Dominant Reaction Research Articles

Influence of physical interactions on spatiotemporal patterns.

Spatiotemporal patterns are often modeled using reaction-diffusion equations, which combine complex reactions between constituents with ideal diffusive motion. Such descriptions neglect physical interactions between constituents, which might affect resulting patterns. To overcome this, we study how physical interactions affect cyclic dominant reactions, like the seminal rock-paper-scissors game, which exhibits spiral waves for ideal diffusion. Generalizing diffusion to incorporate physical interactions, we find that weak interactions change the length- and time scales of spiral waves, consistent with a mapping to the complex Ginzburg-Landau equation. In contrast, strong repulsive interactions typically generate oscillating lattices, and strong attraction leads to an interplay of phase separation and chemical oscillations, like droplets co-locating with cores of spiral waves. Our work suggests that physical interactions are relevant for forming spatiotemporal patterns in nature, and it might shed light on how biodiversity is maintained in ecological settings.

Effects of pressure and heating rate on coal pyrolysis: A study in simulated underground coal gasification

Underground coal gasification (UCG) is a promising technology which in-situ converts coal into fuel gases through controlled chemical reactions. In order to precisely control coal pyrolysis and increase the char yield, it is vital to understand the influences of operating factors such as heating rate and pressure, on coal pyrolysis. In this study, the effects of heating rate and pressure on the char formation of bituminous coal pyrolysis are investigated. The reaction mechanism of coal pyrolysis and the solid-state kinetic model are firstly reviewed. Subsequently, thermal experiments are conducted to study the effects of heating rate and pressure on coal pyrolysis characteristics. Moreover, the connection between the dominant coal pyrolysis reaction type and corresponding solid-state kinetic model is revealed. An empirical model of coal pyrolysis rate, pressure, and heating rate is also developed, which can be used to quantitatively predict pyrolysis rates under varying heating rate and pressure conditions. The results show that the optimal heating rate for char generation is at around 10 °C/min. On the other hand, when the pressure exceeds 2 MPa, it will enhance the char production by obstructing the physical release of volatiles and has insignificant impact on the reaction type. This study contributes to our understanding of the coal pyrolysis mechanism, and the proposed empirical model can provide valuable insights for optimizing operating parameters during UCG process.

The influence of pulse repetition frequency on reactive oxygen species production in pulsed He+H2O plasmas at atmospheric pressure

Atmospheric pressure plasmas generated from a helium gas with admixtures of water vapor have numerous applications in biomedicine. It is important that the chemistry of such plasmas can be tightly controlled so that they may be tailored for their intended use. In this study, computational modeling is used to vary the pulse repetition frequency of a nanosecond-pulsed, pin-to-pin He + 0.25% H2O discharge in the range of 1–100 kHz to determine the influence of the pulse repetition frequency on the resulting densities of reactive oxygen species and the rates of dominant reaction pathways involving them. The plasma is simulated using the 0D plasma-chemical kinetics model GlobalKin. The pulse shape is kept constant. The afterglow duration is, therefore, dependent on the repetition frequency. Analysis of the bulk plasma chemistry after the plasma has reached equilibrium shows that the peak electron density is only weakly dependent on the pulse repetition frequency. Increasing the pulse repetition frequency is shown to increase the density of H, O, and OH radicals, while the relationship between the repetition frequency and the densities of species with longer lifetimes, namely, H2O2 and O3, is found to be more complex. These are formed throughout the afterglow, and their density depends on the availability of reactant species, the afterglow duration, and the background gas temperature. This work concludes that the pulse repetition frequency is not a simple control parameter, especially for species that are predominantly produced in the afterglow. Detailed modeling is required for accurate control of species densities using the pulse repetition frequency.

Experimental and Numerical Studies on the Explosion Characteristics of Ethanol–Air Mixtures under Aviation Conditions

As a representative renewable biofuel, ethanol can reduce mankind’s dependence on petroleum resources and the emission of greenhouse gases and other pollutants. In recent years, the application of ethanol in the aviation field has begun to be a concern of scholars. As ethanol is a flammable liquid, it is significant to study its explosion characteristics in aviation conditions from a safety perspective. In this work, at 20 kPa, the explosion characteristics of ethanol–air mixtures (concentration 6~12%) were experimentally and numerically studied under an initial temperature range of 303 K~363 K. The effects of the initial temperature and concentration on the maximum explosion pressure, maximum rate of pressure rise, explosion time, and fast burning time were analyzed. In addition, the heat loss fraction and sensitivity analysis were examined and discussed. The main conclusions are as follows: A linear relationship exists between the maximum explosion pressure and the reciprocal of the initial temperature. The maximum rate of a pressure rise appears to decrease or at least approach a constant value as the initial temperature increases. The explosion time is significantly dependent on the concentration. At a constant concentration, the proportions of heat loss are approximately constant except for 12%. In our sensitivity analysis, R1 (H + O2 <=> O + OH) was the dominant elementary reaction.

