Adsorption Of CH3Cl Research Articles

Dissociative adsorption of supersonic CH3Cl on Cu oxide Surfaces: Cu2O(111) and bulk Cu2O precursor “29”-Structure on Cu(111)

To examine the elementary steps of the Rochow-Müller process we placed copper oxides, viz., Cu2O(111) and the bulk Cu2O precursor “29”-structure on Cu(111), under supersonic molecular beams (SSMB) of CH3Cl. The SSMB energies range from 0.5-1.9 eV. We employed X-ray photoemission spectroscopy (XPS) in conjunction with synchrotron radiation (SR) to determine the resulting adsorbed species present. We identified two reaction paths, viz., Reaction I and Reaction II. Reaction I involves dissociative adsorption of CH3Cl. In Reaction II, CH3Cl also dissociates, but with Cl as the dominant adsorbed species (higher than that of adsorbed carbonaceous species, as observed for Reaction I). For the incident energies and exposure conditions considered, we found Reaction II as the dominant reaction path for CH3Cl reaction on both Cu2O(111) and the “29”-structure on Cu(111).

Atomic regulation to improve the sensing-performance of CoPc and NiPc monolayer toward chloromethane molecule: Insights from DFT calculations

The development of a high-performance gas sensor for efficient detection of harmful chloromethane (CH3Cl) is of great importance to environmental monitoring and human health. Herein, the density functional theory (DFT) method was employed to compare the adsorption behaviors and electronic properties of CH3Cl on two-dimensional monometal modified phthalocyanines (CoPc, NiPc) and metal dimer modified phthalocyanines (CoTMPc and NiTMPc, TM = Ti∼Zn) surfaces. The studied results indicate that the CoPc and NiPc monolayers are not suitable as gas-sensitive materials for the detection of CH3Cl molecule due to their weak adsorption ability and low sensitivity. However, the adsorption strength and electronic properties of single-layer CoTMPc and NiTMPc towards CH3Cl can be effectively regulated through the synergistic effect of bimetallic species. Among them, the CoVPc, Co2Pc, NiVPc and NiZnPc monolayers exhibit moderate affinity for CH3Cl molecule, with the adsorption energies of −0.84 eV, −0.62 eV, −0.89 eV and −0.54 eV, respectively. The microscopic interaction mechanisms between CH3Cl molecule and bimetallic phthalocyanine monolayers are revealed through the analyses of total charge density, charge density difference and density of states. Furthermore, significant changes in bandgap are observed for Co2Pc and NiZnPc upon CH3Cl adsorption, while CoVPc and NiVPc monolayers exhibit noticeable variations in magnetic moments, indicating their high sensitivity towards CH3Cl. Considering the balance of adsorption strength, sensitivity and recovery time, the CoVPc, Co2Pc, NiVPc and NiZnPc monolayers are regarded as a great potential as gas-sensitive materials for recyclable CH3Cl gas sensors.

Identification of CH3F, CH3Cl, and CH3Br molecules by boron phosphide nanosheets: a DFT study

This paper adopted the 2D periodic boundary-condition (PBC) density functional theory (DFT) to examine the adsorption of CH3Br, CH3Cl, and CH3F halomethanes into not only bare boron phosphide (BP) nanosheets but also gallium- and aluminium-doped ones. Geometric optimisation was applied to all the structures at the B3LYP/6-311 + G (d) level of theory. Moreover, the CAM-B3LYP/6-311 + G(d), ωB97X-D3, and M06-2X levels of theory were implemented to calculate the single point energy. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were carried out, evaluating the donor–acceptor interactions, partial natural charge, and Wiberg bond index (WBI). The adsorption energy values demonstrated that the gallium-doped BP had the highest adsorptive capability, while the lowest adsorption occurred in the bare BP. However, the adsorption of CH3Cl, with much smaller adsorption energy, was maximised in the aluminium-doped BP and minimised in the bare BP. Furthermore, CH3Br and CH3Cl showed the highest and lowest tendencies to be adsorbed onto the nanosheet surfaces, respectively. Gallium- and aluminium-doped BP structures appear to be efficient and effective in the development of new solid-state sensors of halomethanes.

Diffusion-controlled synthesis of Cu-based for the Rochow reaction

The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in Cu x Si phase after the removal of oxygen atoms in Cu2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.

