Methanol Formation Rate Research Articles

Highly dispersed Cu catalyst based on the layer confinement effect of Cu/Zn/Ga-LDH for methanol synthesis

The small amount of promoter has shown increase in the methanol formation rate by several folds. Hence, hydrotalcite having sufficient trivalent cations are preferred; however, traditional coprecipitation route often leads to poor Cu dispersion owing to higher cationic charge in the layered structure that result in aggregation of the sheets. The present paper reports synthesis of porous, nanostructured Cu/ZnO/Ga2O3 catalysts from pure phase hydrotalcite precursors by using aqueous miscible organic solvent treatment method. The 20% Ga containing catalyst showed ca. 2.5-fold increase in both surface area and % dispersion of the exposed Cu as compared to that prepared from standard coprecipitation method with similar composition. The stabilization induced by mutual dispersion of Cu, Zn and Ga components in the exfoliated sheets resulted in confinement of the Cu particle size up to 5 nm in the spent catalyst. The best performing catalyst of the series, Cu0.4Zn0.4Ga0.2-LDO exhibited STY of 762 mg•gCat−1•h−1 for methanol formation from syngas which was decreased by only 8.6% during 50 h of the reaction on stream. Further, it was revealed that, Ga is more conductive to stabilization of Cu as compared to Al, resulting in 23% higher methanol formation rate as compared to the Al containing catalyst.

Engineering the Cu/Mo2CTx (MXene) interface to drive CO2 hydrogenation to methanol

Development of efficient catalysts for the direct hydrogenation of CO2 to methanol is essential for the valorization of this abundant feedstock. Here we show that a silica-supported Cu/Mo2CTx (MXene) catalyst achieves a higher intrinsic methanol formation rate per mass Cu than the reference Cu/SiO2 catalyst with a similar Cu loading. The Cu/Mo2CTx interface can be engineered due to the higher affinity of Cu for the partially reduced MXene surface (in preference to the SiO2 surface) and the mobility of Cu under H2 at 500 °C. With increasing reduction time, the Cu/Mo2CTx interface becomes more Lewis acidic due to the higher amount of Cu+ sites dispersed onto the reduced Mo2CTx and this correlates with an increased rate of CO2 hydrogenation to methanol. The critical role of the interface between Cu and Mo2CTx is further highlighted by density functional theory calculations that identify formate and methoxy species as stable reaction intermediates.

Ultrahigh surface density of Co-N2C single-atom-sites for boosting photocatalytic CO2 reduction to methanol

Cobalt species as active sites for photocatalytic reduction of CO2 to valuable products such as methanol have received increasing attention, however, it remains a huge challenge to achieve the high activity. Herein, a pyrolysis-induced-vaporization strategy was successfully employed to fabricate Co/g-C3N4 single-atom catalysts (Co/g-C3N4 SACs) with surface Co atom loading up to 24.6 wt%. Systematic investigation of Co/g-C3N4 SACs formation process disclosed that concentrated-H2SO4 exfoliation of g-C3N4 nanosheets (g-C3N4 NSs) as the substrate followed by a two-step calcination process is essential to achieve ultrahigh metal loading. It was found that the ultrahigh-density of Co single-atom sites were anchored on the g-C3N4 substrate surface and coordinated with two nitrogen and one carbon atoms (Co-N2C). These single dispersed Co-N2C sites on the g-C3N4 surface were found to act not only as electron gathering centers but also as the sites of CO2 adsorption and activation, subsequently, boosting the photocatalytic methanol generation during light irradiation. As a result, the methanol formation rate at 4 h (941.9 μmol g−1) over Co/g-C3N4-0.2 SAC with 24.6 wt% surface Co loading was 13.4 and 2.2 times higher than those of g-C3N4 (17.7 μmol g−1) and aggregated CoOx/g-C3N4-0.2 (423.9 μmol g−1), respectively. Simultaneously, H2 (18.9 μmol g−1 h−1), CO (2.9 μmol g−1 h−1), CH4 (3.4 μmol g−1 h−1), C2H4 (1.1 μmol g−1 h−1), C3H6 (1.4 μmol g−1 h−1), and CH3OCH3 (3.3 μmol g−1 h−1) products were detected over Co/g-C3N4-0.2 SAC. Besides, the photocatalytic activity of the Co/g-C3N4-0.2 SAC for the reduction of CO2 to methanol was stable within 12-cycle experiments (~48 h). This work paves a strategy to boost the photoreduction CO2 activity via loading ultrahigh surface density single atomically dispersed cobalt active sites.

