Hydrocarbon Species Research Articles

Joint evolution of equatorial oscillation and interhemispheric circulation in Saturn’s stratosphere

Planetary stratospheres are characterized by a subtle interplay between dynamics, radiation and chemistry. Observations of Saturn’s stratosphere have revealed a semi-annual equatorial oscillation of temperature and hinted at an interhemispheric circulation of hydrocarbon species. Both the forcing mechanisms of the former and the existence of the latter have remained debated. Here we use a new troposphere-to-stratosphere Saturn global climate model to argue that those two open questions are intimately connected. Our Saturn climate model reproduces a stratospheric oscillation exhibiting the observed semi-annual period, amplitude and downward propagation. In the same Saturn simulation, a prominent stratospheric summer-to-winter hemispheric circulation develops at the solstices, controlled by both the seasonal radiative gradients and Rossby-wave pumping in the winter-subsiding branch, analogous to Earth’s Brewer–Dobson circulation. Furthermore, we show that Saturn’s equatorial oscillation is driven by the seasonal variability of both the resolved planetary-scale wave activity and the interhemispheric circulation, akin to Earth’s Semi-Annual oscillation. A high-resolution three-dimensional global climate model of Saturn captures the small-scale dynamics of its stratosphere. It is able to reproduce the observed semi-annual equatorial oscillation and finds evidence of an interhemispheric meridional circulation that can explain the periodicity of its equatorial oscillation and the seasonal behaviour of hydrocarbon abundances.

Investigation of the adsorption properties of cyclic C6 molecules on h-BN/Rh(111) surface, efforts to cover the boron nitride nanomesh by graphene

The 2D atomic structure of h-BN would be an excellent dielectric layer to complement graphene electronics. When grown sequentially on metal substrates to create GR/h-BN/metal sandwich structures, these nanomaterials can be used in various applications. To this end, in this project we studied the adsorption and dissociation of cyclohexene and benzene on clean and h-BN covered Rh(111) surfaces at low and at high temperatures. Although we observed that both molecules adsorb on the h-BN/Rh(111) surface at 160 K, there is only a weak interaction between these molecules and h-BN. Moreover, h-BN proved to be completely inert to the split of cyclohexene and benzene after low temperature exposures. In our high temperature experiments, we tested the stability of h-BN towards oxygen, hydrogen and we also followed the effects of high exposure adsorption of the C6 molecules on the nanomesh. We observed a different behavior following the decomposition of the two hydrocarbon species. In one case we developed a graphene-like carbon structure in parallel with BN, while in the other process the carbon layer formed on top of the surface of h-BN/Rh(111). Our results were evidenced by Auger Electron Spectroscopy (AES), High Resolution Electron Energy Loss Spectroscopy (HREELS) and Mass Spectrometry (MS).

Achievements and Challenges of Graphene Chemical Vapor Deposition Growth

AbstractGraphene, since the first successful exfoliation of graphite, has continuously attracted attention due to its remarkable properties and applications. Recently, the research focus on graphene synthesis has been directed to the controllable synthesis of large‐area and high‐quality graphene. In the last decade, there has been great progress in the chemical vapor deposition (CVD) growth of graphene. Theoretical investigations have led to an enhanced understanding of puzzles on hydrocarbon species stability, key reaction pathways, the role of hydrogen gas, the morphology of graphene islands, and the alignment of graphene on substrates. Experimentally, high‐quality graphene is epitaxially grown on both insulating and metal substrates. Progress has also been reported on low‐temperature graphene growth and on controlling the thickness and stacking of graphene layers. In this review, the authors summarize the previous theoretical and experimental studies on graphene CVD growth and discuss the future challenges on the growth of graphene i) on insulating substrates, ii) at low temperature, iii) with controllable thickness, and iv) with selected stacking twist angles. The authors assert that the key to the continuous advancement of graphene growth is the synergy of experimental and theoretical investigations.