Characteristics of Detonation Propagating in Silane-Nitrous Oxide-Nitrogen Mixtures

ABSTRACT The present study investigated for the first time the characteristic length scale and chemical dynamics of steady and quasi-steady detonation waves propagating in silane-nitrous oxide-nitrogen mixtures, which are widely used in the semi-conductor industry and can be a promising additive for propulsion application. The conditions investigated cover the following ranges: equivalence ratio = 0.5–5; initial pressure = 10–1000 kPa; nitrogen mole fraction = 0–0.8; initial temperature = 300 K. The energy released by the formation of SiO(s) and SiO2(s) was taken into account whereas the phase change from gas to liquid/solid was neglected. It was found that detonation in these silane-based mixtures is characterized by unusually large Mach numbers which result in up to 128.5 times pressure jump across the leading shock, and few micrometer-long induction zone length. For steady planar waves, the shortest induction distances were identified in the range = 2–4, while for curved detonations, the most resilient wave to curvature-induced losses was identified at around 1.5 for undiluted mixtures. Such phenomena are the results of the enhanced formation of SiO(s) under fuel-rich conditions, which also contributes to stabilizing the detonation wave, though the mixture should still be classified as unstable, according to traditional stability parameters. Detailed thermo-chemical analyses were performed to investigate the chemical dynamics. The study of the heat release per reaction shows the dominant contributions of R65: H+N2O=N2+OH, R207: SiH4(+M)=H2+SiH2(+M), R377: N2O+SiH2=H2SiO+N2, R379: N2O+Si=N2+SiO, and R400: 2SiO = 2SiO(s). The dominant reactions for heat release are not modified by the curvature-induced loss according to sensitivity analyses.

Effect of Hydrogen on the Dissolution of Uranium Dioxide in Peroxide-Containing Environments

The ability of hydrogen (H2) to scavenge hydroxy radicals (OH•) created by the dissociation of hydrogen peroxide (H2O2) on the surface of uranium dioxide (UIVO2) has been studied in a chloride/bicarbonate (pH = 9.5) solution. The oxidation/reduction of the oxide surface was monitored by measuring the corrosion potential as a function of time in this solution, containing various concentrations of H2O2 sparged with either Ar or an Ar/H2 mixture. The surface oxidation was subsequently determined using X-ray photoelectron spectroscopy. In the absence of H2, the peroxide oxidized the surface to UIV 1–2xUV 2xO2+x with x varying with H2O2 concentration and eventually achieved a composition of UIV 0.34UV 0.66O2.33. At this surface composition, the surface becomes unstable with respect to dissolution, but the dominant reaction is H2O2 decomposition. In the presence of H2, the initial oxidation of the UIVO2 when H2O2 was added was reversed by the ability of H2 to scavenge the OH• with the H• radicals formed. This led to a reduction of the oxidized surface. The efficiency of this process is determined by the relative concentrations of H2O2 and H2.

Experimental and numerical investigation of combustion characteristics of carbon-free NH3/H2 blends in N2O