Physisorption of CH3Cl on HOPG -Dynamics and Kinetics-

We report a study of dynamics and kinetics in physisorption of CH3Cl on an highly-oriented pyrolytic graphite (HOPG). The oriented molecular beam scattering was used to monitor the dynamical interaction of CH3Cl with HOPG in the zero coverage limit, demonstrating that the CH3Cl scattering intensity depends on the molecular orientation of the incident CH3Cl. The observed steric preference is not sensitive to the surface temperature. These results suggest that the moderate anisotropy in the interaction potential induces the molecular-orientation dependence of energy dissipation during the transient trapping into the physisorption well. On the other hand, the thermal energy atom scattering (TEAS) was used to probe the kinetics of thermal CH3Cl adsorption on HOPG during the coverage evolution. The desorption energy of CH3Cl on HOPG changes from 0.25 to 0.30 eV with increasing surface coverage, suggesting the attractive interaction between CH3Cl molecules on the surface.

Reaction-Path Selection with Molecular Orientation of CH3Cl on Si{100}

We report direct evidence of steric effects in the dissociative adsorption of CH3Cl on Si{100} during the evolution of the coverage. The sticking probability (S) as a function of the amount of accumulated CH3Cl on the surface reveals the typical mobile precursor-mediated adsorption. For the Cl end collision, the decrease of S starts with a lower CH3Cl accumulation than for the CH3 end collision. Moreover, this steric effect depends on the surface temperature.

New Development of Ultrahigh-Vacuum Oriented-Molecular-Beam Machine and Its Application to Chemical Reactions on Silicon Surface

The stereochemical control of surface reactions is one of the ultimate goals of surface scientists. An oriented-molecular-beam technique based on the Stark effect of a molecule in an inhomogeneous hexapole electrostatic field is a potential tool for achieving such a goal. This technique allows us to select a specific rotational quantum state and also an orientation of a reagent molecule. We have designed, built and tuned up a new UHV-compatible oriented-molecular-beam machine for the elucidation of the reaction dynamics on surfaces and for surface manufacturing application. In the dissociative adsorption of CH3Cl on a Si{100} surface, we found a dynamical steric effect on the initial sticking probability (S0) using the new machine. S0 in Cl-end collision is larger than that in CH3-end collision at an incident energy of 120 meV. To our knowledge, this is the first measurement of the steric effect in the chemisorption of a molecule on a Si surface.

Dissociative adsorption of methyl chloride on Si(001) studied by scanning tunneling microscopy

Chemical reactions of methyl chloride (CH3Cl) on a clean Si(001) surface at approximately 300 K are studied by means of scanning tunneling microscopy (STM) under ultra-high-vacuum conditions. The features appearing in the STM images are identified with the possible products of dissociated CH3 and Cl, and their distribution is also evaluated as well as the development of their distribution with increasing CH(3)Cl doses. The amount of Cl atoms found on the surface is approximately twice as large as that of the CH3 molecules. This leads to the conclusion that dissociative adsorption of CH3Cl on Si occurs in different processes: CH3Cl(precursor) --> CH3(ad) + Cl(ad) and CH3Cl(precursor) --> CH3(gas) + Cl(ad).

Adsorption mechanism of CH3Cl on Si(1 0 0)-2×1

The adsorption mechanism of CH3Cl on Si(100)-2×1 has been studied by the experiment and semiempirical calculations. For adsorption at room temperature, the existence of a precursor state was confirmed from the dependence of the sticking probability of CH3Cl on the surface coverage and substrate temperature. From Auger electron spectroscopy measurements, we have found the difference in activation barrier heights for chemisorption and desorption from the precursor state, (Ed−Ea), to be 0.28±0.01 eV, indicating a nonactivated adsorption process. The optimized precursor state and the potential energy curve for the adsorption of CH3Cl on Si(100)-2×1 were also calculated by the semiempirical PM3 method based on a cluster model.

Adsorption and reactions of CH 3Cl on Mo 2C based catalyst

The adsorption of CH 3Cl on ZSM-5, Mo 2C/ZSM-5 and Mo 2C/SiO 2 was investigated by temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR). The formation of methoxy species was clearly identified on all the three catalysts. Three elementary steps were considered to explain the absorption bands observed in the IR spectra and to describe the reaction products found at higher temperatures: (i) the interaction of CH 3Cl with the OH groups of ZSM-5, (ii) dissociation of CH 3Cl yielding CH 3, and (iii) the elimination of HCl from the adsorbed CH 3Cl to give CH 2 species. A new finding was the identification of the alkenyl carbocation formed on the Lewis acidic sites of ZSM-5. The decomposition of CH 3Cl on ZSM-5 proceeded at 673 K with a high conversion yielding propylene, ethylene, butane, methane and benzene in decreasing selectivities. Deposition of Mo 2C on ZSM only slightly modified the catalytic behavior of ZSM-5. Its promoter effect came into prominence on silica surface.

