DFT Calculations and Monte Carlo Simulations of the Co-Adsorption of Hydrogen Atoms and Ethylidyne Species on Pt(111)

Podkolzin, Simon G.; Watwe, Ramchandra M.; Yan, Qiliang; Pablo, and Juan J. de; Dumesic, James A.

doi:10.1021/jp0104076

Cited by 28 publications

(39 citation statements)

References 45 publications

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“…It is interesting that the differential chemisorption free energy of hydrogen atoms is not significantly affected by the self-interaction until a very high coverage is reached, as shown in Figure c. This phenomenon was also mentioned in the previous work of Podkolzin et al …”

Section: Resultsmentioning

confidence: 99%

Quantitative Studies of the Key Aspects in Selective Acetylene Hydrogenation on Pd(111) by Microkinetic Modeling with Coverage Effects and Molecular Dynamics

Xie

Ding

et al. 2021

ACS Catal.

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Selective acetylene hydrogenation as a vital industrial reaction has been studied for decades. However, some key issues remain elusive. Herein, a detailed microkinetic model using density functional theory energies is developed to comprehensively investigate the key aspects of acetylene hydrogenation on Pd(111). The coverage-dependent kinetic simulation, factoring in both self and cross-interactions of adsorbates as well as the coverage effects on the transition states of each elementary step, is compared with the coverage-independent kinetic calculation derived from energies obtained at low coverages. The accurate determination of the free-energy barrier of ethylene desorption using ab initio molecular dynamics (AIMD) with umbrella sampling adds further crucial insights into the microkinetic model. By combining the coverage-dependent calculations and AIMD results, we achieve a full first-principles kinetic simulation with all the kinetic parameters being systematically calculated to understand the acetylene hydrogenation. We show that the coverage-dependent microkinetic model gives a much more reasonable turnover frequency result of 1.41 s −1 at 300 K than that calculated using the coverage-independent model (3.16 × 10 −24 s −1 ). The microkinetic results, including activity and selectivity, are tested against the experimental data, yielding a good agreement. A comprehensive set of kinetic analyses is performed. It is found that the activity is mainly determined by the barriers of the first two hydrogenation steps. The step with the major effect on the reaction activity is gradually transitioned from the second hydrogenation step, C 2 H 3 * + H* ↔ C 2 H 4 * + *, to the first hydrogenation step of C 2 H 2 * + H* ↔ C 2 H 3 * + * as the temperature increases. Both the desorption barrier of ethylene and the hydrogenation barrier of C 2 H 4 * cause significant impacts on the selectivity of ethylene, but the former is found to be the most prominent physical quantity affecting the ethylene selectivity.

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Section: Resultsmentioning

confidence: 99%

Quantitative Studies of the Key Aspects in Selective Acetylene Hydrogenation on Pd(111) by Microkinetic Modeling with Coverage Effects and Molecular Dynamics

Xie

Ding

et al. 2021

ACS Catal.

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“…has been estimated to be 0.085 kJ/(kmol H) [17]. This is a perfectly reasonable result because the absolute entropy of H 2 (i.e., H 2 → 2H) is 0.13 kJ/(kmol H 2 ) [18] [or 0.065 kJ/(kmol H)], and the adsorbed atomic H on the surface should have relatively much smaller entropy.…”

Section: Model For Hydrogen Chemisorptionmentioning

confidence: 91%

A three-site Langmuir adsorption model to elucidate the temperature, pressure, and support dependence of the hydrogen coverage on supported Pt particles

