Advanced Fuels Research Articles

A CFD Modelling Approach of Fuel Spray under Initial Non-Reactive Conditions in an Optical Engine

A better understanding of why and how pollutant emissions from compression ignition engines are produced is one of the strategies to reduce them, and to achieve this it is important to understand what happens in the fuel injection inside the combustion chamber and in the combustion process. Experimentally, it is difficult to analyse the fuel spray right at the initial moments when it enters the combustion chamber due to its high velocity. These initial moments of the fuel spray affect its complete development and, consequently, the combustion process inside the chamber. This fact has motivated the approach of this work, in which a parametric study of the spray penetration as a function of variables that can be measured has been proposed. The purpose of this model is to understand which variables of the injection system significantly affect the spray penetration in the initial instants and how they affect it. This study was carried out using diesel and serves as a reference framework for similar studies using pure or blended sustainable advanced fuels. A computational fluid dynamics (CFD) model that determines the spray penetration at initial instants under different injection pressures and nozzle hole diameters is presented in this work. To tune the model, experiments were carried out on an optical engine. The modelled and experimental results exceed 94.8% agreement in all cases studied.

Experimental Study of Fuel Combustion and Emission Characteristics of Marine Diesel Engines Using Advanced Fuels

Abstract In order to explore the potential application of oxygenated fuels, polyoxymethylene dimethyl ethers (PODE), as an alternative fuel for marine diesel engines, the fuel combustion performance and gas emission characteristics of pure diesel oil, diesel-blended PODE, and pure PODE were tested on a marine diesel engine under different running conditions. The experimental results indicate that oxygen consumption can be reduced by diesel-blended PODE and pure PODE. The in-cylinder pressure and exothermic curve were consistent with the trend of diesel oil. Also, the ignition delay of diesel-blended PODE and pure PODE decreased, and the diffusion rate was accelerated, which helped to improve the combustion performance of diesel engines. Diesel blended PODE and pure PODE reduced the particulate matter (PM) emissions by up to 56.9% and 86.8%, respectively, and CO emissions by up to 51.1% and 56.3%, respectively. NOx emissions were gradually decreased with engine load. CO2 emissions were slightly increased, and the effective fuel consumption was increased up to 48% and 132%, respectively. It was shown that PODE could provide comparable power in a marine diesel engine and improve the fuel combustion and gas emission of the engine as a clean alternative fuel for marine diesel engines.

Effect of Performance by Excessive Advanced Fuel Injection Timing on Marine Diesel Engine

The injection timing of fuel in a diesel engine affects the combustion condition. Advanced fuel injection prolongs the ignition delay, positively impacting the increase in maximum combustion pressure and improving output. However, excessively advanced fuel injection can cause knocking. Moreover, premature ignition results in increased compression work when the maximum combustion pressure occurs before top dead center (TDC). This study aimed to diagnose and rectify starting failures, noise, and vibrations in a commercially operated ship engine by measuring the combustion pressure during low load operation. The target engine was a 4-stroke diesel, and the fuel injection system was mechanically controlled by a camshaft. The measured engine exhibited a 4.5 °CA error between the TDC, determined by the flywheel mark and the actual TDC. This discrepancy was influenced by excessively advanced fuel injection timing. It was confirmed that fuel injection and ignition were excessively advanced in all cylinders. After readjusting the engine by delaying the fuel injection timing by approximately 10 °CA, the combustion pressure was remeasured. The ignition was delayed by approximately 6.5 °CA at the same load, and the ignition intervals were uniformly adjusted. As the ignition timing was retarded, the compression work decreased and the expansion work increased in each cylinder, resulting in improved output across all cylinders. The amplitude of crankshaft angular velocity variation significantly decreased, improving uneven rotational force.

Relationship between molecular structure and dehydrogenation performance of cycloalkanes

Polycyclic alkanes are not only the important components of high-density fuels, but also can be used to cool the overheating parts of hypersonic vehicle through catalytic endothermic dehydrogenation reaction. However, the dehydrogenation performances of cycloalkanes with different molecule structures vary widely. Herein, we investigated the effects of cycloalkane structures, including the length of branched chains, the number of branched chains, the number of rings, and the shape of rings, on the dehydrogenation performance. The results show that cyclohexane (CH) exhibits the best dehydrogenation performance (600 °C, 3 MPa) with >99% conversion, >99% benzene selectivity, and highest total heat sink of 4.47 MJ/kg. The branched chains, ring number and five-membered rings all have negative effects on dehydrogenation. Among them, the number of rings has the minimum negative impact. Moreover, we correlated the density, volumetric net heat of combustion (NHOC) and heat sink with the molecular structure of the cyclic alkanes and found that the polycyclic alkanes with low H/C ratio and high M have both high density, high volumetric NHOC and high heat sink. This work can provide guidance for development and design of advanced fuels for endothermic dehydrogenation.

