The Interaction of Noble Metal With La1–xSrxMnO3 (001) Surface and Catalytic Role for Oxygen Adsorption: A Density Functional Theory Study

Adsorption mechanisms of noble metals (Ag, Pd, Pt) on MnO₂‐terminated (001) surface and their catalytic role for oxygen adsorption have been investigated using the first‐principles density functional theory calculations. The analysis of the adsorption energies reveals that the energetically favorable configuration for Ag and Pd adsorption is at the O site, whereas one for Pt adsorption is at the Mn site. Pt atom exhibits the largest adsorption energy, followed by Pd and Ag atoms. Both bond population and PDOS (partial density of states) analysis confirm the formation of adatom–O–Mn bonds. Adsorption is accompanied by a charge transfer between adatoms and surface atoms. Significantly, we predict that the order on the increase of O₂ adsorption energy follows the Pd > Ag > Pt due to pre‐adsorbed noble metal atoms. The calculated bond length and bond population of O₂ molecule demonstrate that pre‐adsorbed noble metal atoms facilitates O₂ molecule dissociate to O atoms, thus contributing to the surface oxygen diffusion process. Our calculations identify an important catalytic role of noble metal in LSM‐based catalysts, which may improve electrochemical performance for SOFCs cathodes.     

CO2 adsorption and activation over γ-Al2O3-supported transition metal dimers: A density functional study

Catalytic conversion of CO₂ to liquid fuels has the benefit of reducing CO₂ emission. Adsorption and activation of CO₂ on the catalyst surface are key steps of the conversion. Herein, we used density functional theory (DFT) slab calculations to study CO₂ adsorption and activation over the γ-Al₂O₃-supported 3d transition metal dimers (M₂/γ-Al₂O₃, M = Sc–Cu). CO₂ was found to adsorb on M₂/γ-Al₂O₃ negatively charged and in a bent configuration, indicating partial activation of CO₂. Our results showed that both the metal dimer and the γ-Al₂O₃ support contribute to the activation of the adsorbed CO₂. The presence of a metal dimer enhances the interaction of CO₂ with the substrate. Consequently, the adsorption energy of CO₂ on M₂/γ-Al₂O₃ is significantly higher than that on the γ-Al₂O₃ surface without the metal dimer. The decreasing binding strength of CO₂ on M₂/γ-Al₂O₃ as M₂ changes from Sc₂ to Cu₂ was attributed to decreasing electron-donation by the supported metal dimers. Hydroxylation of the support surface reduces the amount of charge transferred to CO₂ for the same metal dimer and weakens the CO₂ chemisorption bonds. Highly dispersed metal particles maintained at a small size are expected to exhibit good activity toward CO₂ adsorption and activation.     

Influence of adsorbed carbon dioxide on hydrogen electrosorption in palladium-platinum-rhodium alloys

Carbon dioxide electroreduction was applied to examine the processes of hydrogen electrosorption (adsorption, absorption and desorption) by thin electrodeposits of Pd-Pt-Rh alloys under conditions of cyclic voltammetric (CV) experiments. Due to different adsorption characteristics towards the adsorption product of the electroreduction of CO₂ (reduced CO₂) exhibited by the alloy components hydrogen adsorption and hydrogen absorption signals can be distinguished on CV curves. Reduced CO₂ causes partial blocking of hydrogen adsorbed on surface Pt and Rh atoms, without any significant effect on hydrogen absorption into alloy. It reflects the fact that adsorbed hydrogen bonded to Pd atoms does not participate in CO₂ reduction, while hydrogen adsorbed on Pt and Rh surface sites is inactive in the absorption reaction. In contrast, CO is adsorbed on all alloy components and causes a marked inhibition of hydrogen sorption (both adsorption and absorption)/desorption reactions.     