Competitive adsorption of methane and ethane on organic-rich shale at pressure up to 30 MPa: Experimental results and geological implications

Methane and ethane are the two most abundant hydrocarbon species in shale gas, while the adsorption behavior of their binary mixture in shale is still ambiguous. In this study, the adsorptions of methane, ethane, and their binary mixture on twelve dried mature lacustrine organic-rich shale samples were measured at 60 °C and variable pressures ranging from 0.001 to 30 MPa. The Langmuir and supercritical Dubinin–Radushkevich (SDR) models combined with the ideal adsorbed solution theory (IAST) and Extended Langmuir (EL) model were used to describe the raw adsorption isotherms. By contrast, the Langmuir model with consistent adsorbed phase volume can better describe the ethane excess adsorption. The IAST and EL models matched binary gas excess adsorption equally well. The adsorption capacity of pure ethane was about 1.6 times as large as pure methane, while the Langmuir pressure for ethane was lower. For the adsorption of pure and binary gas, organic matter was the primary contributor, followed by clay minerals. The adsorption selectivity of ethane over methane ranged from 3.49 to 8.85, which strongly depended on total organic carbon (TOC), and weakly negatively correlated with clay mineral content. The estimated gas-in-place (GIP) of binary gas ranged from 4.57 cm3/g to 8.08 cm3/g, which was about 30% larger than that of pure methane. A two-stage trend, first falling and then rising, was observed in relationship between binary gas GIP and TOC. This phenomenon could be attributed to the opposite effects of residual bitumen on shale porosity and gas adsorption. This study provides better insight in the storage mechanisms of shale gas and a basis for the reliable estimation of shale gas potential.

A Search for Heterocycles in GOTHAM Observations of TMC-1.

We have conducted an extensive search for nitrogen-, oxygen-, and sulfur-bearing heterocycles toward Taurus Molecular Cloud 1 (TMC-1) using the deep, broadband centimeter-wavelength spectral line survey of the region from the GOTHAM large project on the Green Bank Telescope. Despite their ubiquity in terrestrial chemistry, and the confirmed presence of a number of cyclic and polycyclic hydrocarbon species in the source, we find no evidence for the presence of any heterocyclic species. Here, we report the derived upper limits on the column densities of these molecules obtained by Markov Chain Monte Carlo (MCMC) analysis and compare this approach to traditional single-line upper limit measurements. We further hypothesize why these molecules are absent in our data, how they might form in interstellar space, and the nature of observations that would be needed to secure their detection.

Study on the influencing factors of spontaneous wettability transition behaviour on metallic-based surfaces

Hydrophobic surfaces and coatings have attracted more and more interest in recent years due to their broad applications in diverse areas. In many cases, a metallic surface would demonstrate a reversible wettability from hydrophilic state to hydrophobic state spontaneously. However, the wetting behavior and hydrophobic mechanism of metallic surfaces are far from clear. In this work, 304 stainless steel (SS) surface and Ni–Cu–P coatings have been chosen to investigate the intrinsic mechanism of the surface wettability transition with the help of X-ray photoelectron spectroscopy (XPS) and ambient air/vacuum storage treatment. The surface topographies, wetting behaviors and surface chemistry were studied systemically. The results showed that water contact angle (WCA) variation of the as-prepared surfaces changing from hydrophilic state to hydrophobic state is largely associated with the specific surface area. The recovery of water repellency is related to a time constant which mainly depends on micro-scale surface convolution or surface roughness. Rougher surface tends to accelerate the surface adsorption of airborne hydrocarbon species in the ambient atmosphere, leading to a more intensive WCA increase. The study provides a generic theoretical justification for relevant time-dependent wettability studies.

