Formic acid stability in different solvents by DFT calculations

CONTEXT

New technologies have been developed toward the use of green energies. The production of formic acid (FA) from carbon dioxide (CO[Formula: see text]) hydrogenation with H[Formula: see text] is a sustainable process for H[Formula: see text] storage. However, the FA adduct stabilization is thermodynamically dependent on the type of solvent and thermodynamic conditions. The results suggest a wide range of dielectric permittivity values between the dimethyl sulfoxide (DMSO) and water solvents to stabilize the FA in the absence of base. The thermodynamics analysis and the infrared and charge density difference results show that the formation of the FA complex with H[Formula: see text]O is temperature dependent and has a major influence on aqueous solvents compared to the FA adduct with amine, in good agreement with the experiment. In these conditions, the stability thermodynamic of the FA molecule may be favorable at non-organic solvents and dielectric permittivity values closer to water. Therefore, a mixture of aqueous solvents with possible ionic composition could be used to increase the thermodynamic stability of H[Formula: see text] storage in CO[Formula: see text] conversion processes.

METHODS

Using the Quantum ESPRESSO package, density functional theory (DFT) calculations were performed with periodic boundary conditions, and the electronic wave functions were expanded in plane waves. For the exchange-correlation functional, we use the vdW-DF functional with the inclusion of van der Waals (vdW) forces. Electron-ion interactions are treated by the projector augmented wave (PAW) method with pseudopotentials available in the PSlibrary repository. The wave functions and the electronic densities were expanded employing accurate cut-off energies of 6.80[Formula: see text]10[Formula: see text] and 5.44[Formula: see text]10[Formula: see text] eV, respectively. The electronic density was computed from the wave functions calculated at the [Formula: see text]-point in the first Brillouin-zone. Each structural optimization was minimized according to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, with force and energy convergence criteria of 25 meV[Formula: see text]Å[Formula: see text] and 1.36 meV, respectively. The electrostatic solvation effects were performed by the [Formula: see text] package with the Self-Consistent Continuum Solvation (SCCS) approach.

Base Metal Catalyst for Indirect Hydrogenation of CO2

We herein report a novel Mn-SNS-based catalyst, which is capable of performing indirect hydrogenation of CO2 to methanol via formylation. In this domain of CO2 hydrogenation, pincer ligands have shown a clear predominance. Our catalyst is based on the SNS-type tridentate ligand, which is quite stable and cheap as compared to the pincer type ligands. The catalyst can also be recycled effectively after the formylation reaction without any significant change in efficiency. Various amines including both primary and secondary amines worked well under the protocol to provide the desired formylated product in good yields. The formed formylated amines can also be reduced further at higher pressures of hydrogen. As a whole, we have developed a protocol that involves indirect CO2 hydrogenation to methanol that proceeds via formylation of amines.

Hydrogenation of CO2 to MeOH Catalyzed by Highly Robust (PNNP)Ir Complexes Activated by Alkali Bases in Alcohol

Despite receiving significant attention, well-defined homogeneous complexes for hydrogenation of carbon dioxide (CO2) to methanol (MeOH) are scarce and suffer issues of low catalyst turnover numbers (TONs) at high catalyst concentrations and deactivation in the presence of CO and at elevated temperatures. Herein, we disclose a system deploying sterically demanded (PNNP)Ir complexes for a sustained activity for hydrogenation of CO2 to MeOH at temperatures ∼200 °C in an alcohol solvent. Through reaction optimization, we achieved a TON of ∼9000 for MeOH formation, which exceeds most active homogeneous systems reported to date, and robustness on par with or exceeding most reactive systems utilizing amine additives was demonstrated. The key to achieving sustained catalyst turnover for the system was utilizing a catalytic amount of an alkali base additive, which serves the dual purpose of facilitating more efficient outer-sphere reduction of CO2 and HCO2Et and enhancing the selectivity of MeOH over in situ formed CO.