The development of future options for aqueous recycling of spent nuclear fuels

Since 2017, the UK Government has invested in research and technology development of advanced nuclear technologies including options for the future recycling of spent nuclear fuels. Whilst the UK has previously reprocessed and recycled uranium and plutonium from spent fuels, industrial scale reprocessing has finished and future fuels are being stored ready for disposal in a deep geological repository around the end of the century (i.e.transition to the open fuel cycle). Nevertheless, it is possible that an expansion of the use of nuclear energy to help meet Net Zero carbon emission targets and changing public perceptions or geopolitical situations over this period may necessitate a return to some form of closed fuel cycle. Consequently, the Advanced Fuel Cycle Programme (AFCP) has been developing advanced recycling options using both aqueous and pyro-chemical methods that would reduce wastes, costs and environmental impacts but with enhanced flexibility and barriers against nuclear proliferation risks. As well as technology development, AFCP has developed approaches for evaluating the benefits and disbenefits of future fuel cycle options under the framework of sustainability. This article provides an overview of the progress made under AFCP on the aqueous recycling of spent fuels, including the management of secondary wastes arising from the reprocessing schemes.

Upgrading of solid recovered fuel (SRF) by dechlorination and catalytic pyrolysis over nanocrystalline ZSM-5 zeolite

Globally increasing concern related to municipal solid waste generation is encouraging research efforts on developing alternative routes to valorize mixed refused wastes. In this way, catalytic pyrolysis is emerging as an interesting and efficient technology due to its great flexibility in terms of feedstock. In the current work, upgrading of a Solid Recovered Fuel (SRF) has been investigated by catalytic pyrolysis over nanocrystalline ZSM-5 zeolite (n-ZSM-5), paying special attention to dechlorination effects due to the high Cl content of the raw waste. Thus, pretreatment of the SRF by water washing and mild thermal processing allows for a significant reduction of the Cl concentration. Regarding the catalytic pyrolysis step, the best conditions correspond with a temperature of 400 °C in the catalyst bed and 0.50 catalyst/SRF mass ratio, which lead to ca. 30 wt% oil yield (rich in aromatic hydrocarbons) together with about 40 wt% gas yield (rich in C3–C4 olefins). Accordingly, these products could find use as raw chemicals or for the production of advanced fuels. In addition, zeolite reutilization has been tested for several cycles, denoting a progressive modification of the products distribution because of coke deposition. However, an almost total recovery of the n-ZSM-5 zeolite catalytic performance is achieved after regeneration by air calcination, affording the production of an oil fraction with a Cl content as low as 40 ppm.

Investigations on mechanical, thermodynamic and surface properties of U–Si alloys

The investigation of U–Si alloys as advanced technology fuels or accident tolerance fuels (ATFs) has gained momentum due to their higher uranium density and exceptional thermal conductivity. Density functional theory (DFT) calculations were used to examine the mechanical, thermodynamic and surface properties of U–Si alloys. Voigt-Reuss-Hill model was used to evaluate the mechanical properties such as Young's modulus, shear modulus, bulk modulus and so on. The results suggest that U3Si2 possesses an inherent brittleness, as opposed to the remaining U–Si alloys which demonstrate reliable ductility. In comparison to the hardness of other U–Si alloys (40–80 GPa), U3Si2 exhibits a significantly lower hardness (∼10 GPa). The results of anisotropy show that U3Si2 exhibits a lower anisotropy compared to USi2 (I41/amd) and U3Si (Pm-3m). Also, based on these mechanical properties, the sound velocity and Debye temperature are determined. Additionally, the study calculates the internal energy, Helmholtz free energy, entropy and heat capacity as a function of temperature, which is beneficial for fuel design and other applications. The surface energies and work function are investigated comprehensively for 161 surface slab models and used to obtain other surface properties, including equilibrium morphology, dominant surface orientations, area-weighted surface energy and area-weighted work function.

