Reaction Equilibrium Research Articles

Thermodynamic Analysis of Ammonia Synthesis

The paper researches the effect of temperature on ammonia synthesis. The ammonia synthesis reaction is exothermic with a negative entropy change. ∆G < 0 condition is fulfilled at lower temperatures up to 464K (Le Chatelierov principle). It is a constant equilibrium of the ammonia synthesis reaction at lower temperatures, which means that the NH3(g) synthesis reaction is shifted in the direction of NH3(g) formation (higher production of ammonia). The downside of lowering the temperature is that more ammonia is obtained, but the reaction rate slows down. Above 464K, the free enthalpy of the NH3(g) synthesis reaction is greater than zero, so the reaction enters thermodynamically unfavorable conditions. By increasing the reaction temperature, the ammonia yield NH3(g) decreases in the equilibrium mixture. At 400K, it is 0.5127kmol/kmol (51.27%) and at 700K, the synthesis process NH3(g) is practically complete.

Effect of pH on the extraction and stability of anthocyanins from jaboticaba berries

Anthocyanins are water-soluble plant pigments whose stability is strongly influenced by pH. The effects of pH on the extraction of anthocyanins from jaboticaba berries were investigated using an ultrasound-assisted method. A strong acidic condition (pH 1.5) was found to produce a higher yield and monomeric anthocyanin content, particularly at longer ultrasonication time (30 min). The small pH increment of 0.3 over 2 weeks following a zero-order kinetic model. The monomeric anthocyanins increased more rapidly in refrigerated samples, with a kinetic constant of 0.017 mg/g per day, following a first-order kinetic model. Anthocyanins underwent a two-step mechanism in which colour intensity was reduced significantly in the first week, followed by lightness reduction in the second week. The decline of browning index suggested enzymatic reactions contributed to colour darkening. Negative activation energy reflected the complexity of biochemical reactions, possibly involving a balance of reversible and irreversible processes where the reaction equilibrium was influenced by temperature.

Synergetic enzymatic reactive crystallization of cefaclor catalyzed by PGA

In the context of the severe global carbon emission crisis, green and sustainable enzymatic reactions are garnering widespread attention in the industry. However, these processes still face numerous challenges, such as limitations imposed by reaction equilibrium, product decomposition, and inhibition. Product removal via crystallization has the potential to address these issues. More importantly, crystal product properties can be directly manipulated during enzymatic reactive crystallization (ERC), such as polymorphic purity, size, and morphology in a single batch. In the synthesis of cefaclor catalyzed by penicillin G acylase (PGA), primary and secondary hydrolysis greatly limited the efficiency of the reaction. Thus, ERC was performed to combine the advantages of green enzymatic reactions and controllable direct crystallization. Initially, a supersaturated solution of the substrate was established, and cefaclor crystals were seeded to the enzymatic reaction system at a proper time. Subsequently, operating parameters were adjusted to facilitate selective crystallization of cefaclor. It is noteworthy that both immobilized and free enzymes were examined in our research. Ultimately, cefaclor crystals with purity exceeding 99% were obtained directly. The yield of cefaclor reached as high as 88%. It is believed that this method held significant promise for the green and efficient production of high-purity cefaclor and demonstrated considerable potential for application in more similar pharmaceutical scenarios.

A Rootless Duckweed-Inspired Flexible Artificial Leaf from Plasmonic Photocatalysts.

