Reaction Enthalpy Research Articles

Chemical Potential Analysis as an Alternative to the van't Hoff Method: Hypothetical Limits of Solar Thermochemical Hydrogen.

The van't Hoff method is a standard approach for determining reaction enthalpies and entropies, e.g., in the thermochemical reduction of oxides, which is an important process for solar thermochemical fuels and numerous other applications. However, by analyzing the oxygen partial pressure pO2, e.g., as measured by thermogravimetric analysis (TGA), this method convolutes the properties of the probe gas with the solid-state properties of the examined oxides, which define their suitability for specific applications. The "chemical potential method" is here proposed as an alternative. Using the oxygen chemical potential ΔμO instead of pO2 for the analysis, this method does not only decouple gas-phase and solid-state contributions but also affords a simple and transparent approach to extracting the temperature dependence of the reduction enthalpy and entropy, which carries important information about the defect mechanism. For demonstration of the approach, this work considers three model systems; (1) a generic oxide with noninteracting, charge-neutral oxygen vacancy defects, (2) Sr0.86Ce0.14MnO3(1-δ) alloys with interacting vacancies, and (3) a model for charged vacancy formation in CeO2, which reproduces the extensive experimental TGA data available in the literature. The reduction behavior of these model systems obtained from the chemical potential method is correlated with simulated results for the thermochemical water splitting cycle, highlighting the exceptional behavior of CeO2, which originates from defect ionization. The theoretical performance limits for solar thermochemical hydrogen within the charged defect mechanism are assessed by considering hypothetical materials described by a variation of the CeO2 model parameters within a plausible range.

Implementing the Blowers–Masel Approximation to Scale Activation Energy Based on Reaction Enthalpy in Mean-Field Microkinetic Modeling for Catalytic Methane Partial Oxidation

Implementing the Blowers–Masel Approximation to Scale Activation Energy Based on Reaction Enthalpy in Mean-Field Microkinetic Modeling for Catalytic Methane Partial Oxidation

Active Thermochemical Barrier Coatings Using Metal Oxides: First Experimental Results.

A new concept of active thermal coating based on the use of reversible thermochemical reactions is presented in this paper. The new active thermal barrier coating uses redox reactions to buffer the temperature changes that a metallic component may suffer at high temperatures. The heat is stored when the temperature is equal/above the reduction temperature of the active coating (endothermic reaction) and the heat is released when the temperature is equal/below the oxidation temperature (exothermic reaction). The paper describes the development and testing of a reactive thermal barrier coating based on the redox reaction of Co3O4 and its cyclability. Co3O4 was chosen as a reference material due to the high enthalpy of reaction (844 kJ/kg) and redox reversibility. The activity of coatings with 1, 2, and 3 Co3O4 layers was demonstrated by simultaneous thermal analysis, showing good stability for 5 five cycles.

Measurement of the reaction enthalpy of CO2 in aqueous solutions with thermographic and gravimetric methods

In this work, a new concept for the approximate determination of the reaction enthalpy of the reaction between CO2 and monoethanolamine (MEA) in aqueous solution was developed. For this purpose, a CO2 gas stream was flowed into aqueous MEA solutions with different concentrations of 1 wt%, 2.5 wt% and 7.5 wt%. The weight difference ∆T, which is based on the increase in CO2 bound by the MEA over time, was documented using a thermographic camera. The mass difference ∆m, which is also based on the increase in CO2 bound by the MEA over time, was determined using a balance. By determining ∆T and ∆m, an approximate calculation of the reaction enthalpy is possible. The deviation from the values from the data known from the literature was less than 5% in all experiments.

Ionic Pairs-Engineered Fluorinated Covalent Organic Frameworks Toward Direct Air Capture of CO2.

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO2 (400ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400ppm) CO2 from gas mixtures via O─C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13C-labeled CO2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40kJmol-1 between CO2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO2 insertion. The as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO2 in crystalline scaffolds.