Understanding the Origin of Structure Sensitivity in Nano Crystalline Mixed Cu/Mg−Al Oxides Catalyst for Low‐Pressure Methanol Synthesis

AbstractCu nanoparticles of size 5–10 nm supported on Mg−Al mixed oxide were prepared by the sol‐gel method. Cu loading was varied from 2.5 to 10 wt % on the support to investigate the effect on particle size and activity/selectivity of the catalyst. The Cu/Mg−Al catalysts containing small copper nanoparticles favor high selectivity of methanol, while the rate of CO formation was higher for larger copper particles. The high methanol selectivity (∼99 %) and methanol formation rate (0.016 mol gCu−1 h−1) over the 4.8Cu/Mg−Al catalyst was due to the combined effect of the presence of high Cu dispersion, Cu surface area, and strong interaction between small Cu particles with Mg−Al support. The high stability of the catalyst was attributed to the strong binding of the Cu cluster (−179.7 kJ/mol) to the MgO/γ‐Al2O3 support, as shown by the DFT study. Additionally, the adsorption energy calculated using DFT showed preferential adsorption of CO2 and H2 at the Cu/MgO(100) active site (−120.9 kJ/mol, −130.4 kJ/mol) compared to the Cu/γ‐Al2O3(100) (−64.2 kJ/mol, −85.7 kJ/mol)active site. The high selectivity of the catalyst towards methanol can be attributed to the higher stability of the formate (HCOO) intermediate (−257.2 kJ/mol) compared to the carboxylate (COOH) intermediate (−131.0 kJ/mol).

In situ XPS studies of MoS2-based CO2 hydrogenation catalysts

Various formulations of Co, Ni and K modified MoS2-based catalysts were synthesized hydrothermally and compared in their catalytic performance in CO2 hydrogenation at 21 bar and 220 °C–330 °C. The products were CO, CH4 and methanol. The addition of K reduced the selectivity to CH4 and moved the maximum of the methanol formation rate to a higher temperature. The materials were characterized by N2 physisorption, temperature programmed oxidation, temperature programmed reduction, and x-ray diffraction spectra (XRD). Under reducing conditions the catalysts were stable until 700 °C and under oxidizing conditions until 300 °C. XRD had shown mainly a MoS2 phase, as well as metal sulfide in the cobalt and nickel promoted catalysts. Different species of Mo and O were observed under reaction conditions by in situ x-ray photoelectron spectroscopy (XPS). When switching from H2 to CO2 + H2 an increase in the amount of oxygen, both lattice oxygen and surface adsorbates, was observed as a consequence of CO2 addition and H2O formation in the reaction. The amount of lattice oxygen correlates with the minor amount of Mo(VI) detected. Increasing reaction temperature and thus conversion led to an increase of the O 1s signals at 533 eV assigned to surface OH, formate and adsorbed H2O. XPS measurements in CO2 + H2 feed showed an effect of K addition on the adsorbate-related O 1s peak, which appeared at lower binding energy (532 eV) and was assigned to carbonates. This may indicate a different reaction mechanism in the presence of the promoter.

Inside the reaction mechanism of direct CO2 conversion to DME over zeolite-based hybrid catalysts