Validation of octane hyperboosting phenomenon in prenol and structurally related olefinic alcohols

Hyperboosting is a recently discovered phenomenon in which the research octane number (RON) of a blend is higher than both the neat blendstock and the neat fuel it was blended into. RON is a measure of a fuel’s resistance to knock, and knock is a cause of engine inefficiency. Blends which exhibit hyperboosting are blends in which an overall improvement in engine efficiency may be expected. The first discovery of hyperboosting came from blending experiments in which prenol was blended into several different base fuels. Here, ignition delay time (IDT) measurements taken using a commercially available constant volume combustion chamber called the Advanced Fuel Ignition Delay Analyzer (AFIDA) are presented. The data show that some prenol blends have longer IDTs (lower reactivity) than either neat prenol or the base fuel, providing further evidence of hyperboosting. Additionally, more blending data is presented in which the base fuel is varied, which allows for a better understanding of hyperboosting sensitivity to chemical classes. The data indicate that aromatics may inhibit, and branched alkanes may enhance the magnitude of hyperboosting observed. Enthalpy of vaporization estimates are also given for several molecules which are blended into a 4-component surrogate. These estimates are derived from Equation of State simulations and reveal that there is no observable correlation between hyperboosting and enthalpy of vaporization. Blending data for molecules which share structural similarities with prenol are also presented. Structure property relationships are suggested, in which the double bond motif of prenol seems to play an important role in hyperboosting. This may help to understand hyperboosting and its underlying mechanism. Lastly, blending curves of surrogate blends with prenol experienced hyperboosting under lean (Homogeneous Charged Compression Ignition-HCCI) operating conditions, which validates that hyperboosting is not an artifact of the octane test methods, but inherent to the properties of prenol.

Al-Doped Core-Shell-Structured Ni@Mesoporous Silica for Highly Selective Hydrodeoxygenation of Lignin-Derived Aldehydes.

Selective deoxygenation of chemicals using non-noble metal-based catalysts poses a significant challenge toward upgrading biomass-derived oxygenates into advanced fuels and fine chemicals. Herein, we report a bifunctional core-shell catalyst (Ni@Al3-mSiO2) consisting of Ni nanoparticles closely encapsulated by the Al-doped mesoporous silica shell that achieves 100% vanillin conversion and >99% yield of 2-methoxy-4-methylphenol under 1 MPa H2 at 130 °C in water. Due to the unique mesoporous core-shell structure, no significant decrease in catalytic activity was observed after 10 recycles. Furthermore, incorporating Al atoms into the silica shell significantly increased the number of acidic sites. Density functional theory calculations reveal the reaction pathway of the vanillin hydrodeoxygenation process and uncover the intrinsic influence of the Al sites. This work not only provides an efficient and cost-effective bifunctional hydrodeoxygenation catalyst but also offers a new synthetic protocol to rationally design promising non-noble metal catalysts for biomass valorization or other widespread applications.

Innovative and advanced fuel based on nuclear waste transuranic nuclides: An alternative fuel for TRIGA Mark II research reactor

Exploiting nuclear waste transuranic (TRU) inventories could be the promising key to developing reliable, clean, and sustainable nuclear energy. Towards this objective, different strategies are being considered, and one of the most effective strategies is the development of advanced fuels based on TRU nuclides. In this paper, a novel advanced TRU-based fuel is proposed and investigated as an alternative to the traditional fuel U-ZrH1.65 for the existing Moroccan research reactor TRIGA Mark II. The TRU nuclides used were derived from a typical 60 GWd/ton PWR-UOX reactor’s spent nuclear fuel (SNF) after one use and five years of storage. Before any new fuel loading, several studies must be performed. Hence, The current study focused on the neutronic fuel burnup point of view. MCNP6.2 stochastic code with its burn capability, CINDER90, was used to perform the calculations. In order to get a comprehensive view of the fuel conversion, analyses were performed for the reactor with the traditional fuel U-ZrH1.65, and the results were used as the basis for comparative studies of the reactor with the proposed TRU-based fuel. According to the findings, using TRU-based fuel has numerous advantages over traditional fuel U-ZrH1.65, such as long lifetime operation, better reactivity control, and low production of some biological hazardous fission products (short-lived fission products, 90Sr, and 99Tc). Furthermore, the fuel has highly significant plutonium (Pu) and minor actinides (MAs) burning ratios of about 95.1% and 92.5%, respectively. The results indicate a practical fuel option for the near future, which could be the first step towards using TRU nuclides in existing TRIGA-type reactors.

