Initial Stage Of Reaction Research Articles

Physicochemical analysis of infiltrated cathode symmetric cells for intermediate temperature SOFCs

This study investigated the cathode parameter changes before and after infiltration based on Jamnik and Maier's MIEC transmission line model. To consider additional factors such as surface adsorption capacitance, chemical capacitance Cchem, and general capacitance effect CHN were introduced in parallel. To obtain the appropriate temperature dependence, oxygen partial pressure dependence, and current density dependence trends of transmission line parameters, the trend of Cchem was fixed according to each measurement condition using the thermodynamic parameters of previous papers. Infiltrating Sm0.5Sr0.5CoO3-δ (SSC), a better catalyst material, into the widely used La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) perovskite electrode resulted in a decrease in surface reaction resistance Rp by about 1 order of magnitude and a decrease in oxygen ion diffusion resistance Rs. The oxygen ion adsorption capacitance CHN0 on the surface is larger after infiltration due to the larger surface area of the infiltrated electrode, which can be explained by the two arcs clearly separated in the impedance spectra of the infiltrated cell. Additionally, after infiltration, the diffusion characteristics depending on oxygen partial pressure changed relatively from bulk diffusion to surface diffusion. The value of Rs is larger than Rp under almost all conditions, indicating that the overall rate-determining step (rds) is the diffusion reaction in the current direction. Furthermore, to observe the changes in surface reaction characteristics only, the characteristics of Rp before and after infiltration were analyzed based on the Butler-Volmer-type equation and oxygen partial pressure dependence of the exchange current density of surface reactions. As a result, the rds of surface reactions changed from the reduction reaction of the intermediate stage of electrode reactions after infiltration to the dissociative adsorption reaction of the initial reaction stage.

Thermal Characteristics Analysis of Conveyor Belt During Ignition

ABSTRACT Conveyor belt fires are the most serious fires that occur exogenous mine fires. To study the thermal characteristics of the PVC conveyor belt during the fire process, the softening characteristics of the conveyor belt underground in the mine were simulated by using the temperature rise oxidation system. Based on the C600 microcalorimeter, the oxidation heat release law of the PVC conveyor belt and pulverized coal with different softening temperatures was studied at an environmental range of 40–500°C, and the combustion law, heat release and heat absorption, HRR,combustion stages and activation energy were analyzed. The results show that with increasing softening temperature, the law of heat absorption and heat release of the PVC conveyor belt in the initial stage of the independent reaction is opposite, while the heat absorption and heat release in the coupling with pulverized coal increase gradually, and 106% and 107% more heat is released in the rapid development state than in the independent reaction state. The change rule of the heat release acceleration of the PVC conveyor belt remains basically the same whether it is alone or coupled with pulverized coal. The maximum difference in heat release acceleration increases with increasing softening temperature. According to the division of the combustion stages of the conveyor belt according to the heat flow value, when the PVC conveyor belt reacts alone, the temperature range of the heated softening zone is approximately 140°C smaller than when it is coupled with pulverized coal, and the temperature range of the melting pyrolysis zone is expanded by 100°C.It shows that when the conveyor belt is coupled with pulverized coal, fire is more likely to occur and the fire risk is greater. The average HRR at the softening temperature of 100°C is the largest, the ignition time is the shortest, and the danger is the greatest. The activation energy decreases with increasing softening temperature when it is coupled with pulverized coal, indicating that the higher the softening temperature is, the more likely an oxidation reaction will occur. The heat release characteristics and combustion stages division of the conveyor belt proposed in this paper have certain guiding significance for the replacement and maintenance of mine conveyor belts and the prevention and control of mine fires.

