Values Of Reaction Enthalpies Research Articles

Theoretical characterization of the endohedral metalloborospherenes M@B36 (M = Ti, Zr, Hf, Ce, Th, Pa+, U2+, Np3+, and Pu4+)

A series of endohedral metalloborospherenes M@B36 (M = Ti, Zr, Hf, Ce, Th, Pa+, U2+, Np3+, and Pu4+) were investigated through density functional theory. This series of metal atom/ion encapsulated B36 cage meet the 32-electron principle as evidenced with the strong participations of An 7s, 7p, 6d and 5f orbitals in the orbital hybridizations. High stabilities of the endohedral metalloborospherenes have been rationalized in terms of larger HOMO-LUMO gap and negative values of reaction enthalpy and free energy. Electron density topological analyses were performed with QTAIM and AdNDP methods to understand the binding nature of these complexes. Furthermore, IR and PES spectra were simulated to aid future experimental characterization of studied species.

THERMODYNAMIC AND KINETIC INVESTIGATION OF ANTIRADICAL POTENTIAL OF CYANIDIN

In the present paper, M05-2X/6-311+G(d,p) level of theory was used to investigate antiradical activity of cyanidin towards highly damaging radical species (.OH, .OCH3, .OOH and .OOCH3). The applied method successfully reproduces the values of reaction enthalpies (ΔHBDE, ΔHIP, and ΔHPA). These parameters are important to determine which of the mechanisms are preferred. Reaction enthalpies related to the antioxidant mechanisms of the investigated species were calculated in water and DMSO. The enthalpies of reactions indicate the preferred radical scavenging mechanisms in polar (water) and polar aprotic (DMSO) solvents. Single- electron transfer followed by proton transfer (SET-PT) is not a favorable reaction pathway under any conditions. Both remaining mechanisms, HAT and SPLET, are suitable for the reaction of cyanidin with •OH and •OCH3 in all solvents under investigation. On the other hand, in the reaction of cyanidin with •OOH and •OOCH3, the SPLET mechanism is possible in both solvents. Simulation of the reaction of the cyanidin anion with the hydroxy radical confirmed that position 3` of Cy‒O- is the most suitable for reaction with •OH through electron transfer mechanism (ET) in both solvents.

Adsorption of Nickel and Chromium From Aqueous Solutions Using Copper Oxide Nanoparticles: Adsorption Isotherms, Kinetic Modeling, and Thermodynamic Studies

The research was conducted with an aim to assess the efficiency of copper oxide nanoparticles as an adsorbent to remove Ni and Cr. The effect of pH, adsorbent dosage, contact time, initial concentration of metals (Ni and Cr) on the adsorption rate was evaluated and removal of these elements from aqueous solutions was measured using Atomic Absorption Spectrum System (Conter AA700). Moreover, the kinetic and isotherm besides thermodynamic adsorption models were assessed. The highest Ni and Cr removal rate occurred at an optimal pH of 7, and an initial concentration of 30 mg/L, a time period of 30 minutes, and 1 g/L of copper oxide nanoparticles. In fact, with the increase of adsorbent dosage and contact time, the removal efficiency increased and with initial concentration increase of Ni and Cr ions, the removal efficiency reduced. The correlation coefficient of isotherm models viz. Langmuir, Freundlich, Temkin, Redlich-Peterson, and Koble-Corrigan showed that Ni and Cr adsorption via copper oxide nanoparticles better follows the Langmuir model in relation to other models. The results showed that kinetic adsorption of Ni and Cr via copper oxide nanoparticles follows the second order pseudo model with correlation coefficients above 0.99. In addition, the achieved thermodynamic constants revealed that the adsorption process of metals (i.e., Ni and Cr) via copper oxide nanoparticles was endothermic and spontaneous and the reaction enthalpy values for these metals were 17.727 and 11.862 kJ/mol, respectively. In conclusion, copper oxide nanoparticles can be used as effective and environmentally compatible adsorbents to remove Ni and Cr ions from the aqueous solutions

Thermodynamic parameters of Am(III), Cm(III) and Eu(III) extraction by CyMe4-BTPhen in cyclohexanone from HNO3 solutions

The thermodynamic parameters of the extraction system consisting of CyMe4-BTPhen dissolved in cyclohexanone and Am(III), Cm(III) and Eu(III) in HNO3 in the aqueous phase have been determined. Kinetic extraction experiments were carried out under various temperatures (15–45 °C) and the corresponding over-all mass transfer coefficients were used for the calculation of apparent activation energy and frequency factor values. The values of reaction enthalpy and entropy were also calculated using the distribution coefficients resulting from the experiments mentioned above. Based on the calculated data, the rate-controlling processes and the exothermic character of the studied extractions were determined.

