CH4 Partial Pressure Research Articles

Effect of CO2 injection on CH4 desorption rate in poor permeability coal seams: An experimental study

CO2 injection into coal seams is an effective way for reducing greenhouse gas emissions and increasing gas recovery in coal seams. To study the influence rule of CO2 injection on the CH4 desorption rate, an experimental system of CO2 displacing CH4 was used to analyse the changes in gas composition, outlet flow rate, coal seam temperature, and displacement efficiency parameters during CO2 injection. From the perspective of enhancing CH4 recovery, the CO2 critical injection amount (Vinc) is 297.4 L and critical injection time is 188.75 min. When the CO2 injection amount V < Vinc, the amount of CH4 desorption, CO2 storage, and CH4/CO2 gas content all increased. When V > Vinc, except CH4 desorption amount remained almost unchanged, the other parameters increased. In the process of CO2 displacing CH4, the coal seam temperature rises (exothermic process), showing a law of “hierarchical displacement”. With the injection of CO2, the pore pressure first decreased and then increased, the CH4 partial pressure decreased, and the effective diffusion coefficient first increased and then decreased. After the injection of CO2, the desorption time of CH4 was 269.45min earlier and the desorption rate of CH4 was increased by 12.43 %.

Eutrophication decreased CO2 but increased CH4 emissions from lake: A case study of a shallow Lake Ulansuhai

Eutrophic lakes, especially shallow eutrophic lakes, disproportionately contribute to greenhouse gas (GHG) emissions. To investigate the effects of eutrophication on GHG dynamics, we conducted field measurements every three months from January 2019 to October 2019 in Lake Ulansuhai, a shallow eutrophic lake (mean depth of 0.7 m) located in a semi-arid region in Northern China. We found that Lake Ulansuhai was a predominantly source of atmospheric carbon dioxide (CO2); however, it converted to a CO2 sink in July due to eutrophication. It was also a strong source of methane (CH4) with a mean CO2 emission of 35.7 ± 12.1 mmol m−2 d−1 and CH4 emission of 5.9 ± 2.9 mmol m−2 d−1. The CO2 concentrations in most sites and CH4 concentrations in all sites were supersaturated, with the average partial pressure of CO2 (pCO2) being 654±34 μatm and the partial pressure of CH4 (pCH4) being 157±37 μatm. The partial pressures and emissions of the greenhouse gases exhibited substantial seasonal and spatial variations. The correlation analysis between the trophic level index and the partial pressure of the greenhouse gases indicated that eutrophication could significantly decrease the CO2 emissions but increase the CH4 emissions from the lake, resulting in a CH4 and CO2 emission ratio of approximately 2 in terms of global warming potential. Eutrophication decreased the pCO2 in the lake and subsequently increased the pCH4 due to nutrient input, thereby enhancing primary production. The results indicated that shallow eutrophic lakes in arid regions are strong sources of CH4 and that eutrophication could alter the greenhouse gas emission patterns.

Adsorption of CH4, N2, CO2, and their mixture on montmorillonite with implications for enhanced hydrocarbon extraction by gas injection

Understanding the adsorption behaviors of CH4, N2, CO2, and their mixture in clay minerals is crucial to the approach of enhanced hydrocarbon recovery using gas injection with application in clay-rich gas-shale reservoirs. In this study, the adsorption measurements of CH4, N2, CO2, and their mixture on montmorillonite were conducted using a gravimetric technique. The underlying competitive adsorption mechanism of CH4, N2, and CO2 on montmorillonite was discussed using Henry's constant, adsorption selectivity, and thermodynamic variables. The adsorption selectivity of CO2 over N2 (αCO2/N2) was the highest, followed by the selectivity of CO2 over CH4 (αCO2/CH4) and that of CH4 over N2 (αCH4/N2). The αCO2/CH4 value was greater than one, confirming that CO2 can stimulate CH4 desorption through molecular swapping. Reducing the temperature increased the selectivity and the desorption of the pre-adsorbed gas was more easily triggered by the injection of the favorably adsorbing gas at lower temperatures. The uptake and affinity of CO2 were the highest, whereas N2 exhibited the smallest uptake and affinity. In addition, CO2 adsorption was more spontaneous than CH4 and N2 adsorption. Although N2 adsorption was less favorable than CH4 adsorption, injecting N2 could lower the spontaneity of CH4 adsorption by decreasing the CH4 partial pressure. The adsorbed CO2 molecules were the most ordered, and the freedom of adsorbed N2 molecules was the highest. The adsorption isotherm of the mixed gases was closer to that of the strong adsorption component. Thus, a strong adsorption gas plays a leading role in the adsorption of mixed gases.