Direct observation of radiation-induced graft polymerization on a polyethylene film

Radiation-induced graft polymerization is widely used in the synthesis of polymeric materials with various functionalities; however, the details of the reaction mechanism are still unresolved. Herein, the initial stage of the graft polymerization reaction was investigated through atomic force microscopy (AFM). We used glycidyl methacrylate (GMA) in methanol (monomer solution) and a high-density polyethylene (HDPE) film with a well-ordered lamellar structure as the substrate. Using polymer film surfaces with a maximum grafting degree of 0.5%, AFM can distinguish between crystalline and amorphous polyethylene (PE) phases as well as a grafted polymer GMA (PGMA) phase. The graft polymerization reaction started from the interface between the crystalline and amorphous PE phases. As the reaction proceeded, the PGMA covered the crystalline PE phase: i.e., the entire surface of the PE film were covered by the PGMA. Further, the crystalline lamellae of the PE film eventually became a scaffold for the formation of aggregates comprising grafted polymer chains alone. The graft polymerization reaction mechanism was explained by comparing the solubility parameters of the monomer solution, substrate, and grafted polymer chains. Understanding the reaction mechanism at a low grafting degree obtained in this study may contribute to enhancing the efficiency of the graft polymerization reaction on any polymeric material.

The response of nitrifying activated sludge to chlorophenols: Insights from metabolism and redox homeostasis

The specialized wastewater treatment plants for the chemical industry are rapidly developed in China and many other countries. But there is a common bottleneck in that the toxic pollutants in chemical wastewater often cause shock impacts on biological nitrogen removal systems, which directly affects the stability and cost of operation. As the research on nitrification inhibition characteristics is not sufficient till now, there is a great lack of theoretical guidance on the control of the inhibition. This study investigated the response of nitrifying activated sludge to chlorophenols (CPs) inhibition in terms of metabolism disorder and oxidative stress. At the initial stage of reaction (i.e., 1 h), reactive oxygen species (ROS)-induced membrane damage which might account for declining nitrification performance. Simultaneously excessive extracellular polymeric substances (EPS) were secreted to alleviate oxidative stress injury and protected microorganisms to some extent. In particular tyrosine-like substances in LB-EPS with a Fmax increase of 242.30% were confirmed to efficiently resist phenols inhibition. Thus, as the inhibition proceeded, metabolism disorder replaced oxidative stress as the main cause of nitrification inhibition. The affected metabolic processes include weakened enzyme catalysis, restricted electron transport and lessened energy generation. At 4 h, nitrifying production of sludge amended with 5 mg/L chlorophenols was 89.27 ± 9.51%–98.15 ± 9.60% lower than blank, the inhibition could be attributed to comprehensively affected metabolism. The structural equation modeling indicated that phenols restricted nitrification enzymes and bacterial electron transport efficiency which was critical to nitrification performance. Moreover, the lessened energy generation weakens enzyme activity to further suppress nitrification. These findings enriched our knowledge of nitrifiers’ responses to CPs inhibition and provided the basis for addressing nitrification inhibition.

Kinetics mechanism on the efficiency of C substituting B in the MgB2 tape fabrication

Effective carbon doping is essential for MgB2 superconductors due to its enhancement on in-field critical current density. However, C-doped MgB2 samples prepared with different boron powders exhibit varying levels of C substitution efficiency, which directly affect the superconducting properties. In this article, to further investigate the factors influencing C substitution efficiency, a two-stage carbon doping process was established based on the in-situ X-ray diffraction (XRD) measurement. The process begins with the initial in-situ ternary reaction of Mg, B and C, followed by the subsequent diffusion of C into the MgB2 lattice. Through the analysis of thermodynamic equations, it can be inferred that the key factor in improving the C substitution efficiency for MgB2 is to align the activity of the B and C precursor powders, which enables a greater participation of carbon in the initial stage of the ternary reaction. According to the systematic study on nano-C doped MgB2 tapes, the C substitution efficiency in MgB2 tapes prepared using nano amorphous boron powder is notably lower compared to those prepared using micron crystalline boron powder. These findings suggest that high-activity amorphous B powder necessitates a C dopant with a lower activation energy to enhance its C substitution efficiency.