Koot

Eerden

et al. 2007

Journal of Catalysis

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The three-site adsorption model, previously developed to describe H adsorption on small Pt particles, was used to gain insight into dependence of hydrogen coverage on temperature, pressure, and support ionicity. The three sites, in order of decreasing Pt-H bond strength, involve H in an atop, a threefold, and an ontop Pt site. The ontop site designates H bonded in an atop site surrounded by occupied threefold sites (hence referred to as ontop site). The model includes an emptying of the H atop sites into H threefold sites with increasing H pressure to reduce lateral interactions. Hydrogen chemisorption on an acidic Pt/H-USY and a basic Pt/NaY and TPD results on a acidic Pt/H-LTL and basic Pt/K-LTL are modeled using a Langmuir isotherm for each H site. The H/M data can be directly compared with Pt L 2,3 XANES results on the same samples. A new analysis method (Delta XANES technique) using the difference in the absorption coefficient, μ = μ(H/Pt) − μ(Pt), allows an in situ spectroscopic determination of the type of H adsorption site and H coverage. The adsorption enthalpies ( H 's) for the atop, threefold, and ontop sites are found to be highly dependent on the support ionicity, increasing for ionic (basic) supports consistent with previous results. The calculations using the three-site model confirm that the support-induced changes in the Pt-H bond strength produce dramatically different H coverages and dominant adsorption sites at catalytic reaction temperatures and pressures. Depending on uptake versus desorption of H, a hysteresis is found in the atop to threefold site rearrangement, believed to result from a requirement for collective rearrangement involving an entire domain or island of H on the surface.

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“…When propylene adsorbs dissociatively, it forms propylidyne by splitting off one H atom from the CH 2 group and transferring the remaining H atom to the CH group, similarly to ethylidyne formation from ethylene. [28][29][30][31] On Ni, propylidyne preferentially adsorbs with an adsorption energy of 99 kJ/mol on a long bridge site by binding to two additional Ni atoms in the second layer in a μ 4 η 1 configuration (Figure 10a). Propylidyne can also adsorb in a threefold site in a μ 3 η 1 configuration with a slightly lower adsorption energy of 97 kJ/mol (Figure 10b).…”

Section: Dft Calculationsmentioning

confidence: 99%

Propane Dehydrogenation to Propylene and Propylene Adsorption on Ni and Ni‐Sn Catalysts

et al. 2022

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Temperature programmed reaction (TPR) measurements with propane over silica-supported Ni, NiÀ Sn and Sn catalysts show that the reaction products change significantly from mostly methane, hydrogen and surface carbon over Ni to propylene and hydrogen over NiÀ Sn. Propylene formation over NiÀ Sn starts at a moderate temperature of 630 K. Since the activity of Sn by itself is low, Sn serves as a promoter for Ni. The promoter effects are attributed to a lower adsorption energy of molecularly adsorbed propylene and suppression of propylidyne formation on NiÀ Sn based on temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) measurements as well as density functional theory (DFT) calculations for propylene adsorption on Ni(110) and c(2 × 2)-Sn/Ni(110) single-crystal surfaces. On Ni, propylene forms a π-bonded structure with ν(C=C) at 1500 cm À 1 , which desorbs at 170 K, and a di-σ-bonded structure with ν(C=C) at 1416 cm À 1 , which desorbs at 245 K. The di-σ-bonded structure is asymmetric, with the methylene C atom being in the middle of the NiÀ Ni bridge site, and the methylidyne C atom being above one of these Ni atoms. Therefore, this structure can also be characterized as a hybrid between di-σ-and π-bonded structures. Only a fraction of propylene desorbs from Ni because propylene can convert into propylidyne, which decomposes further. In contrast, propylene forms only a π-bonded structure on NiÀ Sn with ν(C=C) at 1506 cm À 1 , which desorbs at 125 K. The low stability of this structure enables propylene to desorb fully, resulting in high reaction selectivity in propane dehydrogenation to propylene over the NiÀ Sn catalyst.

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DFT Calculations and Monte Carlo Simulations of the Co-Adsorption of Hydrogen Atoms and Ethylidyne Species on Pt(111)

Cited by 28 publications

References 45 publications

Quantitative Studies of the Key Aspects in Selective Acetylene Hydrogenation on Pd(111) by Microkinetic Modeling with Coverage Effects and Molecular Dynamics

Quantitative Studies of the Key Aspects in Selective Acetylene Hydrogenation on Pd(111) by Microkinetic Modeling with Coverage Effects and Molecular Dynamics

A three-site Langmuir adsorption model to elucidate the temperature, pressure, and support dependence of the hydrogen coverage on supported Pt particles

Propane Dehydrogenation to Propylene and Propylene Adsorption on Ni and Ni‐Sn Catalysts

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