Kinetic modeling and reaction pathways for thermo-catalytic conversion of carbon dioxide and methane to hydrogen-rich syngas over alpha-alumina supported cobalt catalyst

This study investigates the kinetic modeling and reaction pathway for the thermo-catalytic conversion of methane (CH4) and Carbon dioxide (CO2) over alpha-alumina supported cobalt catalyst. Rate data was obtained from the thermo-catalytic reaction at a temperature range of 923–1023 K and varying CH4 and CO2 partial pressure (5–50 kPa). The rate data was significantly influenced by the changes in the reaction temperature as well as the CH4 and CO2 partial pressure. To estimate the kinetic parameters, the rate data were fitted with five Langmuir-Hinshelwood kinetic models. The discrimination of the kinetic models using different parameters revealed that the Langmuir-Hinshelwood kinetic model with the assumption of CH4 being associatively adsorbed on a single and CO2 being dissociative adsorbed with bimolecular surface reaction best described the rate data. The analysis of the kinetic model using a non-linear regression solver results in activation energies of 15.88 kJ/mol, 36.78 kJ/mol, 65.51 kJ/mol, and 41.08 kJ/mol for CH4 consumption, CO2 consumption, H2 production, and CO production, respectively. The thermo-catalytic reaction was influenced by carbon as indicated by the rate of carbon deposition which was mainly caused by methane cracking. The reaction pathway for the thermo-catalytic conversion of the CH4 and CO2 over the alpha-alumina supported cobalt catalyst can best be described as by CH4 associative adsorption on the alpha-alumina supported cobalt catalyst single site and CO2 dissociative adsorption with bimolecular surface reaction.

Self-Pillared Ultramicroporous Carbon Nanoplates for Selective Separation of CH4 /N2.

There is growing evidence that pillaring up a densely packed ultramicroporous two-dimensional (2D) structure is an effective strategy to reduce their internal diffusion. Reliable pillaring paradigms, however, is rather challenging. Here we report a one-pot multi-component sequential assembly method for the preparation of a new self-pillared 2D polymer and ultramicroporous carbon with integrated surface protrusions. The molecular level pillaring process is surprisingly fast, that is, in 10 min. The thickness of nanoplate edge and the density (roughness), angle as well as height of protrusions can be precisely tuned. Exemplified in coal bed methane purification/separation, this unique pillared 2D carbons exhibit a CH4 /N2 selectivity up to 24 at a low CH4 partial pressure and two orders of magnitude faster CH4 diffusion kinetics than the commercial carbon molecular sieves. This solution synthesis methodology is generalizable for creation and fine tuning of pillared 2D heterostructures.

Self‐Pillared Ultramicroporous Carbon Nanoplates for Selective Separation of CH4/N2

AbstractThere is growing evidence that pillaring up a densely packed ultramicroporous two‐dimensional (2D) structure is an effective strategy to reduce their internal diffusion. Reliable pillaring paradigms, however, is rather challenging. Here we report a one‐pot multi‐component sequential assembly method for the preparation of a new self‐pillared 2D polymer and ultramicroporous carbon with integrated surface protrusions. The molecular level pillaring process is surprisingly fast, that is, in 10 min. The thickness of nanoplate edge and the density (roughness), angle as well as height of protrusions can be precisely tuned. Exemplified in coal bed methane purification/separation, this unique pillared 2D carbons exhibit a CH4/N2 selectivity up to 24 at a low CH4 partial pressure and two orders of magnitude faster CH4 diffusion kinetics than the commercial carbon molecular sieves. This solution synthesis methodology is generalizable for creation and fine tuning of pillared 2D heterostructures.

A potential catalyst for continuous methane partial oxidation to methanol using N2O: Cu-SSZ-39.

