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International audience; Porous ceria-based architected materials offer high potential for solar fuels production via thermochemical H 2 O and CO 2-splitting cycles. Novel porous morphologies and micro-scale architectures of redox materials are desired to provide suitable thermochemical activities and long-term stability. Considering particle-based solar reactors, porous ceria microspheres are promising because of their excellent flowability and large surface area. In this work, such porous microspheres with perfect spherical shape, high density and interconnected pore network were fabricated by a chemical route involving ion-exchange resins. The method involved the cationic loading of the resin in aqueous medium followed by thermal treatment for oxide formation and porous microstructure stabilization. The utilization of these microspheres (~150-350 µm in size) as redox materials for solar fuel production was investigated in packed-bed solar reactors (directly and indirectly-irradiated). Superior redox performance was obtained for the pure ceria microspheres in comparison with other morphologies (powders and reticulated foams). Low p O2 values thermodynamically favored the reduction extent and associated fuel yield, whereas high p CO2 kinetically promoted the oxidation rate. The highest fuel production rate reached 1.8 mL/min/g with reduction step at 1400°C and low total pressure (~0.1 bar), and oxidation step below 1050°C under pure CO 2. Low pressure during reduction both improved reduction extent (oxygen under-stoichiometry  up to 0.052) and associated fuel production yield (331 µmol/g CO). After 19 redox cycles (~32h under high-flux solar irradiation), the porous microspheres maintained their individual integrity (no agglomeration), spherical shape, and internal porosity, with great potential for stable fuel production capacity in particle-based solar reactors.

Inspired by the promising hydrogen production in the solar thermochemical (STC) cycle based on non-stoichiometric oxides and the operation temperature decreasing effect of methane reduction, a high-fuel-selectivity and CH4-introduced solar thermochemical cycle based on MoO2/Mo is studied. By performing HSC simulations, the energy upgradation and energy conversion potential under isothermal and non-isothermal operating conditions are compared. In the reduction step, MoO2:CH4 = 2 and 1020 K < Tred < 1600 K are found to be most favorable for syngas selectivity and methane conversion. Compared to the STC cycle without CH4, the introduction of methane yields a much higher hydrogen production, especially at the lower temperature range and atmospheric pressure. In the oxidation step, a moderately excessive water is beneficial for energy conversion whether in isothermal or non-isothermal operations, especially at H2O: Mo = 4. In the whole STC cycle, the maximum non-isothermal and isothermal efficiency can reach 0.417 and 0.391 respectively. In addition, the predicted efficiency of the second cycle is also as high as 0.454 at Tred = 1200 K and Toxi = 400 K, indicating that MoO2 could be a new and potential candidate for obtaining solar fuel by methane reduction.

Induced by promising hydrogen production of CeO2-based solar thermochemical cycle and evident temperature decreasing effect of methane reduction, a moderately high-temperature solar thermochemical ceria-methane cycle is investigated thermodynamically. In this paper, isothermal and non-isothermal solar-to-fuel efficiencies (ηsolar-to-fuel) under different temperatures and reactant ratios are compared carefully. The calculated results indicate that the condition of CH4:CeO2 = 0.5 is favorable for oxygen release, fuel selectivity and methane conversion. The introduction of methane could increase the maximum yield of H2, and more solar energy could be converted to chemical energy as the increase of nH2O:nCeO2. nH2O:nCeO2 = 0.5, Tred = 1400 K and Toxi = 750 K are suggested for the maximum non-isothermal ηsolar-to-fuel of 0.35, which is larger than the maximum isothermal ηsolar-to-fuel of 0.24. The result shows that non-isothermal solar thermochemical ceria-methane cycle is more feasible for fuel production.

