228,857 research outputs found

    First-principles extrapolation method for accurate CO adsorption energies on metal surfaces

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    We show that a simple first-principles correction based on the difference between the singlet-triplet CO excitation energy values obtained by DFT and high-level quantum chemistry methods yields accurate CO adsorption properties on a variety of metal surfaces. We demonstrate a linear relationship between the CO adsorption energy and the CO singlet-triplet splitting, similar to the linear dependence of CO adsorption energy on the energy of the CO 2π\pi* orbital found recently {[Kresse {\em et al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations underestimate the CO singlet-triplet excitation energy ΔEST\Delta E_{\rm S-T}, whereas coupled-cluster and CI calculations reproduce the experimental ΔEST\Delta E_{\rm S-T}. The dependence of EchemE_{\rm chem} on ΔEST\Delta E_{\rm S-T} is used to extrapolate EchemE_{\rm chem} for the top, bridge and hollow sites for the (100) and (111) surfaces of Pt, Rh, Pd and Cu to the values that correspond to the coupled-cluster and CI ΔEST\Delta E_{\rm S-T} value. The correction reproduces experimental adsorption site preference for all cases and obtains EchemE_{\rm chem} in excellent agreement with experimental results.Comment: Table sent as table1.eps. 3 figure

    Towards estimation of CO<sub>2</sub> adsorption on highly porous MOF-based adsorbents using gaussian process regression approach

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    In recent years, new developments in controlling greenhouse gas emissions have been implemented to address the global climate conservation concern. Indeed, the earth's average temperature is being increased mainly due to burning fossil fuels, explicitly releasing high amounts of CO(2) into the atmosphere. Therefore, effective capture techniques are needed to reduce the concentration of CO(2). In this regard, metal organic frameworks (MOFs) have been known as the promising materials for CO(2) adsorption. Hence, study on the impact of the adsorption conditions along with the MOFs structural properties on their ability in the CO(2) adsorption will open new doors for their further application in CO(2) separation technologies as well. However, the high cost of the corresponding experimental study together with the instrument's error, render the use of computational methods quite beneficial. Therefore, the present study proposes a Gaussian process regression model with four kernel functions to estimate the CO(2) adsorption in terms of pressure, temperature, pore volume, and surface area of MOFs. In doing so, 506 CO(2) uptake values in the literature have been collected and assessed. The proposed GPR models performed very well in which the exponential kernel function, was shown as the best predictive tool with R(2) value of 1. Also, the sensitivity analysis was employed to investigate the effectiveness of input variables on the CO(2) adsorption, through which it was determined that pressure is the most determining parameter. As the main result, the accurate estimate of CO(2) adsorption by different MOFs is obtained by briefly employing the artificial intelligence concept tools

    Mechanism of efficient carbon monoxide oxidation at Ru(0001)

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    We performed density-functional theory calculations using the generalized gradient approximation for the exhange-correlation functional to investigate the unusual catalytic behavior of Ru under elevated gas pressure conditions for the carbon monoxide oxidation reaction, which includes a particularly high CO_2 turnover. Our calculations indicate that a full monolayer of adsorbed oxygen actuates the high rate, enabling CO_2 formation via both scattering of gas-phase CO molecules as well as by CO molecules adsorbed at oxygen vacancies in the adlayer, where the latter mechanism is expected to be very efficient due to the relatively weak adsorption energy of both CO and O, as well as the close proximity of these reactants. In the present paper we analyse the bonding and electronic properties associated with the reaction pathway for CO_2 production via the scattering reaction. We find that the identified ``bent'' transition state is due to electron transfer into the unoccupied 2 pi orbitals of the CO molecule which reduces the Pauli repulsion between the impinging CO and the O-covered surface. Bond formation to CO_2 then proceeds by electron transfer back from the CO 2 pi orbitals into the bonding region between CO and the adsorbed O atom.Comment: 20 pages, 7 figures. J. Vac. Sci. and Techn., in press (submitted September 1996

