isothermal Solar Fuel Generation from H2O/CO2 Splitting in Membrane Reactors

Solar fuel generation from thermochemical H₂O or CO₂ splitting is a promising and attractive approach for harvesting fuel without CO₂ emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H₂O or CO₂ splitting reactions. In this research, solar-driven fuel production via H₂O or CO₂ splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O₂ pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H₂O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO₂ splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H₂O splitting and CO₂ splitting at 2000 °C. An efficient O₂ separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0–20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H₂O or CO₂ splitting systems (e.g., chemical cycling) due to similar thermodynamics.     

CO2‐to‐Methanol Hydrogenation on Zirconia‐Supported Copper Nanoparticles: Reaction Intermediates and the Role of the Metal–Support Interface

Methanol synthesis by CO₂ hydrogenation is a key process in a methanol‐based economy. This reaction is catalyzed by supported copper nanoparticles and displays strong support or promoter effects. Zirconia is known to enhance both the methanol production rate and the selectivity. Nevertheless, the origin of this observation and the reaction mechanisms associated with the conversion of CO₂ to methanol still remain unknown. A mechanistic study of the hydrogenation of CO₂ on Cu/ZrO₂ is presented. Using kinetics, in situ IR and NMR spectroscopies, and isotopic labeling strategies, surface intermediates evolved during CO₂ hydrogenation were observed at different pressures. Combined with DFT calculations, it is shown that a formate species is the reaction intermediate and that the zirconia/copper interface is crucial for the conversion of this intermediate to methanol.     

Enhanced effect of plasma on catalytic reduction of CO_2 to CO with hydrogen over Au/CeO_2 at low temperature

In terms of the reaction of CO_2 reduction to CO with hydrogen, CO_2 conversion is very low at low temperature due to the limitation of thermodynamic equilibrium(TE). To overcome this limitation, plasma catalytic reduction of CO_2 to CO in a catalyst-filled dielectric barrier discharge(DBD) reactor is studied. An enhanced effect of plasma on the reaction over Au/CeO_2 catalysts is observed. For both the conventionally catalytic(CC) and plasma catalytic(PC, Pin= 15 W) reactions under conditions of 400 °C, H_2/CO_2= 1,200 SCCM, GHSV = 12,000 mL·g~(-1)cat·h~(-1), CO_2 conversions over Au/CeO_2 reach 15.4% and 25.5% due to the presence of Au, respectively, however, those over CeO_2 are extremely low and negligible. Moreover,CO_2 conversion over Au/CeO_2 in the PC reaction exceeds 22.4% of the TE conversion. Surface intermediate species formed on the catalyst samples during the reactions are determined by in-situ temperatureprogrammed decomposition(TPD) technique. Interestingly, it disclosed that in the PC reaction, the formation of formate intermediate is enhanced by plasma, and the acceleration by plasma in the decomposition of formate species is much greater than that in the formation of formate species on Au/CeO_2. Enhancement factor is introduced to quantify the enhanced effect of plasma. Lower reactor temperature, higher gas hourly space velocity(GHSV), and lower molar ratio of H_2/CO_2 would be associated with larger enhancement factor.     

CO2 Conversion with Alcohols and Amines into Carbonates,Ureas, and Carbamates over CeO2 Catalyst in the Presence and Absence of 2‐Cyanopyridine

Recent progress on the CeO₂ catalyzed synthesis of organic carbonates, ureas, and carbamates from CO₂+alcohols, CO₂+amines, and CO₂+alcohols+amines, respectively, is reviewed. The reactions of CO₂ with alcohols and amines are reversible ones and the degree of the equilibrium limitation of the synthesis reactions is strongly dependent on the properties of alcohols and amines as the substrates. When the equilibrium limitation of the reaction is serious, the equilibrium conversion of the substrate and the yield of the target product is very low, therefore, the shift of the equilibrium reaction to the product side by the removal of H₂O is essential in order to get the target product in high yield. One of the effective method of the H₂O removal from the related reaction systems is the combination with the hydration of 2‐cyanopyridine to 2‐picolinamide, which is also catalyzed by CeO₂.     