A detailed experimental and numerical investigation of the combustion characteristics of carbon-free NH3/H2 blends in N2O was performed in the present work. The experiments with various hydrogen fractions (α = 0–1.0) and equivalence ratios (φ = 0.6–1.4) were performed at ambient pressure (1 atm) and temperature (283 K) in a standard 3.375-L cubic combustion vessel. The explosion behaviors (maximum explosion pressure Pmax and maximum pressure rise rate (dp/dt)max) were obtained from the pressure-time curves. Further, the combustion characteristics (e.g. laminar burning velocity (SL), thermal expansion ratio (σ), flame thickness (δ), effective Lewis number (Leeff) and Markstein length (Lb)) were calculated numerically by means of chemical kinetic analysis using Zhang's mechanism (Zhang et al., Combust. Flame, 2017, 182: 122–141). Besides, sensitivity analyses of the explosion pressure and laminar burning velocity were performed to identify the contribution of dominant elementary reactions. The results show that, for combustion supported by N2O, the flame instability and the potential of deflagration to detonation transition (DDT) should be considered for the evaluation of Pmax and (dp/dt)max. Moreover, the hydrodynamic instability of premixed H2/NH3/N2O flame reaches its peak near the stoichiometric ratio and increases monotonously with the hydrogen fraction. The diffusion-thermal instability is more significant in the leaner mixture, and it is not invariably enhanced with the increase of hydrogen fraction but is relevant to the composition of the mixture. In addition, the sensitivity analysis of explosion pressure demonstrates that R80 (N2O + H2N2+H2O) and R70 (N2O+(M) = N2+O (+M)) are the most dominant reactions contributing to the pressure rise. The sensitivity analysis of laminar burning velocity shows that R70 (N2O+(M) = N2+O (+M)), R71 (N2O + HN2+OH) and R80 (N2O + H2N2+H2O) are the most dominant reactions enhancing laminar burning velocity.

Electrode Design for Effective Electrochemical Regeneration of an Alkaline CO2 Capture Solution

The use of a membrane electrochemical cell to drive carbon capture has the potential to exceed the performance of conventional, thermally driven methods. KOH is a common solvent for CO2 capture, as it spontaneously reacts with CO2 to form carbonates (K2CO3 or KHCO3) at ambient conditions. Previous work has shown the use of an anion exchange membrane electrochemical cell to simultaneously regenerate an alkaline carbon capture solution on the cathode (feed) side and concentrate CO2 on the permeate (anode) side of the cell. Supplying H2 to the anode side of the cell allows hydrogen oxidation to be the dominant reaction, which reduces cell overpotentials compared with oxygen evolution. The CO2-enriched H2 stream can be used for methanol synthesis as a versatile energy carrier. Through experimental optimization and modeling work, we demonstrate the use of rational design to reduce cell overpotentials and improve faradaic efficiency. The balance of operating parameters such as current density and specific energy consumption have important implications for the overall cost and scalability of the process.

Investigation of an Intermediate Temperature SOFC Operation in Series with a CPOx Reformer

Solid oxide fuel cells are known for their fuel flexibility which makes them a great candidate for decentralized power generation and off-grid applications. Depending on the target application, there have been different system configurations such as steam reforming vs. CPOx reforming, external reforming vs. internal reforming, anode recirculation vs. single pass. The CPOx reforming in series with SOFC with single pass configuration opens up the intermittent power source market, due to its unique benefit of low cost, short startup time and easy maintenance. In this scheme fuel cell electrochemical performance is directly related to the syngas composition, i.e. H2 and CO fractions in the fuel stream, as well as any unreformed methane.In this study a computational fluid dynamics (CFD) model has been developed to study the dynamic and steady state behavior of a commercial intermediate temperature SOFC stack operating in series with a CPOx reformer. The CFD model of the SOFC accounts for the charge, species, momentum and energy balances, whereas a reduced order model for the CPOx incorporates equilibrium thermodynamics. CPOx is an exothermic catalytic reaction with an overall balance of:CH4+1/2O2 → 2H2+CO (1)which is defined in stoichiometric ratios. In practice the air flow is regulated to control the reactor temperature and syngas yield. Hence, along with temperature and pressure the ratio of oxygen to carbon (O-C ratio) in the left hand side of Eq. 1 is a critical parameter for determining the overall performance and efficiency of the system. Moreover, the CPOx operation typically has different routes to achieve desired products which constitutes a system with various reaction equilibria [i]. However, apart from Eq.(1) the dominant reaction paths can be summarized as [ii]:Reformation CH4+CO2 ↔ 2H2+2CO (2)Water gas shift CO+H2O ↔ H2+CO2 (3)Boudouard CO2 + C ↔ 2CO (4)CH4 Combustion CH4+2O2 → 2H2O+CO2 (5)CO Combustion 2CO+O2 → 2CO2 (6)H2 Combustion 2H2+O2 → 2H2O (7)Of these, combustion reactions can be practically considered as irreversible. Overall system equilibrium is a result of these reactions and is a function of temperature, pressure and O/C ratio. Any changes in these parameters shift the reaction equilibrium, hence the conversion efficiency and syngas yield. As a result, SOFC performance will be directly dependent on these parameters.In this study different operating regimes of CPOX and SOFC have been investigated. The model is validated experimentally with polarization data and gas chromatography analysis. The model predictions show good agreement with the GC data for both the CPOX and SOFC outlet gas compositions.Performance of the SOFC running on syngas obtained as a result of different CPOx equilibria is compared and a fuel cell efficiency map as a function of temperature and O-C ratio has been constructed. Also, dynamic response of SOFC to the changes in CPOx operating parameters is estimated with the transient simulations. Moreover, selectivity of SOFC toward H2 and CO has been investigated by outlining the different energy conversion paths inside the fuel cell electrode. It is found that SOFC at intermediate temperatures has an overall tendency for CO conversion due to enhanced WGSR reaction inside the electrodes although the standalone CO oxidation overvoltage is higher than that of H2 oxidation. Finally, SOFC performance is analyzed for injecting various amounts of unreformed CH4 into the syngas stream.[i] Bjørn Christian Enger, Rune Lødeng, Anders Holmen, A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts, Applied Catalysis A: General 346 (2008) 1–27.[ii] Ruoshui Ma, Bang Xu, Xiao Zhang, Catalytic partial oxidation (CPOX) of natural gas and renewable hydrocarbons/oxygenated hydrocarbons—A review, Catalysis Today 338 (2019) 18–30. Figure 1