A kinetic study of the NO to NO2 oxidation mechanism over Fe-FER: A combined analysis of operando surface and gas phase data

Abstract Diesel engines when compared with gasoline engines produce higher amount of NOx due the operating conditions. Among the NOx produced NO represents the great majority while, under air excess conditions, the removal of NOx is necessarily catalytic and still challenging. In the ammonia based SCR, it is often admitted that, when dealing with the original formulation developed for stationary sources (V/TiO2), the fast SCR proceeds in presence of an equimolar mixture of NO and NO2. Most of the catalytic formulations developed up to now (except Cu based zeolites) thus suffer the same rate determining step consisting in the NO to NO2 oxidation. Aiming at improving the catalytic efficiency through the catalyst composition, it is fundamental to understand the reaction mechanism at its elementary steps in order to properly design the active sites. The choice regarding the distinct possible hypothetical mechanisms was thus here guided by the nature of the active sites. It is indeed worth knowing, for a better tuning of the catalyst formulation, whether isolated, oligomeric or dual iron sites are involved in the catalytic loop. The approach in this work consists in a systematic study of the influence of the inlet NO concentration under O2 excess on both the initial reaction rate (NO to NO2 conversion level kept below 10%) and the NO coverage level onto iron measured by operando FTIR. Isothermal experiments were performed over an aged FeFER catalyst at three distinct temperatures. The whole set of data was then processed and compared to the expected evolution derived from five possible mechanisms. The best mechanism determined in the frame of this study involves isolated iron sites onto which NO and O2 co-adsorb and the corresponding rate determining step consists in the dissociation of the so-formed Fe_NOO2 intermediate species. The associated activation energy and reaction enthalpy values are then evaluated.

On the misincorporation of nucleotides opposite mutagenic cyclic 1,N2-propanoguanine: A computational investigation

The misincorporation properties of exocyclic DNA adduct, cyclic 1,N2-propanoguanine with nucleobases have been investigated using DFT and DFT-D methods. Number of possible and stable mispairing conformations of cyclic 1,N2-propanoguanine with A,T,G and C have been considered for our investigation. The single point energy calculations have been carried out at the M06/6–311++G**, ωB97XD/6–311++G** and MP2/6–311++G** levels on corresponding optimized geometries. The reaction enthalpy values were employed at the M06/6-31 + G* and ωB97XD/6-31 + G* levels. The energies have been compared among the cyclic 1,N2-propanoguanine adduct with nucleobases to find the most stable conformer. The CPCM model was utilized on account of solvent phase and overall polarizability. The computed binding energies follow the order as CPr-Gua-G(2)(-23.2 kcal/mol) > CPr-Gua-C(1) (−16.1 kcal/mol) > CPr-Gua-A(2)(-10.6 kcal/mol) > CPr-Gua-T(2)(-9.6 kcal/mol) in the gas phase at M06 level, which indicates the guanine and cytosine are favorable for mispairing with the cyclic 1,N2-propanoguanine adduct. The obtained results using computational tools are in good agreement with the experimental observation.

