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1.
ABSTRACT

The stable configurations, electronic structures and catalytic activities of single-atom metal catalyst anchored silicon-doped graphene sheets (3Si-graphene-M, M?=?Ni and Pd) are investigated by using density functional theory calculations. Firstly, the adsorption stability and electronic property of different gas reactants (O2, CO, 2CO, CO/O2) on 3Si-graphene-M substrates are comparably analysed. It is found that the coadsorption of O2/CO or 2CO molecules is more stable than that of the isolated O2 or CO molecule. Meanwhile, the adsorbed species on 3Si-graphene-Ni sheet are more stable than those on the 3Si-graphene-Pd sheet. Secondly, the possible CO oxidation reactions on the 3Si-graphene-M are investigated through Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and new termolecular Eley–Rideal (TER) mechanisms. Compared with the LH and TER mechanisms, the interaction between 2CO and O2 molecules (O2?+?CO → CO3, CO3?+?CO → 2CO2) through ER reactions (< 0.2?eV) are an energetically more favourable. These results provide important reference for understanding the catalytic mechanism for CO oxidation on graphene-based catalyst.  相似文献   

2.
ABSTRACT

Metal-free catalysts have attracted more attention due to their highly active in catalytic oxidation reactions. The electronic structure and catalytic property of BC3 sheet are investigated by using first-principles calculations. It is found that the BC3 sheet as the active surface can effectively regulate the adsorptive stability of reactive gases. Besides, the possible reaction processes for CO oxidation on the BC3 sheet are comparably analysed through different reaction mechanisms, which include the Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and termolecular Eley–Rideal (TER). In the CO oxidation reactions, the decomposition of O2 molecule as the starting state (0.40?eV) is an energetically more favourable process than those of other processes, the Eley–Rideal (ER) reactions (2Oads+2CO→CO2) are more prone to take place with lower energy barriers (3 sheet. These results provide an important guidance on exploring the highly efficiency metal-free catalyst for CO oxidation.  相似文献   

3.
Cu-based oxides oxygen carriers and catalysts are found to exhibit attractive activity for CO oxidation, but the dispute with respect to the reaction mechanism of CO and O2 on the CuO surface still remains. This work reports the kinetic study of CO oxidation on the CuO (111) surface by considering the adsorption, reaction and desorption processes based on density functional theory calculations with dispersion correction (DFT-D). The Eley–Rideal (ER) CO oxidation mechanism was found to be more feasible than the Mars-van-Krevelen (MvK) and Langmuir–Hinshelwood (LH) mechanisms, which is quite different from previous knowledge. The energy barrier of ER, LH, and MvK mechanisms are 0.557, 0.965, and 0.999 eV respectively at 0 K. The energy barrier of CO reaction with the adsorbed O species on the surface is as low as 0.106 eV, which is much more active in reacting with CO molecules than the lattice O of CuO (111) surface (0.999 eV). A comparison with the catalytic activity of the perfect Cu2O (111) surface shows that the ER mechanism dictates both the perfect Cu2O (111) and the CuO (111) surface activity for CO oxidation. The activity of the perfect Cu2O (111) surface is higher than that of the perfect CuO (111) surface at elevated temperatures. A micro-kinetic model of CO oxidation on the perfect CuO (111) surface is established by providing the rate constants of elementary reaction steps in the Arrhenius form, which could be helpful for the modeling work of CO catalytic oxidation.  相似文献   