A Theoretical Study of NH2 Radical Reactions with Propane and Its Kinetic Implications in NH3-Propane Blends’ Oxidation

The reaction of NH2 radicals with C3H8 is crucial for understanding the combustion behavior of NH3/C3H8 blends. In this study, we investigated the temperature dependence of the rate coefficients for the hydrogen abstraction reactions of C3H8 by NH2 radicals using high-level theoretical approaches. The potential energy surface was constructed at the CCSD(T)/cc-pV(T, Q)//M06-2X/aug-cc-pVTZ level of theory, and the rate coefficients were computed using conventional transition state theory, incorporating the corrections for quantum tunneling and hindered internal rotors (HIR). The computed rate coefficients showed a strong curvature in the Arrhenius behavior, capturing the experimental literature data well at low temperatures. However, at T > 1500 K, the theory severely overpredicted the experimental data. The available theoretical studies did not align with the experiment at high temperatures, and the possible reasons for this discrepancy are discussed. At 300 K, the reaction of NH2 with C3H8 predominantly occurs at the secondary C-H site, which accounts for approximately 95% of the total reaction flux. However, the hydrogen abstraction reaction at the primary C-H site becomes the dominant reaction above 1700 K. A composite kinetic model was built, which incorporated the computed rate coefficients for NH2 + C3H8 reactions. The importance of NH2 + C3H8 reactions in predicting the combustion behavior of NH3/C3H8 blends was demonstrated by kinetic modeling.

Group IV Complexes with Sterically Congested N-Aryl-adamantylcarbamidate Ligands.

Metalation of N-(2,6-dibenzhydryl-4-tolyl)adamantane-1-carboxamide (1, Ar*N(H)-C(O)-Ad) with M(NMe2)4 (M = Ti, Zr, Hf) yields amidate complexes Ar*N=C(Ad)-O-Ti(NMe2)3 (2) as well as bis(amidate) compounds (Ar*N=C(Ad)-O)2M(NMe2)2 (M = Zr (3), Hf (4)). In 2, the amidate ligand acts as a monodentate base via the oxygen atom with the Ti center in a slightly distorted tetrahedral environment. The steric requirement of the amidate ligand stabilizes the small coordination number of four of the Ti atom. In congeners 3 and 4, two bidentate amidate ligands exist in the coordination spheres, leading to hexacoordinate group IV metal atoms. The small bite angles of the Zr- and Hf-bound amidate ligands lead to severe distortion of the octahedral environments of the Zr and Hf centers. Titanium compound 2 is an unsuitable choice to catalyze hydrofunctionalization of alkynes with amines and phosphane oxides and despite the significantly smaller pKa value of the carboxylic amide, formation of carboxamide 1 is the dominant reaction upon addition of amines or phosphane oxides to release intramolecular steric strain introduced by the very bulky adamantylamidato ligand.