Physical-chemical coupling excitation of low activity coal gasification slag solid waste and its application as a backfill cementitious material

To realize the green mining and clean utilization of coal resources, environmental issues such as coal mine subsidence and coal gasification slag (CGS) solid waste storage require urgent resolution. High residual carbon and low activity serve as bottlenecks for CGS to achieve safe, efficient and resourceful consumption. Therefore, in this study, we proposed the concept of graded utilization of CGS and conducted a study on physical–chemical coupling to stimulate the hydration activity of CGS. We prepared a modified coal gasification slag-based cement paste backfill material (MCGS-CPB) to meet the technical requirements of coal mine backfilling. Through various experimental tests and microscopic characterization methods (uniaxial compressive strength, hydration heat and microscopic tests, etc.), we elucidated the modification mechanism of CGS, and the synergistic reaction law of MCGS-CPB was clarified. The following results were obtained. (1) The best excitation approach for CGS hydration activity was salt modification, and the early strength of MCGS-CPB prepared with CGS excited by sodium sulfate (SS) developed rapidly, while the later strengths showed expansion and deterioration. The strength development of MCGS-CPB prepared by CGS activated with calcium chloride (CC) was relatively stable, and the excitation effect was ideal. (2) The salt modification of CGS had a significant effect on the early hydration process of MCGS-CPB. The durations of the initial dissolution, acceleration, deceleration and slow reaction stages were prolonged, and the duration of the induction stage was shortened, while the hydration heat release rate increased. (3) The salt modification of CGS had a significant effect on the microstructure of MCGS-CPB, primarily due to the difference in excitation effect of salt modification on CGS on pozzolanic activity. This study provided theoretical guidance for the safe, efficient and resourceful utilization of CGS.

Analysis of the initial reaction mechanism of TKX-50 based on Raman intensity.

Dihydroxylammonium 5,5'-biotetrazolium-1,1'-diolate (TKX-50) has two important properties of typical azole energy-containing ionic salts, including high energy and safety. Therefore, in today's era where more emphasis is placed on explosive performance and explosive detonation control conditions, TKX-50 is a very important object of research, and its reaction process in the initial stage of detonation is gradually receiving more and more attention from researchers in the field of energy-containing materials research. In this paper, based on first-principles density-functional theory (DFT), the mechanism of chemical bond breakage of TKX-50 under pressure was determined based on the analysis of the strength and stability of chemical bonds inside the TKX-50 molecules using Raman spectroscopy relative intensity analysis. The results show that TKX-50 is dominated by N-H bond breaking and followed by H-O bond breaking in the initial reaction stage. These reactions lead to the reorganization and structural changes within the molecule, which eventually lead to the decomposition of TKX-50.

Development and field application of a modified magnesium slag-based mine filling cementitious material

How to make high value use of solid waste is a key issue in achieving sustainable development. In this study, a modified magnesium slag-based cementitious material (M·C) for mine filling was developed using industrial solid waste modified magnesium slag (MMS), fly ash (FA), and desulfurization gypsum (DG); the mechanical properties, stability, hydration heat and synergistic reaction mechanism of M·C were investigated; and the M·C with optimized ratios was used to prepare cemented aeolian sand/coal gangue backfill material for industrial mine backfill tests. The results revealed that (1) the uniaxial compressive strength (UCS) of M·C at 28 d was 5.60–19.30 MPa, and the FA and DG contributed significantly to the development of the UCS of M·C. A combination of 65–90% MMS, 2.5–7.5% DG and 5–35% FA was determined to be optimum for the preparation of M·C. (2) The expansion rate (Ex) of M·C increased rapidly in the early stage, increased slowly after 28 d, and stabilized after 90 d. E28 of M·C was 0.107%–0.188%, which satisfied the requirement of Ex ≤ 0.6% in GB/T 2938. (3) The hydrated exothermic process of M·C was divided into initial dissolution, induction, acceleration, deceleration and slow reaction stages. DG can effectively promote the early hydration process of M·C, while the contribution of FA is not noticeable, and even reduces the hydration heat of M·C. (4) The hydration of MMS generates C-S-H gels and CH to increase the strength and form an alkaline environment. DG promotes the dissolution and polymerization of MMS and FA into C-S(A)-H gels and ettringite, a process that consumes Ca2+ and OH− and promotes the hydration of MMS. (5) The UCS of the 28 d downhole cores from the Changxing and Mahuangliang coal mines were 7.73 and 12.62 MPa, respectively, and the leaching indexes met the requirements stated in GB/T 14848 (Ⅲ), both of which reach the requisites for safe underground backfill. The results of this study demonstrate the feasibility and advancements of the new all-solid waste M·C replacement cement and its backfill application, and also standardizes the production and filling application route of M·C and accelerates the industrialization process of this technology.