Elucidation of novel mechanisms to produce value-added chemicals from vapour phase conversion of ferulic acid

Ferulic acid is one of high molecular weight phenolic compounds of raw bio-oil produced from thermochemical conversion of lignocellulosic biomass. Due to its unique chemical fragmentation, it can be converted into various specialty chemicals such as methyl-2-phenylacetate, cinnamic acid, methyl-benzoate, methyl- and ethyl-cinnamate and others. In this numerical study, ferulic acid is converted into aforementioned specialty chemicals with analyses of their potential energy surfaces, activation energies, and thermodynamic feasibilities by density functional theory using B3LYP functional. The selection of B3LYP functional is also demonstrated by comparing single point energy of a couple of reaction pathways with those obtained by M05-2X functional. In the thermochemical analyses, all reaction schemes are subjected at a wide range of temperature conditions varying from 598 to 898 K. The productions of phenol and cinnamic acid required overall activation energy of only 5 kcal/mol due to the same rate-determining step. Further conversion of phenol into the end product methyl-benzoate is not advantageous because of high-energy demands and positive values of reaction free energy and reaction enthalpy at each temperature. According to thermochemical analysis, the production of methyl-2-phenylacetate is highly spontaneous even at the lower temperature; however, at elevated temperature conditions, its spontaneity decreases and exothermicity improves further.

Role of Lithium Decoration on Hydrogen Storage Potential

Hydrogen storage potential of two sets of lithium containing systems, viz., Li-doped borazine derivatives and various bondstretch isomers of Li3Al4 - is studied at the B3LYP/6-311+G(d) level of theory occasionally supplemented by the results from the associated MP2/6-31+G(d) calculations. Negative values of interaction energy, reaction enthalpy, reaction electrophilicity, and desorption energies for the gradual hydrogen-trapping processes justify the efficacy of these systems as the hydrogen storage material. Presence of Li as well as aromaticity improves the situation. Various conceptual density functional theory based reactivity descriptors like electronegativity, hardness, and electrophilicity and the associated electronic structure principles such as the principles of maximum hardness and minimum electrophilicity lend additional support

Thermal decomposition of europium sulfates Eu2(SO4)3·8H2O and EuSO4

Reactions of europium sulfates Eu2(SO4)3·8H2O and EuSO4 complete decomposition were studied by Simultaneous Thermal Analysis. It was revealed that one-step dehydratation of Eu2(SO4)3·8H2O crystallohydrate is accompanied by the formation of amorphous anhydrous europium sulfate Eu2(SO4)3. Crystallization of amorphous europium (III) sulfate occurs at 381.1°С (in argon) and 391.3°C (in air). The average enthalpy values for dehydratation reaction of Eu2(SO4)3·8H2O (ΔH° = 141.1kJ/mol), decomposition reactions of Eu2(SO4)3 (ΔH = 463.1kJ/mol), Eu2O2SO4 (ΔH = 378.4kJ/mol) and EuSO4 (ΔH = 124.1kJ/mol) were determined. The step process mechanisms of thermal decomposition of europium (III) sulfate in air and europium (II) sulfate in inert atmosphere were established and justified. The kinetic parameters of complete thermal decomposition of europium (III) sulfate octahydrate were calculated by Kissinger model. The standard enthalpies of compound formation were calculated using thermal effects and formation enthalpy data for binary compounds.

A Comparative Thermodynamic Analysis of Gas–Solid Sorption System Based On H 2 –La 0.9 Ce 0.1 Ni 5 /LaNi 4.7 Al 0.3 and NH 3 –NaBr/MnCl 2

Sorption cooling system based on gas–solid reaction is a newly emerged energy conversion technology which is benign to environment. In this work, sorption cooling system, based on the gas–solid pairs of H2–La0.9Ce0.1Ni5/LaNi4.7Al0.3 and NH3–NaBr/MnCl2 is thermodynamically analyzed using the first and second law of thermodynamics. The COP of H2 – La0.9Ce0.1Ni5/LaNi4.7Al0.3 and NH3–NaBr/MnCl2 based sorption system is 0.70 and 0.41 respectively while neglecting mass ratio and 0.23 and 0.33 respectively while considering mass ratio as 4. Also it is observed that the sorption cooling system based on NH3–NaBr/MnCl2 can produce refrigeration effect below 0 °C while H2–La0.9Ce0.1Ni5/LaNi4.7Al0.3 sorption system can be operated at a low temperature of about 130 °C. Irreversibility in H2–La0.9Ce0.1Ni5/LaNi4.7Al0.3 sorption system is small in comparison to NH3–NaBr/MnCl2 based system, due to lower reaction enthalpy values of regenerating material in case of H2–La0.9Ce0.1Ni5/LaNi4.7Al0.3 system. The reactor mass contributes significantly in the irreversibility of the system.