Hydrogen production thermochemical cycles, based on the recirculation of sulfur-based compounds, are among the best suited processes to produce hydrogen using concentrated solar power. The sulfuric acid decomposition section is common to each sulfur-based cycle and represents one of the fundamental steps. A novel direct solar receiver-reactor concept is conceived, conceptually designed and simulated. A detailed transport phenomena model, including mass, energy and momentum balance expressions as well as suitable decomposition kinetics, is described adopting a finite volume approach. A single unit reactor is simulated with an inlet flow rate of 0.28 kg/s (corresponding to a production of approximately 11 kgH2/h in a Hybrid Sulfur process) and a direct solar irradiation at a constant power of 143 kW/m2. Results, obtained for the high temperature catalytic decomposition of SO3 into SO2 and O2, demonstrate the effectiveness of the proposed concept, operating at pressures of 14 bar. A maximum temperature of 879 °C is achieved in the reactor body, with a corresponding average SO2 mass fraction of 27.8%. The overall pressure drop value is 1.7 bar. The reactor allows the SO3 decomposition into SO2 and O2 to be realized effectively, requiring an external high temperature solar power input of 123.6 kJ/molSO2 (i.e. 123.6 kJ/molH2).

Nuclear energy is considered a key alternative to overcome the environmental issues caused by fossil fuels. It offers opportunities with an improved operating efficiency and safety for producing power, synthetic fuels, delivering process heat and for multigeneration applications. The high-temperature nuclear reactors, although possess great potential for integration with thermochemical water-splitting cycles for hydrogen production, are not yet commercially established. Current nuclear reactor designs providing heat at relatively low temperature can be utilized to produce hydrogen using thermochemical cycles if the temperature of their thermal heat is increased. In this paper, a hybrid chemical-mechanical heat pump system is proposed for upgrading the heat of the Enhanced CANDU (EC6) reactor design to the quality required for the copper-chlorine (Cu–Cl) hybrid thermochemical water splitting cycle operating at 550–600 °C. A modification to the heat pump is proposed to bring the heat to temperature higher than 650 °C with operating coefficient of performance estimated as 0.65.

In this paper, A0.5Sr0.5MnO3 perovskites (where, A = La, Nd, Sm, Gd, Tb, Pr, Dy, and Y) were examined towards thermochemical CO2 splitting (CS) reaction. The solution combustion synthesis (SCS) method was employed for the preparation of the A0.5Sr0.5MnO3 perovskites, in which glycine was used as the fuel. The characterization of the as-prepared and reacted A0.5Sr0.5MnO3 perovskites was accomplished by means of powder X-ray diffractometer (PXRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS). A Seteram Setsys Evolution TGA set-up was utilized to estimate the amounts of O2 released (nO2) and CO produced (nCO) by each SCS synthesized A0.5Sr0.5MnO3 perovskite in multiple thermochemical cycles. Obtained TGA results confirmed that all the A0.5Sr0.5MnO3 perovskites attained thermal and redox stability from second thermochemical cycle. It was also understood that all the A0.5Sr0.5MnO3 perovskites shows significantly higher nO2 and nCO as compared to the phase pure CeO2. Among all the A0.5Sr0.5MnO3 perovskites investigated, PrSM shows maximum nO2 = 144.8 μmol/g·cycle and nCO = 252.3 μmol/g·cycle with an average CO/O2 molar ratio of 1.74. The experimental findings also indicate that the fuel production aptitude of all the A0.5Sr0.5MnO3 perovskites can be upsurged if longer CS reaction time is employed. This publication was made possible by the NPRP grant ( NPRP8-370-2-154 ) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of author(s). Scopus

Separation of O2 from air to produce a high-purity stream of N2 is considered via a two-step solar thermochemical cycle based on aluminum-doped strontium ferrite reduction/oxidation reactions. The cycle steps encompass the (1) thermal reduction, driven by concentrated solar irradiation; and (2) re-oxidation with atmospheric air to produce a N2 stream. Samples were synthesized via the sol-gel method, and crystalline structures were confirmed with x-ray powder diffractometry. Thermogravimetry was used to measure the nonstoichiometry at chemical equilibrium for molar B-site Al dopant fractions between 0 and 0.20, temperatures between 673 and 1373 K, and volumetric gas flow compositions between 1 and 90% O2–Ar. The compound energy formalism was applied to thermogravimetric measurements to predict equilibrium nonstoichiometry as a function of dopant fraction, temperature, and O2 partial pressure. The results were used to predict partial reaction enthalpies and entropies. Aluminum doping increased the strontium ferrite oxygen affinity but reduced the range of nonstoichiometries. A strontium ferrite sample underwent 10 thermal reduction-oxidation steps in an upward flow reactor coupled to a high-flux solar simulator to study cyclability. A thermodynamic cycle analysis was performed, and cycle efficiencies were determined relative to an ideal separation process. For a solar reactor at 1073 K, 0.59 mol N2 per mol strontium ferrite could be produced at a purity of nearly 99% with a cycle efficiency of 4.0%.