Experimental Photodegradation of OPs and CBs by Advanced Oxidation Techniques in the Aqueous TiO2 Suspensions

The reaction of pesticides with the OH radical, is the most dominant annihilation reaction ofthe atmosphere. Phosmet, Azamethiphos, Coumaphos and Temephos were used as organophosphorouspesticides, and Methiocarb, Carbofuran and Pirimicarb compounds were used as carbamate pesticideswith the aim of investigating the kinetics of the reactions of Organophosphorous (OPs) and Carbamate(CBs) Pesticides with the OH radicals. In aqueous TiO2 suspensions, the degradation reactions viaphotocatalytic-effect of the seven pesticides selected as pollutants were analysed, and the impact of theinitial concentration was calculated. All experiments were conducted in the same photoreactor and underthe same conditions as three repetitions. The optimum amount of photocatalyst for the studied pesticidewas determined and TiO2 concentration for all experiments were taken as 0.2 g/100 mL. Considering thatorganic pollutants are present in water in trace amount, the initial concentrations for all organiccompounds were added so as to be1.0x10-4 molxL-1, into the suspensions and the solution containing theorganic pollutant. In this study, degradation speed of pesticides were determined experimentally, and thefastest degrading pesticide was tried to be found out.

Possible Effects of Playing Video Games With Explicit Violence on Player Aggression

Video games have become the most significant phenomenon of popular culture, and one of the most widespread forms of entertainment in society of the Industrial Revolution 4.0. This prevalence corresponds with profitability, and the video game industry records the highest revenues in the cultural and entertainment industries. Simultaneously, the level of the scientific study of the phenomenon and its impact remains disproportionately small, while moral panic and the banalized and oversimplified accusation of video games for causing violence and evil in people are the dominant social attitude and reaction. That is why the influence of playing violent video games on the development of aggression and violent behavior in individuals has been thoroughly researched. While some studies indicate that gaming has no effect at all, or even a cathartic effect, others claim that playing violent video games is associated with increased aggression and antisocial behavior. The aim of this paper is to examine the effects of explicit violence in video games on the aggressiveness and violence of players of such games. Using various analytical methods, by exploring stereotypes, cultural factors, and the potential negative effects of playing violent video games, this comprehensive analysis challenges the incorrect preconception that video games inherently encourage real-world violence. While acknowledging certain negative effects like the promotion of a culture of competitive militarism and desensitization to violence in the real world, this paper recommends responsible gaming, parental control and guidance, and positive social influence as crucial factor in shaping moral attitudes and behavior.

A theoretical study on gas-phase reactions of CF3CH=CF2 with OH: mechanism, kinetics and insights

The mechanism and kinetics of the CF3CH=CF2 + OH reaction were studied by using density functional theory (DFT) and transition state theory (TST). All possible mechanisms are taken into account, including F-abstraction, H-abstraction and OH-addition/elimination. Results reveal that the OH-addition/elimination reaction of P1 (CF2O + CF3CH2) and P7 (CHF2 + CF3CHO) are the dominant reaction pathways. Other pathways on the potential energy surface (PES) are less competitive from the thermodynamic and kinetic consideration. Moreover, the kinetics of all the important pathways are analysed according to transition state theory (TST). The rate constants of IM1, IM2, IM3 and IM5 increases firstly and then decreases as the temperature increasing. The rate constants of P1 and P7 reveals positive temperature dependence. The calculated rate constants are consistent with the experimental value. The atmospheric lifetime of CF3CH=CF2 in the existence of OH is computed to be about 15.75 days, which is agreement with the experimental data.

Investigation of the thermal hazard and decomposition mechanism of 1,1-di(tert-butylperoxy) cyclohexane by experiment and DFT simulation

1,1-Di (tert-butylperoxy) cyclohexane (1, 1-DTBCH), as an important organic peroxide, is commonly used as initiator, curing agent and crosslinking agent in the chemical industry. Due to the presence of peroxy bonds, the thermal instability of 1, 1-DTBCH may incur a decomposition reaction and cause further thermal runaway. The thermal decomposition characteristics and runaway reaction characteristics of 1, 1-DTBCH were investigated by differential scanning calorimetry (DSC) and accelerated rate calorimetry (ARC). The kinetic triplet and thermal safety parameters were calculated by using non-isothermal method. The gaseous products and pyrolysis products of 1, 1-DTBCH was investigated by thermogravimetric and infrared spectroscopy (TG-FTIR) and gas chromatography/mass spectrometry (GC/MS). The thermal decomposition pathway of 1, 1-DTBCH was explored with density functional theory (DFT). The exothermic dominant reaction in the thermal decomposition process of 1, 1-DTBCH was explored by combining experiment and theoretical calculation. The corresponding safety control measures were provided to reduce the thermal runaway hazard of 1, 1-DTBCH.