Continuous catalytic methanol production from methane is reported on Cu-SSZ-39 using N2O as an oxidant. Through optimization of CH4, N2O and H2O partial pressures, a methanol formation rate of 499 μmolCH3OH g-1 h-1 and a methanol selectivity of 34% is achieved.

On the effect of biogas composition on the H2 production by sorption enhanced steam reforming (SESR)

Abstract Biogas is a valuable source of renewable energy produced from biodegradable organic materials via anaerobic digestion. The production of H2 by sorption enhanced steam reforming (SESR) of biogas has been studied thermodynamic and experimentally. A Pd/Ni–Co catalyst and dolomite as CO2 sorbent were used. The effect of biogas composition (CH4/CO2 vol%) on the process was evaluated at 600 and 650 °C in a fluidized bed reactor using biogas CO2 concentrations of 5–50 vol%. During conventional biogas steam reforming (SR), high CH4 partial pressures in the feed favor the process, producing high H2 concentrations. During biogas SESR, CO2 was effectively removed from the gas phase by the sorbent for all the biogas compositions, and it did not alter the process compared to pure methane. Steam methane reforming (SMR) and water-gas shift (WGS), together with carbonation, were the main reactions occurring during biogas SESR. Dry (or CO2) methane reforming did not occur under the conditions studied due to the relatively low temperature and the presence of steam. High H2 purity (98.4 vol%) and H2 yield (91%) were experimentally obtained, pointing out the biogas SESR as a promising technology for the efficient production of high-purity high-yield hydrogen from a renewable source.

Response Surface Optimization of Hydrogen‐Rich Syngas Production by Greenhouse Gases Reforming

AbstractThe effect of process interaction and response surface optimization of hydrogen‐rich syngas production by catalytic carbon dioxide (CO2) reforming of methane (CH4) was evaluated. The Box‐Behnken design was applied to investigate the influence of CH4 partial pressure, CO2 partial pressure, and temperature on the hydrogen yield. The analysis of variance indicated that temperature and CH4 partial pressure had the most significant impact on the hydrogen yield. Under optimum conditions a maximum hydrogen yield of 71.38 % was achieved. Model validation with the ideal conditions confirmed close agreement of the predicted hydrogen yields with experimental values.

The reactivity and initial carbonization of an Unsupported Nickel catalyst in dry reforming of methane

High speed product gas analysis during the dry reforming of CH4 allows the observation of transient elevated H2 and CO production rates, combined with high initial conversions of CH4 and CO2. The transients are observed in the first 120 s of the reaction, followed by a lower steady-state production rate after 3–5 min. The catalytic reactivity in the initial 120 s is important in understanding the catalyst performance and determining the reactions responsible for carbon deposition. Monitoring the changes in the H2 and CH4 partial pressures from the start, through the transient production regime, and on through the steady-state regime, shows that the transient reactivity is directly related to the decomposition of CH4. This finding is further supported by the linear trend found between the H2/CO ratio and the carbon deposition in the peak region of the product gas profile. Although significant amounts of carbon are deposited on the Ni surface, it is not completely deactivated at any of the reaction temperatures in the 500–800 °C range explored herein. Characterizing the initial reactivity in terms of carbon deposition and catalyst performance in dry reforming of CH4 may lead to changes in the sampling technique for researchers working with reforming reactions, and optimized catalysts that exhibit reduced initial carbon deposition.

Bidirectional properties of TiC, TiN and TiNC thin films deposited by radio frequency magnetron sputtering.

Titanium nitride (TiN), titanium carbide (TiC) and titanium carbonitride (TiNC) thin films show promising practical applications due to their photoelectric properties and corrosion behaviour. In this work, we investigated the factors which may affect the optical properties and the corrosion behaviour of these coatings. The titanium coatings were carried out by sputtering using the target of Ti6Al4V (purity 99.96%) with different N2, CH4 and Ar partial pressures. XRD, FTIR, Raman and SEM with EDX studies show the formation of titanium nitride, titanium carbide coatings. Uv-vis spectroscopy was carried out to estimate the optical properties using the numerical Swanepoel method. Potentiodynamic polarization studies in Hank's solution show that the corrosion resistance is found to be in the order of C-TiN(2) > C-TiN(1) > TiN > TiC. A high protective efficiency was determined (60%) when comparing TiNC(2) and TiC corrosion current densities, which confirms the lower corrosion velocity and the higher passivation stability of the coatings composed with TiN and TiC phases. Electrochemical impedance spectroscopy studies show that the Rct increases in the following order: TiC < TiN < C-TiN(1) < C-TiN(2), highlighting the fact that C-TiN(2) coating has the higher corrosion resistance.