Specific features of enzymatic hydrolysis of cellulose

In this article, the features of enzymatic hydrolysis of cellulose samples with different structural characteristics were studied. It was discovered that outer paracrystalline layers of crystallites are accessible and susceptible to hydrolysis along with the poorly ordered amorphous domains of cellulose. The thermodynamic analysis showed that the hydrolysis process of cellulose samples at 298 K is exothermic. Since reaction enthalpy is negative and the temperature-entropy factor is positive, the Gibbs potential of this process becomes negative, which contributes to the implementation of enzymatic hydrolysis of cellulose. Moderate enhancement in temperature to optimal value, 323 K, increases the negative value of Gibbs potential and thereby promotes the hydrolysis of cellulose substrates. The most negative Gibbs potential was observed for the hydrolysis of the most accessible amorphous cellulose. Thus, amorphization of cellulose substrates facilitates enzymatic hydrolysis. On the other hand, the enzymatic hydrolysis of high-ordered crystalline domains of cellulose cannot be performed even at optimal temperature since the Gibbs potential of this process is close to zero.

Theoretical investigation of hydrogen-rich fuel production through ammonia decomposition

Abstract Considering the challenges related to hydrogen storage and transportation which hinder its widespread adoption, ammonia has emerged as a carbon-free carrier for hydrogen due to several advantages such as simple inexpensive storage. But, due to some limitations related to net ammonia combustion, the suggestion is to store hydrogen in the form of ammonia and convert it into hydrogen-rich fuel before utilization in different applications like engines and turbines. Therefore, in this article, a comprehensive thermodynamic analysis of hydrogen-rich fuel production via ammonia decomposition is conducted utilizing Aspen Plus V.12, to assess the impact of operating parameters on key criteria such as conversion rate (CR) and enthalpy of reaction, to establish the maximum level of efficiency of the process. The results show that at a specific temperature, the CR of ammonia decreases as the pressure rises so that the CR of more than 50% occurred at temperatures of 427 and 513 K for pressures of 1 and 10 bar, respectively. Moreover, the adiabatic flame temperature of hydrogen-rich fuel is investigated so that increasing the molar percentage of hydrogen from 0 to 50 leads to an increase in the maximum adiabatic flame temperature from 2,079 to 2,216 K.

Enhancing the catalytic activity of Pd nanoparticles in the hydrolysis of ethylenediamine-bisborane through sulfonation of graphene oxide as a solid support

Ethylenediamine-bisborane (EDB), with its high hydrogen storage capacity, has been in the limelight among researchers. In this study, a new catalytic hybrid material (Pd@rGO-SO3H), comprising sulfonated reduced graphene oxide (rGO-SO3H) and palladium (Pd), was developed. This material serves as a highly efficient and reusable catalyst in the hydrogen production from EDB hydrolysis. The synthesized EDB, rGO-SO3H, and Pd@rGO-SO3H were characterized using ICP-OES, PXRD, XPS, SEM, TEM, and TEM/EDX tools. The initial TOF value of the Pd@rGO-SO3H catalyst in hydrogen production from EDB hydrolysis was calculated as 136 min−1. This TOF value was found to be remarkably high compared to related studies in the literature. The reusability performance of Pd@rGO-SO3H was observed to be quite stable. Finally, activation parameters, such as activation energy (Ea), activation enthalpy (ΔH#), and activation entropy (ΔS#) for the hydrolysis reaction, were calculated by conducting catalytic reactions at different temperatures using relevant equations.

ZnSnO3 - SnO2 nanocomposite as a catalyst for efficient hydrogen production through sodium borohydride methanolysis

In this work, we describe a straightforward modified sol gel approach for producing zinc stannate-tin oxide (ZnSnO3-SnO2) nanocomposite particles by combining tin chloride and zinc acetate using EDTA ammonium salt as an electrosteric inhibition agent. The acquired samples were characterized using simultaneous thermal gravimetric and differential scanning calorimetry (TGA/DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and scanning electron microscopy (SEM). The catalyst activity of ZnSnO3-SnO2 particles in hydrogen production was determined by the methanolysis reaction from NaBH4. The hydrogen generation rate TOF (Turnover Frequency) The hydrogen generation rate, activation energy (Ea), enthalpy (ΔH) and entropy (ΔS) values of the hydrogen production reaction were calculated as 374.11 ml min−1.g−1 (832.38 h−1), 43.19 kJ mol−1, 40.65 kJ mol−1 and -178.96 J/mol.K, respectively. The prepared ZnSnO3-SnO2 composite can be recycled and used without obvious loss of activity; This makes the procedure economical and environmentally friendly.