CO2 hydrogenation in ionic liquids: Recent update

The suppression of CO₂ emission is an important global issue. Therefore, CO₂ hydrogenation is a hopeful method for capturing and recycling of CO₂. Ionic liquids have been known to have a high affinity with CO₂, indicative of the expectation for the enhancement of CO₂ hydrogenation in case used as reaction medium. In this article, progress of this area in 2018–2021 is mainly reviewed, namely, formic acid, hydrocarbons, methanol formation, hydroformylation, enzymatic methanol formation, and electro-reduction of CO₂ (CO₂RR). Various products are obtained with coupling of catalysts and ILs with changing properties. It is convincing that promising methodologies are growing for the sustainable society.     

Toward efficient catalysts for electrochemical CO2 conversion to C2 products

With impressive progress in carbon capture and renewable energy, carbon dioxide (CO₂) conversion into useful chemicals has become a potential tool against climate change. Electrochemical CO₂ conversion into C₂ products (ethylene and ethanol) is an especially economically promising approach and an active research area. Nonetheless, catalyst layer design for CO₂ conversion is challenging because of the complex CO₂-to-C₂ reaction pathways. In this review, we highlight key ideas in catalyst layer design for CO₂ conversion to C₂ in the past few years. We identify three fundamental principles to control catalyst selectivity—local CO₂ and CO concentration, local pH, and intermediate–catalyst interaction. To achieve these goals, we introduce design strategies for both catalytic materials and overall catalyst layer morphology.     

Enzymatic Electrosynthesis of Glycine from CO2 and NH3

Enzymatic electrosynthesis has gained more and more interest as an emerging green synthesis platform, particularly for the fixation of CO₂. However, the simultaneous utilization of CO₂ and a nitrogenous molecule for the enzymatic electrosynthesis of value-added products has never been reported. In this study, we constructed an in vitro multienzymatic cascade based on the reductive glycine pathway and demonstrated an enzymatic electrocatalytic system that allowed the simultaneous conversion of CO₂ and NH₃ as the sole carbon and nitrogen sources to synthesize glycine. Through effective coupling and the optimization of electrochemical cofactor regeneration and the multienzymatic cascade reaction, 0.81 mM glycine was yielded with a highest reaction rate of 8.69 mg L⁻¹ h⁻¹ and faradaic efficiency of 96.8 %. These results imply a promising alternative for enzymatic CO₂ electroreduction and expand its products to nitrogenous chemicals.     

On the hydrogenation of CO and CO2 over copper/zirconia and palladium/zirconia catalysts

Summary Zirconia-supported hydrogenation catalysts were obtained by activation of the amorphous precursors Cu₇₀Zr₃₀ and Pd₂₅Zr₇₅ under CO₂ hydrogenation conditions. Catalysts of comparable compositions prepared by co-precipitation and wet impregnation of zirconia with copper- and palladium salts, respectively, served as reference materials. The catalyst surfaces under reaction conditions were investigated by diffuse reflectance FTIR spectroscopy. Carbonates, formate, formaldehyde, methylate and methanol were identified as the pivotal surface species. The appearance and surface concentrations of these species were correlated with the presence of CO₂ and CO as reactant gases, and with the formation of either methane or methanol as reaction products. Two major pathways have been identified from the experimental results. i) The reaction of CO₂/H₂-mixtures on Cu/zirconia and Pd/zirconia primarily yields surface formate, which is hydrogenated to methane without further observable intermediates. ii) The catalytic reaction between CO and hydrogen yields -bonded formaldehyde, which is subsequently reduced to methylate and methanol. Interestingly, there is no observable correlation between absorbed formaldehyde or methylate on the one hand, and gas phase methane on the other hand. The reactants, CO₂ and CO, can be interconverted catalytically by the water gas shift reaction. The influence of the metals on this system of coupled reactions gives rise to different product selectivities in CO₂ hydrogenation reactions. On zirconia-supported palladium catalysts, surface formate is efficiently reduced to methane, which consequently appears to be the principal CO₂ hydrogenation product. In contrast, there is a favorable reaction pathway on copper in which CO is reduced to methanol without C-O bond cleavage; surface formate does not participate significantly in this reaction. In CO₂ hydrogenations on copper/zirconia, methanol can be obtained as the main product, from a sequence of the reverse water gas shift reaction followed by CO reduction.     