To perform thermochemical cycles using non-volatile metal oxides to split water and produce hydrogen, a directly irradiated fluidized bed reactor is designed and fabricated for beam-down configuration. As the main aim of this investigation is to analyze the heat transfer and particulate flow of the reactor, chemically inert particles are used. A transient 3D heat and mass transfer model is formulated by the combined approach of discrete element method and computational fluid dynamics. The radiative transfer is solved using the discrete ordinate radiation model. Experimental validation is accomplished by the measured temperatures, obtained with the fluidized bed reactor prototype tested under 30 kWth high-flux solar simulator. The model is applied to analyze the granular flow characteristics and efficiency of the reactor for various superficial gas velocities and bed masses. The results indicate that higher gas flow rate increases the velocity and convection loss of the bed and decreases the bed temperature and efficiency of the reactor.

Two step water-splitting cycles by using metal ferrites are considered as a clean and sustainable hydrogen production method, when concentrated solar energy is used to drive the thermochemical reactions. This process involves the reduction at very high temperature of the ferrite, followed by the water reoxidation to the original phase at moderate temperature, with the release of hydrogen. In order to decrease the temperature required to decompose the oxide, mixed ferrites of the type MFeO with spinel crystal structure have been examined. In this sense, ferrites with the partial substitution of Co and Ni for Fe appear as successful materials in terms of hydrogen production and cyclability. In this work, commercial Ni and synthetic Co ferrites have been subjected to two water splitting cycles. The solid products obtained after thermal reduction and water decomposition reactions have been chemically and structurally characterized by WDXRF, XRD, XPS and SEM techniques, in order to get a deeper understanding of the mechanisms controlling the water splitting process. This knowledge contributes to improve the process involved in thermochemical cycles and to understand the lower efficiencies (H/O) for Co ferrite thermochemical cycles in comparison with those corresponding to Ni ferrite., European Regional Development Fund is gratefully acknowledged by the partial funding of the XRF and XRD equipment employed for this study (Projects FEDER 2004 CIEM05-34-030 and FEDER 2004 CIEM05-34-031).

A pure barium borate of BaB8O11(OH)4·3H2O has been synthesized and characterized by XRD, FT-IR, TGA, and chemical analysis. The molar enthalpies of solution of BaB8O11(OH)4·3H2O in 1 mol dm−3 HCl(aq), and Ba(OH)2·8H2O in the mixture solvent of {2.00 cm3 of 1 mol·dm−3 HCl + H3BO3(aq)} were measured by microcalorimeter at T = 298.15 K, respectively. With the use of previously determined enthalpy of solution of H3BO3 (s) in 1 mol·dm−3 HCl(aq), and the standard molar enthalpies of formation for Ba(OH)2·8H2O(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of −(7500.6 ± 6.5) kJ·mol−1 at T = 298.15 K was obtained based on an appropriate thermochemical cycle. Moreover, the molar enthalpy of formation of −6091.7 kJ mol−1 for [B8O11(OH)4]2− was estimated by a group contribution method, which was used to predict the ΔfHmo of a series of alkaline-earth metal borates for MB8O11(OH)4 (M = Ca, Sr, Ba).

Ammonia (NH3) is one of the most valuable chemicals due to its multipurpose utilization in many applications. Beside major application as fertilizer in agriculture, NH3 is a promising hydrogen (H2) carrier because it has a high content of H2 and technically available storage and transportation systems. At present, most of NH3 is synthesized from a series of steam reforming process to the feedstock of H2 and nitrogen (N2) production, followed with the catalytic Haber-Bosch reaction. In this study, an integrated system of N2 production system, NH3 synthesis system and a power generation process is proposed to produce NH3 efficiently. Thermochemical cyclic process of an endothermic reaction of Al2O3 reduction by carbon in N2 atmosphere, is coupled with oxidation/steam-hydrolysis of aluminum nitride (AlN) back to Al2O3, producing NH3 without catalyst and the need of H2 production system. The thermal energy required for reduction reaction is covered by the heat generated during exothermic reaction and combustion process, and the remaining heat is utilized in power generation. Heat circulation optimization is carried out by applying the enhanced process integration, resulting in a highly efficient system. The proposed system is analyzed through an adjustment of the main parameters: oxidation temperature, steam turbine inlet pressure, and temperature, to observe their effect on system performance and efficiency. The proposed system can reach a very high system efficiency of 69.3%. The oxidation reaction temperature is observed to play major role in determining the system performance due to temperature dependent NH3 yield.