Non-equilibrium modeling on the aerothermodynamic characteristics of hypersonic inflatable reentry vehicle

In this study a 2D two-temperature chemical non-equilibrium model is established to investigate the flow characteristics and chemical reactions processes around hypersonic inflatable reentry vehicle at different flight altitudes and reentry velocities. This chemical kinetic model is based on the Gupta model and modified by comparing the species mole fractions at thermal equilibrium condition with the results obtained by Saha equation. In order to validate the model, the calculations are performed for a blunt cone ELECTRE and a cylinder, the predicted heat flux and pressure are compared with experimentally measured data and the maximum differences on heat flux and wall pressure are less than 20% and 5%, respectively. Then the flow characteristics behind the shock wave and wall heat flux are discussed in detail for Titans vehicle. It is found that the pressure declines with the increase of altitude and reentry velocity, this variation trend is opposite to the wall heat flux, whose maximum value increases from 58 kw/m2 to 107 kw/m2 with the rise of flight altitude from 79 to 88 km due to the large temperature and component gradients. This indicates that the aerodynamic force and heat flux should be taken into account simultaneously for the design of inflatable reentry vehicle. By analyzing the chemical reactions processes behind the strong shock wave, it is seen that not only the dissociation reactions of N2 and O2 molecules play an important role, but also the neutral species exchange reactions contribute to the density change of species. The dominant ionization reactions are N+O→NO++e and NO+M→4NO++e+M4, while the ionization processes are weak, and the maximum ionization degree is smaller than 1%. The analysis of dominant chemical reactions can provide a reference for the numerical modeling study of hypersonic reentry vehicle.

Investigation of performance and mechanism of zinc removal from polluted water by concrete fines derived from aggregate recycling: From problematic byproducts to effective adsorbent

Concrete fines are byproducts produced from aggregate recycling. Because of their properties, they cannot be directly recycled for use in concrete manufacturing, which is problematic to move the cement and concrete industry toward sustainable development goals and reduce its environmental impact. Taking advantage of concrete fines unique properties was regarded as a possible research direction. The hydrated cement fraction was expected to provide alkalinity to neutralize the acidic solutions, while calcium related compounds were expected to provide the function of heavy metals removal. In this research, concrete fines were used to remove Zn from acid mine drainage as an active treatment. The removal performance was comprehensively investigated. The maximum capacity of Zn-adsorption is 111.9 mg/g, and almost 100% Zn can be removed for an initial Zn concentration of 20 mg/L. The dominant reaction mechanism of Zn adsorption to concrete fines was determined to be ion-exchange reaction with surface complexation and precipitation. The Zn2+ ions in solution can exchange with the Ca2+ ions in calcium silicates and calcium silicate hydrates in concrete fines and replace the protons released by ionization of the silanol group for complexation, and thus Zn removal is not limited to an alkaline environment or high initial Zn concentration. The acidity was alkalized by hydration reaction, mainly consuming calcium hydroxide. Based on these mechanisms, concrete fines are effective adsorbent to remove Zn without the need for the synergistic reactions of other metals and for making the aqueous solution strongly alkaline, even in the strongly acidic environments and in effluents with high Zn concentration. Through evaluation and comparison of Zn adsorption capacity with other materials, concrete fines were regarded as promising alternative adsorbent for Zn removal.

Intra-catalyst CH4 oxidation pathways on a Pd/Al2O3/CeZrOx-based commercial catalyst and implications on NOx conversion profiles for a natural gas vehicle exhaust under lambda modulation