Kinetics of Transesterification of 1,4‐Butanediol With Methyl Acetate by the Ion‐exchange Resin

The dihydric alcohol transesterification of 1,4‐butanediol with methyl acetate catalyzed by the ion‐exchange resin is researched. The chemical system involves two transesterification reactions in series, with 1,4‐butanediol monoacetate as an intermediate product. The effects of the catalyst type, catalyst size, catalyst loading, stirrer speed, the initial reactant ratio, and the reactive temperature have been meticulously studied. The results show that this consecutive transesterification is exothermic and the experimental values of reaction enthalpy are −8.50 and −6.85 kJ/mol, which are in good agreement with the values computed from the standard formation enthalpy. Three kinetic models (PH, LH, and ER) are applied to correlate the experimental data, of which ER model gives the best result with the lowest mean relative error. The activation energies are calculated to be 38.53 and 51.06 kJ/mol by ER model, demonstrating that the overall reaction rates are controlled by the reaction on the catalyst surface.

Microfluidic chip reactor and the stereoselective hydrogenation of methylacetoacetate over (R)-Ru-BINAP in the [N8222][Tf2N]/methanol/water mixed phase

Homogeneous asymmetric catalysts represented by organometallics of transition elements reveal very high activity and stereoselectivity in asymmetric hydrogenation of β-ketoesters. Recently, it appeared efficient to use ionic liquids of the [NR222][Tf2N] type for accommodation of the chiral catalytic complex. Even on the industrial scale it is becoming attractive to carry out hydrogenations with such immobilised complexes in a continuous regime in microreactors. Attention was paid to the stereoselective hydrogenation of methylacetoacetate (MAA) to isomeric (R)−(+) or (S)−(−)-methyl-3-hydroxybutanoates over a chiral ([RuCl((R)-BINAP)(p-cymene)]Cl) complex immobilised in the mixed [N8222][Tf2N]/methanol/water solvent phase, and performed inside of a microfluidic chip reactor. It was shown that the reaction could be successfully carried out in such an arrangement with a very high enantioselectivity (above 99%) and at very high conversion of MAA (above 97%). It was proven that the participation of a specific solvent (methanol or the mixture [N8222][Tf2N]/methanol/water) essentially influences the mechanism of the reaction. The solvents actively participate in the re-coordination of the catalytic complex in a series of reactions which is reflected in the values of reaction enthalpies. The specific process output was also evaluated.

Computational exploration of regioselectivity and atmospheric lifetime in NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3

The NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3 have been investigated by the BHandHLYP method in conjunction with the 6–311G(d,p) basis set. Thermodynamic and kinetic data are further refined using the comparatively accurate CCSD(T) method. According to the values of reaction enthalpies (ΔHr,298θ) and reaction Gibbs free energies (ΔGr,298θ) from CH3OCH2CH3 with NO3 system, we find that H-abstraction pathway from the α-CH2 group is more exothermic. It is further confirmed by the calculated CH bond dissociation energy of CH3OCH2CH3 molecule. All the rate constants, computed through means of canonical variational transition state with small-curvature tunneling correction, are fitted to the three-parameter expressions k1=1.54×10−23T3.34exp(−1035.53/T) and k2=3.55×10−26T4.31exp(−281.24/T)cm3molecule−1s−1 and branching ratios are computed over the temperature range 200–600K. The branching ratios are also discussed. The atmospheric lifetimes of CH3OCH3 and CH3OCH2CH3 determined by the NO3 radical are about 270 and 29days, respectively.