Pt/CeO2 as Catalyst for Nonoxidative Coupling of Methane: Oxidative Regeneration.

Direct nonoxidative coupling is a promising route for methane upgrading, yet its commercialization is hindered by the lack of efficient catalysts. Pt/CeO2 catalysts with isolated Pt species have attracted an increasing amount of interest in recent years. Herein, we studied the catalytic role and evolution of isolated Pt centers on CeO2 prepared by flame spray pyrolysis under the harsh reaction conditions of nonoxidative methane coupling. During the reaction at 800 °C, the isolated Pt sites sinter, leading to a loss of the ethylene and ethane yield. The agglomerated Pt can be redispersed by using an in situ regeneration strategy in oxygen. We found that isolated Pt centers are able to activate methane only at the initial reaction stage, and the CePt5 alloy acts as the active phase in the prolonged reaction.

Mechanism study on the auto-ignition and reaction kinetic characteristics of hydrogen/n-dodecane mixture under mid and high temperature conditions

To acquire the ignition promotion methods for scramjet engine, the auto-ignition and reaction kinetic characteristics of hydrogen/n-dodecane mixture under mid and high temperatures were revealed by detailed chemical kinetic mechanism and experimental data. The results illuminated that the increases of n-dodecane's content and ϕ significantly declined the ignition delay time (IDT) of hydrogen mixture (by two orders of magnitude at most) at mid-temperature high-pressure (T = 950 K&p = 40 bar). The addition of n-dodecane induced the OH radical formation in initial stage and the advance of fuel's H-abstraction reactions (hydrogen: R3, n-dodecane: R2741/R2742/R2743/R2746). Whereas, the corresponding reduction in hydrogen content inhibited the establishment of active radical pool in dual-fuel reaction system before ignition time point. The ignition promoting effect of advanced initial reaction stage overweighted the ignition inhibiting effect of weakened rapid reaction stage in mid-temperature low-reactivity dual-fuel reaction system. Interestingly, at high-temperature high-pressure (T = 1300 K&p = 40 bar), the IDT firstly decreased (by 18.8%), and then continuously increased (by 105.3% at most) with the elevating n-dodecane's content. The minor addition of n-dodecane (1% of mole fraction) at high-temperature had a similar ignition promoting effect as that at mid-temperature. Whereas, the further reduction in hydrogen content dramatically suppressed the formation of active radical pool (H/OH/HO2/H2O2), which overweighted the ignition promoting effect of slightly advanced initial reaction stage. In other words, the hydrogen played a more critical role than the n-dodecane in high-temperature reaction system due to the originally high reactivity of hydrogen. The auto-ignition properties of hydrogen/n-dodecane mixture relied on the competition relationship of initial and rapid reaction stages under specific thermodynamic conditions and blending ratios. This investigation not only reveals internal interaction mechanism between fuels and active radicals in hydrogen/n-dodecane reaction system, but also provides fundamental insights for the precisely ignition promition methods of hydrogen/aviation-kerosene dual-fuel scramjet engine.

Identification and yield of metabolites of chlorinated paraffins incubated with chicken liver microsomes: Assessment of their potential to convert into metabolites

Chlorinated paraffins (CPs) are emerging environmental pollutants. Although metabolism has been shown to affect the differential accumulation of short-chain (SCCPs), medium-chain (MCCPs) and long-chain (LCCPs) CPs in birds, CP metabolites have rarely been reported and the extent to which they are formed is still unclear. In this study, single and mixed CP standards were incubated with chicken liver microsomes in vitro to study the generation of CP metabolites. Putative aldehyde/ketone and carboxylic acid metabolites identified by mass spectroscopy data were shown to be false positive results. Phase I metabolism of CPs first formed monohydroxylated ([M-Cl+OH]) and then dihydroxylated ([M-2Cl+2OH]) products. The yields of monohydroxylated metabolites of CPs decreased with increasing carbon chain length and chlorine content at the initial stage of reaction. Notably, the yield of monohydroxylated metabolites of SCCPs with 51.5% Cl content reached 21%, and that of 1,2,5,6,9,10-hexachlorodecane (C10H16Cl6) was as high as 71%. Thus, monohydroxy metabolites of CPs in birds should not be ignored, especially those of SCCPs. This study provides important data that could support improvements to the ecological/health risk assessment of CPs.