4.
When using coal-derived syngas or coal as fuel in chemical looping combustion (CLC), CO as a representative pyrolysis/gasification product and H2S as the main sulfurous gas coexist in fuel reactor. Either CO or H2S can absorb on the surface of CuO (the active component of Cu-based oxygen carriers), and reactions will occur among them. In this study, density functional theory (DFT) calculations are conducted to investigate the interaction among H2S, CO, and CuO, including: the reaction between CO and H2S over CuO particle, the influence of CO on the H2S dissociation and further reaction process, and the impact of H2S dissociation products on CO oxidation. Firstly, the co-adsorption results suggest that H2S might directly react with CO to produce COS via the Eley–Rideal mechanism, while CO prefers to react with HS* or S* via the Langmuir–Hinshelwood mechanism. This means that the reaction mechanisms between CO and H2S will change as the H2S dissociation proceeds, which has already been forecasted by the co-adsorption energies and verified by all of potential Eley–Rideal and Langmuir–Hinshelwood reaction pathways. Then, the influence of CO on the H2S dissociation process is examined, and it is noted that the presence of CO greatly limits the dissociation of H2S due to the increased energy barrier of the rate-determining dehydrogenation step. Furthermore, the impact of H2S dissociation products on CO oxidation by CuO is also investigated. The presence of H2S and S* significantly supresses the CO oxidation activity, while the presence of HS* slightly promotes the CO oxidation activity. Finally, the complete interaction mechanisms among H2S, CO, and CuO are concluded. It should be noted that COS will be inevitably produced via the Langmuir–Hinshelwood reaction between surface S* and CO*, which is prior to H2O generation and subsequent sulfidation reaction.  相似文献   

5.
The adsorption of CO, O2, and H2O was studied on both the (111) and [6(111) × (100)] crystal faces of iridium. The techniques used were LEED, AES, and thermal desorption. Marked differences were found in surface structures and heats of adsorption on these crystal faces. Oxygen is adsorbed in a single bonding state on the (111) face. On the stepped iridium surface an additional bonding state with a higher heat of adsorption was detected which can be attributed to oxygen adsorbed at steps. On both (111) and stepped iridium crystal faces the adsorption of oxygen at room temperature produced a (2 × 1) surface structure. Two surface structures were found for CO adsorbed on Ir(111); a (√3 × √3)R30° at an exposure of 1.5–2.5 L and a (2√3 × 2√3)R30° at higher coverage. No indication for ordering of adsorbed CO was found on the Ir(S)-[6(111) × (100)] surface. No significant differences in thermal desorption spectra of CO were found on these two faces. H2O is not adsorbed at 300 K on either iridium crystal face. The reaction of CO with O2 was studied on Ir(111) and the results are discussed. The influence of steps on the adsorption behaviour of CO and O2 on iridium and the correlation with the results found previously on the same platinum crystal faces are discussed.  相似文献   

6.
The heats of adsorption at several coverages of the linear and bridged CO species (denoted L and B, respectively) adsorbed on the Pt0 sites of the 2.9 wt% Pt/10% K/Al2O3 catalyst are determined using the Adsorption Equilibrium Infrared spectroscopy method. The addition of K on 2.9% Pt/Al2O3 modifies significantly the adsorption of CO on the Pt particles: (a) the ratio L/B is decreased from 8.4 to 1, (b) a new adsorbed CO species is detected with an IR band at 1763 cm−1, (c) the heats of adsorption of L and B CO species are significantly altered and the positions of their IR bands are shifted. The heats of adsorption of L CO species are decreased: i.e. 206 and 105 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively. Two B CO species denoted B1 and B2, with different heats of adsorption are observed on Pt/K/Al2O3. The heats of adsorption of B2 CO species (major B CO species) are significantly larger than those measured in the absence of K: i.e. 94 and 160 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively, whereas those of B1 CO species (minor species) are similar: 90 kJ/mol at low coverages. These values are consistent with the qualitative High Resolution Electron Energy Loss Spectrometry literature data on Pt(1 1 1) modified by potassium.  相似文献   

7.
孙建平*  缪应蒙  曹相春 《物理学报》2013,62(3):36301-036301
基于第一性原理的密度泛函理论研究了单个O2和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O2和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O2后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.  相似文献   