A Self-Separating Multiphasic System for Catalytic Hydrogenation of CO2 and CO2 -Derivatives to Methanol

Catalytic conversion of CO₂ and hydrogen to methanol was achieved in a self-separating multiphasic system comprising the tailor-made complex [Ru(CO)ClH(MACHO-C₁₂ )] (MACHO-C₁₂ =bis{2-[bis(4-dodecylphenyl)phosphino]ethyl}amine) in n-decane as the catalyst phase. Effective catalyst recycling was demonstrated for the carbonate and the amine-assisted pathway from CO₂ to methanol. The polar products MeOH or MeOH/H₂ O generated from the catalytic reactions spontaneously formed a separate phase, allowing product isolation and catalyst separation without the need for any additional solvent. In the amine-assisted hydrogenation of CO₂ , the catalyst phase was recycled over ten subsequent runs, reaching a total turnover number to MeOH of 19200 with an average selectivity of 96 %.

Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy

The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO₂ emissions. Outpacing the natural carbon cycle, atmospheric CO₂ levels increased by 50 % since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chemical recycling of CO₂ to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO₂ , CO and their derivatives as potential low-temperature alternatives to the commercial processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the critical assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.

Recent developments in first-row transition metal complex-catalyzed CO2 hydrogenation

Our modern civilization is currently standing at a crossroads due to excessive emission of anthropogenic CO₂ leading to adverse climate change effects. Hence, a proper CO₂ management strategy, including appropriate CO₂ capture, utilization, and storage (CCUS), has become a prime concern globally. On the other hand, C₁ chemicals such as methanol (CH₃OH) and formic acid (HCOOH) have emerged as leading materials for a wide range of applications in various industries, including chemical, biochemical, pharmaceutical, agrochemical, and even energy sectors. Hence, there is a concerted effort to bridge the gap between CO₂ management and methanol/formic acid production by employing CO₂ as a C₁-synthon. CO₂ hydrogenation to methanol and formic acid has emerged as one of the primary routes for directly converting CO₂ to a copious amount of methanol and formate, which is typically catalyzed by transition metal complexes. In this frontier article, we have primarily discussed the abundant first-row transition metal-driven hydrogenation reaction that has exhibited a significant surge in activity over the past few years. We have also highlighted the potential future direction of the research while incorporating a comparative analysis for the competitive second and third-row transition metal-based hydrogenation.

Hydroboration of CO2 to Methyl Boronate Catalyzed by a Manganese Pincer Complex: Insights into the Reaction Mechanism and Ligand Effect

The conversion of carbon dioxide to fuels, polymers, and chemicals is an attractive strategy for the synthesis of high-value-added products and energy-storage materials. Herein, the density functional theory method was employed to investigate the reaction mechanism of CO₂ hydroboration catalyzed by manganese pincer complex, [Mn(Ph₂PCH₂SiMe₂)₂NH(CO)₂Br]. The carbonyl association and carbonyl dissociation mechanisms were investigated, and the calculated results showed that the carbonyl association mechanism is more favorable with an energetic span of 27.0 kcal/mol. Meanwhile, the solvent effect of the reaction was explored, indicating that the solvents could reduce the catalytic activity of the catalyst, which was consistent with the experimental results. In addition, the X ligand effect (X = CO, Br, H, PH₃) on the catalytic activity of the manganese complex was explored, indicating that the anionic complexes [Mn^I - Br]^- and [Mn^I - H]^- have higher catalytic activity. This may not only shed light on the fixation and conversion of CO₂ catalyzed by earth-abundant transition-metal complexes but also provide theoretical insights to design new transition-metal catalysts.