The Reaction Mechanism and Its Kinetic Model of CO2 Reforming with CH4 over Ni-Mg15@HC Catalyst

In this paper, the kinetic of CO2 dry reforming with CH4 (DRM) over the Ni-Mg15@HC catalyst was studied after excluding the influence of internal and external mass transfer at 700–850 °C. At the same time, the partial pressures of CH4 and CO2 were varied from 10 to 50 kPa. The experimental results demonstrated that the reaction rate was sharply increased with the increase of CH4 partial pressure, while the increase of CO2 partial pressure led to a relative increase of the reaction rate. Therefore, it could be said that CH4 dissociation was the rate determining step for DRM reaction. Moreover, the apparent activation energy of CH4 consumption (48.6 kJ/mol) during DRM reaction was higher than that of CO2 consumption (30.1 kJ/mol), which also confirmed the above assumption. On the basis of the reaction mechanism, a Langmuir–Hinshelwood kinetic rate model was developed, and the kinetic parameters were also estimated by the nonlinear least square regression method. The developed model could satisfactorily fit the experimental data, and R2 was as high as 0.965. The apparent activation energy of CH4 consumption during DRM reaction was higher than that of CO2, then the rate determining step was determined. A kinetic rate model was developed, which could well describe the experiment.

Numerical study on injection of flue gas as a heat carrier into coal reservoir to enhance CBM recovery

A hydraulic-mechanical-thermal coupled numerical model for enhanced CBM recovery by injecting the flue gas (flue gas ECBM) is established, which fully couples the gas-water two-phase flow, competitive adsorption and temperature change as well as coal deformation. The model is first validated, then used to analyze the effects of different injectant components and temperature on CH4 production, CO2 storage and the evolution of permeability. The mechanism that enhanced CBM recovery and CO2 sequestration by injecting flue gas is discussed from the perspectives of competitive adsorption and selective diffusion in the molecule scale as well as the permeability evolution. CO2 can be competitively adsorbed on the surface of coal pores to desorb adsorbed CH4, while N2 desorbs adsorbed CH4 by effectively reducing the CH4 partial pressure in the pores, enhanced CBM recovery by injection of flue gas is the result of the combination of these two effects. During the flue gas ECBM process, the permeability first decreases under the coaction of coal matrix expansion and effective stress increase; subsequently, the desorption of adsorbed CH4 induced by the N2 component is dominant, which leads to a significant increase in permeability. Appropriately increasing the injection temperature of flue gas is conducive to the desorption of adsorbed CH4 , and thus beneficial to the permeability and CO2 sequestration. Before the arrival of CO2, some adsorbed CH4 can be desorbed first under the action of N2, which is not only beneficial to permeability, but also provides more adsorption sites for CO2 adsorption. However, the strategies for managing N2 breakthroughs are needed to achieve an optimal balance between CH4 production, CH4 purity and CO2 sequestration over the entire project period.

Artificial Intelligence Modelling Approach for the Prediction of CO-Rich Hydrogen Production Rate from Methane Dry Reforming

This study investigates the applicability of the Leven–Marquardt algorithm, Bayesian regularization, and a scaled conjugate gradient algorithm as training algorithms for an artificial neural network (ANN) predictively modeling the rate of CO and H2 production by methane dry reforming over a Co/Pr2O3 catalyst. The dataset employed for the ANN modeling was obtained using a central composite experimental design. The input parameters consisted of CH4 partial pressure, CO2 partial pressure, and reaction temperature, while the target parameters included the rate of CO and H2 production. A neural network architecture of 3 13 2, 3 15 2, and 3 15 2 representing the input layer, hidden neuron layer, and target (output) layer were employed for the Leven–Marquardt, Bayesian regularization, and scaled conjugate gradient training algorithms, respectively. The ANN training with each of the algorithms resulted in an accurate prediction of the rate of CO and H2 production. The best prediction was, however, obtained using the Bayesian regularization algorithm with the lowest standard error of estimates (SEE). The high values of coefficient of determination (R2 &gt; 0.9) obtained from the parity plots are an indication that the predicted rates of CO and H2 production were strongly correlated with the observed values.

