Ethylene hydrogenation on Mo(CO)6 derived model catalysts in ultrahigh vacuum: From oxycarbide to carbide to MoAl alloy

Gao, Feng; Wang, Yilin

doi:10.1016/j.molcata.2006.01.016

Cited by 3 publications

(3 citation statements)

References 34 publications

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“…A priori, it is not clear if the C or Mo centers are the active sites for the hydrogenation of C=C and C≡C bonds on Mo 2 C catalysts, although many studies assume that the chemical transformations take place on Mo centers. 5,21,22 Among the crystal phases of molybdenum carbide, 23 three of them are the most used in catalysis, viz. cubic, 13,22,[24][25][26][27][28][29] hexagonal 11,[30][31][32] and orthorhombic.…”

Section: Introductionmentioning

confidence: 99%

“…Molybdenum carbides can adopt different structures depending on the carbon/metal ratio, and they can exhibit terminations of C and Mo atoms, leading to different bonding modes on these terminations. A priori, it is not clear if the C or Mo center is the active site for the hydrogenation of CC and CC bonds on Mo 2 C catalysts, although many studies assume that the chemical transformations take place on Mo centers. ,, …”

Section: Introductionmentioning

confidence: 99%

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Acetylene and Ethylene Adsorption on a β-Mo₂C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

et al. 2017

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Mo 2 C catalysts are widely used in hydrogenation reactions, however, the role of the C-and Moterminations in these catalysts is not clear. Understanding the binding of adsorbates is key for explaining the activity of Mo 2 C. The adsorption of acetylene and ethylene, probe molecules representing alkynes and olefins, respectively, was studied on a β-Mo 2 C(100) surface with Cand Mo-terminations using calculations based on periodic density functional theory. Moreover, the role of the C/Mo molar ratio was investigated to compare the catalytic potential of cubic (δ-MoC) and orthorhombic (β-Mo 2 C) surfaces. The geometry and electronic properties of the clean δ-MoC(001) and β-Mo 2 C(100) surfaces have strong influence on the binding of unsaturated hydrocarbons. The adsorption of ethylene is weaker than that of acetylene on the surfaces of the cubic and orthorhombic systems; adsorption of the hydrocarbons was stronger on β-Mo 2 C(100) than on δ-MoC(001). The C-termination in β-Mo 2 C(100) actively participates in both acetylene and ethylene adsorption and is not merely a spectator. The results of this work suggest that the β-Mo 2 C(100)-C surface could be the one responsible for the catalytic activity during the hydrogenation of unsaturated C≡C and C=C bonds, while the Mo-terminated surface could be poisoned or transformed by the strong adsorption of C and CH x fragments.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Acetylene and Ethylene Adsorption on a β-Mo₂C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

et al. 2017

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“…However, high H 2 concentration in reaction 2 can also lower the growth rate of MoS 2 , as discussed in Section 3.4. The reaction pathway (1), which normally requires temperatures above the DES pyrolysis onset ≳600 °C, see Figure 4c, can even occur at lower temperatures in the presence of Mo(CO) 6 (Figure 4d), possibly due to surface-templated reactions on the SiO 2 substrate 83 and hydrodesulfurization of DES at the catalytically active edge sites of growing MoS 2 , 44 as discussed in Section 3.4. Reaction 4 is the sum of reactions 1, 2, and 3.…”

Section: Resultsmentioning

confidence: 99%

Carbon Incorporation in MOCVD of MoS₂ Thin Films Grown from an Organosulfide Precursor

et al. 2021

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With the rise of two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors and their prospective use in commercial (opto)electronic applications, it has become key to develop scalable and reliable TMD synthesis methods with well-monitored and controlled levels of impurities. While metal–organic chemical vapor deposition (MOCVD) has emerged as the method of choice for large-scale TMD fabrication, carbon (C) incorporation arising during MOCVD growth of TMDs has been a persistent concernespecially in instances where organic chalcogen precursors are desired as a less hazardous alternative to more toxic chalcogen hydrides. However, the underlying mechanisms of such unintentional C incorporation and the effects on film growth and properties are still elusive. Here, we report on the role of C-containing side products of organosulfur precursor pyrolysis in MoS2 thin films grown from molybdenum hexacarbonyl Mo(CO)6 and diethyl sulfide (CH3CH2)2S (DES). By combining in situ gas-phase monitoring with ex situ microscopy and spectroscopy analyses, we systematically investigate the effect of temperature and Mo(CO)6/DES/H2 gas mixture ratios on film morphology, chemical composition, and stoichiometry. Aiming at high-quality TMD growth that typically requires elevated growth temperatures and high DES/Mo(CO)6 precursor ratios, we observed that temperatures above DES pyrolysis onset (≳600 °C) and excessive DES flow result in the formation of nanographitic carbon, competing with MoS2 growth. We found that by introducing H2 gas to the process, DES pyrolysis is significantly hindered, which reduces carbon incorporation. The C content in the MoS2 films is shown to quench the MoS2 photoluminescence and influence the trion-to-exciton ratio via charge transfer. This finding is fundamental for understanding process-induced C impurity doping in MOCVD-grown 2D semiconductors and might have important implications for the functionality and performance of (opto)electronic devices.

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Optimization of experimental procedure and statistical data treatment for kinetics of ethylene hydrogenation on a copper-magnesia catalyst

Pirard

Heinrichs

Heyen

et al. 2008

Chemical Engineering Journal

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Ethylene hydrogenation on Mo(CO)6 derived model catalysts in ultrahigh vacuum: From oxycarbide to carbide to MoAl alloy

Cited by 3 publications

References 34 publications

Acetylene and Ethylene Adsorption on a β-Mo₂C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Acetylene and Ethylene Adsorption on a β-Mo₂C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Carbon Incorporation in MOCVD of MoS₂ Thin Films Grown from an Organosulfide Precursor

Optimization of experimental procedure and statistical data treatment for kinetics of ethylene hydrogenation on a copper-magnesia catalyst

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Ethylene hydrogenation on Mo(CO)6 derived model catalysts in ultrahigh vacuum: From oxycarbide to carbide to MoAl alloy

Cited by 3 publications

References 34 publications

Acetylene and Ethylene Adsorption on a β-Mo2C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Acetylene and Ethylene Adsorption on a β-Mo2C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Carbon Incorporation in MOCVD of MoS2 Thin Films Grown from an Organosulfide Precursor

Optimization of experimental procedure and statistical data treatment for kinetics of ethylene hydrogenation on a copper-magnesia catalyst

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Acetylene and Ethylene Adsorption on a β-Mo₂C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Acetylene and Ethylene Adsorption on a β-Mo₂C(100) Surface: A Periodic DFT Study on the Role of C- and Mo-Terminations for Bonding and Hydrogenation Reactions

Carbon Incorporation in MOCVD of MoS₂ Thin Films Grown from an Organosulfide Precursor