Kinetic Parameter Estimation for Catalytic H2–D2 Exchange on Pd

Golio, Nicholas; Sen, Irem; Guo, Zhitao; Railkar, Rucha; Gellman, Andrew J.

doi:10.1007/s10562-022-03961-0

Cited by 3 publications

(11 citation statements)

References 42 publications

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“…The full monolayer of H surf can be formed already at 100 K and at H 2 exposure of a few Langmuir. , In contrast, the formation of subsurface H sub species proceeds in an activated process after prolonged (typically more than 300 L) H 2 exposures, after which H surf and H sub coexist. , Importantly, it was shown that with growing H 2 pressure in the range 10 –8 –2 × 10 –5 mbar, the coverage of the surface H surf species does not change up to 300 K and remains unity, while the abundance of subsurface H sub strongly increases by at least an order of magnitude. , These findings are also in agreement with the results of a more recent study on HD exchange over Pd by Golio et al Additional discussion on the population of H surf and H sub on Pd can be found in the SI.…”

Section: Resultsmentioning

confidence: 99%

“…17,18 Importantly, it was shown that with growing H 2 pressure in the range 10 −8 − 2 × 10 −5 mbar, the coverage of the surface H surf species does not change up to 300 K and remains unity, while the abundance of subsurface H sub strongly increases by at least an order of magnitude. 17,18 These findings are also in agreement with the results of a more recent study on HD exchange over Pd by Golio et al 41 Additional discussion on the population of H surf and H sub on Pd can be found in the SI. surface.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Crucial Effect of Subsurface Hydrogen on Low-Barrier Hydrogenation and Keto–Enol Tautomerization of Carbonyl Compounds

Haugg,

Smyczek,

Hubert

et al. 2024

ACS Catal.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Crucial Effect of Subsurface Hydrogen on Low-Barrier Hydrogenation and Keto–Enol Tautomerization of Carbonyl Compounds

Haugg,

Smyczek,

Hubert

et al. 2024

ACS Catal.

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“…Analysis of the rate laws derived from these mechanisms under conditions where P H2 ≫ P D2 and θ ≅ 1 revealed that the 2H′ mechanism is consistent with n H2 = 0 observed in the earlier work using this Ag x Pd 1−x CSAF. 49 In a more recent study, 42 we estimated the kinetic parameters for adsorption, desorption, and surface-to-subsurface diffusion associated with the LH, 1H′, and 2H′ mechanisms by fitting the rate law given by each model to the measured rate of H 2 −D 2 exchange on the pure Pd region of this Ag x Pd 1−x CSAF at different reaction temperatures and inlet pressures of H 2 and D 2 . By fitting each model to the reaction data, we obtained estimates for the energy barrier to H 2 adsorption, ΔE ads ‡ , the energy barrier to H 2 desorption, ΔE des ‡ , and the surface-to-subsurface diffusion energy of adsorbed H on Pd, ΔE ss .…”

Section: Introductionmentioning

confidence: 99%

“…Numerous studies of H 2 on Pd surfaces have shown that it adsorbs with a negligible barrier to dissociation and a high heat of adsorption. − On the other hand, H 2 does not adsorb dissociatively onto Ag single crystal surfaces at room temperature, and its adsorption is predicted to be endothermic. − The most straightforward approach for modeling H 2 –D 2 exchange on Ag x Pd 1– x binary alloys involves applying the traditional Langmuir–Hinshelwood (LH) framework, which parametrizes the reaction by just two rate constants: k ads for the dissociative adsorption of H 2 and k des for the associative desorption of H 2 . It has been well-documented that the kinetic behavior predicted by the LH mechanism has been found to be inconsistent with several experimental observations.…”

Section: Introductionmentioning

confidence: 99%

H₂–D₂ Exchange Activity and Electronic Structure of Ag_xPd_1–x Alloy Catalysts Spanning Composition Space

Golio,

Sen,

et al. 2024

ACS Catal.

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Many computational studies of catalytic surface reaction kinetics have demonstrated the existence of linear scaling relationships between physical descriptors of catalysts and reaction barriers on their surfaces. In this work, the relationship between catalyst activity, electronic structure, and alloy composition was investigated experimentally using a Ag x Pd 1−x Composition Spread Alloy Film (CSAF) and a multichannel reactor array that allows measurement of steady-state reaction kinetics at 100 alloy compositions simultaneously. Steady-state H 2 −D 2 exchange kinetics were measured at atmospheric pressure on Ag x Pd 1−x catalysts over a temperature range of 333−593 K and a range of inlet H 2 and D 2 partial pressures. X-ray photoelectron spectroscopy (XPS) was used to characterize the CSAF by determining the local surface compositions and the valence band electronic structure at each composition. The valence band photoemission spectra showed that the average energy of the valence band, ε ̅ v , shifts linearly with composition from −6.2 eV for pure Ag to −3.4 eV for pure Pd. At all reaction conditions, the H 2 −D 2 exchange activity was found to be highest on pure Pd and gradually decreased as the alloy was diluted with Ag until no activity was observed for compositions with x Pd < 0.58. Measured H 2 −D 2 exchange rates across the CSAF were fit using the Dual Subsurface Hydrogen (2H′) mechanism to extract estimates for the activation energy barriers to dissociative adsorption, ΔE ads ‡ , associative desorption, ΔE des ‡ , and the surface-to-subsurface diffusion energy, ΔE ss , as a function of alloy composition, x Pd . The 2H′ mechanism predicts ΔE ads ‡ = 0−10 kJ/mol, ΔE des ‡ = 30−65 kJ/mol, and ΔE ss = 20−30 kJ/mol for all alloy compositions with x Pd ≥ 0.64, including for the pure Pd catalyst (i.e., x Pd = 1). For these Pd-rich catalysts, ΔE des ‡ and ΔE ss appeared to increase by ∼5 kJ/mol with decreasing x Pd . However, due to the coupling of kinetic parameters in the 2H′ mechanism, we are unable to exclude the possibility that the kinetic parameters predicted when x Pd ≥ 0.64 are identical to those predicted for pure Pd. This suggests that H 2 −D 2 exchange occurs only on bulk-like Pd domains, presumably due to the strong interactions between H 2 and Pd. In this case, the decrease in catalytic activity with decreasing x Pd can be explained by a reduction in the availability of surface Pd at high Ag compositions.