Decomposition of activated CO2 species on Ni(110): Role of surface diffusion in the reaction mechanism

Chemisorption and decomposition of CO₂ on Ni(110) surface have been studied by means of spin-polarized density functional theory calculations. Several possible CO₂/Ni(110) conformations with similar adsorption energies were found. The bonding nature of the adsorbed CO₂ was further analyzed on the basis of partial density of states (PDOS) and effective bond order (EBO) results, indicating the enhanced charge transfer and significant activation of the CO bond. Climbing image nudged elastic bound calculations provide an insight into CO₂/Ni(110) → CO/Ni(110) + O/Ni(110) reaction mechanism. All computed reaction pathways can be separated into two stages: 1) surface diffusion of CO₂ to the one energetically favored conformation; 2) breakage of the coordinated C–O bond. The total reaction barrier (relative to the energy of CO₂/Ni(110)) was found about 0.44 eV.     

Adsorption behavior of aqueous europium on kaolinite under various disposal conditions

This work investigated the adsorption behavior of europium on kaolinite under various disposal conditions. Batch-wise adsorption and precipitation experiments and equilibrium model calculations were performed over a pH range of 4–10 and CO₂ concentration range of 0%, 0.03%, and 10%. Experimental precipitation behaviors are in agreement with the results of equilibrium model calculations using the geochemical code MINTEQA2. Aqueous species of Eu³⁺ exists mainly at pH 5 or below and solid phases of Eu(OH)₃(s), Eu(OH)CO₃(s), and Eu₂(CO₃)₃·3H₂O(s) are formed at higher pH ranges. Adsorption behavior of Eu on kaolinite in the low pH range can be explained by interlayer ion-exchange reaction. The significant increase in adsorbed amount at pH 5–6 is due to the surface complexation at the edge site of kaolinite. In the high pH range, precipitation of Eu contributes mainly to the adsorption quantity. The rapid decrease in adsorbed amount above pH 7 under 10% CO₂ condition occurs by the formation of anionic europium species of Eu(CO₃) ₂ ^- .The adsorption of Eu on kaolinite could be well interpreted by the Freundlich adsorption isotherm. The data except for the highest equilibrium concentration ranges were also explained by Langmuir isotherm and the maximum adsorbed quantity of Eu on kaolinite,b, is 1.2 mg/g.     

月桂基咪唑啉对Q235钢的缓蚀吸附作用

采用失重法和电化学方法研究了月桂基咪唑啉（IM-11）、1-氨乙基-2-月桂基咪唑啉（AIM-11）和1-羟乙基-2-月桂基咪唑啉（HIM-11）三种化合物在CO₂饱和的3%NaCl溶液中对Q235钢的缓蚀性能,探讨了其在Q235钢表面的吸附行为。结果显示,3种化合物均具有较好的抗相似文献   

Density functional theory based treatment of amino acids adsorption on single-walled carbon nanotubes

In this paper, the adsorption of a few amino acids on (10, 0) carbon nanotubes (CNTs) were investigated through calculations within density functional theory based methods. Results show that the zwitterionic-glycine adsorption is bound stronger to the nanotube surface in comparison to nonionic-glycine counterparts, as well as on phenylalanine, histidine and cysteine side chain groups. Our calculations indicate that, when zwitterionic-glycine was adsorbed on the CNTs wall the C–C bond of glycine was broken and a CO₂ molecule was released. Furthermore, the mechanism of the C–C bond breaking is studied by density functional based tight binding molecular dynamics calculations which have been carried out at room temperature.     

Computational study of linear carbon chains on gold and silver surfaces

Density-functional-theory calculations were carried out for hydrogen capped linear carbon chains, polyynes and cumulenes, adsorbed dissociatively on the (1 1 1) and (2 1 1) surfaces of gold and silver. In the studied adsorption reactions, carbon–hydrogen bonds are broken and covalent carbon–metal bonds are created. The adsorption of cumulenes is highly endothermic, whereas the adsorption of polyynes is near thermoneutral. Also, the hydrogenation of adsorbed polyynyl radicals (·C_nH) into adsorbed cumulene carbenes (:C_nH₂) was investigated, which was found to be exothermic on both metals. Vibrational calculations were conducted on the adsorption systems, and the results were compared with experimental surface enhanced Raman scattering spectra. An interpretation is proposed for the spectra of polyyne–silver solutions, and features of polyyne–gold spectra are predicted.     