Magnitudes and Drivers of Greenhouse Gas Fluxes in Floodplain Ponds During Drawdown and Inundation by the Three Gorges Reservoir

AbstractHydropower reservoirs are well‐known emitters of greenhouse gases to the atmosphere. This is due in part to seasonal water level fluctuations that transfer terrestrial C and N from floodplains to reservoirs. Partial pressures and fluxes of the greenhouse gases CH4, CO2, and N2O are also a function of in situ biological C and N cycling and overall ecosystem metabolism, which varies on a diel basis within inland waters. Thus, greenhouse gas emissions in hydropower reservoirs likely vary over seasonal and diel time scales with local hydrology and ecosystem metabolism. China's Three Gorges Reservoir is among the largest and newest in the world, with a floodplain that encompasses approximately one third of the reservoir area. We measured diel partial pressures and fluxes of greenhouse gases in ponds on the Three Gorges Floodplain. We repeated these measurements on the submerged floodplain following inundation by the Three Gorges Reservoir. During reservoir drawdown, CH4 ebullition comprised 60–68% of emissions from floodplain ponds to the atmosphere. Using linear mixed effects modeling, we show that partial pressures of CH4 and CO2 and diffusive CO2 fluxes in floodplain ponds varied on a diel basis with in situ respiration. Floodplain inundation by the Three Gorges Reservoir significantly moderated areal CH4 diffusion and ebullition. Diel pCO2, pCH4, pN2O, and diffusive fluxes of CO2 on the submerged floodplain were also driven by in situ respiration. The drawdown/inundation cycle of the Three Gorges Reservoir therefore changes the magnitudes of aquatic greenhouse gas fluxes on its floodplain.

Poly-β-hydroxybutyrate Production by Methylosinus trichosporium OB3b at Different Gas-phase Conditions.

BackgroundThe utilization of methane for production of Poly-β-hydroxybutyrate (PHB) not only cuts the emissions of greenhouse gases but also greatly reduces PHB production cost.ObjectivesThe aim of this study was to determine the effects of gas-phase conditions on PHB production by Methylosinus trichosporium OB3b.Materials and MethodsBacterial cultivation and PHB production were conducted in a series of sealed serum bottles. Nitrogen-free mineral salts medium was used to induce PHB production in the presence or absence of N2 in the headspace.ResultsIn the absence of N2, the highest PHB content (i.e., 52.9% of the dry cell weight with a PHB concentration of 814.3 mg.L-1) was obtained at a ratio of CH4:O2=2:1. Further study at different O2 concentrations with a fixed CH4 partial pressure in absence of N2 showed that PHB accumulation by methanotroph could be tolerated high oxygen partial pressure and its respond to the variation of the oxygen concentration depends on the methane partial pressure. In presence of N2, with headspace gas replenished only when oxygen was almost depleted, the degradation of intracellular PHB has appeared. In the regimen of updating headspace gas at the point when the PHB content began to decrease, the highest PHB content (i.e., 55.5% of the dry cell weight with 901.8 mg.L-1 PHB concentration and 12.5 mg.L-1.h-1PHB productivity) was obtained at 0.2 atm O2 and PHB accumulation was depressed with an oxygen concentration greater than 0.3 atm.ConclusionsThe methanotroph responses differentially to the increase in the oxygen partial pressure with regard to PHB accumulation either in the presence or in the absence of N2.