Molecular dynamics study of fluid-fluid and solid-fluid interactions in mixed-wet shale pores

Mixed wet pores are abundant in shales, yet there is little to no information on the behavior of fluids confined within pores characterized by one hydrophilic and one hydrophobic surface. This mixed wettability can impact fluid storage, distribution, capillary pressures and transport. In this study, we use molecular dynamics simulations to describe the initial distribution of reservoir fluids, such as multicomponent hydrocarbon mixtures and water, in mixed-wet pores. This is an essential pre-requisite to additional studies documenting fluid transport in such pores. The molecular model of the mixed wet pore used consists of kerogen separated by some distance from two clay surfaces. We evaluate spatial distribution of water and individual hydrocarbon species, at varying values of water concentration. Throughout the entire study, the results from the equilibrated system indicate a high affinity between the heavy components, such as the asphaltene/resin fraction and the kerogen surfaces. The more surprising result is the hydrogen bonding observed between the polar constituents in the asphaltene/resin fraction and water. This creates a situation where the asphaltene/resin fraction shows an affinity towards water. When this happens, the hydrophilic clay surface effectively becomes hydrophobic. A pore bounded by an asphaltene layer on one side and kerogen on the other is more oil-wetting than mixed-wet. The presence of asphaltenes can therefore expect to create conditions of modified wettability that will impact oil recovery, oil transport and distribution. Another surprising result in this work is that water forms structures that bridge between opposing surfaces of the model. These water bridges are seen to happen for water concentration values larger than 20%. In other words, water is not merely just adsorbed on to the clay surfaces, but also forms these bridge-like structures. Nevertheless, we still observe a strong affinity between the asphaltene/resin fraction and water leading to a lesser degree of mixed wettability. This study is the first, to the best of our knowledge, that considers water and multicomponent hydrocarbon mixtures in mixed-wet pores with realistic surface chemistry and constitutes a necessary first step towards additional studies related to water and hydrocarbon transport and EOR processes in shale nanopores.

Investigating the detectability of hydrocarbons in exoplanet atmospheres with JWST

Aims. We investigate at what abundances various hydrocarbon molecules (e.g. acetylene (C2H2), ethylene (C2H4), and methane (CH4)) become detectable when observing the atmospheres of various planets using the James Webb Space Telescope (JWST). Methods. We focused on atmospheric models based on the parameters of a small sample of planets: HD 189733b, HD 209458b (hot Jupiters orbiting bright stars); HD 97658b (a sub-Neptune/super-Earth orbiting a bright star); and Kepler-30c (a warm Jupiter orbiting a faint star). We computed model transmission spectra, assuming equilibrium chemistry and clear atmospheres for all planets apart from HD 189733b, where we also computed spectra with a moderate cloud layer included. We used the Bayesian retrieval package ARCiS for the model atmospheres, and simulated observed spectra from different instruments that will be on board JWST using the PandExo package. We subsequently ran retrievals on these spectra to determine whether the parameters input into the forward models, with a focus on molecular abundances, can be accurately retrieved from these simulated spectra. Results. We find that generally we can detect and retrieve abundances of the hydrocarbon species as long as they have a volume mixing ratio above approximately 1 × 10−7–1 × 10−6, at least for the brighter targets. There are variations based on planet type and instrument(s) used, and these limits will likely change depending on the abundance of other strong absorbers. We also find scenarios where the presence of one hydrocarbon is confused with another, particularly when a small wavelength region is covered; this is often improved when two instruments are combined. Conclusions. The molecules C2H2, CH4, and C2H4 will all be detectable with JWST, provided they are present in high enough abundances, and that the optimal instruments are chosen for the exoplanet system being observed. Our results indicate that generally a combination of two instruments, either NIRSpec G395M and MIRI LRS, or NIRCam F322W2 and MIRI LRS, are best for observing these hydrocarbons in bright exoplanet systems with planets of various sizes, with NIRSpec G395M and MIRI LRS the best option for the HD 189733b-like atmosphere with clouds included. The use of NIRSpec Prism is tentatively found to be best for fainter targets, potentially in combination with the MIRI LRS slit mode, although the target we test is too faint to draw any strong conclusions. Instrument sensitivity, noise, and wavelength range are all thought to play a role in being able to distinguish spectral features.

