Thermochemistry of thermal plasma chemical reactions. Part I. General rules for the prediction of products

Equilibrium calculations based on the standard technique of minimization of the Gibbs free energy, with consideration of both gas and condensed phases, are shown to be inadequate for predicting the yield or even the proper composition of the products from thermal plasma reaction systems. This is due to the dominating influence of nucleation kinetics, a nonequilibrium effect.In this paper a modification of the equilibrium approach is proposed, whereby the supersaturation of a phase which may condense is calculated, and species with low supersaturation pressures which are unlikely to precipitate are subsequently removed from consideration.A comparison is made between the former equilibrium predictions and these quasi-equilibrium predictions. When compared with experimental data taken from the extant literature and from the authors' own research, the quasi-equilibrium modification is seen to provide excellent agreement with respect to product composition and yield. Examples are discussed including the thermal plasma production of hydrogen cyanide, ammonia, acetylene, silicon carbide, silicon nitride, and titanium carbide.     

Quasi-equilibria in reduced Liouville spaces

The quasi-equilibrium behaviour of isolated nuclear spin systems in full and reduced Liouville spaces is discussed. We focus in particular on the reduced Liouville spaces used in the low-order correlations in Liouville space (LCL) simulation method, a restricted-spin-space approach to efficiently modelling the dynamics of large networks of strongly coupled spins. General numerical methods for the calculation of quasi-equilibrium expectation values of observables in Liouville space are presented. In particular, we treat the cases of a time-independent Hamiltonian, a time-periodic Hamiltonian (with and without stroboscopic sampling) and powder averaging. These quasi-equilibrium calculation methods are applied to the example case of spin diffusion in solid-state nuclear magnetic resonance. We show that there are marked differences between the quasi-equilibrium behaviour of spin systems in the full and reduced spaces. These differences are particularly interesting in the time-periodic-Hamiltonian case, where simulations carried out in the reduced space demonstrate ergodic behaviour even for small spins systems (as few as five homonuclei). The implications of this ergodic property on the success of the LCL method in modelling the dynamics of spin diffusion in magic-angle spinning experiments of powders is discussed.     

Avoid the quasi-equilibrium assumption when evaluating the electrocatalytic oxygen evolution reaction mechanism by Tafel slope analysis

Tafel slope analysis is a powerful tool in comparing experimental data to a proposed reaction mechanism. Typically, in order to simplify the analysis, the non-rate-determining steps in the reaction mechanism are assumed to be in quasi-equilibrium. Here, Tafel analysis of the oxygen evolution reaction following the electrochemical oxide mechanism is performed using a full kinetic model. It is shown that this model (which uses the steady-state assumption) predicts a larger number of Tafel slopes than if the quasi-equilibrium assumption is used and provides and predicts the surface coverages which underpin these Tafel slopes. Importantly, this model predicts Tafel slopes of 30, 40, 60, and 120 mV, all of which are experimentally found on IrO₂ and RuO₂ anodes. Models using the quasi-equilibrium assumption fail to predict some Tafel regions, as these can occur when a non-rate-determining step is not at quasi-equilibrium.     

Development of a Unifying Framework for Modeling Multi-component Diffusion in Polymer Solutions

In this work a unifying framework for modeling multi-component diffusion in mixed solvent polymer solutions is developed by introducing additional restrictions such as the Onsager reciprocal relations (ORR) and the quasi-equilibrium postulate. More specifically, three different multi-component diffusion models, namely the Zielinski and Hanley model, the Dabral et al. theory and the Alsoy–Duda model are revised by using the above restrictions which are based on sound principles of non-equilibrium thermodynamics. Realistic simulations for the solvent(s) evaporation from the water/acetone/cellulose acetate (CA) and formamide/acetone/CA systems were obtained by combining the above multi-component diffusion models with the ORR and the quasi-equilibrium postulate. It is believed that the results of this work could be used to further study diffusion in multi-component systems appearing in coating and membrane formation.     

Microkinetic Modeling of Ethane Hydrogenolysis on Metals

The microkinetic analysis of ethane hydrogenolysis in the framework of the Sinfelt-Taylor mechanism is carried out using UBI-QEP data on the energetics of elementary steps. On single-crystalline surfaces of Pd(111), Pt(111), and Ni(111), the reaction predominantly occurs via ethyl formation in which the C-C bond is cleaved. The surface concentration of ethylidyne is very low, and ethyl has the highest concentration among all hydrocarbon fragments. For the conditions studied in this work, the activity in ethane hydrogenolysis increases in the series Pd(111) < Pt(111) < Ni(111). According to the results of kinetic modeling, the reaction occurs via quasi-equilibrium steps of adsorption and dissociation of hydrogen and ethane and further, practically irreversible formation of methane.     