Recent progress in homogeneous hydrogenation of carbon dioxide to methanol

The requirement of running a new generation of fuel production is inevitable due to the limitation of oil production from reservoirs. On the other hand, enhancing the CO2 concentration in the atmosphere brings global warming phenomenon and leads to catastrophic disasters such as drought and flooding. Conversion of carbon dioxide to methanol can compensate for the liquid fuel requirement and mitigate CO2 emissions to the atmosphere. In this review, we surveyed the recent works on homogeneous hydrogenation of CO2 to CH3OH and investigated the experimental results in detail. We categorized the CO2 hydrogenation works based on the environment of the reaction, including neutral, acidic, and basic conditions, and discussed the effects of solvents’ properties on the experimental results. This review provides a perspective on the previous studies in this field, which can assist the researchers in selecting the proper catalyst and solvent for homogenous hydrogenation of carbon dioxide to methanol.

Hydrogenation of CO2 or CO2 Derivatives to Methanol under Molecular Catalysis: A Review

The atmospheric CO2 concentration has been continuously increasing due to fossil fuel combustion. The transformations of CO2 and CO2 derivatives into high value-added chemicals such as alcohols are ideal routes to mitigate greenhouse gas emissions. Among alcohol products, methanol is very promising as it fulfills the carbon neutral cycle and can be used for direct methanol fuel cells. Herein, we summarize the recent progress in the hydrogenation of CO2 or CO2 derivatives to methanol, and focus on those systems with homogeneous catalysts and molecular hydrogen as the reductant. Discussions on the catalytic systems, efficiencies, and future outlooks will be given.

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

As the world pledges to significantly cut carbon emissions, the demand for sustainable and clean energy has now become more important than ever. This includes both production and storage of energy carriers, a majority of which involve catalytic reactions. This article reviews recent developments of homogeneous catalysts in emerging applications of sustainable energy. The most important focus has been on hydrogen storage as several efficient homogeneous catalysts have been reported recently for (de)hydrogenative transformations promising to the hydrogen economy. Another direction that has been extensively covered in this review is that of the methanol economy. Homogeneous catalysts investigated for the production of methanol from CO₂, CO, and HCOOH have been discussed in detail. Moreover, catalytic processes for the production of conventional fuels (higher alkanes such as diesel, wax) from biomass or lower alkanes have also been discussed. A section has also been dedicated to the production of ethylene glycol from CO and H₂ using homogeneous catalysts. Well-defined transition metal complexes, in particular, pincer complexes, have been discussed in more detail due to their high activity and well-studied mechanisms.

Acid-assisted hydrogenation of CO2 to methanol using Ru(II) and Rh(III) RAPTA-type catalysts under mild conditions

A highly efficient homogeneous catalyst system for production of CH3OH from CO2 using single molecular defined ruthenium and rhodium RAPTA-type catalysts [Ru(η6-p-cymene)X2(PTA)] (X = I(1), Cl(2); PTA = 1,3,5-triaza-7-phosphaadamantane) and rhodium catalysts [Rh(η5-C5Me5)X2(PTA/PTA-BH3)] (X = Cl(3), H(4) and PTA-BH3, H(5)) developed in acidic media under mild conditions. A TON of 4752 is achieved using a [Ru(η6-p-cymene)I2(PTA)] catalyst which represents the first example of CO2 hydrogenation to CH3OH using single molecular defined Ru and Rh RAPTA-type catalysts.

Hydrogenation of CO2 to methanol catalyzed by a manganese pincer complex: insights into the mechanism and solvent effect

Herein, density functional theory (DFT) calculations were employed to explore the reaction mechanism of three cascade cycles for the hydrogenation of carbon dioxide to methanol (CO2 + 3H2 → CH3OH + H2O) catalyzed by a manganese pincer complex [Mn(Ph2PCH2SiMe2)2N(CO)2]. The three cascade cycles involve: the hydrogenation of CO2 to formic acid, the hydrogenation of formic acid to methanediol and the decomposition of methanediol to formaldehyde and water, and the hydrogenation of formaldehyde to methanol. The calculated results demonstrate that hydrogen activation is the rate-determining step of each catalytic cycle under solvent-free conditions, and the energy span of the whole reaction is 27.1 kcal mol-1. Furthermore, the solvent was found to be of importance in this reaction. In three different solvents, the rate-determining steps of this reaction are all the hydrogen transfer step of the formic acid hydrogenation stage, and the corresponding energy spans in water, toluene and THF solvents are 21.3, 20.8 and 20.4 kcal mol-1, respectively. Such a low energy span implies that this manganese complex could be a promising catalyst for the efficient conversion of CO2 and H2 to methanol at temperatures below 100-150 °C.