Effect of ultrasound geometry on the production efficiency of damaged starch: Determining rheology parameters, and non-isothermal reaction kinetics

Present study investigates the effects of probe size geometry on thermodynamic kinetics, rheology, and microstructure of wheat and tapioca starch. Ultrasound treatment using different probe diameters (20 mm and 100 mm) significantly influenced the gelatinization process. Results showed reduced enthalpy (ΔH) and Gibbs energy (ΔG), indicating enhanced gelatinization efficiency. According to the results, using a 20 mm and 100 mm probe leads to a reduction of 52.7 % and 68.6 % in reaction enthalpy for wheat starch compared to native starch, respectively. Microstructure analysis revealed structural changes, with ultrasound treatment leading to granular fractures and a sheet-like structure with air bubbles. The rheological behavior of the starches is found to exhibit shear thinning behavior, with the Casson model providing the best fit for the experimental data. Moreover, rheology modeling using Herschel-Bulkley and power law models showed increased viscosity and shear stress in larger probes. Numerical simulation data demonstrated that probe size influenced ultrasonic pressure, sound pressure level, and thermal power dissipation density, affecting fluid motion and velocity field components. Moreover, the maximum dissipated power decreases from 8.43 to 0.655 mW/m3 with an increase in probe diameter from 20 to 100 mm. The average yield shear stress values are calculated as 3.36 and 3.14 for wheat and tapioca starches, respectively. The larger probe diameter leads to greater entropy increases, with tapioca starch showing a 4.72 % increase and wheat starch a 4.97 % increase, compared to 2.56 % and 3.11 %, respectively, with the smaller probe. Additionally, the Keller-Miksis model provided insights into bubble dynamics, revealing increased pressure and temperature with higher pressure amplitudes.

Kinetic analysis of T4 polynucleotide kinase via isothermal titration calorimetry

T4 polynucleotide kinase (T4 PNK) phosphorylates the 5′-terminus of DNA and RNA substrates. It is widely used in molecular biology. Single nucleotides can serve as substrates if a 3′-phosphate group is present. In this study, the T4 PNK-catalyzed conversion of adenosine 3′-monophosphate (3′-AMP) to adenosine-3′,5′-bisphosphate was characterized using isothermal titration calorimetry (ITC). Although ITC is typically used to study ligand binding, in this case the instrument was used to evaluate enzyme kinetics by monitoring the heat production due to reaction enthalpy. The reaction was initiated with a single injection of 3′-AMP substrate into the sample cell containing T4 PNK and ATP at pH 7.6 and 30 °C, and Michaelis-Menten analysis was performed on the reaction rates derived from the plot of differential power versus time. The Michaelis-Menten constant, KM, was 13 μM, and the turnover number, kcat, was 8 s−1. The effect of inhibitors was investigated using pyrophosphate (PPi). PPi caused a dose-dependent decrease in the apparent kcat and increase in the apparent KM under the conditions tested. Additionally, the intrinsic reaction enthalpy and the activation energy of the T4 PNK-catalyzed phosphorylation of 3′-AMP were determined to be −25 kJ/mol and 43 kJ/mol, respectively. ITC is seldom used as a tool to study enzyme kinetics, particularly for technically-challenging enzymes such as kinases. This study demonstrates that quantitative analysis of kinase activity can be amenable to the ITC single injection approach.

Intact Transition Epitope Mapping-Force Interferences by Variable Extensions (ITEM-FIVE).