The surface and grain boundary properties of uranium boride: A DFT calculation

Uranium borides are currently being investigated as an accident tolerance fuel or advanced technology fuels (ATFs) to replace conventional UO2 fuel due to their high uranium density and high thermal conductivity. The surface properties of diverse facets of a crystal are pivotal for understanding different corrosion behaviors, fission gas bubble behaviors, and equilibrium morphologies. In this study, we employ density functional theory (DFT) calculations to investigate the surface properties of uranium borides. The surface orientations with maximum miller index up to 4, 1, and 2 for UB2, UB4 and UB12 were analyzed, respectively. Based on the calculated surface energies, the other surface properties of uranium borides were obtained through Wulff construction, including equilibrium morphology, dominant surface orientations, area-weighted surface energy and work function. Additionally, grain boundaries (GBs) have a significant impact on material properties, such as mechanical properties, corrosion behavior, and resistance to irradiation. Therefore, we use DFT calculations to determine the GB energies and work of separation for three low-Σ (7) symmetrical tilt GBs (STGB) and two twist GBs (TGB).

Airborne radioactivity concentration measurement in Compact Reprocessing of Advanced Fuels in Lead Cells reprocessing facility during off ventilation condition

Abstract Periodic maintenance of stack aviation lamps was taken up in the Compact Reprocessing of Advanced Fuels in Lead Cells reprocessing plant in Kalpakkam. The entire ventilation system of the plant had to be shut down during this maintenance work. When the ventilation system is switched off, natural radioactivity will build up in the working environment. The increased magnitude of the natural radioactivity concentration was estimated by counting the air samples (AS) at predetermined intervals to ensure no long-lived radionuclide (LLR) was present in the AS. The extent of the natural radioactivity rose to a factor of 100, and no LLR was present in the collected AS. In addition, the collected AS and data analysis of the same revealed that there was no breach of containment during the work.

Households’ Clean Cooking Fuel Poverty: Testing the Energy-Ladder Hypothesis in the Case of Bangladesh

The study explores clean cooking fuel poverty in Bangladeshi households based on the energy ladder hypothesis stating that as income increases, households switch towards cleaner cooking fuels. Data from the Bangladesh Demographic and Household Survey (BDHS) 2017-18 reveals that 20.45% of households use advanced or cleaner cooking fuels, while a majority (79.23%) still rely on primitive or traditional cooking fuels. Electricity is used by a very small percentage (0.57%), while LPG is used by a slightly higher proportion (6.96%). Biogas usage is minimal (0.11%), and a small percentage (0.03%) still relies on kerosene. Wood is the dominant fuel (46.25%), and other minor sources include charcoal (0.10%), straw/shrubs/grass (0.63%), agricultural crop residues (25.96%), and animal dung (6.39%). The results reveal that only a small proportion of households (20.45%) are classified as "clean cooking fuel non-poor," indicating a limited adoption of cleaner cooking technologies in Bangladesh. Further analysis indicates a gradual increase in clean cooking fuel usage as wealth status improves. Only 0.25% of the poorest households use clean fuels, while the percentage increases to 0.68% in the "poorer" category, 3.92% in the "middle" wealth category, and 24.51% in the "richer" category. Among the wealthiest households, 70.64% use clean cooking fuels. The study highlights the urgent need for policymakers in Bangladesh to address clean cooking fuel poverty by implementing measures like subsidies, awareness campaigns, and infrastructure development to promote cleaner cooking technologies, thereby improving public health and environmental sustainability.

Integrated Catalytic Upgrading of Biomass-Derived Alcohols for Advanced Biofuel Production