Catalytic Hydrogenation of CO2 to Methanol Using Multinuclear Iridium Complexes in a Gas-Solid Phase Reaction

We report a novel approach toward the catalytic hydrogenation of CO₂ to methanol performed in the gas-solid phase using multinuclear iridium complexes at low temperature (30-80 °C). Although homogeneous CO₂ hydrogenation in water catalyzed by amide-based iridium catalysts provided only a negligible amount of methanol, the combination of a multinuclear catalyst and gas-solid phase reaction conditions led to the effective production of methanol from CO₂. The catalytic activities of the multinuclear catalyst were dependent on the relative configuration of each active species. Conveniently, methanol obtained from the gas phase could be easily isolated from the catalyst without contamination with CO, CH₄, or formic acid (FA). The catalyst can be recycled in a batchwise manner via gas release and filling. A final turnover number of 113 was obtained upon reusing the catalyst at 60 °C and 4 MPa of H₂/CO₂ (3:1). The high reactivity of this system has been attributed to hydride complex formation upon exposure to H₂ gas, suppression of the liberation of FA under gas-solid phase reaction conditions, and intramolecular multiple hydride transfer to CO₂ by the multinuclear catalyst.

Unraveling the catalytically preferential pathway between the direct and indirect hydrogenation of CO2 to CH3OH using N-heterocyclic carbene-based Mn(i) catalysts: a theoretical approach

The mechanistic investigation of direct vs. indirect CO₂ hydrogenation to methanol using single molecular NHC-based Mn(i) complexes.

Homogeneous and heterogeneous catalysts for hydrogenation of CO2 to methanol under mild conditions

This review summarizes the concepts, mechanisms, drawbacks and challenges of the state-of-the-art catalysis for CO₂ to MeOH under mild conditions. Thoughtful guidelines and principles for future research are presented and discussed.

CO2 Reduction to Methanol in the Liquid Phase: A Review

Excessive carbon dioxide (CO₂ ) emissions have been subject to extensive attention globally, since an enhanced greenhouse effect (global warming) owing to a high CO₂ concentration in the atmosphere could lead to severe climate change. The use of solar energy and other renewable energy to produce low-cost hydrogen, which is used to reduce CO₂ to produce bulk chemicals such as methanol, is a sustainable strategy for reducing carbon dioxide emissions and carbon resources. CO₂ conversion into methanol is exothermic, so that low temperature and high pressure are favorable for methanol formation. CO₂ is usually captured and recovered in the liquid phase. Herein, the emerging technologies for the hydrogenation of CO₂ to methanol in the condensed phase are reviewed. The development of homogeneous and heterogeneous catalysts for this important hydrogenation reaction is summarized. Finally, mechanistic insight on CO₂ 's conversion into methanol over different catalysts is discussed by taking the available reaction pathways into account.

Catalytic coproduction of methanol and glycol in one pot from epoxide, CO2, and H2

An atom (100%) and energy-efficient approach to coproduce two commodity chemicals, methanol and glycol, has been demonstrated for the first time using H₂, CO₂, and epoxide as feeds. A basic medium used for CO₂ capture, polyethyleneimine (PEI₆₀₀), is shown to facilitate the formation of a key reaction intermediate, cyclic carbonates. Upon hydrogenation of cyclic carbonates in the presence of a homogenous Ru-PNP catalyst, a 1 : 1 mixture of methanol and glycol is produced. This approach has been demonstrated in one pot by adding all the required reactants directly or stepwise. The stepwise addition of reactants resulted in good yields (>95% for PG and 84% for methanol) and selectivity of products.