The performance of a three-way catalyst (TWC) in natural gas-powered vehicles is enhanced by periodic changes in air-to-fuel ratio (λ-modulation). The reaction networks and sequences inside the catalyst that facilitate such enhanced performance have not been extensively investigated. This work applied intra-catalyst measurements (SpaciMS) to analyze the transient spatiotemporal gas concentrations inside a Pd-based TWC to establish relationships between CH4, NOx, CO and H2 conversion pathways. Steam reforming and partial oxidation were revealed to be the main CH4 conversion routes. The cyclic rich-lean conditions combined with the oxygen storage capacity (OSC) of the TWC generate reduced and oxidized zones that are constantly moving within the catalyst, changing the dominant chemical reactions occurring on the surface. In the reduced zones, OSC is depleted while CH4 is converted through steam reforming and NOx is converted through reactions with H2, CO, and other surface-bound reducing fragments formed by CH4 conversion. In the oxidized zones, OSC is replenished, CH4 is converted by partial oxidation, and H2, CO, and NH3 are oxidized. The length of lean-rich phases impacts the catalyst performance significantly; too short or too long of a rich or lean phase can lower the overall conversion of reactive species. An inhibition of CH4 conversion was observed during the rich phase possibly due to CO-poisoning of active sites. The intra-catalyst measurements revealed that the catalyst consists of three distinct reaction zones and their lengths vary with modulation conditions. Various modulation frequencies, amplitudes, λ-centers, and temperatures were investigated which allowed an understanding of how these parameters affect the reaction zones and catalyst utilization. Understandings from this work can enable adaptive λ-control strategies to optimize the overall TWC performance over a range of vehicle operating conditions.

The mechanism of ethanol blending on the variation of chemical heat sink in n-decane thermal cracking process

The cracking of on-board hydrocarbon fuels is a strong endothermic reaction and can provide an additional chemical heat sink in the cooling process of the hypersonic vehicle. However, the cooling capacity of current hydrocarbon fuels can hardly meet the cooling requirements of the hypersonic vehicle at higher flight speeds. Blending ethanol is an effective method to improve the chemical heat sink of hydrocarbon fuels, but the mechanism of ethanol on chemical heat sink is unclear. In this study, n-decane was selected as a model compound of hydrocarbon fuels to investigate the physical and chemical effect of ethanol on the chemical heat sink of n-decane cracking by analyzing the chemical reactions involved through experimental study and chemical dynamic simulation. The results indicate that there is an optimum ethanol blend ratio to achieve the maximum chemical heat sink. The carbon monoxide methanation reaction which is an exothermic reaction can deteriorate endothermic process at 300–375 °C. With ethanol blending ratio above 20 wt%, ethanol vaporization deteriorates chemical heat sink by reducing the residence time in the temperature range of 225–250 °C. Pressure can suppress the reduction of residence time caused by ethanol evaporation and also suppress the positive reaction of ethanol cracking. The kinetic model of ethanol and n-decane mixture cracking was established. The calculated results verify that ethanol cracking (C2H5OH=CO+CH4+H2) and methane cracking (CH4=C+2H2) are dominant reactions in ethanol-assisted n-decane thermal cracking below 475 °C.

Effective parameters on in-situ oil upgrading with nanocatalyst in large scale: Kinetics modeling

Thermal enhanced oil recovery (EOR) methods are the main techniques used to produce oil from heavy oil reservoirs. But this methods are associated with environmental challenges and do not reduce viscosity permanently. One of the new methods with less environmental challenges that can permanently improve oil quality and enhanced oil recovery is the in-situ oil upgrading with nanocatalyst. In the present study, effectiveness of the in-situ oil upgrading with nanocatalyst in improving the quality of oil and increasing the oil production have been investigated at a large-scale heavy oil reservoir with the aid of STARS simulator. Reactive flow was considered in the simulation by kinetic modelling of a reaction network with 5 pseudo-components. Also, effect of temperature and type of oil have been studied. Details on how to carry out reactions and changes in oil components over time have been investigated. In addition, steam flooding and in-situ oil upgrading with nanocatalyst were compared from the point of view of the amount of released CO2 gas and the required water. The results show that in-situ oil upgrading with nanocatalyst is a time-consuming process and causes a 40% increase in the cumulative production and 23.58% decrease in the density compared to the steam flooding.There is an optimum temperature (300 °C) for the in-situ oil upgrading process with nanocatalyst at which the maximum amount of oil is produced and has a better recovery on heavier oils. The major part of VR is converted into distillate in the heavier oil, while in the lighter oil, the dominant reaction was conversion of VR to VGO. In addition, in-situ oil upgrading with nanocatalyst reduces the required water and emission of CO2 compared to the steam flooding method and among the three factors of injection flow rate, temperature, and steam quality, the most effective factor to reduce environmental problems with the help of in-situ oil upgrading with nanocatalyst is injection flow rate.