The naturally existing leaves are ubiquitous two-dimensional flexible solar-to-chemical conversion systems that can run continuously in a sustainable manner. However, the current artificial photocatalytic systems are unable to achieve this due to the grand challenge in integrating existing photocatalysts in a flexible layout with high conversion efficiency and the ability to function independently. Here, we report on a rootless duckweed-inspired artificial leaf based on a lightweight, flexible, Janus plasmonic nanosheet-integrated sponge. The Janus plasmonic catalytically active nanosheet was made from self-assembled gold nanocube nanoassemblies grown on the porous sponges, which were further coated with an ultrathin palladium layer on one side via a ligand symmetry-breaking method. This sponge-based photocatalytic system is lightweight yet able to float on a water surface and conducts the gas-liquid reaction without auxiliary pumping and mixing devices. In a model reaction of 4-nitrophenol reduction, this floating leaf could achieve 2.5-fold and 65-fold higher efficiency than the corresponding dispersion and precipitation systems, respectively. The film theory is used to explain the sponge-based lightweight solar-to-chemical conversion system in a detailed kinetic and thermodynamic analysis, including the reaction rate constant, activation energy, enthalpy, entropy, Gibbs energy, and equilibrium constant.

Efficient sulfur accumulation in biological desulfurisation and denitrification induced by microbial and chemical interactions

ABSTRACT Efficient accumulation of sulfur from simultaneous desulfurisation denitrification process can achieve high economic and environmental benefits. This work aims to study the effect of product accumulation on elemental sulfur production and understand its potential mechanism. The addition of the intermediate product thiosulfate and the final product sulfate during the reaction led to an increase in the production of biological elemental sulfur ( S bio 0 ). The effect is mainly reflected in the efficient accumulation effect of S bio 0 at high sulfide loads. When the sulfide feed water load was 300 mg/L, the S bio 0 production reached 65.94 mg/L in 24 h with the addition of 30 mg/L thiosulfate and 20 mg/L sulfate, which was 3.11 times higher than that of the control group. The addition of sulfate increased the content of aromatic protein I and aromatic protein II, and accelerated the propagation of Thiobacillus denitrificans, whose viable bacterial amount was 1.12–2.98 times higher than that of the control group. On the one hand, low-dose sulfate induced Thiobacillus denitrificans to participate in the sulfur-producing reaction ( S 2 − → S bio 0 ) more quickly by accelerating the propagation of the strains in the pre-reaction stage. On the other hand, the addition of sulfate shifted the overall reaction equilibrium to the left and inhibited the formation of thiosulfate, thus accelerating the accumulation of S bio 0 in the whole reaction stage. This study would provide guidance for artificially promoting efficient sulfur accumulation in desulfurisation denitrification treatments.

Assessing the effect of deep eutectic solvents on α-chymotrypsin thermal stability and activity.

Optimizing the liquid reaction phase holds significant potential for enhancing the efficiency of biocatalytic pro- cesses since it determines reaction equilibrium and kinetics. This study investigates the influence of the addition of deep eutectic solvents on the stability and activity of α-chymotrypsin, a proteolytic enzyme with industrial rele- vance. Deep eutectic solvents, composed of choline chloride or betaine mixed with glycerol or sorbitol, were added in the reaction phase at various concentrations. Experimental techniques, including kinetic and fluorometry, were employed to assess the α-chymotrypsin activity, thermal stability, and unfolding reversibility. Atomistic molecular dynamics simulations were also conducted to assess the interactions and provide molecular-level insights between α-chymotrypsin and the solvent. The results showed that among all studied mixtures, adding choline chloride + sorbitol improved thermal stability up to 18 °C and reaction kinetic efficiency up to two-fold upon adding choline chloride + glycerol. Notably, the choline chloride + sorbitol system exhibited the most substantial stabilization effect, attributed to the surface preferential accumulation of sorbitol, as corroborated by the computational anal- yses. This work highlights the potential of tailoring liquid reaction phase of α-chymotrypsin catalyzed reaction using neoteric solventsto enhance α-chymotrypsin performance and stability in industrial applications.

Simulation of lithium hydroxide decomposition using deep potential molecular dynamics.

