Heterogeneous Catalysis in Production and Utilization of Formic Acid for Renewable Energy.

To meet the global climate goals agreed upon regarding the Paris Agreement, governments and institutions around the world are investigating various technologies to reduce carbon emissions and achieve a net-negative energy system. To this end, integrated solutions that incorporate carbon utilization processes, as well as promote the transition of the fossil fuel-based energy system to carbon-free systems, such as the hydrogen economy, are required. One of the possible pathways is to utilize CO2 as the base chemical for producing a liquid organic hydrogen carrier (LOHC), using CO2 as a mediating chemical for delivering H2 to the site of usage since gaseous and liquid H2 retain transportation and storage problems. Formic acid is a probable candidate considering its high volumetric H2 capacity and low toxicity. While previous studies have shown that formic acid is less competitive as an LOHC candidate compared to other chemicals, such as methanol or toluene, the results were based on out-of-date process schemes. Recently, advances have been made in the formic acid production and dehydrogenation processes, and an analysis regarding the recent process configurations could deem formic acid as a feasible option for LOHC. In this study, the potential for using formic acid as an LOHC is evaluated, with respect to the state-of-the-art formic acid production schemes, including the use of heterogeneous catalysts during thermocatalytic and electrochemical formic acid production from CO2. Assuming a hydrogen distribution system using formic acid as the LOHC, each of the production, transportation, dehydrogenation, and CO2 recycle sections are separately modeled and evaluated by means of techno-economic analysis (TEA) and life cycle assessment (LCA). Realistic scenarios for hydrogen distribution are established considering the different transportation and CO2 recovery options; then, the separate scenarios are compared to the results of a liquefied hydrogen distribution scenario. TEA results showed that, while the LOHC system incorporating the thermocatalytic CO2 hydrogenation to formic acid is more expensive than liquefied H2 distribution, the electrochemical CO2 reduction to formic acid system reduces the H2 distribution cost by 12%. Breakdown of the cost compositions revealed that reduction of steam usage for thermocatalytic processes in the future can make the LOHC system based on thermocatalytic CO2 hydrogenation to formic acid to be competitive with liquefied H2 distribution if the production cost could be reduced by 23% and 32%, according to the dehydrogenation mode selected. Using formic acid as a LOHC was shown to be less competitive compared to liquefied H2 delivery in terms of LCA, but producing formic acid via electrochemical CO2 reduction was shown to retain the lowest global warming potential among the considered options.

Electrochemical reduction of carbon dioxide (CO(2)) to useful chemical materials is of great significance to the virtuous cycle of CO(2). However, some problems such as high overpotential, high applied voltage, and high energy consumption exist in the course of the conventional electrochemical reduction process. This study presents a new CO(2) reduction technique for targeted production of formic acid in a microbial electrolysis cell (MEC) driven by a microbial fuel cell (MFC). The multiwalled carbon nanotubes (MWCNT) and cobalt tetra-amino phthalocyanine (CoTAPc) composite modified electrode was fabricated by the layer-by-layer (LBL) self-assembly technique. The new electrodes significantly decreased the overpotential of CO(2) reduction, and as cathode successfully reduced CO(2) to formic acid (production rate of up to 21.0 ± 0.2 mg·L(-1)·h(-1)) in an MEC driven by a single MFC. Compared with the electrode modified by CoTAPc alone, the MWCNT/CoTAPc composite modified electrode could increase the current and formic acid production rate by approximately 20% and 100%, respectively. The Faraday efficiency for formic acid production depended on the cathode potential. The MWCNT/CoTAPc composite electrode reached the maximum Faraday efficiency at the cathode potential of ca. -0.5 V vs Ag/AgCl. Increasing the number of electrode modification layers favored the current and formic acid production rate. The production of formic acid was stable in the MFC-MEC system after multiple batches of CO(2) electrolysis, and no significant change was observed on the performances of the modified electrode. The coupling of the catalytic electrode and the bioelectrochemical system realized the targeted reduction of CO(2) in the absence of external energy input, providing a new way for CO(2) capture and conversion.