8.
We have studied adsorption of CO on Fe3O4(1 1 1) films grown on a Pt(1 1 1) substrate by temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS) and high resolution electron energy loss spectroscopy (HREELS). Three adsorption states are observed, from which CO desorbs at ∼110, 180, and 230 K. CO adsorbed in these states exhibits stretching frequencies at ∼2115-2140, 2080 and 2207 cm−1, respectively. The adsorption results are discussed in terms of different structural models previously reported. We suggest that the Fe3O4(1 1 1) surface is terminated by 1/2 ML of iron, with an outermost 1/4 ML consisting of octahedral Fe2+ cations situated above an 1/4 ML of tetrahedral Fe3+ ions, in agreement with previous theoretical calculations. The most strongly bound CO is assigned to adsorption to Fe3+ cations present on the step edges.  相似文献   

9.
《Current Applied Physics》2018,18(6):626-632
The selective catalytic reduction (SCR) system for NOX removal in coal-fired power plants has a promoting effect on the oxidation and removal of elemental mercury. In this study, basic mechanism of mercury oxidation by V2O5-based SCR catalyst is investigated via density functional theory method and the periodic slab models. Calculations are conducted to determine the adsorption energies and geometries of Hg0, HgCl, HgCl2 and HCl on V2O5(001) surface, and to reveal the energy profile of oxidation reaction and the structures of relative transition states and intermediates. The results indicate that HCl can significantly promote Hg0 oxidation on V2O5(001) surface, by forming an intermediate HgCl-surface which is important for Hg0 oxidation. The Hg0 oxidation goes through Hg0 → HgCl → HgCl2, and the two stages of the reaction follow Eley–Rideal mechanism and Langmuir-Hinshelwood mechanism, respectively. The formation of HgCl2 is the rate-determining step due to its high energy barrier. Three detailed reaction pathways are obtained, and the related energy profiles and structures are analyzed in detail. The Hg0 oxidation reaction can take place through all three pathways even if differences exist in each other, while pathways I and II have relatively low energy barriers.  相似文献   

10.
《Surface science》1986,172(1):151-173
The electronic properties of monolayers of copper atoms adsorbed onto a Ru(0001) single crystal surface have been studied with thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (EELS) utilizing carbon monoxide (CO), dioxygen (O2), methanol (CH3OH), and to some extent water (H2O) as chemical probes. Whereas a three-monolayer-thick film exhibits most properties of a Cu(111) crystal distinct deviations are found at lower Cu coverages. TDS as well as EELS show a weakened RuCO bond and a strengthened CuCO bond as a result of metal-metal interaction. The stronger CuCO bond is accompanied by a higher probability for O2 dissociation. The mobilities of copper and oxygen atoms are such that annealing to 650 K produces an overlayer structure which is independent of adsorption sequence: Cu/O2 or O2/Cu, but where RuO as well as CuO vibrations can be identified. Methanol adsorbs reversibly on a monolayer of copper atoms. Metal bound methoxy species are formed in the presence of oxygen atoms. The decomposition paths of such methoxy intermediates alter towards more formaldehyde (CH2O) relative to CO with increasing copper and methoxy coverages.  相似文献   

11.
The adsorption of thiophene (C4H4S) on the clean and sulfided Mo(100) crystal surface has been studied. A fraction of the adsorbed thiophene desorbs molecularly while the remainder decomposes upon heating, evolving H2 and leaving carbon and sulfur deposits on the surface. The reversibly adsorbed thiophene exhibits three distinct desorption peaks at 360, 230–290 and 163–174 K, corresponding to binding energies of 22, 13–16 and 7–9 kcal/mol respectively. Sulfur on the Mo(100) surface preferentially blocks the highest energy binding state and causes an increase in the amount of thiophene bound in the low binding energy, multilayer state. The thiophene decomposition reactions yield H2 desorption peaks in the temperature range 300–700 K. We estimate that 50–66% of the thiophene adsorbed to the clean Mo(100) decomposes. The decomposition reaction is blocked by the presence of c(2 × 2) islands of sulfur and is blocked completely at θs = 0.5, at which point thiophene adsorption is entirely reversible.  相似文献   