Pd-based membranes performance under hydrocarbon exposure for propane dehydrogenation processes: Experimental and modeling

In this work, a novel Pd–Ag double-skinned (DS-) membrane is used for the first time in conditions typical of propane dehydrogenation (PDH). This membrane presents a protective layer on top of the H2-selective one, which acts as shield against chemical deactivation and mechanical erosion under reaction conditions. While the protective layer is already been proven as an efficient barrier against membrane erosion in fluidized beds, there is no validation yet under PDH reaction. The DS- membrane performance is compared with a conventional (C-) Pd–Ag membrane under alkane/alkene exposure, at 400–500 °C and 3 bar, to investigate whether the incorporation of the protective layer would be suited for H2 separation in PDH systems, and if coking rate would be affected. The novel membrane shows a H2 permeance of 2.28 × 10−6 mol∙m−2 s−1∙Pa−1 at 500 ᵒC and 4 bar of pressure difference, overcoming the performance of the conventional PdAg one (1.56x∙10−6 mol m−2 s−1∙Pa−1). Both membranes present a stable H2 flux under alkane exposure, while deactivation occurs under exposure to alkenes. A model able to describe the H2 flux through Pd-based membranes is presented to fit the experimental data and predict membrane performance. The model includes mass transfer limitations in the retentate and a corrective inhibition factor to account for the competitive adsorption of hydrocarbon species in the H2 selective layer. The experimental results obtained under alkene exposure deviates from model predictions; this can be attributed to carbon deposition on the surface of the selective layer, as further detected on the DS-membrane by Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Analysis (EDX), which is the main factor for membrane deactivation.

Evolution of unregulated hydrocarbons distribution with different post injection strategies in a common-rail diesel engine

The experiments were carried out to investigate the influence of different post injection timing and post injection rate on the performance of combustion and unregulated hydrocarbons species emissions from a common-rail diesel engine. Fourier transform infrared spectroscopy was used to measure and analyze the unregulated hydrocarbons emissions which include light hydrocarbons (HCs), aromatic hydrocarbon (AHC), and n-octane (NC8). The results showed that the emissions of individual hydrocarbon species were the similar to that of single injection when the post injection time was at 20 °CA and 40 °CA. In the measured hydrocarbons components, CH4 and C4H6 species maintained a low level and weak sensitivity to the different post injection conditions. The overall variation of NC8 species emission was similar to that of THC emission and accounted for most of the THC, which indicated that most of the fuel had no chemical change and entered the exhaust directly under different post injection conditions. It should be noticed that the olefin species decreased and the alkane species increased gradually as the HCs species raised from C1 to C4. Furthermore, the distribution of HC species at 60 °CA was less changed than that of 40 °CA under different post injection rates and was closer to the required after-treatment gas atmosphere due to its larger proportion of highly reactive components.

High-crystallinity single-walled carbon nanotube aerogel growth: Understanding the real-time catalytic decomposition reaction through floating catalyst chemical vapor deposition

In this study, high-purity single-walled carbon nanotubes (SWCNTs) are synthesized with additional carrier gas through floating catalyst chemical vapor deposition. The presence of Ar during the SWCNT aerogel formation affects to the precursor decomposition and to the formation of different reactive hydrocarbons. Furthermore, the concentration of produced various carbon species is sensitive to the carrier gas compositions. The in-situ sampling methods prove the thermodynamic pathway for the hydrocarbon cracking during carbon nanotube (CNT) aerogel formation process. The addition of Ar promoted the formation of reactive hydrocarbon species, such as CH3, CH4, and C2H4/CO, to improve CNT morphology and graphitization. Ar has improved purity of CNTs compared to when only H2 is used. The synthesized CNTs were narrow in size, and the diameter decreased from 1.8 to 1.2 nm with the carrier gas composition (Rx) according to Ar addition. The IG/ID ratio of the CNTs changed from 78 to 3 at R0.1 and R0.57, respectively. Furthermore, the purity also increased to approximately 10% from 78% to 91% depending on Rx.