Photocatalytic Overall Water Splitting Reaction Feature on Photodeposited NixP/γ-Ga2O3Nanosheets

Solar light-driven overall water splitting for hydrogen production is an ideal solution to climate warming and energy shortage issues. Obtaining a highly efficient and stable photocatalyst remains a major challenge at present. Herein, NixP/γ-Ga2O3 nanosheets, which were synthesized from NiCl2, NaH2PO2, and home-made γ-Ga2O3 nanosheets by the photodeposition method under 254 UV irradiation for 30 min, are found as a highly active and durable photocatalyst for pure water splitting into H2 and O2 without a sacrificial reagent. The H2 production rate is as high as 5.5 mmol·g–1·h–1 under 125 W high-pressure mercury lamp irradiation, which is 3.4 and 2.5 times higher than that on the pristine γ-Ga2O3 nanosheets and Pt/γ-Ga2O3 nanosheets, respectively, and is 2.0 times higher than that on the 0.5 wt % Ni2P/γ-Ga2O3 reported previously. However, the O2 evolution rate is much less than the H2 evolution rate in the initial reaction stage. On prolonging the irradiation time, H2 evolution declines, while O2 evolution increases until it reaches its stoichiometric value corresponding to H2. The reason for the photocatalytic behavior of NixP/γ-Ga2O3 is studied and the corresponding mechanism is suggested. The absent or low oxygen evolution in the initial reaction stage is because the dioxygen generated from water oxidation by the photogenerated holes is wholly or partially captured by the surface oxygen vacancies to form the surface peroxide bonds (−O–O−). Once the oxygen vacancies are eliminated by the photogenerated O2, the overall water splitting reaction would reach the steady state. Thereafter, H2 production decreases from 5.5 to 2.0 mmol·g–1·h–1, but the O2 evolution gradually approaches the corresponding stoichiometric value, especially for the photocatalyst treated with H2O2 for 24 h.

Mechanistic Insights into the Formation of CO and C2 Products in Electrochemical CO2 Reduction─The Role of Sequential Charge Transfer and Chemical Reactions

The electrochemical reduction of CO2 presents an attractive opportunity to not only valorize CO2 as a feedstock for chemical products but also to provide a means to effectively store renewable electricity in the form of chemical bonds. The recent surge of experimental and computational studies of electrochemical CO2 reduction (ECR) has brought about significant scientific and technological advances. Yet, considerable gaps in our understanding of and control over the reaction mechanism persist, in particular for the formation of products. Moreover, while theoretical and computational studies have proposed many candidate reaction pathways, comprehensively reconciling these models with experimental observations remains challenging and elusive. The conventional electrochemical analysis of catalyst activity and selectivity generally relies on steady-state measurements. In a departure from this convention, we show in this study that time-resolved measurements (i.e., chronoamperometry) provide a powerful diagnostic tool to gain valuable insights into the complex interplay of electrochemical reactions, chemical reactions, and mass transport. We show that the initial stages of the ECR reaction show signatures of an electrochemical reaction followed by a homogeneous chemical reaction. These signatures have important mechanistic implications and inform dominant reaction pathways, specifically for the sequential electron and proton transfer steps leading to the formation of formate intermediates (*COOH–). We hope that the methods and insights presented in this work will inspire future studies to exploit chronoamperometric analysis to resolve outstanding questions in ECR and other multi-step electrochemical reaction pathways.