Sustainable biofuel production is necessary to meet the daunting challenge of “fueling” growing economies with a significantly reduced carbon footprint. Although its higher oxygen content often hinders the direct conversion of lignocellulosic biomass (LCB) into energy-dense biofuels, microbial biofuel production from LCB still has potential. The production of primary alcohols by acetone–butanol–ethanol (ABE) fermentation has been practiced for more than a century to attain near-theoretical maximum. However, ABE produced conventionally by native microorganisms is not equivalent to fossil fuel-based aviation fuels in terms of energy density, volatility, and cost-efficiency. Various strategies have been adapted for the microbial synthesis of advanced fuels from renewable feedstock with the advancements in genetic engineering. Yet, the presence of inhibitors and the inefficiency of microbes to utilize or transport the sugar mixtures from LCB often impede titer and yield. However, ABE mixtures can act as platform chemicals to synthesize high-value biofuels by biocatalytic or chemo-catalytic applications. Chemical catalysts, in particular, are used to produce higher alcohols ranging from 3-carbon to 20-carbon fuels from the ABE fermentation mixture. This article reviews the recent trends in the production of higher biofuels from ABE mixtures using biological and chemical catalysts. Focus is placed on genomic and metabolic engineering strategies implemented to upgrade microbes for higher biofuel production via the fermentation of renewable feedstocks. This paper also summarizes the advancements in the chemical conversion route of an ABE fermentation mixture into higher biofuels. Finally, the review provides insights into future research toward commercializing renewable and sustainable higher biofuels and chemicals.

Plasma and Thermal Physics

Symmetrically designed fusion and heat concepts, space propulsion, and energy conversion issues with a particular interest in kinetic analysis, plasma power balance, advanced fuels, and alternative systems as new trends in experiments and theory, in physics, power engineering, and in very specific related areas such as space processes, cosmology, and turbulence are very important in fundamental and applied science from an engineering physics perspective [...]

The impact of internet use on rural household energy transition: moderating effect based on social interaction

Introduction: Household energy transition is the key to changing and upgrading China’s energy consumption pattern. Directly using traditional biomass fuels is not only one of the reasons why the opportunity between urban and rural areas is inequality but also a critical symbol of the inequality of energy consumption within rural areas.Method: This study investigates the association between two information acquisition mechanisms, namely, Internet use and social interaction, and rural household energy transition, using CGSS 2015. After converting the consumption of each fuel to standard coal, according to the energy ladder theory, this study classifies the main types of household energy into three categories: primitive fuels, transition fuels, and advanced fuels. Then this study uses the ordered probit model to empirically analyze 1023 rural household samples in China.Results: The results show that, compared to rural households that never use the Internet, an increase in the frequency of Internet use significantly enhances the probability of rural households using advanced fuels, while decreasing the probability of using primitive and transition fuels simultaneously. However, the effect direction of social interaction works is the opposite of Internet use completely. The intrinsic mechanism result shows that although social interaction reduces the strength of the role of Internet use in rural household energy transition, it has not yet completely offset the positive effect of Internet use on the rural household energy transition.Discussion: The results of this study provide references for removing the blocking barriers to contact and use of the Internet by rural residents, improving the perceived quality of obtained information through social interaction, and solidly promoting rural energy transition and sustainable development of resources and the environment.

Thermal Assessment of Repository Footprint Requirement for Advanced Fuel Cycles

Decay heat is an important constraint for repository size and design because it can drive processes that affect performance and compromise critical materials. This paper investigates how compliance with repository thermal limits is affected by three decay heat management strategies: waste package loading, waste package spacing, and surface storage time. In particular, this paper focuses on how repository area, a result of package spacing, is impacted by waste loading and surface storage time. A two-part analytical heat transfer model is presented and executed iteratively to determine the minimum allowable repository area. The analysis considers three generic close-contact repository designs along with the wastes generated from the 40 fuel cycle analysis examples used to generate metric data for the Fuel Cycle Evaluation and Screening study. Detailed results are presented for two fuel cycles: the once-through use of low-enriched uranium fuel in light water reactors and the continuous recycling of U and Pu in sodium fast reactors. Two limits for surface storage time are identified: the time required for disposal to be possible at all and the time at which further surface storage time yields no gains. The impact of waste loading is also diminished with increasing surface storage time. In general, the generic salt repository is most flexible to accept high-heat-generating wastes with less surface storage time than other repository environments. Limited-recycle fuel cycles are shown to pose a disposal challenge because of elevated, sustained decay heat generation in the waste.