This paper aims at shedding more light on the reaction mechanism behind the direct hydrogenation of CO2 streams into DME in presence of hybrid catalysts. Starting from the physico-chemical properties of an optimized CuO-ZnO-ZrO2/HZSM-5 catalytic system, whose synergy among active sites of different nature (i.e., metal/oxide and acid/base) was recently proposed as the key to overcome the typical limitations showed by random mixing of two preformed catalysts, new evidences are herewith reported about catalytic performance, conditions for activation of reactants, limiting steps and product formation. Likewise to other proposed mechanisms at the state of the art, the catalyst efficiency is resulted to be dependent on several catalyst features, related not only to the metal-oxide phase responsible for CO2 activation/hydrogenation, but also to specific characteristics of the zeolite (i.e., porosity, specific surface area, population, location and strength of acid sites, interaction with active metals, …), influencing the activity-selectivity pattern. The production of DME is conditioned by the rate of methanol formation in proximity of the metal-oxide interface, followed by a rapid transferring of methanol towards the neighboring acid sites of the zeolite. Operando spectroscopic investigations performed under simulated reaction conditions (30 bar, 200−260 °C) have shown that the intermediates formation strongly depends upon a concurrence of texture, structure and surface aspects; however, depending on the reaction conditions, methanol formation normally passes through the formation of formate species. From a technological point of view, a reaction pressure of 30 bar appears as the ideal compromise between CO2 conversion and limitation of operative costs, while, due to thermodynamic restrictions, a reaction temperature not higher than 200 °C is necessary to attain DME selectivity close to 90 %.

Structure-sensitivity of direct oxidation methane to methanol over Rhn/ZrO2-x (1 0 1) (n = 1, 4, 10) surfaces: A DFT study

The size-dependence of methane direct oxidation to methanol over Rhn/ZrO2-x (101) (n = 1,4,10) was studied by density functional theoretical (DFT) calculations. We envisioned several paths for methanol formation using H2O2 or O2 as oxidant respectively. The CH3* directly oxidized to methanol by OOH* was considered the optimal route for methanol formation over Rhn/ZrO2-x (101) in our present calculation. Moreover, the C-O bond formation via the O* as the oxidant shown a higher barrier than that of OH* or OOH*, indicating more active of H2O2 than O2 due to more available Rh sites. More importantly, the high stability of CH3* favors the CH3OH formation. With the increasing of the size of clusters, the activation energy of H* abstracted from CH3* was decreased, resulting in a reduction of methanol formation as Rh size growths. Besides, the larger Rh clusters were more facility for methanol decomposition to CO than Rh1/ZrO2-x (101), leading the lower productivity for methanol further. Especially for Rh4/ZrO2-x (101) and Rh10/ZrO2-x (101), the surface was even poisoned by CO. From the view of kinetic, our present results show that the methanol formation rate increased with increasing the Rh dispersion, particularly for the atomically dispersed Rh catalyst. So, the atomically dispersed Rh catalyst has the higher productivity and selectivity for the methanol production, which means a strongly structure-sensitivity for methanol formation catalyzed by supported Rh catalysts.

Tuning the interfacial sites between copper and metal oxides (Zn, Zr, In) for CO2 hydrogenation to methanol

The influence of different metal oxides (ZnO, ZrO2, In2O3) in CO2 hydrogenation to methanol over Cu-based catalysts was studied. The catalysts were characterized using x-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), N2-physisorption, N2O chemisorption, H2 temperature-programmed reduction (H2-TPR), and CO2 temperature-programmed desorption (CO2-TPD). It was found that impregnating ZrO2 onto Cu/ZnO enhances the methanol formation rate from 14.7 mmol∙gcat−1∙h−1 to 15.6 mmol∙gcat−1∙h−1 (230 °C, 30 bar, 38 000 cm3/(gcat h)), which is attributed to the formation of Cu-ZrO2 sites. The results also indicate that In-doping of the Cu-based catalysts generates CuxIny alloys, which seems to inhibit the active sites on the Cu surface. However, new sites for methanol synthesis are present when Cu/ZrO2/In2O3 is prepared by co-precipitation. This is attributed to In-Zr mixed oxide species that increases the methanol formation rate from 53.2 mmol∙gcat−1∙h−1 to 60.5 mmol∙gcat−1∙h−1 (270 °C, 30 bar, 140 000 cm3/(gcat h)).

CO2 hydrogenation to methanol on ZnO-ZrO2 solid solution catalysts with ordered mesoporous structure

CO2 hydrogenation to methanol is becoming a potential route for reducing CO2 emission, benefiting from the worldwide growth of renewable energy for H2 production. In this work, the ZnO-ZrO2 solid solution catalysts with ordered mesoporous structure were constructed by the evaporation-induced self-assembly (EISA) process using triblock copolymer P123 as the template. The 20% ZnO-ZrO2 catalyst prepared by the evaporation-induced self-assembly process shows a methanol formation rate of 22.1 mmol·h-1·gcat-1 at 320°C, 5.5 MPa, which is 1.35 times that of the catalyst prepared by co-precipitation. Characterizations prove that the EISA catalysts have larger specific surface areas and more sites for the activation of CO2 and H2, which are related to the higher CO2 conversion.