Deposition and Thermal Stability of DLC/Si-N Composite Films Synthesized Using a Sputtering-PBII Hybrid System

Diamond-like carbon (DLC) is a metastable amorphous material that exhibits unique properties. However, there are many limitations regarding the use of this material due to factors such as its tribological characteristics at high temperature and limited thermal stability. In this study, the thermal stability and tribological properties of DLC/silicon-nitrogen (DLC/Si-N) composite films were investigated and compared to those of pure DLC films. All the films were synthesized using a combination of radio frequency (RF) magnetron sputtering and plasma-based ion implantation (PBII) (a so-called sputtering-PBII hybrid system) which is newly developed by us. A high purity silicon nitride (99.9%) disk was used as the target, applying an RF power in the range of 500 - 700 W and a negative pulsed bias voltage of 5 kV to the substrate. An Ar-CH4 mixture was used as the reactive gas. The CH4 partial pressure was varied between 0 and 0.15 Pa, while the total gas pressure and total gas flow were fixed at 0.30 Pa and 30 sccm, respectively. The structures of the resulting films were characterized using Raman spectroscopy, while the thermal stabilities were assessed using thermogravimetric-differential thermal analysis (TG-DTA) and friction coefficients were obtained via ball-on-disk friction tests. The results indicate that the DLC/Si-N composite films produced in this work exhibit improved thermal stability relative to that of pure DLC owing to the presence of thermally stable atomic-scale Si-N compound in the carbon main flame networks. A DLC/Si-N film containing approximately 11 at.%Si and 18.5 at.%N shows good thermal stability in air over 800°C up to 1100°C, together with excellent tribological performance at 500°C in air. Overall, the data demonstrate that DLC/Si-N composite films offer improved thermal stability and superior tribological performance at high temperatures.

Influence of surface energy and elastic strain energy on the graphene growth in chemical vapor deposition

Polycrystalline metal substrates such as copper (Cu) have been intensively used to grow graphene in chemical vapor deposition (CVD) technique. It has been observed that crystal orientations affect the quality of graphene produced to some degree. The existence of crystal orientations caused graphene to grow randomly on top of Cu which also resulted on the formation of polycrystalline graphene. Despite this, the influence of crystal orientations on the quality of graphene produced are not yet fully understood. There are two possible factors that could affect graphene growth from crystal orientation point of view; surface energy and elastic strain energy. The understanding towards these both factors might beneficial to control the quality of graphene. This paper thus aims to highlight the influence of surface energy and elastic strain energy on the graphene growth in CVD. Substrate used were single crystal Cu with (111), (110) and (100) orientations. The graphene was grown inside a closed reaction chamber with the presence of argon (Ar), hydrogen (H2) and methane (CH4) gases with partial pressure ratio of 0.6: 0.2: 0.2 at 1 atm, 1000 ˚C in 30 minutes. The quality of the as-grown graphene was identified using Raman spectroscopy. The Raman spectra show the existence of graphene peak for all the Cu substrates. The calculation of ID/IG ratio revealed that the Cu (100) possessed the lowest amount of defects compared to Cu(110) and Cu(111). While I2D/IG ratio fluctuated between 0.22 to 0.34 suggested that the crystal orientation does not control the thickness of graphene layer at these reaction conditions. The usage of higher CH4 partial pressure produced a thicker graphene. It is assumed that the thickness of the graphene exceeded the critical thickness thus elastic strain energy becomes the dominant factor in controlling graphene growth. Larger lattice mismatch causes major defects on graphene and this result has been shown in graphene grown on top of Cu(111). These findings thus would give a new insight to tailor the high-quality large-area graphene growth in CVD.

Oxygen Reduction Reaction Properties for Dry-Process Synthesized Pt/TaCx Nanoparticles

Oxygen reduction reaction (ORR) activity and electrochemical structural stability of Pt/Ta-carbide nanoparticles (Pt/TaCx NPs) were investigated. The Pt/TaCx NPs were fabricated via arc plasma deposition (APD) of Ta under CH4 partial pressure (0.05 Pa) onto a highly oriented pyrolytic graphite (HOPG) substrate, followed by electron-beam deposition of Pt in ultra-high vacuum (UHV; ~10-8 Pa). X-ray diffraction patterns of the APD-TaCx samples showed that the diffraction peak due to TaC (rock-salt structure), exhibiting tantalum carbide which can be synthesized through the APD of Ta in CH4 atmosphere. The ORR activity of pristine Pt/TaCx samples is higher than that of the Pt/Ta alloy NPs prepared in UHV. Furthermore, the accelerated durability test results showed that the carbonization of Ta improves the ORR durability. The results clearly reveal that early transition metal carbides, e.g., TaC, are effective as core materials of core-shell-type Pt-based ORR catalysts.