12.
In order to exploit the potential applications of graphene as gas sensors, the adsorptions of a series of small gas molecules (such as CO, O2, NO2 and H2O) on pristine graphene (PG) and Si-doped graphene (SiG) have been investigated by ab initio calculations. Our results indicate that the electronic properties of PG are sensitive to O2 and NO2 molecules, but not changed much by the adsorption of CO and H2O molecules. Compared with PG, SiG is much more reactive in the adsorption of CO, O2, NO2 and H2O. The strong interactions between SiG and the adsorbed molecules induce dramatic changes to the electronic properties of SiG. Therefore, we suggest that SiG could be a good gas sensor for CO, O2, NO2 and H2O.  相似文献   

13.
本文利用程序升温脱附技术研究了氧空位浓度对甲基基团和CO在R-TiO2(110)表面吸附的影响. 结果表明,随着氧空位浓度的变化,吸附在桥氧位的甲基基团和吸附在五配位Ti4+位点上的CO分子的脱附温度呈现了不同的趋势,揭示了表面缺陷可能对R-TiO2(110)不同位点上的物质吸附具有重要影响.  相似文献   

14.
李敏  张俊英  张跃  王天民 《中国物理 B》2012,21(6):67302-067302
The adsorptions of CO and 02 molecules individually on the stoichiometric Cu-terminatcd Cu20 (111) surface are investigated by first-principles calculations on the basis of the density functional theory. The calculated results indicate that the CO molecule preferably coordinates to the Cu2 site through its C atom with an adsorption energy of-1.69 eV, whereas the 02 molecule is most stably adsorbed in a tilt type with one O atom coordinating to the Cu2 site and the other O atom coordinating to the Cul site, and has an adsorption energy of -1.97 eV. From the analysis of density of states, it is observed that Cu 3d transfers electrons to 2π orbital of the CO molecule and the highest occupied 5σ orbital of the CO molecule transfers electrons to the substrate. The sharp band of Cu 4s is delocalized when compared to that before the CO molecule adsorption, and overlaps substantially with bands of the adsorbed CO molecule. There is a broadening of the 2π orbital of the 02 molecule because of its overlapping with the Cu 3d orbital, indicating that strong 3d-2π interactions are involved in the chemisorption of the 02 molecule on the surface.  相似文献   

15.
当一束具有一定能量和强度的电子束轰击超高真空系统中残余的水汽、一氧化碳和二氧化碳时,将导致这些气体分子通过如下反应:H2O→Oad+H2,CO2→Oad+CO,CO→Oad+Cad分解并共吸于镍表面。碳和氧的原子各自占据镍(001)面部份四重吸附位置,形成结构为p(2×2)或c(2×2)的许多独立的吸附畴,电子束轰击促进畴的成核、长大、连结和有序化。当氧和碳的原子占据了镍(001)面约一半的四重吸附位后,上述吸附反应将与导致氧和碳的脱附反应:C*+Oad→CO,O*+Cad→CO平衡,氧化镍与碳化镍开始成核。由于残余含氧气体中氧的含量超过碳,氧化镍成核占优势,使碳的吸附被排斥,已吸附的碳被排挤,形成电子束斑内氧高碳低、束斑外碳高氧低的“互补”分布。电子束轰击过程中碳的俄歇峰形的变化反映着碳原子与基底原子的不同结合状态。电子束的解离效应在吸附的初始阶段起重要作用,而其热效应对氧化镍的长大起重要作用。 关键词:  相似文献   

16.
Mesoporous γ-Fe2O3/SiO2 nanocomposite containing 30 mol% of γ-Fe2O3 was prepared by a template-free sol-gel method, and its removal ability for methyl orange (MO) was investigated. The nanocomposite was characterized using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FTIR) absorption measurements, nitrogen adsorption-desorption measurements, and magnetic measurements. The synthesized γ-Fe2O3/SiO2 nanocomposite has a mesoporous structure with an average pore size of 3.5 nm and a specific surface area of 245 m2/g, and it exhibits ferrimagnetic characteristics with the maximum saturation magnetization of 20.9 emu/g. The adsorption of MO on the nanocomposite reaches the maximum adsorbed percentage of ca. 80% within a few minutes, showing that most of MO can be removed in a short time. The MO adsorption data fit well with both Langmuir and Freundlich adsorption isotherms. The maximum adsorption capacity of MO is estimated to be 476 mg/g.  相似文献   