Theoretical study of the influence of H-SAPO-34 modified with Zn2+ on the formation of butadiene

In the process of methanol to olefin (MTO), dienes are the precursors of aromatic species. Experimental study showed that Zn2+ modified H-SAPO-34 (Zn@H-SAPO-34) promoted aromatics formation at the initial stage of MTO reaction. Our recent work reported the reaction mechanism of the aromatization of dienes to low methylbenzene aromatics catalyzed by Zn@H-SAPO-34. Herein, using density functional theory (DFT), the possible reaction pathways of diene formation on H-SAPO-34 with and without Zn doping were systematically investigated with propene as the initial olefin. After Zn2+ modification, the acidic strength of adjacent Brønsted acid sites (BAS) is enhanced, which is conductive to the alkene-mediated butadiene formation pathway catalyzed by B-acid, and the Lewis acid produced by Zn2+ provides catalytic site for the transfer dehydrogenation reaction of methanol with propene, which promotes the formation of formaldehyde and induces the formaldehyde-mediated mechanistic pathway. Further microkinetic calculation reveals that formaldehyde-mediated pathway is the optimal reaction pathway for butadiene formation. This study demonstrates that the synergistic effect of BAS and LAS improves the formation activity of diene on Zn@H-SAPO-34. This work will help to deepen the understanding of the role of Zn2+ in the early stage of MTO reaction.

Acid pressure oxidation leaching of arsenopyrite in the presence of pyrite: Oxygen consumption kinetics

In the process of extraction of gold from refractory sulphide ores, arsenopyrite and pyrite represent two of the major hosts for gold in solid solution. In this study, the pressure oxidation of arsenopyrite and arsenopyrite-pyrite mixtures in a H2SO4–O2 system have been investigated, with the aim of using the oxygen consumption kinetics to probe the oxidation mechanisms. The effects of temperature (180–220 °C), acidity (pH 0.5–2.5), dissolved iron concentration (10 and 30 g/L) and molar ratios (0:1–3:1) of pyrite-to-arsenopyrite (Py/Aspy) were evaluated. Kinetic analysis of arsenopyrite dissolution at 180–220 °C via a shrinking core model indicated an activation energy (Ea) of 48.46 kJ/mol, suggesting a mixed interface reaction and diffusion control. The order of the reaction to acidity was 0.16 at 200 °C, suggesting that [H+] is likely not the rate-limiting factor under typical reaction conditions. The addition of Fe(II) ions to the feed enhanced arsenopyrite oxidation, due to the formation of Fe(III) as a surrogate oxidant to drive the reaction.The Ea for Py/Aspy of 1:1 exhibited two behaviours, calculated to be 77.32 kJ/mol below 200 °C and decreasing to 34.59 kJ/mol above 200 °C. The former was attributed to surface control due to the oxidation of elemental sulphur, followed by a switch to mixed control at elevated temperatures. As Py/Aspy was increased to 2:1 and 3:1, a single behaviour was observed, with Ea values of 56.01 kJ/mol and 43.35 kJ/mol respectively. These values imply a mixed control and begin to approximate literature values for pyrite oxidation. A time-to-a-given-fraction method was also used to examine changes in Ea with reaction extent. Arsenopyrite was found to be under mixed control for most of the reaction extent. At increasing pyrite fractions, oxidation was observed to be reaction-limited at the initial stage of reaction, potentially reflecting the kinetics of sulphur oxidation.

Dynamic oxygen migration and reaction over ceria-supported nickel oxides in chemical looping partial oxidation of methane

The oxygen species over oxygen carriers determine the reaction performance in chemical looping partial oxidation of methane (CLPOM). This paper describes the dynamic migration and reaction of oxygen species over ceria-supported NiO oxygen carrier for CLPOM. At initial reaction stage, Ni-O species could be consumed rapidly and cause the full oxidation of methane to CO2. Afterwards, the active Ni-O-Ce species dominates the methane partial oxidation to promote the syngas yield. It is found that CO formation rate is linearly related with the content of oxygen species over Ni-O-Ce. Furthermore, the lattice oxygen from CeO2 would migrate through the bulk to complement the consumed Ni-O-Ce oxygen species. Eventually, 5NiO/(40CeO2-Al2O3) exhibit nearly three times as high as methane reaction rate of CeO2/Al2O3 and two times as high as CO formation rate of 5NiO/Al2O3. This work provides the comprehensive understanding of transport and reaction mechanism of oxygen species for chemical looping processes.