2D(r,θ) Simulations of the HBC-4 Power-to-Melt Experiment with the Fuel Performance Code ALCYONE

This paper presents 2D(r, θ ) simulations of the HBC-4 power-to-melt experiment performed with the fuel performance code ALCYONE. The HBC-4 experiment is one of the two test cases selected for the simulation exercise on past fuel melting experiments of the Power to Melt and Maneuverability (P2M) project. The ramp terminal level (RTL) at peak power node (PPN) has been estimated at 66 kW·m−1 by gamma scanning and 70 kW·m−1 based on online measurements of thermal fluxes. The fuel burnup at PPN was close to 60 GWd/tU−1. The cladding failed during the short holding time at a RTL of 40 s. Fuel melting took place at the pellet center, and in particular, in front of clad cracks. In this paper, simulations of the HBC-4 power-to-melt experiment are performed using an updated version of the 2D(r, θ ) scheme of ALCYONE where half of the fuel pellet is described. This configuration allows for the modeling of clad failure by iodine stress corrosion cracking and of its consequences on fuel pellet deformation. The modeling of fuel melting relies on thermochemical equilibrium calculations performed with the OpenCalphad Gibbs Energy Minimizer and the Thermodynamics of Advanced Fuels International Database. The simulation without clad failure indicates that the solidus is reached during the HBC-4 experiment but not the liquidus. The simulation with clad failure leads to a small increase in the fuel temperature that is sufficient to reach the liquidus at the pellet center, in agreement with postirradiation examination (PIE). The impact of water ingress in the rod and vaporization at the pellet surface is discussed, showing that it could explain the pronounced swelling of the fuel pellet reported from the PIE.

Agglomeration of particles stored in a box

Metallic nanoparticles are an essential part of advanced rocket fuels. Because of difficulties caused by hard ignition, incomplete reaction, and large size of combustion residues metallic particles with conventional particle sizes are unfavorable. However, the application of nanosized metallic particles does not show these disadvantages, in contrast, the application of nanosized metallic particles increases burning rates and reduces the two-phase specific impulse losses associated with solid combustion residues. On the other side, nanosized metallic particles are problematic, too. Nanoparticles, especially metallic ones, have a tendency to agglomerate. The formation of agglomerates leads to a reduction of the total surface of the particles and, therefore, to a reduction of the surface energy. This paper is limited to the process of agglomeration. As agglomeration is a random process, meaningful results are possible only using statistical methods. For this paper, a model with random selection of the particles based on Markow chains was applied. To evaluate the stability of the agglomerated product, the entropy was calculated. The results show that, with increasing agglomeration, the entropy increases exponentially. The thermodynamically better criterion is the free enthalpy; however, in lack of adequate materials data, this criterion could not be applied. Therefore, in general, the consideration presented in this paper are not specific for the addition of a specific metal.

The Dynamic Nature of Graphene Active Sites in the H2O Gasification process: A ReaxFF and DFT Study

A steam-rich environment is a more promising application scenario for future coal-fired processes, while active sites are the key factor that determines the reactivity of carbonaceous fuels. The steam gasification process of carbon surfaces with different numbers of active sites (0, 12, 24, 36) was simulated using reactive molecular dynamics in the present study. The temperature for the decomposition of H2O and the gasification of carbon is determined using temperature-increasing simulation. The decomposition of H2O was influenced by two driving forces, thermodynamics and active sites on the carbon surface, which dominated the different reaction stages, leading to the observed segmentation phenomenon of the H2 production rate. The existence and number of initial active sites have a positive correlation with both two stages of the reaction, greatly reducing the activation energy. Residual OH groups play an important role in the gasification of carbon surfaces. The supply of OH groups through the cleavage of OH bonds in H2O is the rate-limiting step in the carbon gasification reaction. The adsorption preference at carbon defect sites was calculated using density functional theory. Two stable configurations (ether & semiquinone groups) can be formed with O atoms adsorbed on the carbon surface according to the number of active sites. This study will provide further insights into the tuning of active sites for advanced carbonaceous fuels or materials. The large-scale atomic/molecule massively parallel simulator (LAMMPS) code combined with the reaction force-field method was used to carry out the ReaxFF molecular dynamics simulation, where the ReaxFF potentials were taken from Castro-Marcano, Weismiller and William. The initial configuration was built using Packmol, and the visualization of the calculation results was realized through Visual Molecular Dynamics (VMD). The timestep was set to 0.1 fs to detect the oxidation process with high precision. PWscf code in QUANTUM ESPRESSO (QE) package, was used to evaluate the relative stability of different possible intermediate configurations and the thermodynamic stability of gasification reactions. The projector augmented wave (PAW) and the generalized gradient approximation of Perdew-Burke-Ernzerhof (PBE-GGA) were adopted. Kinetic energy cutoffs of 50 Ry and 600 Ry, and a uniform mesh of 4 × 4 × 1 k-points were used.