An atom (100%) and energy-efficient approach to coproduce two commodity chemicals, methanol and glycol, has been demonstrated for the first time using H₂, CO₂, and epoxide as feeds.

Toward Combined Carbon Capture and Recycling: Addition of an Amine Alters Product Selectivity from CO to Formic Acid in Manganese Catalyzed Reduction of CO2

Owing to the energetic cost associated with CO₂ release in carbon capture (CC), the combination of carbon capture and recycling (CCR) is an emerging area of research. In this approach, "captured CO₂," typically generated by addition of amines, serves as a substrate for subsequent reduction. Herein, we report that the reduction of CO₂ in the presence of morpholine (generating mixtures of the corresponding carbamate and carbamic acid) with a well-established Mn electrocatalyst changes the product selectivity from CO to H₂ and formate. The change in selectivity is attributed to in situ generation of the morpholinium carbamic acid, which is sufficiently acidic to protonate the reduced Mn species and generate an intermediate Mn hydride. Thermodynamic studies indicate that the hydride is not sufficiently hydritic to reduce CO₂ to formate, unless the apparent hydricity, which encompasses formate binding to the Mn, is considered. Increasing steric bulk around the Mn shuts down rapid homolytic H₂ evolution rendering the intermediate Mn hydride more stable; subsequent CO₂ insertion appears to be faster than heterolytic H₂ production. A comprehensive mechanistic scheme is proposed that illustrates how thermodynamic analysis can provide further insight. Relevant to a range of hydrogenations and reductions is the modulation of the hydricity with substrate binding that makes the reaction favorable. Significantly, this work illustrates a new role for amines in CO₂ reduction: changing the product selectivity; this is pertinent more broadly to advancing CCR.

Research Progress in Conversion of CO2 to Valuable Fuels

Rapid growth in the world's economy depends on a significant increase in energy consumption. As is known, most of the present energy supply comes from coal, oil, and natural gas. The overreliance on fossil energy brings serious environmental problems in addition to the scarcity of energy. One of the most concerning environmental problems is the large contribution to global warming because of the massive discharge of CO₂ in the burning of fossil fuels. Therefore, many efforts have been made to resolve such issues. Among them, the preparation of valuable fuels or chemicals from greenhouse gas (CO₂) has attracted great attention because it has made a promising step toward simultaneously resolving the environment and energy problems. This article reviews the current progress in CO₂ conversion via different strategies, including thermal catalysis, electrocatalysis, photocatalysis, and photoelectrocatalysis. Inspired by natural photosynthesis, light-capturing agents including macrocycles with conjugated structures similar to chlorophyll have attracted increasing attention. Using such macrocycles as photosensitizers, photocatalysis, photoelectrocatalysis, or coupling with enzymatic reactions were conducted to fulfill the conversion of CO₂ with high efficiency and specificity. Recent progress in enzyme coupled to photocatalysis and enzyme coupled to photoelectrocatalysis were specially reviewed in this review. Additionally, the characteristics, advantages, and disadvantages of different conversion methods were also presented. We wish to provide certain constructive ideas for new investigators and deep insights into the research of CO₂ conversion.

Molecularly Defined Manganese Catalyst for Low-Temperature Hydrogenation of Carbon Monoxide to Methanol

Methanol synthesis from syngas (CO/H₂ mixtures) is one of the largest manmade chemical processes with annual production reaching 100 million tons. The current industrial method proceeds at high temperatures (200-300 °C) and pressures (50-100 atm) using a copper-zinc-based heterogeneous catalyst. In contrast, here, we report a molecularly defined manganese catalyst that allows for low-temperature/low-pressure (120-150 °C, 50 bar) carbon monoxide hydrogenation to methanol. This new approach was evaluated and optimized by quantum mechanical simulations virtual high-throughput screenings. Crucial for this achievement is the use of amine-based promoters, which capture carbon monoxide to give formamide intermediates, which then undergo manganese-catalyzed hydrogenolysis, regenerating the promoter. Following this conceptually new approach, high selectivity toward methanol and catalyst turnover numbers (up to 3170) was achieved. The proposed general catalytic cycle for methanol synthesis is supported by model studies and detailed spectroscopic investigations.