Investigations on binding strength differences of non-covalent protein complex components were performed by mass spectrometry. T4 fibritin foldon (T4Ff) is a well-studied miniprotein, which together with its biotinylated version served as model system to represent a compactly folded protein to which an Intrinsically Disordered Region (IDR) was attached. The apparent enthalpies of the gas phase dissociation reactions of the homo-trimeric foldon F-F-F and of the homo-trimeric triply biotinylated foldon bF-bF-bF have been determined to be rather similar (3.32 kJ/mol and 3.85 kJ/mol) but quite distinct from those of the singly and doubly biotinylated hetero-trimers F-F-bF and F-bF-bF (1.86 kJ/mol and 1.08 kJ/mol). Molecular dynamics simulations suggest that the ground states of the (biotinylated) T4Ff trimers are highly symmetric and well comparable to each other, indicating that the energy levels of all four (biotinylated) T4Ff trimer ground states are nearly indistinguishable. The experimentally determined differences and/or similarities in enthalpies of the complex dissociation reactions are explained by entropic spring effects, which are noticeable in the T4Ff hetero-trimers but not in the T4Ff homo-trimers. A lowering of the transition state energy levels of the T4Ff hetero-trimers seems likely because the biotin moieties, mimicking intrinsically disordered regions (IDRs), induced asymmetries in the transition states of the biotinylated T4Ff hetero-trimers. This transition state energy level lowering effect is absent in the T4Ff homo-trimer, as well as in the triply biotinylated T4Ff homo-trimer. In the latter, the IDR-associated entropic spring effects on complex stability cancel each other out. ITEM-FIVE enabled semi-quantitative determination of energy differences of complex dissociation reactions, whose differences were modulated by IDRs attached to compactly folded proteins.

Review on thermal properties and reaction kinetics of Ca(OH)2/CaO thermochemical energy storage materials

AbstractThermochemical energy storage technology is one of the most promising thermal storage technologies, which exhibits high energy storage capacity and long‐term energy storage potentials. The low‐cost, safe, and reliable calcium oxide/calcium hydroxide (CaO/Ca(OH)2) system has become the preferred thermochemical energy storage material system to solve the problem of renewable energy consumption. This study reviews the structural, thermodynamic, and kinetic properties influencing the absorption and desorption reactions of calcium oxide (CaO) and calcium hydroxide (Ca(OH)2) in thermal energy storage applications. It is found that the transformation of crystal structure from cubic to hexagonal upon hydration is attributed to volume expansion and crack formation facilitating diffusion. The specific heat capacities of CaO and Ca(OH)2, as well as reaction enthalpies, are studied across temperature ranges. Most studies on reaction kinetics are focused on the effect of factors such as temperature, particle size, and material content. Strategies to mitigate issues such as particle agglomeration and enhance reaction efficiency are discussed, including the incorporation of enhancing materials such as γ‐Al2O3. This study underscores the importance of the core reaction material content and the enhancing materials that are used to optimise energy density in thermal chemical water‐absorption and ‐desorption reactions.

Thermodynamic analysis of cellulose nitration

In this study, the standard formation enthalpies and entropies of cellulose and nitrocellulose samples were determined. These characteristics were used for thermodynamic analysis of bulk nitration of the entire cellulose sample and local nitration only of amorphous domains (ADs) of cellulose. It was found that the reaction of bulk nitration of cellulose up to a substitution degree (DS) of 1.5 is endothermic and determined primarily by the contribution of the temperature-entropy component to the negative Gibbs potential. However, if DS is higher than 1.5, the bulk nitration becomes exothermic and its feasibility is determined by the impact of enthalpy on the Gibbs potential. In the case of local nitration of cellulose ADs, the main contribution to the Gibbs potential is made by the reaction enthalpy that determines the feasibility of this process. It was shown that with the enhancement in DS of nitrocellulose, the negative value of the Gibbs potential of the reaction increases. Thus, the cellulose nitration to higher DS is thermodynamically favorable. Since the locally nitrated samples are copolymers of amorphous nitrocellulose and crystalline cellulose, they should be significantly less hydrophilic than cellulose. Therefore, it can be expected that the local nitration method will find a wide practical application for inexpensive hydrophobization of cellulose materials.