Investigation of energetic materials prepared by reactions of diamines with picryl chloride

Five compounds containing picryl group(s) were synthesized from reactions of hydrazine, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane and 1,7-diaminoheptane with picryl chloride under hydrothermal conditions in methanol. Hydrazine reaction yielded N-2,4,6-trinitrophenylhydrazine which has a single picryl group, whereas the other reactants formed symmetric products with both amine groups connected to picryl groups. These compounds are N,N′-di-2,4,6-trinitrophenyl-1,2-diaminoethane, bis-N,N′-di-2,4,6-trinitrophenyl-1,3-diaminopropane, bis-N,N′-di-2,4,6-trinitrophenyl-1,4-diaminobutane and bis-N,N′-di-2,4,6-trinitrophenyl-1,7-diaminoheptane. Molecular structures of two of these compounds, N-2,4,6-trinitrophenylhydrazine and bis-N,N′-di-2,4,6-trinitrophenyl-1,3-diaminopropane, were revealed by XRD methods. All compounds were investigated by TG and DSC methods. The thermal behaviour of N-2,4,6-trinitrophenylhydrazine was explosive, undergoing a strong explosion in a very short temperature interval, 180–185 °C. In cases of the other compounds, it was found out that the carbon chain between two picryl groups reduced the explosion enthalpy. In addition, the theoretical formation enthalpy of N-2,4,6-trinitrophenylhydrazine was calculated by running CBS-4 M energy calculations under Gaussian 09 software package. From the calculated value, reaction enthalpy values for the possible explosion pathways were investigated in accordance with the experiment. The path with reaction enthalpy closest to the experimental value was proposed as the explosion mechanism.

Exploration of Unimolecular Gas-Phase Detoxication Pathways of Sarin and Soman: A Computational Study from the Perspective of Reaction Energetics and Kinetics.

A mechanistic investigation has been carried out to explore all possible gas phase unimolecular isomerization as well as decomposition pathways of toxic organophosphorus compounds (OPCs), namely, sarin (GB) and soman (GD), which are better known as nerve agents. We have identified a total of 13 detoxication pathways for sarin, where the α-H, β-H, and γ-H take part in the H-transfer process. However, for soman, due to the presence of ω-H, three additional detoxication pathways are obtained, where the ω-H is involved in the H-transfer process. Among all the pathways, the D3 decomposition pathway, where the phosphorus oxoacid derivative and alkene are generated via the formation of a six-membered ring in the transition state, is identified as the most feasible pathway from the perspective of both activation barrier and reaction enthalpy values. Moreover, we have studied the feasibility of the isomerization and decomposition pathways by performing the reaction kinetics in the temperature range of 300 K-1000 K using the one-dimensional Rice-Ramsperger-Kassel-Marcus (RRKM) master equation. From the RRKM calculation also, D3 pathway is confirmed as the most feasible pathway for both OPCs. The rate constant values associated with the D3 pathway within the temperature range of 600 K-700 K imply that the degradation of the OPCs is possible within this temperature range via the D3 pathway, which is in good agreement with the earlier reported experimental result. It is also observed that at higher temperature range (∼900 K), the increased rate constant values of other detoxication pathways indicate that along with D3, all other pathways become more or less equally feasible. Therefore, the entire work provides a widespread idea about the kinetic as well as thermodynamic feasibility of the explored detoxication pathways of the titled OPCs.

HypCal, a general-purpose computer program for the determination of standard reaction enthalpy and binding constant values by means of calorimetry.

The program HypCal has been developed to provide a means for the simultaneous determination, from data obtained by isothermal titration calorimetry, of both standard enthalpy of reaction and binding constant values. The chemical system is defined in terms of species of given stoichiometry rather than in terms of binding models (e.g., independent or cooperative). The program does not impose any limits on the complexity of the chemical systems that can be treated, including competing ligand systems. Many titration curves may be treated simultaneously. HypCal can also be used as a simulation program when designing experiments. The use of the program is illustrated with data obtained with nicotinic acid (niacin, pyridine-3 carboxylic acid). Preliminary experiments were used to establish the rather different titration conditions for the two sets of titration curves that are needed to determine the parameters for protonation of the carboxylate and amine groups.

The Influence of Solvent on Complex Formation of Crown Ether with Tetraphenylphosphonium Chloride

The host guest interactions of crown ether (18-C-6) with tetraphenylphosphonium chloride (TPPC) were studied in different solvents at 303.15 K. The values of reaction enthalpies, ΔH0, and equilibrium constant, K, have been calculated and the results show that solvation of tetraphenylphosphonium ion (Ph4P+) is not very important. Because the cavity of the 18-C-6 is too small to completely accommodate large Ph4P+ ion. Thus, the interactions between the cation and the oxygen donor atoms of the ligand decrease, the large cation is surrounded by large organic moieties which interact more strongly with the organic environment and therefore it will not have tendency to form complex in non-aqueous solvents.