Valence-level photoemission spectroscopy and photon-stimulated ion desorption studies of CH 3Cl adsorbed on Al(111) surface using synchrotron radiation

The interaction of CH 3Cl adsorbed on Al(111) surface at ∼90 K has been investigated by means of valence-level photoemission spectroscopy (PES), work function change and photon-stimulated ion desorption (PSID) using synchrotron radiation. The one-to-one correspondence between the gas-phase and the condensed-phase CH 3Cl PES spectra suggests that the molecules are molecularly adsorbed without decomposition. Adsorption of CH 3Cl leads to a decrease in work function of Al(111) ( Δø ∼ − 0.6 eV at a monolayer), indicating a dipole pointing away from the substrate and Cl is in direct contact with the metal. In the H + PSID spectra, three weak thresholds are observed, at ∼9.6, ∼13.9 and ∼16.5 eV, and a major threshold appears at ∼18.9 eV. CH + 3 PSID spectra show a weak threshold at ∼13.2 eV and two major thresholds near 9.0 and 16.7 eV. The desorption threshold below 18 eV may be due primarily to the single-hole excitation or Rydberg transition, whereas the ion desorption above 18 eV may result predominantly from excitations of C 2s electron correlation states.

Chemistry of the direct synthesis of methylchlorosilanes from methyl + chlorine monolayers on a Cu3Si surface

The direct process for synthesizing methylchlorosilanes from methyl chloride + silicon in the presence of catalytic amounts of copper has been studied in vacuum using a sample of Cu3Si alloy, the bulk phase that is present in active regions of the catalytic direct process. From the melt containing 23% of excess silicon, a two-phase Cu3Si + Si sample was prepared. Free silicon phase served both to replenish silicon reacted from Cu3Si and to provide the grain boundaries found in an industrial process. Atomically clean surfaces of this material with varying Cu/Si atomic ratios were prepared by ion bombardment over a range of temperatures. While the dissociative adsorption of CH3Cl was observed to be immeasurably slow on these surfaces under ultrahigh vacuum conditions, methyl + chlorine monolayers generated by the coadsorption of methyl radicals and Cl2 led to selective formation of dimethyldichlorosilane. Adsorption of methyl groups alone produced trimethylsilane from two different active sites with very different kinetics. Adsorption of chlorine alone produced SiCl4.

Na growth on Cu 3Si and CH 3Cl adsorption on a Na promoted Cu 3Si surface: an XPS and AES study

The chemical state of silicon at the surface of a bulk Cu 3Si alloy is strongly modified by the silicon segregation induced by annealing. Observed changes are related to the decrease of the copper content in the outermost surface layers. Na growth is found to begin on copper-rich sites of the Cu 3Si surface. For larger Na doses, Thermal desorption (TDS) experiments demonstrate the growth of the second and multilayers at room temperature. Due to Na deposition, the chemical state of the surface silicon is modified as demonstrated by the disappearance of the Si LVV splitting attributed to Si3pCu3d hybridisation. This result is supported by consistent XPS observations when using synchrotron radiation which allows one to conclude to a weaker copper-silicon interaction following sodium deposition. The formation of alkali-chlorine bonds is observed upon CH 3Cl adsorption on Na Cu 3 Si . Though silicon reactivity is known to be enhanced by alloying with copper, there is no evidence of direct interaction of methyl chloride with the copper-silicon substrate.

Effects of potassium on the adsorption and dissociation of CH 3Cl on Pd(100)

The effects of potassium on the adsorption and dissociation of CH 3Cl on a Pd(100) surface has been investigated by ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy (AES), electron energy loss spectroscopy (in the electronic range EELS), temperature-programmed desorption (TPD) and work function change. In contrast to the clean surface, the adsorption of CH 3Cl caused a significant work function increase, 0.9-1.4 eV, of potassium-dosed Pd. Preadsorbed K enhanced the binding energy of CH 3C1 to the surface and induced the dissociation of adsorbed molecules. The extent of the dissociation increased almost linearly with the potassium content. The appearance of a new emission in the UPS spectrum at 9.2 eV, attributed to adsorbed CH 3 species, and the low-temperature formation of ethane suggest that a fraction of adsorbed CH 3Cl dissociates even at 115–125 K on potassium-dosed Pd(100). At the same time, a significant part of adsorbed CH 3 radical is stabilized, the reaction of which occurs only at 250–300 K. By means of TPD measurements, H 2, CH 4, C 2H 6, C 2H 4, KCl and K were detected in the desorbing gases. The results are interpreted by assuming a through-metal electronic interaction at low potassium coverage and by a direct interaction of the Cl in the adsorbed CH 3Cl with potassium at high potassium coverage. The latter proposal is supported by the electron excited Auger fine structure of the Cl signal and by the formation of KCl in the desorbing gases.