On the possible contribution of cationic oxygenated carbon chains CnO+, HCnO+, and OCnO+ (n = 4–9) to the diffuse interstellar bands

ABSTRACT Only four of the diffuse interstellar bands (DIBs) are currently accounted for, ascribed to electronic transitions of C$_{60}^+$. Investigations into carriers of other DIBs historically focus on charged and neutral hydrocarbons, and little information is available regarding oxygenated carbon and hydrocarbon species that result from the two most abundant heavy elements in the interstellar medium, C and O. In this study, we assess whether CnO+, HCnO+, and OCnO+ (n = 4–9) cations are viable candidates to account for DIBs using both density-functional theory (DFT) and coupled cluster single-double and perturbative triple theory, CCSD(T). For these species, the linear structures are the most stable isomers with the lowest dissociation threshold corresponding to CO loss. Optical absorptions of the oxygenated carbon chain cations are characterized by calculated vertical excitation wavelengths and their corresponding oscillator strengths using the equation-of-motion CCSD (EOM-CCSD) method. Aside from HC4O+ and HC2n +1O+, all of the species considered in this study have calculated electronic transitions that lie in the visible or near-infrared spectral regions. Minimal column densities necessary for these cations to account for DIBs have been estimated. Based on present results and the known column densities for neutral oxygenated carbon chains in TMC-1, the growth rate of charged O-bearing carbon chains via ion-neutral reaction mechanisms is judged to be too low to form a sufficient population to give rise to DIBs.

Cobalt-Activated Transfer-Free Synthesis of the Graphene on Si(100) by Anode Layer Ion Source

In this research, the graphene was grown directly on the Si(100) surface at 600 °C temperature using an anode layer ion source. The sacrificial catalytic cobalt interlayer assisted hydrocarbon ion beam synthesis was applied. Overall, two synthesis process modifications with a single-step graphene growth at elevated temperature and two-step synthesis, including graphite-like carbon growth on a catalytic Co film and subsequent annealing at elevated temperature, were applied. The growth of the graphene was confirmed by Raman scattering spectroscopy and X-ray photoelectron spectroscopy. The atomic force microscopy and scanning electron microscopy were used to study samples’ surface morphology. The temperature, hydrocarbon ion beam energy, and catalytic Co film thickness effects on the structure and thickness of the graphene were investigated. The graphene growth on Si(100) by two-step synthesis was beneficial due to the continuous and homogeneous graphene film formation. The observed results were explained by peculiarities of the thermally, ion beam, and catalytic metal activated hydrocarbon species dissociation. The changes of the cobalt grain size, Co film roughness, and dewetting were taken into account.

Petroleum Hydrocarbon Composition of Oily Sludge and Contaminated Soils in a Decommissioned Oilfield Waste Pit under Desert Conditions

Field and laboratory investigations were conducted to characterize the composition of petroleum hydrocarbons in oily sludge and the underlying contaminated soils in a decommissioned oilfield waste pit in Kuwait. The results show that the petroleum hydrocarbon composition in the oily sludge and contaminated soils was spatially variable. Highly toxic petroleum hydrocarbon species such as BTEX and PAHs were generally lacking, and both sludge- and soil-borne hydrocarbons were dominated by long-chain petroleum hydrocarbons. The soil contamination depth was generally very shallow although localized deep profiles (>0.5 m) were found. A loose relationship was established between TPH in the sludge and that in the underlying soil. On average, the soil had a greater percentage of shorter-chain hydrocarbon fractions (either aliphatics or aromatics), as compared to the sludge. The environmental risk from the oily sludge and contaminated soils is considered to be relatively low. For cost-effective management of the environmental risk of decommissioning an oilfield waste pit, containment of the sludge and contaminated soils using a soil-capping approach may be sufficient to minimize the possible adverse environmental impacts from the decommissioned waste pit, and this may represent an option that is superior to other costly remediation strategies.

Understanding High-Temperature Chemical Reactions on Metal Surfaces: A Case Study on Equilibrium Concentration and Diffusivity of C x H y on a Cu(111) Surface.