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks

Thermocatalysis of CO₂ into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal–organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO₂ thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO₂ conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO₂ reaction. The advantages of using noble-metal-free MOF catalysts for CO₂ conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO₂ conversion.     

Xylene Synthesis Through Tandem CO2 Hydrogenation and Toluene Methylation Over a Composite ZnZrO Zeolite Catalyst

Selective synthesis of specific value-added aromatics from CO₂ hydrogenation is of paramount interest for mitigating energy and climate problems caused by CO₂ emission. Herein, we report a highly active composite catalyst of ZnZrO and HZSM-5 (ZZO/Z5-SG) for xylene synthesis from CO₂ hydrogenation via a coupling reaction in the presence of toluene, achieving a xylene selectivity of 86.5 % with CO₂ conversion of 10.5 %. A remarkably high space time yield of xylene could reach 215 mg g_cat⁻¹ h⁻¹, surpassing most reported catalysts for CO₂ hydrogenation. The enhanced performance of ZZO/Z5-SG could be due to high dispersion and abundant oxygen vacancies of the ZZO component for CO₂ adsorption, more feasible hydrogen activation and transfer due to the close interaction between the two components, and enhanced stability of the formate intermediate. The consumption of methoxy and methanol from the deep hydrogenation of formate by introduced toluene also propels an oriented conversion of CO₂.     

CO2 Hydrogenation on Cu/Al2O3: Role of the Metal/Support Interface in Driving Activity and Selectivity of a Bifunctional Catalyst

Selective hydrogenation of CO₂ into methanol is a key sustainable technology, where Cu/Al₂O₃ prepared by surface organometallic chemistry displays high activity towards CO₂ hydrogenation compared to Cu/SiO₂, yielding CH₃OH, dimethyl ether (DME), and CO. CH₃OH formation rate increases due to the metal–oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al₂O₃ promotes the subsequent conversion of CH₃OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO₂ at the metal–oxide interface, and 2) indirectly by the conversion of formate surface species and CH₃OH to methyl formate, which is further decomposed into CH₃OH and CO. This study shows how Al₂O₃, a Lewis acidic and non‐reducible support, can promote CO₂ hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal–oxide interface.     

Direct Conversion of Methane with Carbon Dioxide Mediated by RhVO3− Cluster Anions

Direct conversion of methane with carbon dioxide to value‐added chemicals is attractive but extremely challenging because of the thermodynamic stability and kinetic inertness of both molecules. Herein, the first dinuclear cluster species, RhVO₃^?, has been designed to mediate the co‐conversion of CH₄ and CO₂ to oxygenated products, CH₃OH and CH₂O, in the temperature range of 393–600 K. The resulting cluster ions RhVO₃CO^? after CH₃OH formation can further desorb the [CO] unit to regenerate the RhVO₃^? cluster, leading to the successful establishment of a catalytic cycle for methanol production from CH₄ and CO₂ (CH₄+CO₂→CH₃OH+CO). The exceptional activity of Rh‐V dinuclear oxide cluster (RhVO₃^?) identified herein provides a new mechanism for co‐conversion of two very stable molecules CH₄ and CO₂.     

Catalytic Formation of Acrylate from Carbon Dioxide and Ethene

With regard to sustainability, carbon dioxide (CO₂) is an attractive C1 building block. However, due to thermodynamic restrictions, reactions incorporating CO₂ are relatively limited so far. One of the so‐called “dream reactions” in this field is the catalytic oxidative coupling of CO₂ and ethene and subsequent β‐H elimination to form acrylic acid. This reaction has been studied intensely for decades. However up to this date no suitable catalytic process has been established. Here we show that the catalytic conversion of ethene and CO₂ to acrylate is possible in the presence of a homogeneous nickel catalyst in combination with a “hard” Lewis acid. For the first time, catalytic conversion of CO₂ and ethene to acrylate with turnover numbers (TON) of up to 21 was demonstrated.     