An integrated lab-scale copper-chlorine (Cu-Cl) thermochemical cycle for hydrogen production at the University of Ontario Institute of Technology (UOIT) is presented and analyzed in this paper. In a practical operation of the Cu-Cl cycle, besides the main steps of hydrolysis, thermolysis, electrolysis and drying, the oxidized anolyte (consumed anolyte at the electrolyzer cell) needs to be recycled to be concentrated sufficiently for the electro-chemical process. Recycling of the oxidized anolyte through the separation processes is achieved by distillation of anolyte, drying unit, separation cell, pressure swing distillation and CuCl2 concentrator. This study examines the thermodynamic performance of all unit operations in the lab-scale Cu-Cl cycle. A process simulation model with Aspen Plus is used to assess the system by energy and exergy analyses. For the specific system design characteristics, the cycle is capable of producing 100 L/h of hydrogen. From the simulation results, the overall energy and exergy efficiencies of the lab-scale Cu-Cl cycle are determined to be 11.6% and 34.9%, respectively. Furthermore, after the thermolysis and hydrolysis reactors, the quench cell and CuCl2 concentrator have the highest exergy losses with thermal energy transferred through CuCl solidification and water vaporization phase-change processes at relatively high temperature. Additional results of the processes are presented and discussed.

Two-step thermochemical cycling based on metal oxide is a promising means of harvesting solar energy, in which hydrogen could be obtained through water splitting via the reduction and oxidation reactions driven by concentrated solar heat. A new kind of solar thermochemical cycle-based direct coal liquefaction system for oil production is proposed and analyzed in this paper. The coal gasification part of the traditional coal liquefaction system for hydrogen generation is replaced by thermochemical cycling process. In addition, fuel coal consumption in the coal-fired boiler for the steam generation of the traditional direct coal liquefaction system could be reduced through the heat recovery of gas mixture or oxygen carrier of the thermochemical cycle. To reveal the characteristics of the new system, the reduction of pollutant emissions, energy efficiency and relative coal saving ratio are used as the key parameters. A large amount of SO2, NOx and CO2 in this coupling system could be reduced as the coal-fired boiler part for steam generation is replaced by the heat recovery from solar thermochemical cycling. The new proposed system is optimized with the reduction temperature and different gas or solid heat recovery rate allocation of the thermochemical cycles, in order to improve the energy efficiency and simplify the system device. Solar-to-hydrogen efficiency of the two-step thermochemical cycle part could be improved by proper heat recovery and extra pure oxygen will be obtained by the reduction reaction of the thermochemical cycling part. The theoretical energy efficiency of ∼47% and the relative coal saving ratio of ∼42.6% for the proposed system (the reduction and oxidation temperatures are 1500 °C and 821 °C with 70% solid heat recovery rate from oxygen carrier for water splitting) may indicate a meaningful route for oil production by direct coal liquefaction.

A thermochemical study of [SbCl3(L)] and [BiBr3(L)] complexes, wherein L is 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen), was performed by calorimetric measurements in solution. The complexes were synthesized and characterized by elemental analysis, FTIR spectroscopy and thermal analysis. From the enthalpies of dissolution of the complexes, salts and ligands in combination with auxiliary thermodynamic data, some thermochemical parameters of the complexes were determined by use of thermochemical cycles. Theoretical study on the complexes was performed using M06-2X/def2-TZVPP method. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Our findings suggest that both the reorganization energy of the acceptor metal trihalide MX3 (113–136 kJ · mol−1) and the rigidity of the phen govern the dissociation energy of the complexes. The theoretical results indicated that the chemical stabilities of the complexes decreases in order [BiBr3(phen)] > [SbCl3(phen)] > [BiBr3(bpy)] > [SbCl3(bpy)], agreeing with the experimental enthalpies of coordination in solid state.