Adsorption of CH 3Cl on clean and Cl-dosed Pd(100) surfaces

The adsorption of methyl chloride on a Pd(100) surface has been investigated by ultraviolet photoelectron spectroscopy (UPS), electron energy loss spectroscopy (in the electronic range, EELS), temperature-programmed desorption (TPD) and work function change. CH 3Cl adsorbs with high sticking probability at 80–100 K. UPS and TDS spectra suggest that the adsorption of CH 3Cl is molecular at 100 K, with a little distortion of the corresponding gas-phase molecular electronic structure. No dissociation of CH 3Cl was observed even up to 550 K. By means of TPD, we distinguished two adsorption states with desorption energies of 46.9 and 33.4 kJ/mol. The formation of a condensed layer at 105–110 K was also observed. Adsorption of CH 3Cl caused a significant work function decrease, Δϕ = −0.91 eV, indicating a dipole with positive end pointed away from the surface. The effects of electronegative additives, preadsorbed Cl and O were also examined. Preadsorbed Cl caused a slight destabilization of adsorbed CH 3Cl at lower concentration, prevented the adsorption of CH 3Cl at higher concentration and facilitated the formation of a condensed layer. No such effect was experienced in the presence of preadsorbed O.

Adsorption, decomposition and surface reactions of methyl chloride on metal films of iron, nickel, palladium, lead, gold and copper

Adsorption and decomposition of methyl chloride on metal films of Fe, Ni, Pd, Pb, Au and Cu have been investigated in the temperature range 193–570 K. Both molecular and dissociative adsorption of CH3Cl occurred on all films at 193 K. Above 300 K the dissociative chemisorption of CH3Cl on all the films was accompanied by the evolution of CH4, C2H6 and H2 together with some C2H4 on Fe, Ni, Pb and Au. The gaseous products subsequent to CH3Cl adsorption on the oxidized films of Fe, Ni, Pd, Pb and Cu above 350 K involved CH4, C2H6, H2 and CO gases. The structure of the surface phase was represented as CnHmCl and the minimum values of the ratio m/n on Fe, Ni, Pd, Au and Cu ranged from 2.69 to 2.93, but remained as 2.1 on Pb, indicating the existence of CH3 and CH2 radicals on the surface. Further support for the surface species was derived from the results of CH3Cl adsorption on Fe and Ni films which had been saturated with deuterium. No HCl, CH2O, CH3OH, H2O, CO2 or other gases have been detected at any stage, and the adsorption of chlorine atoms, resulting from CH3Cl decomposition, on the film surface was accompanied by some incorporation in the bulk of the metal. The kinetic data revealed the direct dependence of the reaction rate on CH3Cl pressure and the operation of a compensation effect throughout the interaction of CH3Cl with various surfaces. On the basis of such a compensation and the linearity of the relationship existing between the activation energies (Ea) and the pre-exponential factors of the rate equation (log A), it was possible to arrange the clean and oxidized films in the order of decreasing activity towards CH3Cl adsorption and decomposition. An attempt was also made to estimate the enthalpy changes associated with the dissociative adsorption of CH3Cl on various surfaces, as well as for the subsequent reactions of the resulting species on the basis of the standard enthalpy involved in the respective processes.

Reactions and reaction intermediates on iron surfaces: II. Hydrocarbons and carboxylic acids

The reactions of hydrocarbons and carboxylic acids on Fe(100) were studied by temperatureprogrammed reaction spectroscopy (TPRS) and X-ray photoelectron spectroscopy (XPS). Adsorbed methyl groups were observed to be stable surface intermediates formed from CH 3Cl adsorption. The methyl groups reacted to form H 2 and surface carbide; the rate of this reaction was given by −dσ CH 3 dt = (8 × 10 12 s −1)σ CH 3 exp(− 110 kJ/mole/ RT) . TPRS results did show that oleflns formed stable surface intermediates, though no definitive identification was possible from the studies reported here. Carboxylic acids were found to form stable carboxylate intermediates, which decomposed by first-order kinetics to form H 2 and either CO 2 or CO and adsorbed oxygen. The rates for formate and acetate decomposition were −dσ HCOO dt = (7 × 10 13 s −1)σ HCOO exp (−130 kJ/mole/ RT), −dσ CH 3COO dt = (8 × 10 13 s −1)σ CH 3COO exp(−140 kJ/mole/ RT) . The stability of surface formates on various metal surfaces were compared and shown to correlate with the oxygen metal bond strength.