Adsorption and reduction of NO2 over activated carbon at low temperature

The reactive adsorption of NO₂ over activated carbon (AC) was investigated at 50 °C. Both the NO₂ adsorption and its reduction to NO were observed during the exposure of AC to NO₂. Temperature programmed desorption (TPD) was then performed to evaluate the nature and thermal stability of the adsorbed species. Adsorption and desorption processes have been proposed based on the nitrogen and oxygen balance data. The micropores in AC act as a nano-reactor for the formation of -C(ONO₂) complexes, which is composed by NO₂ adsorption on existing -C(O) complexes and the disproportionation of adsorbed NO₂. The generated -C(ONO₂) complexes are decomposed to NO and NO₂ in the desorption step. The remaining oxygen complexes can be desorbed as CO and CO₂ to recover the adsorptive and reductive capacity of AC.     

Adsorption of CO2 on Zeolite 13X and Activated Carbon with Higher Surface Area

In this work, adsorption isotherms and adsorption kinetics of CO₂ on zeolite 13X and activated carbon with high surface area (AC-h) were studied. The adsorption isotherms and kinetic curves of CO₂ on the adsorbents were separately measured at 328 K, 318 K, 308 K, and 298 K and with a pressure range of 0–30 bar by means of the gravimetric adsorption method. The mass transfer constants and adsorption activation energy E_a of CO₂ on the adsorbents were estimated separately. Results showed that at very low pressure the amounts adsorbed of CO₂ on the zeolite 13X was higher than that on the AC-h, while at higher pressure, the amounts adsorbed of CO₂ on the AC-h was higher than that on the zeolite 13X since the AC-h has a larger surface area and a larger total pore volume compared to the zeolite 13X. The adsorption kinetics of CO₂ can be well described by the linear driving force (LDF) model. With the increase of temperature, the mass transfer constants of CO₂ adsorption on both samples increased. The adsorption activation energy E_a for CO₂ on the two adsorbents decreased with the increase of pressure. Furthermore, at low pressure the E_a for CO₂ adsorption on the zeolite 13X was slightly lower than that on the AC-h, while at higher pressure the E_a for CO₂ adsorption on the zeolite 13X was higher than that on the AC-h.     

Thermodynamics and regeneration of CO2 adsorption on mesoporous spherical-silica particles

Mesoporous spherical-silica particles (MSPs) were modified by N-[3-(trimethoxysilyl) propyl]ethylenediamine (EDA) solution and were employed as sorbents to study thermodynamics and regeneration of CO₂ adsorption from gas streams. The thermodynamic analysis gave low isosteric heats of adsorption, which are typical for physical adsorption. The cyclic CO₂ adsorption on MSP(EDA) showed that the adsorbed CO₂ could be effectively desorbed via thermal treatment at 120 °C for 25 min while the adsorbed CO₂ due to physical interaction could be effectively desorbed via vacuum suction at 0.145 bar for 30 min. If a combination of thermal treatment and vacuum suction was conducted at 120 °C and 0.145 bar, the time for effectively desorbing CO₂ could be shortened to 7.5 min and thus reduces a significant amount of energy penalty. The adsorption capacities and the physicochemical properties of MSP(EDA) were preserved after 15 cycles of adsorption and regeneration. These results suggest that the MSP(EDA) can be stably employed in the prolonged cyclic adsorption and that they are thus possibly cost-effective sorbents for CO₂ capture from flue gases.     