Chemical reactions and vapor-liquid equilibria for molten lithium hydroxide (LiOH) were studied using molecular dynamics simulations and a deep potential (DP) model. The neural network for the model was trained on quantum density functional theory data for a range of conditions. The DP model allows simulations over timescales of hundreds of ns, which provide equilibrium compositions for the systems of interest. Single-phase NPT simulations of the liquid show the decomposition of LiOH into lithium oxide (Li2O) and dissolved water (H2O). These DP results were validated by direct abinitio molecular dynamics simulations that confirmed the accuracy of the model with respect to reaction kinetics and equilibrium properties of the melt. The reactive vapor-liquid behavior of this system was subsequently studied using direct coexistence interfacial DP simulations. Partial pressures of H2O in the vapor are found to be in close agreement with available experimental measurements. By fitting temperature-dependent expressions for the reaction equilibrium and Henry's law constants, the equilibrium composition for any given initial composition and temperature can be quantitatively modeled. For high initial concentrations of Li2O or H2O, mixtures of LiOH + Li2O/H2O are found to undergo phase separation. The present study illustrates how DP-based molecular dynamics simulations can be used for quantitative modeling of multiphase reactive behavior with the accuracy of the underlying abinitio quantum chemical methods.

Reaction Thermodynamic and Kinetics for Esterification of 1-Methoxy-2-Propanol and Acetic Acid over Ion-Exchange Resin.

The esterification of 1-methoxy-2-propanol (PM) and acetic acid (AA) is an important reaction for the production of 1-methoxy-2-propyl acetate (PMA). Herein, we used the macroporous ion-exchange resin Amberlyst-35 as a catalyst to explore the effects of reaction conditions on the reaction rate and equilibrium yield of PMA. Under the optimized conditions of a reaction temperature of 353 K, using the initial reactant PM/AA with a molar ratio of 1:3, and a catalyst loading of 10 wt%, the PMA equilibrium yield reached 78%, which is the highest equilibrium yield so far. The reaction equilibrium constants and activity coefficients were estimated to obtain reaction thermodynamic properties, indicating the exothermicity of the reaction. Furthermore, pseudo-homogeneous (PH), Eley-Rideal (ER), and Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models were fitted based on experimental reaction kinetic data. The results demonstrate that the LHHW model is the most consistent with experimental data, indicating a surface reaction-controlled process and exhibiting an apparent activation energy of 62.0 ± 0.2 kJ/mol. This work represents a valuable example of calculating reaction thermodynamics and kinetics, which are particularly essential for promising industrial reactor designs.

Application of Sortase-Mediated Ligation for the Synthesis of Block Copolymers and Protein-Polymer Conjugates.

Sortase-mediated ligation (SML) has become a powerful tool for site-specific protein modification. However, sortaseA (SrtA) suffers from low catalytic efficiency and mediates an equilibrium reaction. Therefore, ligations with large macromolecules may be challenging. Here, the synthesis of polymeric building blocks for sortase-mediated ligation constituting peptide-polymers with either the recognition sequence for sortaseA (LPX1TGX2) or its nucleophilic counterpart (Gx) is demonstrated. The peptide-polymers are synthesized by solid-phase peptide synthesis followed by photo-iniferter (PI) reversible addition-fragmentation chain-transfer (RAFT) polymerization of various monomers. The building blocks are subsequently utilized to investigate possibilities and limitations when using macromolecules in SML. In particular, diblock copolymers are obtained even when using the orthogonal building blocks in equimolar ratio by exploiting a technique to shift the reaction equilibrium. However, ligations of two polymers can not be achieved when the degree of polymerization exceeds 100. Subsequently, C-terminal protein-polymer conjugates are synthesized. Several polymers are utilized that can replace the omnipresent polyethylene glycol (PEG) in future therapeutics. The conjugation is exemplified with a nanobody that is known for efficient neutralization of SARS-CoV-2. The study demonstrates a universal approach to polymer-LPX1TGX2 and Gx-polymer building blocks and gives insight into their application in SML.