Chemical reactions on metal surfaces are important in various processes such as heterogeneous catalysis and nanostructure growth. At moderate or lower temperatures, these reactions generally follow the minimum energy path, and temperature effects can be reasonably described by a harmonic oscillator model. At a high temperature approaching the melting point of the substrate, general behaviors of surface reactions remain elusive. In this study, by taking hydrocarbon species adsorbed on Cu(111) as a model system and performing extensive molecular dynamics simulations powered by machine learning potentials, we identify several important high-temperature effects, including local chemical environment, surface atom mobility, and substrate thermal expansion. They affect different aspects of a high-temperature surface reaction in different ways. These results deepen our understanding of high-temperature reactions.

Remarkable basic-metal oxides promoted confinement catalysts for CO2 reforming

Methane and carbon dioxide reforming (dry reforming of methane, DRM) is one of the promising methods to utilize these two main greenhouse gases, which make great contribution to the global carbon neutrality strategy. It is well known that the uppermost obstacle of DRM reaction is the carbon deposition, especially at low reaction temperature. Herein, the ultrafine nickel nanoparticles (NPs) promoted by two basic metal oxides (MgO and La2O3) and enveloped in dendritic mesoporous silica (DMS) were designed and prepared (noted as Ni-MgO@DMS and Ni-La2O3@DMS). The results exhibit that the conversion of CH4 and CO2 is up to 35% and 40% in the DRM reaction over the two modified Ni@DMS catalysts at low temperature (550 °C), and no obviously carbon deposition observed during the 8 h stability test, which could be attributed to the alkaline oxides can promoting adsorption and activation of CO2 and generate more active oxygen species to activate the hydrocarbon species (CHx). Furthermore, even the reaction time extended to 50 h, the spent Ni-La2O3@DMS catalyst just has negligible amount of carbon formation. The in situ diffuse reflectance infrared Fourier transform spectroscopy result reveals that the reaction mechanism over the basic metal promoted catalyst is the Langmuir-Hinshelwood mechanism. The alkaline promoted Ni-based catalysts developed in this work could be a good candidate to the industrialization of the DRM reaction.

Characteristics of VOCs and their Potentials for O3 and SOA Formation in a Medium-sized City in Eastern China

To understand the characteristics and environmental effects of volatile organic compounds (VOCs) in a typical medium-sized city in China, manual measurements including 56 species of the nonmethane hydrocarbons (NMHCs) were taken at three urban and suburban sites in Huai’an from April to September 2019, and automatic measurements including 106 species of VOCs were taken at the urban center in May and August 2019. Spatial and temporal characteristics of the VOC concentrations were analyzed. Positive matrix factorization (PMF) model was applied to apportion VOC sources. Ozone (O3) formation potentials (OFPs) and secondary organic aerosol (SOA) formation potentials (SOAFPs) were calculated. The results show that the mean VOC concentration was much lower in the urban center than in the suburbs. Generally, proportions of both alkenes and aromatic hydrocarbons were higher and proportion of alkanes was lower in Huai’an than that in big cities, indicating emissions from solvent usage and industrial process play a more important role in the medium-sized city. The results of source apportionment show that solvent usage and industrial process together contributed 53%, and vehicle emission contributed 27% to the ambient VOCs. The dependence of VOC concentrations on temperature indicates that a considerable part of VOCs may come from fugitive emissions. The two-peak pattern of diurnal variation suggests near-surface emissions contributed a lot to the VOCs. Aromatic hydrocarbons were identified as the key component to the formation of O3 and SOA. Furthermore, biogenic emission could contribute greatly (> 20%) to the ambient VOCs during daytime in summer, which may have significant effects on O3 formation. Aromatic hydrocarbons were identified as the key component to the formation of O3 and SOA, which should be given more attention in developing air pollution control strategies.