Exploring the reactivity of Na3V2(PO4)3/C and hard carbon electrodes in sodium-ion batteries at various charge states

The interest in post-lithium batteries as an alternative to lithium-ion batteries boosted recently due to their substantial abundance, low cost, inherent safety, and sustainability. In recent years, the crucial need for the improvement of battery safety has been emphasized and safety remains a critical barrier for post-lithium technology. Therefore, the thermal stability and reaction enthalpies of electrochemically de-sodiated sodium vanadium phosphate (Na3V2(PO4)3/C) positive electrode and commercial coconut-shell derived hard carbon (HC) at various states of charge (SOCs) were systematically investigated. This study employed the 3D Tian-Calvet calorimeter (C80) and thermogravimetric analysis coupled with mass spectrometry (TGA-MS), to gain comprehensive insights into the thermodynamic aspects of these materials. Thermal stability of electrode materials at distinct sodiation / de-sodiation states draws great attention in cell design and is one of the reasons for the strong state of charge (SOC) dependence of the thermal runaway phenomenon, which represents the most critical safety issue for batteries. This combined experimental approach provides a comprehensive understanding of thermal stability and associated reactions in both, sodium vanadium phosphate (NVP) and hard carbon (HC) electrodes. NVP/C reacts with the electrolyte between 150 and 300 °C, releasing ∼400 J/g heat, although it thermally decomposed beyond 150 °C. The sodiated HC initiates decomposition at 100 °C, releasing ∼750 J/g heat in two steps in a reaction to the electrolyte. These data can facilitate optimizing the design of thermal management systems according to the cell's thermal performance.

Investigation of soybean oil epoxidation process with phase transfer catalyst: Risk of thermal runaway

This paper explores an efficient and eco-friendly epoxidation process using the phase transfer catalyst ([(C18H37)2(CH3)2N]3{PO4[W(O)(O2)2]4}), which offers more advantages over the use of carboxylic and inorganic acids as catalysts in the Prileschajew epoxidation process. Consequently, a study of the process's thermal hazards is imperative. The paper conducts a comprehensive analysis of the process, employing a combination of calorimetric techniques. The critical runaway temperature, stabilization temperature, and required heat dissipation rate to prevent thermal runaway reactions were calculated using the Semenov model. On-line Fourier transform infrared spectroscopy and reaction calorimetry were used to relate the reaction mechanism and exothermic behavior of the actual production process, and a reliable model was developed for the calculation of reaction enthalpy. The findings indicate that the thermal risk depends on the rate of double bond epoxidation, which provides offering valuable insights for safe industrial-scale ESO production.

Reactivities and Bohmian perspectives on pnictogen N-heterocyclic carbene analogues reactions with methane and ethene

The chemical reactions of monocationic pnictogen N-heterocyclic carbene (NHC) analogues [(tBu2DAB)M+, M = N, P, As, Sb, and Bi, and tBu2DAB =1,4-tert-butyl-1,4-diaza-1,3-butadiene] with methane and ethene are studied by the density functional theory. The activation energies and reaction enthalpies are analyzed by the natural energy decomposition analysis (NEDA) to understand the reactivities of the reactions. The activation energies and reaction enthalpies of the ethene reactions, and the activation energies of the methane reactions decrease with the atomic numbers of the pnictogen elements M. However, the reaction enthalpies of the methane reactions do not follow a monotonic trend because the size and geometry of the methane structure are better accommodated by the product states of (tBu2DAB)P+ than (tBu2DAB)N+. The NEDA also suggests that the carbene and hydrocarbon fragments are subject to singlet–singlet interactions for all reactions of this work. The electronic and energetic structures of the reactions involving the N-centered NHC reactant, (tBu2DAB)N+ characteristically differ from all other carbenic reactants, which is in agreement with the well-known fact that the 2s and 2p orbitals of the N atom are more amenable to hybridization than the higher s and p orbitals of other pnictogen elements. The Bohmian perspectives on the stationary states of the pnictogen NHC reactions are also explored. It is found that the Bohmian potentials may reveal some bonding informations of the complexes, but further investigations are still required for deeper understanding.