    FIRST PRINCIPLE INSIGHT INTO Co-DOPED MoS2 FOR SENSING NH3 AND CH4

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    In this work we present the atomistic computational study of the adsorption properties of Co doped MoS2 adsorbed ammonia (NH3) and methane (CH4). The adsorption distance, adsorption energy (Ead), charge transfer (Qt), bandgap, Density of States (DOS), Projected Density of States (PDOS), transport properties, sensitivity and recovery time have been reported. The diffusion property of the system was calculated using Nudge Elastic Band (NEB) method. The calculated results depict that after suitable doping of Co on MoS2 monolayer decreases the resistivity of the system and makes it more suitable for application as a sensor.  After adsorbing NH3 and CH4, Co doped MoS2 bandgap, DOS and PDOS become more enhanced. The adsorption energy calculated for NH3 and CH4 adsorbed Co doped MoS2 are -0.9 eV and -1.4 eV. The reaction is exothermic and spontaneous. The I-V curve for Co doped MoS2 for CH4 and NH3 adsorption shows a linear increase in current up to 1.4 V and 2 V, respectively, then a rapid decline in current after increasing a few volts. The Co doped MoS2 based sensor has a better relative resistance state, indicating that it can be employed as a sensor. The sensitivity for CH4 and NH3 were 124 % and 360.5 %, respectively, at 2 V. With a recovery time of 0.01s, the NH3 system is the fastest. In a high-temperature condition/environment, the Co doped MoS2 monolayer has the potential to adsorb NH3 and CH4 gas molecules. According to NEB, CH4 gas molecules on Co doped MoS2 has the lowest energy barrier as compared to NH3 gas molecules. Our results indicate that adsorbing NH3 and CH4 molecules in the interlayer is an effective method for producing Co doped MoS2 monolayers for use as spintronics sensor materials

    New Porous Heterostructures Based on Organo-Modified Graphene Oxide for CO(2)Capture

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    In this work, we report on a facile and rapid synthetic procedure to create highly porous heterostructures with tailored properties through the silylation of organically modified graphene oxide. Three silica precursors with various structural characteristics (comprising alkyl or phenyl groups) were employed to create high-yield silica networks as pillars between the organo-modified graphene oxide layers. The removal of organic molecules through the thermal decomposition generates porous heterostructures with very high surface areas (>= 500 m(2)/g), which are very attractive for potential use in diverse applications such as catalysis, adsorption and as fillers in polymer nanocomposites. The final hybrid products were characterized by X-ray diffraction, Fourier transform infrared and X-ray photoelectron spectroscopies, thermogravimetric analysis, scanning electron microscopy and porosity measurements. As proof of principle, the porous heterostructure with the maximum surface area was chosen for investigating its CO(2)adsorption properties

    Application of palm shell activated carbon filter as a medium of indoor air contaminant adsorbent for indoor air quality improvement

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    For decades, the inclusion of activated carbon (AC) adsorption technique through filtration has gained significant interest on improvement of indoor air quality (IAQ) by reducing level of pollutant. The interest of reseachers in palm shell AC (PSAC) keep increase owing to the fact that this material has superior characteristic as compared to commercial AC. However, the investigation of PSAC performance for air filtration are still limited and no research could be found on relating the effect of burner for carbonization on PSAC properties. Therefore, the current research was focused on producing PSAC by using new fabricated burner, exploring the effect of combination of physical and chemical activation towards PSAC properties and investigating of PSAC air filter performance used in Mechanical Ventilation Air Conditioning (MVAC) system. Preliminary studies began with IAQ monitoring in different building condition. The present data revealed that at certain situation, the buildings environment was below than satisfactory level and required mitigation plan by introducing new air filtration media in MVAC system. The best quality of charcoal was obtained by Horizontal burner with less fume formation during carbonization process compare to other design. The physical properties analysis of palm shell charcoal showed the carbonization time (CT) 2 hours gained better charcoal properties and highly recommended to continue into the activation process. After the activation process, PSAC physical+chemical shows significantly higher pore development, surface area and adsorption capacity compare to the other process. The lowest density and the highest porosity up to 0.4632 g/cm and 7.11% was calculated while the highest Iodine number of 1091.05 mg/g and BET surface area of 713.7 m 3 /g was obtained respectively in PSAC physical+chemical. Meanwhile, microstructure and composition analysis shows that, PSAC physical+chemical fully produced honeycomb form of porosity and comprised of C, O, K and Ca contents for high adsorption capacity. The improvement of IAQ in the buildings was achieved with the application of PSAC air filter which shows low concentration of CO2 with 302 ppm, CO with 0.4 ppm , TVOC with 0.1 ppm and PM10 with 0.02mg/m 2 respectively compare to the commercial filter