The enthalpies of formation and isomerization energies of P4Sn molecular cages are not experimentally (or theoretically) well known. We obtain accurate enthalpies of formation and isomerization energies for P4Sn cages (n = 3, 4, 5, 6, and 10) by means of explicitly correlated high-level thermochemical procedures approximating the CCSD(T) and CCSDT(Q) energies at the complete basis set (CBS) limit. The atomization reactions have very significant contribution from post-CCSD(T) correlation effects and, due to the presence of many second-row atoms, the CCSD and (T) correlation energies converge exceedingly slowly with the size of the one-particle basis set. As a result, these cage structures are challenging targets for thermochemical procedures approximating the CCSD(T) energy (e.g., W1-F12 and G4). Our best enthalpies of formation at 298 K (∆fH°298) are obtained from thermochemical cycles in which the P4Sn cages are broken down into P2S2 and S2 fragments for which highly accurate ∆fH°298 values are available from W4 theory. For the smaller P4S3 and P4S4 cages, the reaction energies are calculated at the CCSDT(Q)/CBS level and for the larger P4S5, P4S6, and P4S10 cages, they are obtained at the CCSD(T)/CBS level. Our best ∆fH°298 values are − 94.5 (P4S3), − 108.4 (α-P4S4), − 98.7 (β-P4S4), − 126.2 (α-P4S5), − 126.1 (β-P4S5), − 112.7 (γ-P4S5), − 144.7 (α-P4S6), − 153.9 (β-P4S6), − 134.4 (γ-P4S6), − 136.3 (δ-P4S6), − 118.7 (e-P4S6), and − 215.4 (P4S10) kJ mol−1. Interestingly, we find a linear correlation (R2 = 0.992) between the enthalpies of formation of the most stable isomers of each molecular formula and the number of atoms in the P4Sn cages. We use our best ∆fH°298 values to assess the performance of a number of lower-cost composite ab initio methods. For absolute enthalpies of formation, G4(MP2) and G3(MP2)B3 result in the best overall performance with root-mean-square deviations (RMSDs) of 10.6 and 12.9 kJ mol−1, respectively, whereas G3, G3B3, and CBS-QB3 result in the worst performance with RMSDs of 27.0–38.8 kJ mol−1. In contrast to absolute enthalpies of formation, all of the considered composite procedures give a good-to-excellent performance for the isomerization energies with RMSDs below the 5 kJ mol−1 mark.

Thermochemical water splitting cycles (TWSCs) are processes with the potential for large-scale production of carbon-free hydrogen. Among these, the sulfur-family thermochemical cycles are considered the most promising due to both, the use of readily affordable chemical reagents and the temperature required to thermally decompose oxygenated sulfur compounds, which is achievable by solar means. Indeed, solar heat assisted metal sulfate decomposition is a key step, where catalysis can be employed to reduce decomposition temperature. Here we present a green route to synthesize Ag-Pd and Fe-Pd intermetallic alloy catalysts supported over γ-Al2O3 and Si-C by a microwave-assisted method using glycerol both as a solvent and as a reducing and stabilizing agent. The obtained supported catalysts were physicochemically characterized. Fe-Pd/Al2O3 catalyst exhibited the best performance, abating the zinc sulfate decomposition temperature by ca. 85 °C in comparison with other reported catalysts.

Solar thermochemical cycle is considered a promising strategy for hydrogen production. The reaction process and oxygen carrier (OC) are the key issues for solar hydrogen production. In this study, a solar-driven chemical-looping steam methane reforming (S-CL-SMR) process by using perovskite as the oxygen carrier is proposed. In this process, the heat required by the endothermic reduction is supplied by solar heat, and the heat is converted into the chemical energy of solar fuels. Perovskites La1−yCayNi0.9Cu0.1O3 were synthesized and characterized. Meanwhile, the reactivity was studied via thermogravimetry analysis at 400 °C for reduction, and 900 °C for re-oxidation. The results show that the reactivity of the La1−yCayNi0.9Cu0.1O3 is improved as the calcium substitution increases. In the reduction reactor, the fractional oxidation of La0.1Ca0.9Ni0.9Cu0.1O3 reaches to 0.61, and the methane conversion is about 52% with 60% CO selectivity. In the steam reactor, oxygen vacancies and reduced metal ions (Ni2+ and Cu2+) in doped perovskites can provide more active sites to break chemical bonds of H O. It is found that La0.1Ca0.9Ni0.9Cu0.1O3 has the best reactivity, regenerability and high resistance to carbon deposition among the synthesized perovskites. Our study is expected to provide a promising potential for hydrogen production by mid-temperature solar heat.