Screening CO2/N2 selectivity in metal‐organic frameworks using Monte Carlo simulations and ideal adsorbed solution theory

Selective adsorption of CO₂ over N₂ is important in the design and selection of adsorbents such as metal‐organic frameworks (MOFs) for CO₂ capture and sequestration. In this work, single‐component and mixture adsorption isotherms were calculated in MOFs using grand canonical Monte Carlo (GCMC) simulations at conditions relevant for CO₂ capture from flue gas. Mixture results predicted from single‐component isotherms plus ideal adsorbed solution theory (IAST) agree well with those calculated from full GCMC mixture simulations. This suggests that IAST can be used for preliminary screening of MOFs for CO₂ capture as an alternative to more time‐consuming mixture simulations or experiments. © 2011 Canadian Society for Chemical Engineering     

Agricultural by-products as granular activated carbons for adsorbing dissolved metals and organics

Surplus, low value agricultural by-products can be made into granular activated carbons (GACs) which are used in environmental remediation. This study characterized and evaluated GACs, made from these feedstocks, as effective removers of organics and metals from water. The by-products included soft lignocellulosics such as rice straw, soybean hull, sugarcane bagasse, peanut shell, and harder materials such as pecan and walnut shells. The softer materials were combined with a binder, molasses, to produce briquettes and pellets. The precursors were CO₂- or steam-activated, and subsequent treatments included oxidation to enhance metal adsorption. Many of the GACs had acceptable physical GAC attributes, such as durability, for commercial usage. GACs made from pecan and walnut shells adsorbed higher levels of benzene, toluene, methanol, acetonitrile, acetone, and 1,4-dioxane from an aqueous mixture than commercial GACs. Neither CO₂ nor steam activation was particularly advantageous in enhancing metal adsorption. Oxidation using O₂–N₂ gas increased metal adsorption while (NH₄)S₂O₈ solution did not. In a copper solution, oxidized GACs made from soybean hull had three to four times the Cu(II) adsorption capacity of metal-adsorbing, commercial GACs. Oxidized GACs made from soybean hull, sugarcane bagasse, peanut shell, and rice straw adsorbed from a mixture higher amounts of Pb(II), Cu(II), Ni(II), Cd(II) and Zn(II) than any commercial GACs. Commercial GACs adsorbed only Pb(II), Cu(II) and Cd(II). The GACs made from the agricultural by-products have considerable potential for adsorption of organics and metals of environmental concern. © 1998 SCI.     

Influence of pH on the preparation of monometallic rhodium and platinum,and bimetallic RhodiumPlatinum Catalysts supported on γ-Alumina

¹⁹⁵PtNMR and Raman experiments indicated that H₂PtCl₆ adsorbed monomolecularly on the surface of alumina up to a loading of 1 μmol m⁻² during pore volume impregnation. Above this limit crystalline H₂PtCl₆ was formed during the subsequent drying procedure. Adsorption experiments showed that RhCl₃ exhibited the same behaviour, with an even larger monomolecular coverage. The coverage of both metal complexes was dependent on the pH during adsorption and decreased with decreasing pH, due to a shift in the bonding equilibrium between the metal complexes in solution and the complexes adsorbed on the support surface. Because of the acidic properties of RhCl₃ and H₂PtCl₆, the amounts of rhodium and platinum adsorbed during co-adsorption were smaller than during adsorption of the separate metal complexes. The reduction of RhCl₃+H₂PtCl₆ supported on Al₂O₃ was governed by mobile rhodium atoms and small bimetallic clusters. Large metal salt crystals smothered the reduction process.     

Effects of potassium on the chemisorption of CO2 and CO on the Mo2C/Mo(100) surface

The interaction of CO₂ with K-promoted Mo₂C/Mo(100) has been studied with high-resolution electron energy loss spectroscopy, work function measurements and temperature-programmed desorption. Pre-adsorbed potassium dramatically affects the adsorption behavior of CO₂ on the Mo₂C/Mo(100) surface. It increases the rate of adsorption, the binding energy of CO₂ and it induces the dissociation of CO₂ through the formation of negatively charged CO₂. Potassium adatoms also promote the dissociation of adsorbed CO over Mo₂C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Near‐stoichiometric O2 binding on metal centers in Co(salen) nanoparticles