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 µmolCH3OH/gcat/h ) and DME (13.2 µmolDME/gcat/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.

Microfabrication Enables Quantification of Interfacial Activity in Thermal Catalysis.

A myriad of heterogeneous catalysts comprises multiple phases that need to be precisely structured to exert their maximal contribution to performance through electronic and structural interactions at their peripheries. In view of the nanometric, tridimensional, and anisotropic nature of these materials, a quantification of the interface and the impact of catalytic sites located there on the global performance is a highly challenging task. Consequently, the true origin of catalysis often remains subject of debate even for widely studied materials. Herein, an integrated strategy based on microfabricated catalysts and a custom-designed reactor is introduced for determining interfacial contributions upon catalytic activity assessment under process-relevant conditions, which can be easily implemented in the common catalysis research infrastructure and will accelerate the rational design of multicomponent heterogeneous catalysts for diverse applications. The method is validated by studying the high-pressure continuous-flow hydrogenation of CO and CO2 over Cu-ZnO catalysts, revealing linear correlations between the methanol formation rate and the interface between the metal and the oxide. Characterization of fresh and used materials points to the model catalyst preparation as the current challenge of the methodology that can be addressed through further development of nanotechnological tools.

Understanding Selectivity in CO2 Hydrogenation to Methanol for MoP Nanoparticle Catalysts Using In Situ Techniques

Molybdenum phosphide (MoP) catalyzes the hydrogenation of CO, CO2, and their mixtures to methanol, and it is investigated as a high-activity catalyst that overcomes deactivation issues (e.g., formate poisoning) faced by conventional transition metal catalysts. MoP as a new catalyst for hydrogenating CO2 to methanol is particularly appealing for the use of CO2 as chemical feedstock. Herein, we use a colloidal synthesis technique that connects the presence of MoP to the formation of methanol from CO2, regardless of the support being used. By conducting a systematic support study, we see that zirconia (ZrO2) has the striking ability to shift the selectivity towards methanol by increasing the rate of methanol conversion by two orders of magnitude compared to other supports, at a CO2 conversion of 1.4% and methanol selectivity of 55.4%. In situ X-ray Absorption Spectroscopy (XAS) and in situ X-ray Diffraction (XRD) indicate that under reaction conditions the catalyst is pure MoP in a partially crystalline phase. Results from Diffuse Reflectance Infrared Fourier Transform Spectroscopy coupled with Temperature Programmed Surface Reaction (DRIFTS-TPSR) point towards a highly reactive monodentate formate intermediate stabilized by the strong interaction of MoP and ZrO2. This study definitively shows that the presence of a MoP phase leads to methanol formation from CO2, regardless of support and that the formate intermediate on MoP governs methanol formation rate.

A potential catalyst for continuous methane partial oxidation to methanol using N2O: Cu-SSZ-39.

Continuous catalytic methanol production from methane is reported on Cu-SSZ-39 using N2O as an oxidant. Through optimization of CH4, N2O and H2O partial pressures, a methanol formation rate of 499 μmolCH3OH g-1 h-1 and a methanol selectivity of 34% is achieved.

Reaction-driven surface reconstruction of ZnAl2O4 boosts the methanol selectivity in CO2 catalytic hydrogenation

Identifying the surface structure of heterogeneous catalysts is critical for understanding the active sites, but it remains challenging due to the difficulty in characterizing the catalytic surfaces especially at elevated temperatures. Zn-based catalysts are high-efficiency alternatives for high-temperature methanol synthesis from CO2, as well as in bifunctional catalysts for hydrocarbons synthesis. Herein, the surface reconstruction of ZnAl2O4 spinel during CO2 hydrogenation reaction was investigated using detailed spectroscopic characterization. The results indicate that the reaction-driven surface reconstruction leads to the formation of amorphous ZnO on the ZnAl2O4 surface, which is accompanied by the increasing catalytic activity for methanol production. Kinetic analysis, STEM and in situ FTIR results indicate that the amorphous ZnO boosts the methanol formation rate by promoting the activation of H2. This study provides useful insight into the structure-activity relationship of zinc-based catalysts for CO2 hydrogenation and future design of new catalysts.