Role of H3PO4 concentration on the dissolution and reaction kinetics of phosphate acid based metakaolin geopolymer

Reaction kinetics of phosphate acid based metakaolin geopolymer (PMG) is studied by taking H3PO4 concentration and temperature as variables. Results indicate that the increase in H3PO4 concentration results in the increase in dissolution activation energy (Ed) of metakaolin. The maximum reaction rate of PMG is achieved at 353.15 K with the H3PO4 concentration of 8 mol/L. A relatively higher reaction temperature will lower the maximum heat release (Qmax) of PMG. The initial reaction stage of PMG is controlled by chemical reaction, which turns to diffusion-control mode in later reaction stages. The reaction activation energy (Ea) of acceleration stage is larger than that of deceleration and stabilization stages. In all stages, a higher H3PO4 concentration leads to a higher Ea.

Cation Exchange during the Synthesis of Colloidal Type-II ZnSe-Dot/CdS-Rod Nanocrystals.

Cation exchange is known to occur during the synthesis of colloidal semiconductor heteronanoparticles, affecting their band gap and thus altering their optoelectronic properties. It is often neglected, especially when anisotropic heterostructures are discussed. We present a study on the role of cation exchange inevitably occurring during the growth of anisotropic dot-in-rod structures consisting of a spherical ZnSe core enclosed by a rod-shaped CdS shell. The material combination exhibits a type-II band alignment. Two reactions are compared: the shell-growth reaction of CdS on ZnSe and an exchange-only reaction of ZnSe cores to CdSe. Transmission electron microscopy and a comprehensive set of optical spectroscopy data, including linear and time-resolved absorption and fluorescence data, prove that cation exchange from ZnSe to CdSe is the dominant process in the initial stages of the shell-growth reaction. The degree of cation exchange before significant shell growth starts was determined to be about 50%, highlighting the importance of cation exchange during the heteronanostructure growth.

Aluminium – Water hydrogen generator for domestic and mobile application

The study reports a novel hydrogen generation system. The system comprises Al based hydrogen generating composition with a reduced content of activating additives and an original fully automated Al-water hydrogen generator with capsule supply of hydrogen generating composition. The hydrogen generating composition was synthesized by means of mechanochemical activation of aluminum powder. Bi − 3.5 wt%. and Sn − 1.5 wt%. were used as activating additives. The combination of the proposed hydrogen generating composition and the design features of the generator made it possible to provide a high rate of hydrogen evolution (more than 30 ml/sec*g) and a hydrogen yield of 95–99 %. A high rate of hydrogen evolution was ensured by maintaining a temperature of at least 70 °C in the reaction zone. The heat of the aluminum oxidation reaction was utilized to maintain the necessary temperature. Based on the obtained experimental data, an assumption about the mechanism of the initial stage of the Al oxidation reaction was made. Some feasibility estimations of the hydrogen generation system are presented as well.

IrGa Bimetallic Catalyst with Atomical Metal Dispersion for Propane Dehydrogenation with High Stability

AbstractIndustrial catalysts for alkane dehydrogenation to olefins suffer from fast deactivation due to the coking and sintering of active metal under harsh reaction conditions. Herein, iridium, a noble metal rarely applied in C−H activation, has been employed to construct an ultra‐stable IrGa/Al2O3 catalyst with atomical metal dispersion for non‐oxidative propane dehydrogenation (PDH). A synergetic effect between metallic Ir and GaOx is discovered which contributes to both high PDH activity and propylene selectivity. Notably, the Ir0.5Ga2/Al2O3 with 0.5 wt % of Ir and 2.0 wt % of Ga exhibited a propylene selectivity of 98 % at a 19 % propane conversion at 550 °C and 86 % at a 35 % propane conversion at 600 °C. A stable PDH performance of 100 h was observed after a deactivation process at the initial reaction stage. The catalytic performance of the IrGa/Al2O3 is comparable to that of Pt‐based catalysts, endowing the Ir‐based catalyst with great potential in dehydrogenation reactions.