: Hydrogenation of CO2 to energy-rich products over heterogeneous metal catalysts has gained much attention due to their commercial applications. Specifically, the first-row transition metal catalysts are very rarely reported and discussed for the production of formic acid from the hydrogenation of CO2. Herein, hydrotalcite supported copper metal has shown activity and efficiency to produce formic acid from the hydrogenation of CO2, without adding any additional base or promoter and was effectively recycled 4 times after separating by simple filtration without compromising the formic acid yield. Hydrotalcite supported copper-based catalyst (Cu-HT) was synthesized through the coprecipitation method and used as a heterogeneous catalyst for the hydrogenation of CO2. The precise copper metal content determined by ICP in Cu-HT is 0.00944 mmol. The catalyst afforded maximum TOF, 124 h-1 under the employed reaction conditions: 100 mg catalyst, 60 °C, 60 bar total pressure of CO2/H2 (1:1, p/p) with 60 mL of mixed methanol:water (5:1, v/v) solvent. Cu-HT catalyst was synthesised and thoroughly characterized by FT-IR, PXRD, SEM, TEM, XPS and BET surface area. The first-order kinetic dependence with respect to the catalyst amount, partial pressures of CO2, and of H2 was observed and a plausible reaction mechanism is suggested. Background: CO2 hydrogenation to energy-rich products over heterogeneous metal catalysts has gained much attention due to their commercial applications. Specifically, the first-row transition metal catalysts are very rarely reported and discussed for the production of formic acid from the hydrogenation of CO2. Objective: he aim is to investigate the heterogeneous catalyst systems, using solid soft base hydrotalcite supported Cu metal-based catalyst for effective and selective hydrogenation of CO2 to formic acid. Methods: The Cu –HT catalyst was synthesized and characterized by FT-IR, PXRD, SEM, TEM, XPS and BET surface area in which the precise copper content was 0.00944 mmol. The Cu-HT catalysed hydrogenation of CO2 was carried out in the autoclave. Results: The Cu-HT catalyst afforded maximum TOF of 124 h-1 under the employed reaction conditions: 100 mg catalyst, 60 °C, 60 bar total pressure of CO2/H2 (1:1, p/p) with 60 mL of mixed methanol: water (5:1, v/v) solvent, without adding any additional base or promoter and was recycled 4 times by simple filtration without compromising the formic acid yield. Formation of formic acid was observed to depend on the amount of the catalyst, partial pressures of CO2 and H2, total pressure, temperature and time. Conclusion: Cu-HT based heterogeneous catalyst was found to be efficient for selective hydrogenation of CO2 to formic acid and was effectively recycled four times after elegantly separating by simple filtration.

Multi-criteria decision framework for catalyst selection: Production of formic acid as a circular liquid organic hydrogen carrier in the hydrogen economy

Production of formic acid, which has been regarded as an important H2 carrier, from biomass can be a highly potential way to provide human societies with renewable energy source. To attain economically viable production of formic acid from biomass on an industrial scale, the system operation at low reaction temperature is crucially important. In this work, a low‐temperature hydrothermal conversion of carbohydrates such as monosaccharides and disaccharides into formic acid is reported. A good formic acid yield of 80–85% was obtained at a lower temperature of 423 K for only 15–20 min in the presence of NaOH without any other catalyst. The alkali was found to act as two roles in enhancing the production of formic acid. One was inhibition of the formic acid decomposition; another was favorable for the oxidation selectively at C‐1 for aldoses, which leads to the formation of formic acid via the rupture of the C1–C2 bond. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3657–3663, 2016

Hydrogen is deemed as a crucial component in the transition to a carbon-free energy system, and researchers are actively working to realize the hydrogen economy. While hydrogen derived from renewable energy sources is a promising means of providing clean energy to households and industries, its practical usage is currently hindered by difficulties in transportation and storage. Due to the extreme operating conditions required for liquefying hydrogen, various hydrogen carriers are being considered, which can be transported and stored at mild operating conditions and provide hydrogen at the site of usage. Among various candidates, green hydrogen carriers obtained via carbon dioxide utilization have been proposed as an economically and environmentally feasible option.Herein, the potential of using methanol and formic acid as green hydrogen carriers are evaluated regarding various production and dehydrogenation pathways, within a hydrogen distribution system including the recycle of carbon dioxide. Recent progress in carbon dioxide utilization processes, especially conversion of carbon dioxide captured in amine solutions, have demonstrated promising results for methanol and formic acid production. This study analyzes seven scenarios that consider carbon dioxide utilization-based thermocatalytic and electrochemical methanol and formic acid production, as well as different dehydrogenation pathways, and compares them to the scenario of delivering liquefied hydrogen. The scenarios are thoroughly analyzed via techno-economic analysis and life cycle assessment methods. The results of the study indicate that methanol-based options are economically viable, reducing the cost up to 43% compared to liquefied hydrogen delivery. As for formic acid, only the electrochemical production method is profitable, retaining 10% less cost compared to liquefied hydrogen delivery. In terms of environmental impact, all of the scenarios show higher global warming impact values than liquefied hydrogen distribution. However, results show that in an optimistic case where wind electricity is widely used, electrochemical formic acid production is competitive with liquefied hydrogen distribution, retaining 39% less global warming impact values. This is because high conversion can be achieved at mild operating conditions for the production and dehydrogenation reactions of formic acid, reducing the input of utilities other than electricity. This study suggests that while methanol can be a short-term solution for hydrogen distribution, electrochemical formic acid production may be a viable long-term option.

Exploring the continuous cleavage-oxidation mechanism of the catalytic oxidation of cellulose to formic acid: A combined experimental and theoretical study

Sustainable production of formic acid from biomass and carbon dioxide

Formic acid is a familiar product in hydrothermal oxidation of carbohydrates and is an important organic compound. In this study, the production of formic acid from the hydrothermal oxidation of glucose with and without the addition of alkali was investigated with temperature varying from 250 to 300°C, reaction time varying from 30 s to 240 s, and oxygen supply varying from 60 % to 140 %. Results showed that the highest yield of formic acid was only about 24 % in hydrothermal oxidation of glucose without the addition of alkali. It is very interest that the oxidation of glucose with the addition of alkali showed a high selective and effective for the production of formic acid. An excellent formic acid yield of about 74 % was achieved, which occurred at 250°C for 60 s with 120 % oxygen supply and the KOH concentration of 1.25 M.