Integrated CO2 Capture and Conversion to Formate and Methanol: Connecting Two Threads

The capture of CO₂ from concentrated emission sources as well as from air represents a process of paramount importance in view of the increasing CO₂ concentration in the atmosphere and its associated negative consequences on the biosphere. Once captured using various technologies, CO₂ is desorbed and compressed for either storage (carbon capture and storage (CCS)) or production of value-added products (carbon capture and utilization (CCU)). Among various products that can be synthesized from CO₂, methanol and formic acid are of high interest because they can be used directly as fuels or to generate H₂ on demand at low temperatures (<100 °C), making them attractive hydrogen carriers (12.6 and 4.4 wt % H₂ in methanol and formic acid, respectively). Methanol is already produced in huge quantities worldwide (100 billion liters annually) and is also a raw material for many chemicals and products, including formaldehyde, dimethyl ether, light olefins, and gasoline. The production of methanol through chemical recycling of captured CO₂ is at the heart of the so-called "methanol economy" that we have proposed with the late Prof. George Olah at our Institute. Recently, there has been significant progress in the low-temperature synthesis of formic acid (or formate salts) and methanol from CO₂ and H₂ using homogeneous catalysts. Importantly, several studies have combined CO₂ capture and hydrogenation, where captured CO₂ (including from air) was directly utilized to produce formate and CH₃OH without requiring energy intensive desorption and compression steps. This Account centers on that topic. A key feature in the combined CO₂ capture and conversion studies reported to date for the synthesis of formic acid and methanol is the use of an amine or alkali-metal hydroxide base for capturing CO₂, which can assist the homogeneous catalysts in the hydrogenation step. We start this Account by examining the combined processes where CO₂ is captured in amine solutions and converted to alkylammonium formate salts. The effect of amine basicity on the reaction rate is discussed along with catalyst recycling schemes. Next, methanol synthesis by this combined process, with amines as capturing agents, is explored. We also examine the system developments for effective catalyst and amine recycling in this process. We next go through the effect of catalyst molecular structure on methanol production while elucidating the main deactivating pathway involving carbonylation of the metal center. The recent advances in first-row transition metal catalysts for this process are also mentioned. Subsequently, we discuss the capture of CO₂ using hydroxide bases and conversion to formate salts. The regeneration of the hydroxide base (NaOH or KOH) at low temperatures (80 °C) in cation-conducting direct formate fuel cells is presented. Finally, we review the challenges in the yet unreported integrated CO₂ capture by hydroxide bases and conversion to methanol process.

Combined CO2 Capture and Hydrogenation to Methanol: Amine Immobilization Enables Easy Recycling of Active Elements

Amines were immobilized onto solid supports and employed for tandem CO₂ capture and conversion to CH₃ OH using homogeneous hydrogenation catalysts. The hydrogenation proceeded through the formation of formamide intermediates. After hydrogenation, the immobilized amines were easily filtered and collected to be reused. The catalyst and methanol were recovered from the filtrate. Covalently-attached (to polymer support or silica) amine functionalities displayed the highest recycling potential with almost no leaching under the hydrogenation reaction conditions. Using polyethylenimine grafted onto a solid-silica support, the catalyst and amine were successfully recycled, and CO₂ (either pure or from the air) was efficiently captured and converted to CH₃ OH over multiple cycles.

Additive-free cobalt-catalysed hydrogenation of carbonates to methanol and alcohols

Homogeneously cobalt-catalyzed hydrogenation of cyclic and acyclic carbonates: beneficial effects of 2,2,2-trifluoroethanol and triphos-derivatives.