In this work, 2-[(4-nitro-benzoyl)-hydrazone]-propionic acid (C10H9O5N3), a Schiff base compound was synthesized and structurally characterized. The low-temperature heat capacities of C10H9O5N3 were measured with a small sample precision automated adiabatic calorimeter from 78 to 400 K. The curve of experimental heat capacity versus reduced temperature of C10H9O5N3 has been fitted with a polynomial equation by the least-squares method, the fitting result showes that the structure of C10H9O5N3 is stable in the whole temperature region. The smoothed heat capacities and thermodynamic functions of the title compound were calculated by the polynomial equations with an interval of 5 K. The constant-volume combustion energy for C10H9O5N3 was determined by an RBC-II precision rotating bomb combustion calorimeter. According to one designed thermochemical cycle, and combined with some other auxiliary thermodynamic data, the standard molar enthalpy of formation of the C10H9O5N3 was calculated, and ΔfHm° (C10H9O5N3, s) = -(667.31 ± 11.02) kJ·mol−1. In addition, optimized structure, frontier molecular orbitals, and molecular electrostatic potential of C10H9O5N3 were analyzed by using B3LYP calculation with 6-31G (d,p) basis set.

A novel trigeneration integrated system is proposed and analyzed in this paper. The present system utilizes gas turbine exhaust gas for heat recovery and capturing carbon dioxide after expanding in the turbine and generating electricity. Moreover, a Cu-Cl thermochemical cycle is incorporated in the system to produce hydrogen, and a multi-effect desalination is integrated to provide fresh water to the Cu-Cl cycle and for domestic use as well. The present integrated system is modeled and simulated using the Aspen Plus software package for chemical processes and Engineering Equation Solver for the remaining subsystems. Both energy and exergy analyses are performed to study and assess the proposed system through energy and exergy efficiencies. Therefore, the overall energy and exergy efficiencies of the proposed trigeneration system are found to be 39.72% and 55.2% respectively.

The potential of the silica membrane reactors for use in the decomposition of hydrogen iodide (HI) was investigated by simulation with the aim of producing CO2-free hydrogen via the thermochemical water-splitting iodine-sulfur process. Simulation model validation was done using the data derived from an experimental membrane reactor. The simulated results showed good agreement with the experimental findings. The important process parameters determining the performance of the membrane reactor used for HI decomposition, namely, reaction temperature, total pressures on both the feed side and the permeate side, and HI feed flow rate were investigated theoritically by means of a simulation. It was found that the conversion of HI decomposition can be improved by up to four times (80%) or greater than the equilibrium conversion (20%) at 400 °C by employing a membrane reactor equipped with a tubular silica membrane. The features to design the membrane reactor module for HI decomposition of the thermochemical iodine-sulfur process were discussed under a wide range of operation conditions by evaluating the relationship between HI conversion and number of membrane tubes.

Within the general framework of investigating novel routes for solar hydrogen production, the idea of combining a solar centrifugal particle receiver with sulphur thermochemical cycles, involving SO3 dissociation to SO2 and O2 as key step, is pursued. In this perspective, the present work concerns the synthesis, development, evaluation and characterisation of particles suitable to operate as media for direct solar irradiation absorption, transfer and storage as well as catalysts for the SO3 dissociation reaction. Commercial bauxite-based proppants were modified to incorporate raw materials with elements known for their catalytic activity with respect to the SO3 dissociation, namely iron, copper, manganese and their combinations. The catalytic activity of such modified proppants was tested in fixed bed reactor test rigs at 850 °C and ambient pressure with concentrated liquid sulphuric acid as feedstock. Extensive screening tests complemented by physicochemical properties measurements before and after catalytic testing, identified systems that at 850 °C, 1 atm and Gas Hourly Space Velocity of 11,800 h−1 could achieve high SO3 conversions (60%, corresponding to 68% of equilibrium value) for over 125 h of continuous operation. This performance was achieved without degradation of their mechanical strength which, in fact exhibited a slight increase from 53 N in the fresh state to 55 N after long-term exposure to reaction conditions. However such systems were susceptible to colour alteration, affecting adversely their absorptance in the 1000–2500 nm wavelength range. Compositions with the best combination of properties are scheduled for large-scale synthesis and on-site testing in a pilot-scale solar receiver.