Sustainable and selective formic acid production from photoelectrochemical methanol reforming at near-neutral pH using nanoporous nickel-iron oxyhydroxide-borate as the electrocatalyst

To meet the ever-increasing energy demand, the development of effective, renewable, and environmentally friendly sources of alternative energy is imperative. Hydrogen (H2) is a renewable, clean energy carrier, which exhibits a threefold energy density compared to gasoline; H2 is considered one of the most promising alternative energy carriers for enabling a secure, clean energy future. However, the realization of a hydrogen economy is restricted by several unresolved issues. Particularly, one of the most difficult challenges is the development of a safe, efficient hydrogen storage and delivery system. To this end, hydrogen storage techniques based on liquid-phase chemical hydrogen storage materials have become an attractive choice. Formic acid (FA) with a high volumetric capacity of 53 g H2/L demonstrates promise as a safe, convenient liquid hydrogen carrier. However, generating H2 from FA in a controlled manner at ambient temperature is still challenging, which primarily depends on the catalyst used. Hence, for practical purposes, it is imperative to develop high-performance heterogeneous catalysts for the dehydrogenation of FA. Ultrasmall metal NPs with a high surface-to-volume ratio and "clean" surface, and hence a high density of active sites exposed to reactants, are of significance for heterogeneous catalysis. However, the size of these "clean" ultrasmall metal NPs inevitably increase, and these particles undergo aggregation during synthesis and catalysis because of their high surface energy. The immobilization of metal NPs into appropriate support materials affords considerable advantages for catalytic applications, which not only offers spatial confinement to control the nucleation and growth of particles, but also prevents them from aggregation; hence, catalytic performance is significantly enhanced. In addition, the functionalization of the support with electron-rich groups is beneficial to the formation of intermediates for FA dehydrogenation, which in turn promotes the catalytic performance. In this Account, studies of hydrogen generation from FA using heterogeneous catalysts were reviewed, mainly focusing on the results reported by our group. By varying support materials (metal-organic frameworks, silica, graphene, and porous carbons) and synthetic strategies, a wide range of highly active metal NP catalysts for efficient H2 generation from FA under mild conditions were developed. In addition, the design and synthetic strategies were described, by which the size and composition of the NPs, as well as the well-defined NPs-support interactions, can be controlled for the enhancement of catalytic performance for the FA dehydrogenation. Furthermore, the performance of the prepared catalysts for the effective release of H2 from FA for the purpose of liquid-phase chemical hydrogen storage was discussed. Finally, the challenges, expected improvements, and future opportunities in this research area were summarized.

Power management and system optimization for high efficiency self-powered electrolytic hydrogen and formic acid production

This review explores the recent advancements in the application of boron nitride (BN) as a support material for metallic nanoparticles, highlighting its potential in fostering sustainable chemical reactions when employed as a heterogeneous catalyst. Two key processes, both critical to hydrogen storage and transport, are examined in detail. First, the reversible synthesis and decomposition of ammonia using BN-supported metallic catalysts has emerged as a promising technology. This approach facilitates the preparation of Ru nanoparticles with precisely structured surface atomic ensembles, such as B5 sites, which are critical for maximizing catalytic efficiency. Second, the review emphasizes the role of BN-supported catalysts in the production of formic acid (FA), a process intrinsically linked to the reuse of carbon dioxide. In this context, hydrogen and carbon dioxide-potentially sourced from atmospheric capture-serve as reactants. BN's high CO2 adsorption capacity makes it an ideal support material for such applications. Moreover, FA can serve as a source of hydrogen through decomposition or as a precursor to alternative chemicals like carbon monoxide (CO) via dehydration, further underscoring its versatility in sustainable catalysis.

One-pot selective production of levulinic acid and formic acid from spent coffee grounds in a catalyst-free biphasic system

The goal of this project was to develop and test a novel electro-catalytic method for the production of high-value formic acid from coal-derived CO₂ as a strategy to offset the cost of CO₂ capture. Formic acid is currently produced from the conversion of higher-order carbon products such as methane and/or methanol. This electro-catalytic CO₂ reduction process utilizes a highly selective catalyst in a flow-through reactor design to maximize the formic acid production rate. The specific objectives of this proposed study were to; 1) produce and screen highly selective engineered CO₂ reducing catalysts capable of exclusively producing formic acid; 2) immobilize the catalyst within a flow process to continually produce formic acid and increase catalyst lifetime; and 3) assess the stability of the electrocatalyst during long-term operation. The project involved the development and testing of an engineered catalyst to selectively reduce CO₂ directly and exclusively to formic acid. After the best-performing catalyst was selected, it was immobilized and tested inside a flow-through reactor at UK CAER using realistic conditions expected from CO₂ produced during coal combustion and separated by a CO₂ capture plant.