Reaction of aluminum clusters with water

The atomistic mechanism of rapid hydrogen production from water by an aluminum cluster is investigated by ab initio molecular dynamics simulations on a parallel computer. A low activation-barrier mechanism of hydrogen production is found, in which a pair of Lewis acid and base sites on the cluster surface plays a crucial role. Hydrogen production is assisted by rapid proton transport in water via a chain of hydrogen-bond switching events similar to the Grotthuss mechanism, where hydroxide ions are converted to water molecules at the Lewis-acid sites and hydrogen atoms are supplied at the Lewis-base sites. The activation free energy is estimated along various reaction paths associated with hydrogen production, and the corresponding reaction rates are discussed based on the transition state theory.     

INFLUENCE OF RUTHENIUM, RHODIUM AND VANADIUM IONS ON PHOTOPRODUCTION OF HYDROGEN BY Chlorella fusca

Abstract Ru³⁺ and Rh³⁺ supplied at a concentration of 1 x 10⁻⁵ mol/l in the nutrient medium are incorporated preferably by the chloroplasts of Chlorella fusca cells as shown by electron micrographs without using any contrasting agent. Both elements cause a significant increase of production rate as well as of total hydrogen production. In experiments with synchronized C. fusca the maturing cells yielded maximal hydrogen production. Inhibition of hydrogen photoproduction by DCMU indicates that both photosystems are involved. Ru(bipy)3²⁺, an essential component of photocatalysts, also is incorporated to a great extent and preferably bound to the thylakoid membranes of the chloroplasts but shows a negative influence on hydrogen production. V³⁺ is incorporated only to a small extent without any enrichment to the chloroplasts and shows no effect on hydrogen production.     

Computational prediction of kink properties of helices in membrane proteins

We have combined molecular dynamics simulations and fold identification procedures to investigate the structure of 696 kinked and 120 unkinked transmembrane (TM) helices in the PDBTM database. Our main aim of this study is to understand the formation of helical kinks by simulating their quasi-equilibrium heating processes, which might be relevant to the prediction of their structural features. The simulated structural features of these TM helices, including the position and the angle of helical kinks, were analyzed and compared with statistical data from PDBTM. From quasi-equilibrium heating processes of TM helices with four very different relaxation time constants, we found that these processes gave comparable predictions of the structural features of TM helices. Overall, 95 % of our best kink position predictions have an error of no more than two residues and 75 % of our best angle predictions have an error of less than 15°. Various structure assessments have been carried out to assess our predicted models of TM helices in PDBTM. Our results show that, in 696 predicted kinked helices, 70 % have a RMSD less than 2 Å, 71 % have a TM-score greater than 0.5, 69 % have a MaxSub score greater than 0.8, 60 % have a GDT-TS score greater than 85, and 58 % have a GDT-HA score greater than 70. For unkinked helices, our predicted models are also highly consistent with their crystal structure. These results provide strong supports for our assumption that kink formation of TM helices in quasi-equilibrium heating processes is relevant to predicting the structure of TM helices.     

The use of plasmas in catalysis: catalyst preparation and hydrogen production

Plasma technologies are introduced in the field of hydrogen production related to fuel cells. Two ways are described: Plasma synthesis of catalysts and membranes for the production and purification of hydrogen and, direct production of hydrogen based on atmospheric plasma-assisted methane steam reforming.     

Broadening of relaxation and retardation spectra due to uniaxial orientational drawing of polyamide films

The initial and quasi-equilibrium values of relaxation modulus, the mean statistic retardation and relaxation times, and the parameters of retardation and relaxation time distributions have been estimated from the corresponding creep, elastic relaxation, and stress relaxation curves. Changes in the above characteristics with an increase in the draw ratio are analyzed.     

Electric Double Layer at the Membrane/Solution Interface in a Three-Layered Membrane System

Transport of ions through a three-layered membrane system at overlimiting currents is simulated mathematically. To allow for the space charge, the Poisson equation is used in both the first diffusion layer and the membrane. Two modes are shown to exist at overlimiting currents: a quasi-equilibrium state of the interface and a Schottky mode.     

亚心形四爿藻培养和产氢过程一体化平板光生物反应系统

利用整合了燃料电池的平板光生物反应器, 探讨了将亚心型四爿藻高密度培养和产氢两段工艺一体化集成的可行性. 在培养阶段通入体积分数为2%~5%的CO2可使藻细胞迅速增殖, 9 d内即可达到产氢要求的生物量(8.5×106 cell/mL). 通过叶绿素荧光参数分析, 选择2%的CO2培养的藻进行后续的产氢实验. 结果表明, PSⅡ活性和光合电子传递速率均随时间的推移而逐渐下降. 通过对产氢动力学曲线的分析, 计算出最大产氢速率为1.1 mL/(h·L), 持续产氢时间为60 h.     

Revisiting the Limiting Factors for Overall Water‐Splitting on Organic Photocatalysts

In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co‐catalyst (e.g. Pt). For pursuing a carbon neutral and cost‐effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench‐top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half‐reaction, and have so far shown limited success in hydrogen production from overall water‐splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water‐splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar‐to‐hydrogen) conversion efficiency.     