Oxygen Reduction Reaction Properties for Dry-Process Synthesized Pt/TaCx Nanoparticles

Introduction To develop highly active and durable cathode electro-catalysts for polymer electrolyte fuel cell (PEFCs), core-shell type nanoparticles (NPs) have been actively studied. It is well known that oxygen reduction reaction (ORR) properties of the core-shell NPs greatly depend on the core-materials (transition metal elements (M) and/or Pt-M alloys). Particularly, deactivation of ORR under the PEFC operating conditions (low pH, electrochemical potential fluctuations) through elution of M is serious issue. Therefore, developments of highly-stable core materials under the operating conditions have been needed for practical applications of the core-shell type NPs. Ham et al. reported that early transition metal carbides, such as TaCx and HfCx, show high thermal stability and high corrosion resistance under the PEFC operating condition [1]. In this study, we prepared Pt/TaCx NPs by using arc-plasma deposition (APD) of TaCx followed by electron-beam deposition of Pt in ultra-high vacuum (UHV; ~10-8Pa) and investigated the ORR properties (initial activity and electrochemical stability) of the Pt/TaCx NPs. Experimental Highly-oriented pyrolytic graphite (HOPG) was used as a substrate. First, HOPG was scraped by Scotch tape in air and cleaned by annealing for 30 min in UHV. TaCx NPs are synthesized by using APD (Advanced RICO; APS-1) of Ta at substrate temperatures of 1173K or 1273K under CH4 partial pressure of 0.05 Pa. Subsequently, Pt was deposited on the TaCx NPs/HOPG at 873K by electron-beam deposition in UHV. As a reference, Pt/Ta NPs was fabricated through APD of Ta followed by the electron-beam deposition of Pt at 873K in UHV. The prepared Pt/TaCx and Pt/Ta NPs samples were transferred from UHV to electrochemical (EC) setup without air exposure to avoid sample oxidation and contamination. Cyclic voltammetry (CV) was performed in N2-purged 0.1 M HClO4. After that, linear sweep voltammetry (LSV) for ORR was conducted by using rotating disc electrode (RDE) method in O2-saturated 0.1 M HClO4. ORR activity was evaluated as j k values at 0.9 V vs. RHE: the j k value was estimated from Koutecky-Levich plots and electrochemical surface area (ECSA) of Pt. The electrochemical stabilities of the samples were discussed based on change in the j k values during applying square-wave potential cycles (PCs) between 0.6 (3 s) and 1.0 V (3 s) in O2-saturated 0.1 M HClO4 at a room temperature. Crystal structures, surface morphologies, and micro-structures of the prepared NPs samples were observed by XRD, scanning tunneling microscopy (STM), and scanning transmission electron microscope (STEM) combined with energy dispersive X-ray spectrometry (EDS), respectively. Results and Discussion STM images of the Pt/Ta and Pt/TaCx (1173K & 1273K) NPs were shown in Fig. 1(a). The NPs with average diameter of ca. 6 nm are synthesized on the HOPG substrate, irrespective of the Ta deposition conditions (with or without CH4 partial pressure during APD). Fig. 1(b) shows CVs for the corresponding NPs. Hydrogen (QH; 0.05 ~ 0.35 V) and OH-related (QOH; 0.6 ~ 1.0 V) charges for both the Pt/TaCx NPs are higher than that for the Pt/Ta NPs. The evaluated specific ORR activities (j k / ECSA) of the samples are summarized in Fig. 1(c). Filled and hatched bars are the activity before and after 10k PCs of each samples, respectively. One might notice that both Pt/TaCx NPs exhibited much higher activity than the Pt/Ta NPs even after the 10k PCs. Especially, the Pt/TaCx - 1173K shows highest ORR activity and durability among the samples: the retention rate after 10k PCs was ca. 85% of the initial activity. The results clearly reveal that, as for the core materials, tantalum carbide is effective for enhancing ORR activity as well as durability of the core-shell type Pt-based NPs. Acknowledgement This study was supported by the new energy and industrial technology development organization (NEDO) of Japan.