Highly efficient CO2 mineralization: Mechanisms and feasibility of utilizing electrolytic manganese residue as a feedstock and implementing ammonia recycling

Electrolytic manganese residue (EMR) and CO2 emissions from the electrolytic manganese metal (EMM) production process present significant challenges to achieving cleaner production within the industry. Given the high capacity for CO2 sequestration and the stability of the sequestered forms, CO2 mineralization methods utilizing minerals or industrial residues have garnered considerable research interest. The efficacy of such methods is fundamentally dependent on the properties of the materials employed. EMR, due to its calcium sulfate dihydrate (CaSO4·2H2O) content, possesses an intrinsic potential for CO2 solidification. In this study, we propose a novel method for CO2 mineralization utilizing EMR, coupled with NH3·H2O recycling. Experimental results indicated that under conditions of a reaction temperature of 55 °C and a pH of approximately 8, each ton of EMR can sequester 0.16 t of CO2, with equilibrium achieved within 10 min. The mineralization mechanism was elucidated using SEM, TG curves, and XRD analyses, which revealed that Ca2+ ions are initially leached from CaSO4·2H2O in the EMR, subsequently precipitating with CO32− ions to form CaCO3. This CaCO3 layer effectively covers the surface of CaSO4·2H2O, inhibiting further Ca2+ release and stabilizing the reaction equilibrium. Furthermore, the ammonia in the solution is regenerated into NH3·H2O, facilitating its reuse and preventing secondary pollution. The utilization of EMR for CO2 mineralization not only mitigates carbon emissions in the EMM production process but also promotes environmentally sustainable practices in the industry. This study highlights a promising pathway towards achieving carbon neutrality and cleaner production in electrolytic manganese production.

Deciphering Stereoselectivity in Hurd-Claisen Rearrangements: A Comprehensive Study of Electrostatic Interactions from Shubin's Energy Decomposition Analysis.

In this study, we explore the stereoselectivity of Hurd-Claisen Rearrangements, focusing on the influence of two electron-withdrawing groups and eight diverse substituents. Utilizing the Curtin-Hammett principle, we performed energy calculations for reactions, products, and transition states using the M062X/def2TZVPP compound model. Our analysis reveals that kinetic factors predominantly dictate the reaction equilibrium. A key aspect of our research is the application of Shubin's energy decomposition analysis to optimized transition states, highlighting the significant role of electrostatic interactions in determining stereoselectivity. We further dissected each transition state into four fragments: the electron-withdrawing groups ( , ), the Hurd group ( ), various substituents ( , , , , , , , ), and the central fragment. This fragmentation approach enabled an in-depth analysis of group dipole moments, providing insights into the electrostatic forces at play. Our findings shed light on the intricate mechanisms driving stereoselectivity in Hurd-Claisen Rearrangements and enhance the understanding of molecular interactions, offering valuable implications for organic synthesis.

Amine-modified SiO2 aerogel for efficient adsorption of low-pressure CO2: Response surface methodology optimization and adsorption mechanism

Amine-modified SiO2 aerogel (AMSA) has shown tremendous potential in CO2 capture due to its unique three-dimensional network structure and excellent stability. However, it still faces many challenges in the preparation optimization, adsorption enhancement at low CO2 partial pressure, and mechanism elucidation. Hence, in this paper, the response surface methodology is employed for the first time and the optimal preparation conditions for AMSA are determined. A regression model is successfully established to accurately predict the CO2 adsorption capacity of AMSA under different synthesis conditions (with a relative error of only 0.98 %). Additionally, the AMSA prepared at optimal conditions exhibits high CO2 adsorption capacity of 2.11 mmol/g and excellent stability (only decreased by 1.44 % after 8 cycles) at 10 % CO2 partial pressure, indicating enormous application potential. Notably, the CO2 adsorption mechanism by AMSA at different temperatures and partial pressures are revealed in detail through fitting with the Freundlich isotherm and the double-exponential model, as well as thermodynamic parameter calculations. Firstly, the CO2 adsorption behavior belongs to the multi-layer adsorption behavior with uneven energy of active sites. Secondly, the CO2 adsorption capacity and rate are jointly controlled by molecular motion and chemical reaction equilibrium, diffusion and chemical reaction steps, respectively. Finally, the adsorption process is exothermic and spontaneous, and the level of disorder decreases at the gas-solid interface. This study not only achieves efficient adsorption of low-pressure CO2, but also deepens the understanding of gas-solid interface adsorption mechanisms, providing scientific basis and technological support for the development of novel efficient AMSA adsorbent materials.