Inverse ZrO2/Cu as a highly efficient methanol synthesis catalyst from CO2 hydrogenation

Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts through CO2 hydrogenation is one of the major topics in CO2 conversion into value-added liquid fuels and chemicals. Here we report inverse ZrO2/Cu catalysts with a tunable Zr/Cu ratio have been prepared via an oxalate co-precipitation method, showing excellent performance for CO2 hydrogenation to methanol. Under optimal condition, the catalyst composed by 10% of ZrO2 supported over 90% of Cu exhibits the highest mass-specific methanol formation rate of 524 gMeOHkgcat−1h−1 at 220 °C, 3.3 times higher than the activity of traditional Cu/ZrO2 catalysts (159 gMeOHkgcat−1h−1). In situ XRD-PDF, XAFS and AP-XPS structural studies reveal that the inverse ZrO2/Cu catalysts are composed of islands of partially reduced 1–2 nm amorphous ZrO2 supported over metallic Cu particles. The ZrO2 islands are highly active for the CO2 activation. Meanwhile, an intermediate of formate adsorbed on the Cu at 1350 cm−1 is discovered by the in situ DRIFTS. This formate intermediate exhibits fast hydrogenation conversion to methoxy. The activation of CO2 and hydrogenation of all the surface oxygenate intermediates are significantly accelerated over the inverse ZrO2/Cu configuration, accounting for the excellent methanol formation activity observed.

Influence of Defects and H2O on the Hydrogenation of CO2 to Methanol over Pt Nanoparticles in UiO-67 Metal-Organic Framework.

In catalysts for CO2 hydrogenation, the interface between metal nanoparticles (NPs) and the support material is of high importance for the activity and reaction selectivity. In Pt NP-containing UiO Zr-metal–organic frameworks (MOFs), key intermediates in methanol formation are adsorbed at open Zr-sites at the Pt–MOF interface. In this study, we investigate the dynamic role of the Zr-node and the influence of H2O on the CO2 hydrogenation reaction at 170 °C, through steady state and transient isotope exchange experiments, H2O cofeed measurements, and density functional theory (DFT) calculations. The study revealed that an increased number of Zr-node defects increase the formation rates to both methanol and methane. Transient experiments linked the increase to a higher number of surface intermediates for both products. Experiments involving either dehydrated or prehydrated Zr-nodes showed higher methanol and methane formation rates over the dehydrated Zr-node. Transient experiments suggested that the difference is related to competitive adsorption between methanol and water. DFT calculations and microkinetic modeling support this conclusion and give further insight into the equilibria involved in the competitive adsorption process. The calculations revealed weaker adsorption of methanol in defective or dehydrated nodes, in agreement with the larger gas phase concentration of methanol observed experimentally. The microkinetic model shows that [Zr2(μ-O)2]4+ and [Zr2(μ–OH)(μ-O)(OH)(H2O)]4+ are the main surface species when the concentration of water is lower than the number of defect sites. Lastly, although addition of water was found to promote methanol desorption, water does not change the methanol steady state reaction rate, while it has a substantial inhibiting effect on CH4 formation. These results indicate that water can be used to increase the reaction selectivity to methanol and encourages further detailed investigations of the catalyst system.

Identifying the nature of the active sites in methanol synthesis over Cu/ZnO/Al2O3 catalysts

The heterogeneously catalysed reaction of hydrogen with carbon monoxide and carbon dioxide (syngas) to methanol is nearly 100 years old, and the standard methanol catalyst Cu/ZnO/Al2O3 has been applied for more than 50 years. Still, the nature of the Zn species on the metallic Cu0 particles (interface sites) is heavily debated. Here, we show that these Zn species are not metallic, but have a positively charged nature under industrial methanol synthesis conditions. Our kinetic results are based on a self-built high-pressure pulse unit, which allows us to inject selective reversible poisons into the syngas feed passing through a fixed-bed reactor containing an industrial Cu/ZnO/Al2O3 catalyst under high-pressure conditions. This method allows us to perform surface-sensitive operando investigations as a function of the reaction conditions, demonstrating that the rate of methanol formation is only decreased in CO2-containing syngas mixtures when pulsing NH3 or methylamines as basic probe molecules.