Efforts to elucidate the governing factors in the cation radical Newman–Kwart rearrangement are described. Through a combination of spectroscopic and kinetic analyses, it has been shown that the reactive intermediate is a thione cation radical that has significant thiyl radical character. This intermediate undergoes similar chemistry, such as olefin stereomutation, that has been observed for thiyl radicals generated by other means. Moreover, kinetic studies demonstrate that the electronic dependence observed in the system is the result of rate-limiting intramolecular nucleophilic trapping of the thione cation radical. Importantly, the thiyl radical character of the reactive intermediate can be used to rationalize all reaction observations. This mechanistic model is in line with observed rate enhancement at higher dilutions that decreases the formation of an off-cycle intermediate. A thermochemical cycle was devised to predict which substrates will most easily undergo the cation-radical-mediated rearrangement.

The thermochemical Cu Cl cycle has received greater attention by numerous researchers during the past decade as a promising hydrogen production method because of some operational advantages. The present paper analyzes three different configurations of the Cu Cl thermochemical cycle, namely three, four and five step ones thermodynamically. Some comparative parametric studies are conducted in order to investigate the overall energy and exergy efficiencies of the cycles considered. The Aspen plus is the software tool employed for the modeling and simulation of the cycles. The energy and exergy efficiencies of the five-step CuCl cycle are found to be 38.8% and 70.2% while the three-step CuCl cycle has an energy efficiency of 39.6% and an exergy efficiency of 68.1%, respectively. On the other hand, the four-step CuCl cycle provides the highest energy and exergy efficiencies of 41.9% and 75.7%. A parametric study is also conducted to investigate the effect of varying ambient temperature on the exergy efficiencies of all three cycles. The present study results further reveal that the cycle performance can be enhanced by improving the thermal management and reducing the exergy destructions.

Two lanthanide-based metal–organic frameworks, [Tb2(5-nip)3(H2O)5·5H2O]n (1), and [Eu3(5-nip)4(5-Hnip)(H2O)7·9H2O]n (2) (5-H2nip = 5-nitroisophthalic acid), have been synthesized and structurally characterized. 1 features a unique 3D network with two distinct paddlewheel building blocks. 2 displays a 3D supramolecular framework with 1D channels occupied by free water molecules. Solid-state photoluminescence studies indicate that both the compounds 1 and 2 exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible region at room temperature. TG-DSC curves show that the dehydrated products of the title compounds exhibit high stability up to 400 °C. The enthalpy changes of liquid-phase reaction of formation for 1 and 2, Δ r H m θ (l), were determined at 298.15 K by a microcalorimeter to be (10.7 ± 0.1) kJ mol−1 and (30.6 ± 0.1) kJ mol−1, respectively. Based on a designed thermochemical cycle, that of solid-phase reaction of formation and the standard molar enthalpy of formation for 1, Δ r H m θ (s) and Δ f H m θ , were calculated to be (16.9 ± 0.6) kJ·mol−1 and -(3103.2 ± 15.3) kJ mol−1, respectively. Those for 2 were (119.4 ± 0.8) kJ mol−1 and -(4510.2 ± 17.4) kJ mol−1, respectively. Combining the thermochemical data of the reactions and kinetic equations with the data of thermokinetic experiments, the fundamental thermodynamic and kinetic parameters were also achieved.

The potential of copper oxide for both thermal energy storage and oxygen production in a liquid chemical looping thermal energy storage system has been assessed with thermogravimetric analysis. Liquid chemical looping thermal energy storage is a recently proposed system with potential to enable both the storage of thermal energy (through sensible heating, phase change and thermochemical reactions) and oxygen production. The process of isothermal reduction and oxidation of molten copper oxide was verified experimentally by heating the material isobarically, reducing or oxidising it isothermally, and then cooling it again isobarically. The isothermal reduction and oxidation reactions were achieved by varying the partial pressure of oxygen through the change in the concentrations of nitrogen and oxygen. This confirmed that copper oxide can be reduced in the liquid state by changing the partial pressure of oxygen in the system. Nevertheless, the extent of reduction in the assessed range of oxygen partial pressure in the liquid phase is approximately 2%, while this value in solid phase is approximately 10%, which implies that the thermochemical storage is mainly occurred in the solid phase. The reduction and oxidation cycles were repeated for 10 cycles. Superimposed on the cyclical weight change was an additional weight loss that was attribute to a side reaction between the copper oxide and alumina crucible.