Metal-free Catalyst B2S Sheet for Effective CO2 Electrochemical Reduction to CH3OH

Considering the problems of high costs, low catalytic activity and selectivity in the metal-based catalysts for CO₂ electroreduction, we apply boron-containing metal-free B₂S sheet as an alternative to the traditional metal-based catalysts. Reaction energy calculations identify the preferred “Formate” pathway for CO₂ conversion to CH₃OH on B₂S, in which the thermodynamic energy barrier obtained by using the Computational Hydrogen Electrode model is 0.57 eV, and the kinetic energy barrier obtained by searching the transition states is 1.18 eV. Another possible reaction pathway, “RWGS+CO-hydro”, is suppressed and the hydrogen evolution reaction (HER) side reaction is nonspontaneous. Compared to Cu(211) with the highest catalytic activity among all transition metals, B₂S sheet exhibits a better catalytic activity with a lower overpotential for CO₂ reduction and a better selectivity that suppresses the non-target reaction.     

CO2 hydrogenation to methanol and dimethyl ether at atmospheric pressure using Cu-Ho-Ga/γ–Al2O3 and Cu-Ho-Ga/ZSM-5: Experimental study and thermodynamic analysis

CO₂ valorization through chemical reactions attracts significant attention due to the mitigation of greenhouse gas effects. This article covers the catalytic hydrogenation of CO₂ to methanol and dimethyl ether using Cu-Ho-Ga containing ZSM-5 and g-Al₂O₃ at atmospheric pressure and at temperatures of 210 °C and 260 °C using a CO₂:H₂ feed ratio of 1:3 and 1:9. In addition, the thermodynamic limitations of methanol and DME formation from CO₂ was investigated at a temperature range of 100–400 °C. Cu-Ho-Ga/g-Al₂O₃ catalyst shows the highest formation rate of methanol (90.3 µmol_CH3OH/g_cat/h ) and DME (13.2 µmol_DME/g_cat/h) as well as the highest selectivity towards methanol and DME (39.9 %) at 210 °C using a CO₂:H₂ 1:9 feed ratio. In both the thermodynamic analysis and reaction results, the higher concentration of H₂ in the feed and lower reaction temperature resulted in higher DME selectivity and lower CO production rates.     

Optimization of equilibrium carbon dioxide methane reforming parameters by the Gibbs free energy minimization method

The thermodynamic equilibrium in the carbon dioxide conversion of methane is studied by Gibbs energy minimization. The curves that represent the dependences of the degree of coke formation, the content of methane and carbon dioxide in syngas, and the syngas module on the CO₂/CH₄ mole ratio in the initial mixture and on temperature at various pressures, are plotted. The regions in which the CO₂/CH₄ mole ratio is optimal for carbon dioxide conversion and no coke formation occurs, and which are characterized by a minimal content of methane and carbon dioxide in syngas, are revealed.     

Enzymatic Biodiesel Synthesis in Semi-Pilot Continuous Process in Near-Critical Carbon Dioxide

A semi-pilot continuous process (SPCP) for enzymatic biodiesel synthesis utilizing near-critical carbon dioxide (NcCO₂) as the reaction medium was developed with the aim of reducing the reaction time and alleviating the catalyst inhibition by methanol. Biodiesel synthesis was evaluated in both lab-scale and semi-pilot scale reactors (batch and continuous reactors). In a SPCP, the highest conversion (～99.9 %) in four and a half hours was observed when three-step substrate (methanol) addition (molar ratio [oil/methanol]?=?1:1.3) was used and the reaction mixture containing enzyme (Lipozyme TL IM, 20 wt.% of oil) was continuously mixed (agitation speed?=?300 rpm) at 30 °C and 100 bar in a CO₂ environment. The biodiesel produced from canola oil conformed to the fuel standard (EU) even without additional downstream processing, other than glycerol separation and drying.