Mechanistic Studies of Methanol Synthesis Reaction over Cu and Pd–Cu Catalysts

Monometallic copper and bimetallic palladium–copper catalysts supported on ZnO–Al2O3, CeO2–Al2O3 and ZrO2–Al2O3 were prepared by conventional impregnation method and tested in the methanol synthesis reaction in a gradient less reactor under elevated pressure (3.5 MPa) at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, TPR-H2, TPD-NH3, XRD, SEM-EDS and FT-IR techniques. The results of XRD and SEM-EDS measurements showed the formation of Pd–Cu alloy during the activation of bimetallic catalysts. It was found that the formed alloy was responsible for the improved activity and selectivity of catalysts in the studied reaction. Among investigated catalysts, the highest formation rate of methanol was observed with 2%Pd–20%Cu/ZnO–Al2O3 system. Based on the results of FT-IR measurements it can be concluded that hydrogen molecules adsorb dissociatively on the metallic copper surface to form hydrogen atoms, increasing the hydrogen spillover effect on the metal-support interface. In contrast, CO2 adsorb on the oxygen vacancies of the support to form carbonates, which can further undergo hydrogenation to methanol.

Insights into the methanol synthesis mechanism via CO2 hydrogenation over Cu-ZnO-ZrO2 catalysts: Effects of surfactant/Cu-Zn-Zr molar ratio

In this study, we evaluated aspects of the CO2 hydrogenation mechanism, correlating structure-activity relationships of Cu-ZnO-ZrO2 catalysts prepared by one-pot surfactant-assisted co-precipitation with different surfactant ratios. Identifying the CO2 hydrogenation pathway intermediates is key to controlling the reaction selectivity. Experimental evidence shows that the CO2 is dissociating into CO* and O* onto the surface of the Cu-ZnO-ZrO2 catalyst. The adsorption and dissociation of CO2 were evidenced by a combination of in situ ambient-pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Fourier Transform Infrared Spectroscopy (FTIR) with a transmission cell. AP-XPS showed that the catalysts are composed of a Cu2+, Zr3+, and Zr4+ mixture and two kinds of Zn2+ species. After the H2 reduction process, only Cu2+ was reduced to Cu0. The Zn and Zr species were oxidized by the dissociated O* species. In situ transmission FTIR showed that CO was adsorbed onto the Cu+/0 sites. The catalyst with the higher surfactant molar ratio exhibited the highest CO2 conversion close to the equilibrium conversion, as well as a good methanol formation rate.

Theoretical Study of Formation of Methanol under Hydrothermal Conditions.

We have examined the formation process of methanol by the reduction of formaldehyde under hydrothermal conditions. A formaldehyde absorbs a hydrogen molecule and turns to a methanol. Water molecules near a formaldehyde help to transfer protons to proceed the reduction process efficiently. The energy barrier for the reduction of a formaldehyde becomes 32.8 kcal/mol when a water cluster with five water molecules catalyzes the reduction. The ionic product becomes the largest under hydrothermal conditions. We introduce the acid-base catalytic effect due to hydronium and hydroxide on the reduction of formaldehyde. The energy barriers for the reduction of a formaldehyde are further reduced to 29.3 and 10.4 kcal/mol by the acid and base catalytic effects, respectively. The reduction of a formaldehyde is more effectively catalyzed by a hydroxide than a hydronium. The acid-base catalytic effect is not available at the high temperature of supercritical water due to the sudden decrease of the ionic product. It takes too long to form a reactant compound in supercritical water. The transition state theory is applied to calculate the reduction rate of a reactant compound, considering the tunneling effect of a proton. We confirmed that a metastable equilibrium state attains among single-carbon compounds except methanol and methane by reproducing the concentrations of the carbon compounds measured in a laboratory. We calculated the formation rate of methanol using the equilibrium concentration of formaldehyde. We compared the calculated formation rate with that determined by a laboratory experiment and confirmed that the present theoretical calculation is accurately able to describe the oxidative and reductive reaction network of single-carbon compounds under hydrothermal conditions. The present study can be applied to examine a reaction network of single-carbon compounds in hydrothermal vents on the Earth, Enceladus, and other solar system bodies such as Europa.