Prediction of Thermochemical Properties of Long-Chain Alkanes Using Linear Regression: Application to Hydroisomerization.

Linear regression (LR) is used to predict thermochemical properties of alkanes at temperatures (0-1000) K to study chemical reaction equilibria inside zeolites. The thermochemical properties of C1 until C10 isomers reported by Scott are used as training data sets in the LR model which is used to predict these properties for alkanes longer than C10 isomers. Second-order groups are used as independent variables which account for the interactions between the neighboring groups of atoms. This model accurately predicts Gibbs free energies, enthalpies, Gibbs free energies of formation, and enthalpies of formation for alkanes which exceeds the chemical accuracy of 1 kcal/mol and outperforms the group contribution methods developed by Benson et al., Joback and Reid, and Constantinou and Gani. Predictions from our model are used to compute the reaction equilibrium distribution of hydroisomerization of C10 and C14 isomers in MTW-type zeolite. Calculation of reaction equilibrium distribution inside zeolites also requires Henry coefficients of the isomers which can be computed using classical force field-based molecular simulations using the RASPA2 software for which we created an automated workflow. The reaction equilibrium distribution for C10 isomers obtained using the LR model and the training data set for this model are in very good agreement. The tools developed in this study will enable the computational study of hydroisomerization of long-chain alkanes (>C10).

Experimental Device for the “Green” Synthesis of Unbranched Aliphatic Esters C4–C8 Using an Audio Frequency Electric Field

One of the most important reactions in organic synthesis is esterification, and the compounds generated using this process are esters with a wide range of applications in various industries. Numerous approaches have been employed to enhance the ester yield and reaction rate and establish equilibrium in esterification reactions. This study uses a non-catalytic thermal esterification method to obtain unbranched aliphatic esters C4–C8. The effect of an audio frequency electric field instead of a catalyst on the esterification reaction between acetic acid and linear C4–C8 aliphatic alcohols was studied. The main goal of this study was to design and implement a lab-scale device for the synthesis of aliphatic esters in an environmentally sustainable manner using only specific raw materials and an audio frequency electric field at 3 and 6 kHz at 20 °C and 50 °C. A mechanism for the esterification reaction using an audio frequency electric field is also suggested. The proposed experimental device is designed to produce esters in a green and cost-effective manner and could be used on a large scale in the food, cosmetics, and pharmaceutical industries.

Biochar-Sulfate Reducing Bacteria synergy: A green approach for antimony removal and recovery from high-concentrated waters

Environments with elevated antimony (Sb) levels often result from industrial and mining activities, causing harm to ecosystems due to the inherent toxicity. Traditional treatments aim to eliminate or decrease Sb toxicity, yet they often result in the generation of secondary pollution. This study explores a novel approach for enhancing biological sulfate-reduction by biochar addition to cope with high Sb concentrations. Moreover, this research postulates sulfate-reduction bioprocess as a feasible alternative to obtain valuable antimony sulfide. The findings indicate that sulfate reduction effectively removes antimony, particularly at high concentrations, using a non-specialized inoculum. Biochar plays a pivotal role in enhancing sulfate-reduction rates, reducing lag-phase periods, and enriching the microorganisms responsible for sulfate reduction.Interestingly, lower concentrations of Sb(III) (5–40 mg/L) and Sb(V) (5–100 mg/L) exhibited a lower removal percentage compared to higher concentrations of Sb(III) (80–500 mg/L) and Sb(V) (200–1000 mg/L). This phenomenon was attributed to the excess sulfide hindering the equilibrium of the first-order reaction at lower concentrations, while at higher concentrations, the reaction proceeded more rapidly. A combination of biochemical and physicochemical reactions facilitated the removal of >95 % Sb(III) and >97 % Sb(V) using biochar.Furthermore, various taxa displayed a significant logarithmic rate of change in their abundance, influenced by the application of biochar or the introduction of distinct antimony species. The biogenic sulfide generated through the sulfate reduction process reacted with the Sb species, resulting in the precipitation of stibnite (Sb2S3), Na3SbS3, and Na3SbS4. These precipitates are considered crucial precursors in electronic applications.In conclusion, this study constitutes a pioneering exploration of elevated antimony (Sb) concentrations under sulfate-reducing conditions, significantly contributing to an advancement of knowledge in the application of biological processes.