Thermochemical cycles have been predominantly used for energy transformation from heat to stored chemical free energy in the form of hydrogen. The thermochemical cycle based on uranium (UTC), proposed by Oak Ridge National Laboratory, has been considered as a better alternative compared to other thermochemical cycles mainly due to its safety and high efficiency. UTC process includes three steps, in which only the first step is unique. Hydrogen production apparatus with hectogram reactants was designed in this study. The results showed that high yield hydrogen was obtained, which was determined by drainage method. The results also indicated that the chemical conversion rate of hydrogen production was in direct proportion to the mass of Na2CO3, while the solid product was Na2UO4, instead of Na2U2O7. Nevertheless the thermochemical cycle used for hydrogen generation can be closed, and chemical compounds used in these processes can also be recycled. So the cycle with Na2UO4 as its first reaction product has an advantage over the proposed UTC process, attributed to the fast reaction rate and high hydrogen yield in the first reaction step. Keywords: Thermochemical cycle, Hydrogen production, Uranium, Sodium urinate, Energy

A novel water-splitting thermochemical cycle for the production of green hydrogen is introduced. This three-step cycle is based on the thermal decomposition of sodium carbonate. In this work, thermodynamic equilibrium analysis of the cycle's constituent reactions is performed, for a variety of temperatures, pressures, and dilution ratios. Feasible temperature/pressure/dilution operating windows are identified for the cycle's reactions such that the maximum temperature of the cycle can be generated using current concentrated solar power (CSP) technologies, thus enabling the replacement of steam methane reforming (SMR) as the major industrial production method of hydrogen.

Encouraged by recent advances in solar-chemical fuel production, a moderately high-temperature solar thermochemical cycle based on GeO2/Ge is investigated thermodynamically. Since the GeO2/Ge redox has a great oxygen exchange capacity and suffers unfavorable phase change at high temperature, methanothermal reduction is introduced to lower the operation temperature below melting point of redox. The calculated results indicate that reduction conditions of 875 K ⩽ T red ⩽ 1200 K and CH4:GeO2 = 2:1 are conducive to achieving high selectivities of H2 and CO. As for the oxidation step, the H2O:Ge ratio of 8:1 is found abundant enough to ensure complete reoxidation of Ge. Isothermal and non-isothermal solar-to-fuel efficiency ( η solar - fuel ) are compared, where R oxi = 2 and R oxi = 8 are suggested to pursue highest non-isothermal η solar - fuel of 0.47 and isothermal η solar - fuel of 0.28 respectively. In addition, the preferred site of CH4 adsorbing on GeO2 is predicted, and the calculated adsorption energy is lower than that of SnO2, indicating that GeO2 could be a suitable material for substrate before methanothermal reduction.

The cyclability of Mn2O3/MnO thermochemical cycle for solar hydrogen production has been experimentally evaluated. The results of three consecutive cycles show a stable hydrogen production per mass of initial solid that is in agreement with the maximum expected amount according to the stoichiometry of the process. The characterization of the material recovered after each cycle shows a mixture of different manganese oxide phases that are completely converted into MnO in the subsequent thermal reduction, maintaining the productivity of the cycles. Based on that, a modification of the thermochemical cycle scheme is proposed taking into account the differences observed between the first cycle and the following ones. MnO2/MnO thermochemical cycle appears as a promising alternative, working in the same temperature range but with a theoretical hydrogen production per unit mass of solid manganese oxide almost twice than that obtained with the conventional Mn2O3/MnO cycle. Finally, the results of exergy efficiency of the complete cycle give new insights into the commercial possibilities of the cycle for hydrogen production, demonstrating the sustainable cyclability of the process regarding the manganese containing materials at lower temperatures than those theoretically reported in literature and consequently with higher exergy efficiencies that the common values associated to this cycle.