    Scattering at magnetic and nonmagnetic impurities on surfaces with strong spin-orbit coupling

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    Adsorption-induced reduction of surface-state conductivity in epitaxial Bi(111) films, a prototype system with large Rashba-induced surface-state splitting, by adsorbed atoms of Bi, Fe, and Co has been investigated by macroscopic surface magnetotransport measurements at a temperature of 10 K. A detailed analysis of magnetotransport, dc transport, and Hall data reveals that the scattering efficiencies for Co and Fe are larger by a factor of 2 than that for Bi. While for the latter charge transfer and change of band filling near the Fermi level are negligible, we find an increase of hole concentration upon Co and Fe adsorption. These atoms act as acceptors and immobilize on average about 0.5 electrons per adsorbed atom. Besides the dominant classical magnetoconductance signal the films show signatures of weak antilocalization, reflecting the strong spin-orbit coupling in Bi(111) surface states. This behavior can be changed to weak localization by the adsorption of high concentrations (0.1 monolayers) of magnetic impurities (Fe,Co), similarly to results found on the topological insulator Bi2Se3. Our results demonstrate that details of chemical bond formation for impurities are crucial for local spin moments and electronic scattering properties. © 2012 American Physical Society.DFGDAA

    Comparison and evaluation of agglomerated MOFs in gaseous biofuels purification by means of pressure swing adsorption (PSA)

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    Metal-organic frameworks (MOFs) are crystalline structures consisting on metal ions coordinated to organic ligands. Porous MOFs are often formed with extremely high surface areas and other marvelous properties for adsorption processes. Although, to be used in industrial processes, MOFs should be agglomerated, being a key aspect because they properties usually are deteriorated compared with the powder [1]. Among industrial applications of adsorption, the recovery and purification of hydrogen from steam methane reforming (SMR) off-gases and the production of gaseous biofuels such as biomethane from biogas and biohydrogen have a great economic interest. Biomethane and biohydrogen could be recovered from mixtures containing carbon dioxide as main impurity by means of adsorption using pressure swing adsorption (PSA). The knowledge of the adsorption equilibrium and kinetics of the gaseous components in the targeted mixtures is the basis for the design of a PSA process for its separation.The aim of this work is the study of adsorption equilibrium and kinetics of H2, N2, CO, CH4 and CO2 on three different agglomerated MOF structures. The adsorbent performance on a typical PSA unit for hydrogen and methane purification has been evaluated by simulation. Cu-BTC, ZIF-8 and UTSA-16 MOFs have been agglomerated using the procedure described before [1]. These materials have been characterized using scanning electron microscopy (SEM), Hg porosimetry and N2 adsorption isotherm at 77K. The specific surface area of the agglomerated materials decreased less than a 5% compared with powder samples.H2, N2, CO, CH4 and CO2 high pressure equilibrium isotherms up to 50 bar at 298, 313 and 338 K have been measured and the results have been fitted using the Dual Langmuir model (table 1). Henry constants and diffusivities have been calculated using the chromatographic method described elsewhere [2]. Please click Additional Files below to see the full abstract
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