Computational study on reaction enthalpies of urethane‐forming reactions

Computational calculations were performed on urethane‐forming reactions using Gaussian 09 software (i.e. molecular modeling) toward the goal of providing thermodynamic parameters. Total electronic and thermal enthalpies and zero‐point vibrational energies of reactants and products were computed by the software and then reaction enthalpies were calculated based on these results. The location of functional groups has the most significant impact on reaction enthalpies while molecular size, chain length and solvent effect have relatively less impact on reaction enthalpies. By comparison to new experimental studies and values reported in literature, better‐informed recommendations on which values of reaction enthalpies to use for urethane foam process simulation were provided. The utility of computational chemistry results succeeded in being an enabling technology to improve foam process simulation. In turn, simulation of urethane‐forming reactions is useful to bridge the gap between fundamental computational chemistry calculations and practical applications. POLYM. ENG. SCI., 55:1420–1428, 2015. © 2015 Society of Plastics Engineers

A systematic investigation of the performance of copper-, cobalt-, iron-, manganese- and nickel-based oxygen carriers for chemical looping combustion technology through simulation models

The Integrated Gasification Combined Cycle coupled with chemical looping combustion (IGCC-CLC) is one of the most promising technologies that allow generation of cleaner energy from coal by capturing carbon dioxide (CO2). It is essential to compare and evaluate the performances of various oxygen carriers (OC), used in the CLC system; these are crucial for the success of IGCC-CLC technology. Research on OCs has hitherto been restricted to small laboratory and pilot scale experiments. It is therefore necessary to examine the performance of OCs in large-scale systems with more extensive analysis. This study compares the performance of five different OCs – copper, cobalt, iron, manganese and nickel oxides – for large-scale (350–400MW) IGCC-CLC processes through simulation studies. Further, the effect of three different process configurations: (i) water-cooling, (ii) air-cooling and (iii) air-cooling along with air separation unit (ASU) integration of the CLC air reactor, on the power output of IGCC-CLC processes – are also investigated. The simulation results suggest that iron-based OCs, with 34.3% net electrical efficiency and ~100% CO2 capture rate lead to the most efficient process among all the five studied OCs. A net electrical efficiency penalty of 7.1–8.1% points leads to the IGCC-CLC process being more efficient than amine based post-combustion capture technology and equally efficient to the solvent based pre-combustion capture technology. The net electrical efficiency of the IGCC-CLC process increased by 0.6–2.1% with the use of air-cooling and ASU integration, compared with the water- and air-cooling cases. This work successfully demonstrates a correlation between the reaction enthalpies of different OCs and power output, which suggests that the OCs with higher values of reaction enthalpy for oxidation (ΔHr, oxidation) with air-cooling are more valuable for the IGCC-CLC.

Catalytic formation of 2,3,3,3-tetrafluoropropene from 2-chloro-3,3,3-trifluoropropene at fluorinated chromia: A study of reaction pathways

The catalytic gas phase reaction between CF3CClCH2 with HF yielding CF3CFCH2 was investigated regarding the reaction pathways involved. Different from the reaction under liquid phase (homogenous) conditions, in heterogeneous phase CF3CClCH2 does not add HF forming the saturated intermediate CF3CFClCH3 but undergoes direct Cl/F exchange at the starting olefin molecule resulting directly in the formation of CF3CFCH2. This might be caused mainly by the fact that under heterogeneous gas phase conditions higher temperatures are needed as compared to liquid phase conditions thus suppressing the formation of kinetically less stable CF3CFClCH3 under these conditions. Since for all the reaction steps involved in this complex reaction system the Gibbs free reaction enthalpy values are close to zero [1], the selectivity towards several reaction products is strongly dependent on the reaction parameters, e.g. temperature, pressure and molar ratio of the reactants. Based on the catalytic data obtained for fluorinated chromia as catalyst, a reaction path distinguishing direct chlorine against fluorine exchange versus hydrofluorination/dehydrochlorination is proposed.