Stretching single molecules along unbinding and unfolding pathways with the scanning force microscope

Individual molecules can be stretched with a scanning force microscope and the forces required to rupture bonds and to mechanically drive their structures towards new conformations and states can be measured. The tailoring of the experiments, the possibility of carrying them out in quasi-equilibrium conditions, the relationships between single molecule force measurements, and macroscopic kinetics or thermodynamic data are discussed. Mechanochemical experiments are expanding chemistry into new realms between biology and material science.     

碱性电解水高效制氢

与传统化石能源制氢技术相比,利用可再生能源驱动电解水制氢技术具有绿色可持续和制氢效率高等优势,被认为是目前最具前景的制氢方式。然而, 由于电解水两极反应动力学缓慢、 催化剂稳定性较差, 限制了其大规模发展。此外, 阳极析氧反应存在较高的过电势, 从而导致当前制氢能耗与成本较高, 严重制约了其商业化应用。 为了解决上述问题与挑战,本文对当前发展较为成熟的碱性电解水技术进行了综合讨论与分析。 首先, 对电解水发展历程中的重要节点进行了总结, 便于读者了解该领域。进一步, 从电催化剂、 电极、 反应和系统的角度深入总结了提升电解水制氢性能的有效策略。作者分别介绍了近年来层状双金属氢氧化物基电解水催化剂、电解水制氢耦合氧化反应以及可再生能源驱动的电解水系统的重要研究进展; 同时对结构化催化剂在电解水应用中的构效关系进行了深入分析。最后, 对该领域存在的挑战和未来发展方向进行了展望,希望能为氢能的发展和推广提供一定的思路。     

Revisiting the Limiting Factors for Overall Water-Splitting on Organic Photocatalysts

In pursuit of inexpensive and earth abundant photocatalysts for solar hydrogen production from water, conjugated polymers have shown potential to be a viable alternative to widely used inorganic counterparts. The photocatalytic performance of polymeric photocatalysts, however, is very poor in comparison to that of inorganic photocatalysts. Most of the organic photocatalysts are active in hydrogen production only when a sacrificial electron donor (SED) is added into the solution, and their high performances often rely on presence of noble metal co-catalyst (e.g. Pt). For pursuing a carbon neutral and cost-effective green hydrogen production, unassisted hydrogen production solely from water is one of the critical requirements to translate a mere bench-top research interest into the real world applications. Although this is a generic problem for both inorganic and organic types of photocatalysts, organic photocatalysts are mostly investigated in the half-reaction, and have so far shown limited success in hydrogen production from overall water-splitting. To make progress, this article exclusively discusses critical factors that are limiting the overall water-splitting in organic photocatalysts. Additionally, we also have extended the discussion to issues related to stability, accurate reporting of the hydrogen production as well as challenges to be resolved to reach 10 % STH (solar-to-hydrogen) conversion efficiency.     

含Co或Ni的双金属及三金属纳米颗粒制备方法及其催化制氢性能

常见的氢气储存方法有液态储氢、高压气态储氢、有机化合物储氢、金属氢化物储氢、吸附储氢及液相化学储氢材料储氢等,其中液相化学储氢材料由于具有含氢量高、且可按时即需释放氢气的优点,引起了研究人员的广泛关注;选择合适的催化剂催化液相储氢材料制氢已成为一个研究热点。含有Co或Ni的双金属或三金属纳米颗粒是一种极具应用前景的催化剂,具有价格低廉、储量丰富和催化性能优异等众多优点。本文综述了含Co或Ni的双金属或三金属纳米颗粒的制备方法及其催化制氢性能,并提出了其目前研究中存在的问题和未来潜在的发展方向。     

L'hydrogene pour le transport sur route : réalisations et développements

Hydrogen for road transportation : achievements and developments. At the beginning of this millenium, hydrogen appears as a potential energy carrier for the future. Thus, it could serve as a storage medium for renewable energy forms, which should play an increasing part in the world energy supply. In a closer future, hydrogen could also become a fuel for prospective fuel-cell and internal-combustion vehicles. We present here an inventory of the various technologies related to the use of hydrogen in road transportation : propulsion type (fuel cell and electric motor, or internal combustion engine), hydrogen production, on-board storage, infrastructure. Safety, standardization and regulation aspects will also be addressed. Presently, the majority of hydrogen buses are equipped with polymer membrane fuel cells (PEMFC), directly supplied with hydrogen from pressurized vessels (300 bars). On the other hand, car manufacturers are developing various types of experimental vehicles : internal-combustion engine cars with liquid hydrogen storage, fuel cell (PEMFC) cars with storage of hydrogen (liquid, gaseous, hydride) or of methanol. The type of required infrastructured will depend on the type of fuel chosen by the car makers and on the requirements of the oil companies. Several hydrogen supply stations, of different technologies, have already been set up. They deliver gaseous or liquid hydrogen produced by reforming of natural gas or by electrolysis. The building of a hydrogen-based fueling system requires the development of specific means of production, transportation, storage and delivery. Public acceptance will have to be won by guaranteeing safety, reliability, performance and competitivity. Presently, research and development work is mainly carried out on : on-board storage of hydrogen ; on-board systems for the production of hydrogen from methanol and petrol ; standardization and regulation.