Biosynthetic fuels: A marriage of renewable resources and chemical thermodynamics

Terpenes represent a highly diverse group of natural products with wide applications. Terpenoid structures can be derived from different renewable sources and utilized as fuels. Application as fuels requires hydrogenation of the double bonds in the respective molecules to ensure clean combustion. This hydrogenation can be performed either directly with elemental hydrogen or indirectly via transfer hydrogenation with a Liquid Organic Hydrogen Carrier. In this study, the thermochemical fundamentals of these reaction has been evaluated. For this task, for a first time a combination of experimental thermochemistry and quantum-chemical molecular modelling has been applied. The results show the hydrogenation of the respective structures is thermodynamically highly favourable. Correspondingly, dehydrogenation would be comparatively unfavorable. Yet, for a fuel no dehydrogenation is required. As an alternative to conventional hydrogenation, transfer hydrogenation, which is often subject to partial conversions due to limitations by the reaction equilibrium, can be realized with a high degree of conversion. While the entropy of reaction for hydrogen transfer from cyclohexyl-structures to terpene structures is close to zero, the enthalpy of reaction is highly negative. This leads to a Gibbs energy of reaction which is clearly negative and ensures a large thermodynamic driving force for the reaction. As a consequence, downstream processing, which is usually very demanding for transfer hydrogenations, is comparatively easy. These finding underline the great potential of these bio-derived substances for conversion into sustainable fuels.

Modeling & experimental studies on enhancement of H2S conversion using catalytic membrane reactor for hydrogen production

Abstract Acidic gases such as H2S and CO2 are generated in the refineries during coal gasification. These pollutant gases need to be treated before releasing to the atmosphere. Conventionally, H2S gas is treated by Claus process in which H2S is converted to elemental S and H2O, in presence of O2 at ∼1,200 K. In the present energy scenarios, hydrogen has got importance as a source of clean fuel for industrial application. The H2S generated in the refineries can be a potential precursor of hydrogen. If this hydrogen can be obtained by thermal decomposition of H2S, that can increase the overall economic value of the H2S containing streams and the produced hydrogen can be used for hydrocracking and hydro-treating in refineries, as well as to synthesize value-added products for chemical industries. However, H2S thermal decomposition is an endothermic and equilibrium limited reaction (equilibrium conversion is only ∼15 % at 1,000 K), requiring a very high temperature (∼1,500 K) to achieve even a conversion of greater than 40 %. Packed Bed Catalytic Membrane Reactor (PBCMR) for thermal decomposition of H2S can be a potential technology augmentation and process intensification to increase this equilibrium conversion. In this work, modeling and experimental studies of H2S thermal decomposition using in-house designed & developed PBCMR have been carried out. The modeling studies were validated with experimental data. Clay-alumina ceramic tubular membrane (L: 250 mm; OD: 12 mm; thickness: 2 mm) was fabricated using extrusion process having an average membrane pore size of ∼1 μm and with a porosity of ∼20 %. Pt (2 %) coated alumina extrudes were used as catalyst to accelerate the reaction kinetics. Experimental studies showed that H2S to hydrogen conversion of ∼90 % is achieved using PBCMR at ∼1,523 K, compared to only ∼40 % conversion in a conventional packed bed tubular reactor (without membrane). Modelling studies were carried out to study the influence of operating parameters such as, reactor wall temperature, feed temperature, pressure and feed velocity. Studies showed that reactor wall temperature is having the most dominant effect on H2S conversion, which is confirmed by experimental findings. The studies offer useful insights into the application of PBCMR technology for management of waste gas stream containing H2S and recovery of hydrogen.