Ceria-supported niobium oxide catalyst for low-temperature oxidation of 1,3-butadiene

Low-temperature oxidation represents an economically efficient way to convert spinoff hydrocarbons such as butadiene into nontoxic species. This study investigates the catalytic oxidation of 1,3-butadiene over ceria-supported niobium oxide, exploring the synthesis routes and catalytic performances. Experimental characterization techniques, including X-ray spectroscopy and diffractometry, microscopy, and other micro-characterisations, elucidate the structure of the catalysts as corroborated by the density functional theory (DFT) method. DFT calculations constructed the underlying oxidative reaction mechanisms that ensue through accessible activation energies in steps that feature subsequent CC bond fissions, H transfer reactions, CO desorption, and formation of CO2 molecules. The results show that, the niobium oxide assumes mainly the form of Nb2O5 on ceria supports, and plays a significant role in switching the physicochemical nature of ceria and the resulting catalysts. Despite a relatively lower surface area, the NbOx/CeO2 catalysts exhibit superior performances in the conversion of butadiene compared to pure ceria. The catalyst prepared with 10 wt.% of Nb has the best catalytic performance with 82% conversion of butadiene, highest reaction rate, and selectivity towards CO2 of 95% at the temperature range of 300 – 400 °C and a gas hourly space velocity (GHSV) of 34,600 h−1. Obtained results entail practical environmental implications in the catalytic destruction of stable hydrocarbon species.

ПОВЕДЕНИЕ ХИМИЧЕСКИ РЕАГИРУЮЩИХ ОРГАНИЧЕСКИХ ПРИМЕСЕЙ В ЦИРКУЛЯЦИОННОМ НАТРИЕВОМ КОНТУРЕ

Mineral oils and some other organic substances are employed as cooling-agents and lubricators of reactor equipment with movable parts. At normal operation condition these substances are able to penetrate into reactor protective gas plenum in vapor and aerosols forms. Due to their thermolysis and interaction with sodium there are produced hydrogen and different hydrocarbons species, that are detected usually in cover gas. Kinetic of the above processes is dependent on temperature conditions and with temperature increase from 350 to 500 °C the evolution of some hydrocarbons could rise up to 1-2 orders of magnitude. There were published notes on accidental ingress of oil in the primary circuit of fast reactor sodium coolant. Investigation results of such accidents simulation on the experimental sodium circuit are presented in the report. There are discussed results on kinetic of volatile hydrocarbons evolution from oil-pyrolysis products depositions on the circuit pipes walls and gas plenum surfaces. As well, different brands of oil are compared on their behavior in sodium environment.

Significant Effect of Rh on the h-BN-Supported Ni Catalyst for Dry Reformation of CH4: Insights from Density Functional Theory and Microkinetic Analysis

The design of a catalyst by managing catalytic sites on an atomic scale is significant for tuning catalytic performance and offering high activity and selectivity for dry reforming of methane (DRM). We report a synergy effect of two sets of active sites (Ni and Rh) anchored on the surface hexagonal boron anitride nanosheets(h-BN), the whole reaction mechanism of DRM, as well as the competition processes over h-BN sheet-supported Ni-Rh catalysts (labeled as Ni9/h-BN and Ni8Rh1/h-BN) were studied by density functional theory calculations and microkinetic model analysis in the present work. Our present results show that the stability of hydrocarbon species like CHx(x = 1–4) on the Ni8Rh1/h-BN is significantly lower than that of Ni9/h-BN because of less electron transfer, and thus, strong carbon deposition resistance would be expected after the addition of Rh from the perspective of thermodynamics. CO2 activation is more efficient than that of CH4, and both CH4 and CO2 activation on Ni8Rh1/h-BN is more facile than that of pure Ni9/h-BN, and thus, higher catalytic activity of DRM can be expected on Ni8Rh1/h-BN. CO2 tends to decompose directly on both surfaces, and it was also found that O* is the main oxidizing agent for CH* intermediates and through the CH–O oxidation mechanism. Compared with the Ni9/h-BN surface, the selectivity of the DRM reaction is better on the Ni8Rh1/h-BN surface, and the ratio of H2/CO is close to one on the Ni8Rh1/h-BN surface based on the microkinetic model analysis. The microkinetic model result also shows that coke is difficult to form on the surface of Ni8Rh1/h-BN under experimental conditions. These synergistic effects of the two sets of atom sites on the same surface demonstrated a new method for designing a catalyst with high selectivity and stability for DRM.