Co(salen) [cobaltous bis(salicylaldehyde)ethylenediamine] complexes are well‐known O₂ carriers in solution. In the solid phase, these complexes exhibit some O₂ binding but detailed studies have been complicated because few of the known polymorphs of Co(salen) actually bind O₂. The O₂ binding results for nanoparticulate Co(salen) are presented in this study. Rod‐shaped Co(salen) nanoparticles, roughly 100 nm in diameter, were recrystallized by spraying a methylene chloride solution of commercially obtained Co(salen) into supercritical carbon dioxide. Temperature‐programmed desorption, thermogravimetric analysis, and a Rubotherm magnetic suspension balance measurements reveal a reversible O₂ uptake of ～1.51 mmol/(g nanoparticles) at 25°C, consistent with a binding stoichiometry involving a bridging peroxo unit between two Co centers. In contrast, no measurable O₂ uptake was observed with the commercial Co(salen). These results clearly show the potential for bottom‐up design of nanoparticulate metal complexes for enhanced O₂ storage and other applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Adsorption of carbon dioxide and methane on graphene with a high titanium coverage

Using density functional theory and molecular dynamics to explore the adsorption of CO₂ and CH₄ at atmospheric pressure and 300 K we found that both adsorb on a graphene layer modified with titanium at high metal coverage (C₂Ti). The first dissociates to CO and O when adsorbed. The second is not dissociated and desorbs at 600 K.     

Photoinduced activation of CO2 on TiO2 surfaces: Quantum chemical modeling of CO2 adsorption on oxygen vacancies

Chemical processes that utilize CO₂ emissions from coal-fired power plants will be required as the world progresses towards reducing CO₂ emissions. The conversion of CO₂ using light energy (CO₂ photoreduction) has the potential to produce useful fuels or valuable chemicals while decreasing CO₂ emissions from the use of fossil fuels such as coal. Computational studies on the initial steps of photoinduced CO₂ activation on TiO₂ surfaces, necessary to develop a mechanistic understanding of CO₂ photoreduction are a focus of this article.The results from previous quantum mechanical modeling studies conducted by the authors indicated that stoichiometric TiO₂ surfaces likely do not promote electron transfer to CO₂. Therefore, the role of oxygen vacancies in promoting the light-induced conversion of CO₂ (CO₂ photoreduction) on TiO₂ surfaces was examined in this study. Two different side-on bonded bent-CO₂ (bridging Ti-CO₂^δ•−-Ti species) were formed on the reduced rutile (110) and anatase (010), (001) surfaces, indicating charge transfer from the reduced surface to CO₂. Further steps in the photoexcitation of these bent-CO₂ species were investigated with density functional theory calculations. Consistent with CO₂ adsorption and photodesorption on other n-type metal oxides such as ZrO₂, the results suggest that the bent-CO₂ species do not gain further charge from the TiO₂ surface under illumination and are likely photodesorbed as neutral species. Additionally, although the formation of species such as CO and HCHO is thermodynamically possible, the energy needed to regenerate the oxygen vacancy on TiO₂ surfaces (~ 7 eV) is greater than that available through band-gap illumination (3.2 eV). Therefore, CO₂ reactions with water on irradiated anatase TiO₂ surfaces are likely to be stoichiometric.     

CO2 Adsorption Kinetics of K2CO3/Activated Carbon for Low‐Concentration CO2 Removal from Confined Spaces

K₂CO₃ supported on activated carbon (K₂CO₃/AC) is a promising means to remove low‐concentration CO₂ from confined spaces. In this removal process, physical adsorption plays an important role but it is difficult to quantify the amount of CO₂ adsorbed when both H₂O and CO₂ are present. The linear driving force mass transfer model is adopted to study the CO₂ adsorption kinetic characteristics of K₂CO₃/AC by analyzing the experimental data. The effect of K₂CO₃ and H₂O on the adsorption of CO₂ in K₂CO₃/AC was also evaluated. K₂CO₃ loaded on the support is found to increase the mass transfer resistance but decrease the activation energy required for the physical adsorption process. The presence of water vapor is disadvantageous to achieve high physical adsorption capacity since it enhances the chemical sorption in the competitive dynamic sorption process.