Fungible, Multiyear Solar Thermochemical Energy Storage Demonstrated via the Cobalt Oxide Cycle

Abstract We present a proof of concept demonstration of solar thermochemical energy storage on a multiple year time scale. The storage is fungible, and can take the form of process heat or hydrogen. We designed and fabricated a 4-kW solar rotary drum reactor to carry out the solar-driven charging step of solar thermochemical storage via metal oxide reduction- oxidation cycles. During the summer of 2019, the solar reactor was operated in the Valparaiso University solar furnace to effect the reduction of submillimeter cobalt oxide particles in air at approximately 1000°C. A particle collection system cooled the reduced particles rapidly enough to maintain conversions of 84–94% for feed rates of 2.9–60.8 g min−1. The solar-to-chemical storage efficiency, defined as the enthalpy of the reduction reaction at 1000°C divided by the solar energy input, reached 20%. Samples of the reduced cobalt oxide particles were stored in vials in air at room temperature for more than three years. The stored solar energy was released by reoxidizing samples in air in a benchtop reactor and by electrochemically reoxidizing samples to produce H2. Measurements of the oxygen uptake by the reduced metal oxide confirm its promise as a medium to store and dispatch solar energy over long durations. Linear sweep voltammetry and bulk electrolysis demonstrate the promise of H2 production at 0.55 V relative to the normal hydrogen electrode, 0.68 V below the 1.23 V potential required for conventional electrolysis.

Quantum-chemical calculations of thermodynamic characteristics of some heterogeneous catalytic processes with the use of multilayer cluster models

The approaches to estimating the changes in enthalpy, entropy, and Gibbs energy of adsorption processes and heterogeneous catalytic reactions on the basis of the quantum chemical calculation data were studied. By comparing with the experimental data on CO adsorption on the anatase (TiO2) surface, the applicability of the developed multilayer cluster model for calculation of the adsorption energy (enthalpy) was shown. The data on the calculation methods of the entropy change in heterogeneous processes were analyzed. The use of the theories of an ideal two-dimensional gas and an ideal two-dimensional lattice gas for estimating a configuration contribution to the entropy of a heterogeneous process was studied. The density of adsorption centers on the (101) anatase surface and the population corresponding to the standard state of an ideal two-dimensional gas were calculated. The consistency of the studied models at low populations was shown, and the limits of their applicability were established.

Study on the Mechanism of Lipid Peroxidation Induced by Carbonate Radicals.

Based on the reported research, hydroxyl radicals can be rapidly transformed into carbonate radicals in the carbonate-bicarbonate buffering system in vivo. Many of the processes considered to be initiated by hydroxyl radicals may be caused by carbonate radicals, which indicates that lipid peroxidation initiated by hydroxyl radicals can also be caused by carbonate radicals. To date, theoretical research on reactions of hydrogen abstraction from and radical addition to polyunsaturated fatty acids (PUFAs) of carbonate radicals has not been carried out systematically. This paper employs (3Z,6Z)-nona-3,6-diene (NDE) as a model for polyunsaturated fatty acids (PUFAs). Density functional theory (DFT) with the CAM-B3LYP method at the 6-311+g(d,p) level was used to calculate the differences in reactivity of carbonate radicals abstracting hydrogen from different positions of NDE and their addition to the double bonds of NDE under lipid solvent conditions with a dielectric constant of 4.0 (CPCM model). Grimme's empirical dispersion correction was taken into account through the D3 scheme. The energy barrier, reaction rate constants, internal energy, enthalpy and Gibbs free energy changes in these reactions were calculated With zero-point vibrational energy (ZPVE) corrections. The results indicated that carbonate radicals initiate lipid peroxidation primarily through hydrogen abstraction from diallyl carbon atoms. The reaction of hydrogen abstraction from diallyl carbon atoms exhibits the highest reaction rate, with a reaction rate constant approximately 43-fold greater than the second-ranked hydrogen abstraction from allyl carbon atoms. This process has the lowest energy barrier, internal energy, enthalpy, and Gibbs free energy changes, indicating that it is also the most spontaneous process.