17.
The effect of O2 molecules adsorbed on the surface of ytterbium nanofilms on the properties of the volume and surface of these films has been studied. It has been shown that the dependence of the work function of the films on the concentration of O2 adsorbed molecules exhibits a nonmonotonic behavior: originally, the work function decreases, to start increasing again on passing through a minimum. At high oxygen doses, this increase stops. Adsorption of oxygen brings about a fundamental rearrangement of the Auger spectra of ytterbium; indeed, the Auger peaks observed before oxygen adsorption disappear completely after its deposition on the surface, to become replaced by other ones. The results obtained qualitatively agree with similar observations amassed by the present authors in studies of adsorption of CO molecules on the surface of ytterbium films. These results should be ascribed to a manifestation of complex processes of electron exchange between these films and adsorbed O2 molecules. These processes end up in a qualitative rearrangement of the electronic structure of the part of film volume that borders the surface, where ytterbium transforms into the d metal.  相似文献   

18.
The adsorption/desorption characteristics of CO, O2, and H2 on the Pt(100)-(5 × 20) surface were examined using flash desorption spectroscopy. Subsequent to adsorption at 300 K, CO desorbed from the (5×20) surface in three peaks with binding energies of 28, 31.6 and 33 kcal gmol?1. These states formed differently from those following adsorption on the Pt(100)-(1 × 1) surface, suggesting structural effects on adsorption. Oxygen could be readily adsorbed on the (5×20) surface at temperatures above 500 K and high O2 fluxes up to coverages of 23 of a monolayer with a net sticking probability to ssaturation of ? 10?3. Oxygen adsorption reconstructed the (5 × 20) surface, and several ordered LEED patterns were observed. Upon heating, oxygen desorbed from the surface in two peaks at 676 and 709 K; the lower temperature peak exhibited atrractive lateral interactions evidenced by autocatalytic desorption kinetics. Hydrogen was also found to reconstruct the (5 × 20) surface to the (1 × 1) structure, provided adsorption was performed at 200 K. For all three species, CO, O2, and H2, the surface returned to the (5 × 20) structure only after the adsorbates were completely desorbed from the surface.  相似文献   

19.
The effect of electron beam monitored gas adsorption on the clean Si surface is studied using Auger electron spectroscopy. It is shown that the beam affects the AES adsorption signal of CO and O2 on Si by dissociating the adsorbed molecules on the surface and subsequently promoting diffusion of atomic oxygen into the bulk. A qualitative explanation of the adsorption data is presented and the initial sticking probability of O2 on Si (111) surface is estimated to be S0 = 0.21.  相似文献   

20.
The structures, spectra and electronic and magnetic properties of Ag4M and Ag4MCO (M?=?Sc–Zn) clusters have been studied using density functional theory and CALYPSO structure searching method. Structural searches show that M atoms except Zn tend to occupy the highest coordination position in the ground state Ag4M and Ag4MCO clusters. Carbon monoxide is most easily adsorbed on Ag atom of Ag4Zn and M atom of other Ag4M. Infrared and Raman spectra, photoabsorption spectra and photoelectron spectra of Ag4M and Ag4MCO clusters are forecasted and can be used to identify these clusters from experiment. Analysis of electronic properties indicates that the adsorption of CO on Ag4M clusters changes the zero vibrational energy (ZPVE) and increases stability of the host clusters. Dopant atoms except for Zn improve the stability of silver cluster. The Ag4Ni cluster shows high chemical activity and maximum adsorption energy for carbon monoxide. Magnetism calculations reveal that the magnetic moment of Ag4M (M?=?Mn–Ni) cluster adsorbed by carbon monoxide is decreased by 2 μB. The change of magnetic moment makes it possible to be used as a nanomaterial for carbon monoxide detection. Simultaneously, it is found that the adsorption of CO on Ag4Cu cluster is a physical adsorption.  相似文献   

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