Identification of efficient amine transaminase and applicability in dual transaminases cascade for synthesis of L-phosphinothricin

L-phosphinothricin (L-PPT) is the most popular broad-spectrum and highly effective herbicide. Transaminases (TAs) play a pivotal role in asymmetric synthesis of L-PPT, yet encounter the challenge of unfavorable reaction equilibrium. In this study, the novel dual transaminases cascade system (DTCS) was introduced to facilitate the synthesis of L-PPT. The specific amine transaminase BdATA, originating from Bradyrhizobium diazoefficiens ZJY088, was screened and identified. It exhibited remarkable activity, good stability, and required only 2.5 equivalents of isopropylamine to transform pyruvate effectively. By coupling BdATA with previously reported SeTA to construct the DTCS for pyruvate removal in situ, the L-PPT yield escalated from 37.37 % to 85.35 %. Three advantages of the DTCS were presented: the removal of pyruvate alleviated by-product inhibition, the use of isopropylamine reduced reliance on excess L-alanine, and no demand for expensive cofactors like NAD(P)H. It demonstrated an innovative idea for addressing the challenges associated with transaminase-mediated synthesis of L-PPT.

Continuous production of pure formic acid solution from CO2 hydrogenation at room temperature via amine-functionalized PdMn nano-alloy

CO2 hydrogenation into formic acid is of great significance to mitigate CO2 emission. However, conventional routes typically require the addition of unrecyclable bases to shift the reaction equilibrium by the formation of formate, which leads to complex subsequent separation and difficulty in continuous production of pure formic acid solution. Here we report a secondary amine-modified PdMn nanocatalyst for the continuous production of pure formic acid solution in fixed-bed reactors via CO2 hydrogenation. By optimizing fine structure of PdMn nano-alloy, the optimal TOF of up to 26.5 h−1 is obtained under mild reaction conditions (25 ℃, 3.0 MPa). This is one of the highest levels reported for a heterogeneous catalyst without alkali additives under similar conditions. The characterization shows that the two-component alloying effect of PdMn and the synergistic effect between PdMn NPs and secondary amine group (NH) are the key to obtaining superior reactivity. These findings in this work may pave an avenue for conversion of CO2 in a more environmentally friendly way.

The Impact of Metal Centers in the M-MOF-74 Series on Formic Acid Production.

The confinement effect of porous materials on the thermodynamical equilibrium of the CO2 hydrogenation reaction presents a cost-effective alternative to transition metal catalysts. In metal-organic frameworks, the type of metal center has a greater impact on the enhancement of formic acid production than the scale of confinement resulting from the pore size. The M-MOF-74 series enables a comprehensive study of how different metal centers affect HCOOH production, minimizing the effect of pore size. In this work, molecular simulations were used to analyze the adsorption of HCOOH and the CO2 hydrogenation reaction in M-MOF-74, where M = Ni, Cu, Co, Fe, Mn, Zn. We combine classical simulations and density functional theory calculations to gain insights into the mechanisms that govern the low coverage adsorption of HCOOH in the surrounding of the metal centers of M-MOF-74. The impact of metal centers on the HCOOH yield was assessed by Monte Carlo simulations in the grand-canonical ensemble, using gas-phase compositions of CO2, H2, and HCOOH at chemical equilibrium at 298.15-800 K, 1-60 bar. The performance of M-MOF-74 in HCOOH production follows the same order as the uptake and the heat of HCOOH adsorption: Ni > Co > Fe > Mn > Zn > Cu. Ni-MOF-74 increases the mole fraction of HCOOH by ca. 105 times compared to the gas phase at 298.15 K, 60 bar. Ni-MOF-74 has the potential to be more economically attractive for CO2 conversion than transition metal catalysts, achieving HCOOH production at concentrations comparable to the highest formate levels reported for transition metal catalysts and offering a more valuable molecular form of the product.