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“…The inherently low hydrogenation activity of Ag is demonstrated by the absence of measurable activity for the hydrogenation of many molecules, including alkenes, − alkynes, , aldehydes, , and alcohols, ,, on its clean, low Miller index surfaces. Furthermore, H 2 does not dissociate on clean Ag surfaces, and atomic H is only very weakly bound, desorbing from the surface at temperatures below room temperature in temperature-programmed desorption (TPD) experiments. ,, By contrast, it is known that H 2 has a negligible barrier to dissociation on Pd. − Since Pd has a much lower barrier to H 2 dissociation than Ag, it is often the more useful catalyst for hydrogenation reactions. However, the weak binding of H to Ag can be advantageous in AgPd catalysts for reactions in which a partially hydrogenated product is desired.…”

Section: Introductionmentioning

confidence: 99%

Activation by O₂ of Ag_xPd_1–x Alloy Catalysts for Ethylene Hydrogenation

Golio,

Gellman

2023

ACS Catal.

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A composition spread alloy film (CSAF) spanning all of Ag x Pd 1−x composition space, x Pd = 0 → 1, was used to study catalytic ethylene hydrogenation with and without the presence of O 2 in the feed gas. High-throughput measurements of the ethylene hydrogenation activity of Ag x Pd 1−x alloys were performed at 100 Pd compositions spanning x Pd = 0 → 1. The extent of ethylene hydrogenation was measured versus x Pd at reaction temperatures spanning T = 300 → 405 K and inlet hydrogen partial pressures spanning P H2 in = 70 → 690 Torr. The inlet ethylene partial pressure was constant at P C2H4 in = 25 Torr, and the O 2 inlet partial pressure was either P O2 in = 0 or 15 Torr. When P O2 in = 0 Torr, only those alloys with x Pd ≥ 0.90 displayed observable ethylene hydrogenation activity. As expected, the most active catalyst was pure Pd, which yielded a maximum conversion of ∼0.4 at T = 405 K and P H2 in = 690 Torr. Adding a constant O 2 partial pressure of P O2 in = 15 Torr to the feed stream dramatically increased the catalytic activity across the CSAF at all experimental conditions and catalyst compositions without inducing catalytic ethylene combustion and without measurable O 2 consumption. The presence of P O2 in = 15 Torr more than doubled the maximum achievable conversion on Pd to ∼0.9 and activated alloys with as little as x Pd = 0.6 for ethylene hydrogenation. Measurement of the reaction order with respect to hydrogen, n H2 , showed that n H2 ≈ 0 when P O2 in = 15 Torr on high x Pd alloys but that n H2 increases to values between 0.5 and 1 as x Pd decreases or when P O2 in = 0 Torr. We attribute this P O2 in -induced change in n H2 to a change in the reaction mechanism resulting from different functional catalyst surfaces: one that is O 2 -activated and Pd-rich and one that is Ag-capped with low activity. Both are extremely sensitive to the bulk alloy composition, x Pd , and the reaction temperature, T. These results show that the activity of AgPd catalysts for ethylene hydrogenation depends strongly on the operational conditions. Furthermore, we demonstrate that the exposure of AgPd catalysts to 15 Torr of O 2 at moderate temperatures leads to enhanced catalyst performance, presumably by stimulating both Pd segregation to the topmost surface and Pd activation for ethylene hydrogenation.

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Kinetic Parameter Estimation for Catalytic H2–D2 Exchange on Pd

Cited by 3 publications

References 42 publications

Crucial Effect of Subsurface Hydrogen on Low-Barrier Hydrogenation and Keto–Enol Tautomerization of Carbonyl Compounds

Crucial Effect of Subsurface Hydrogen on Low-Barrier Hydrogenation and Keto–Enol Tautomerization of Carbonyl Compounds

H₂–D₂ Exchange Activity and Electronic Structure of Ag_xPd_1–x Alloy Catalysts Spanning Composition Space

Activation by O₂ of Ag_xPd_1–x Alloy Catalysts for Ethylene Hydrogenation

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Kinetic Parameter Estimation for Catalytic H2–D2 Exchange on Pd

Cited by 3 publications

References 42 publications

Crucial Effect of Subsurface Hydrogen on Low-Barrier Hydrogenation and Keto–Enol Tautomerization of Carbonyl Compounds

Crucial Effect of Subsurface Hydrogen on Low-Barrier Hydrogenation and Keto–Enol Tautomerization of Carbonyl Compounds

H2–D2 Exchange Activity and Electronic Structure of AgxPd1–x Alloy Catalysts Spanning Composition Space

Activation by O2 of AgxPd1–x Alloy Catalysts for Ethylene Hydrogenation

Contact Info

Product

Resources

About

H₂–D₂ Exchange Activity and Electronic Structure of Ag_xPd_1–x Alloy Catalysts Spanning Composition Space

Activation by O₂ of Ag_xPd_1–x Alloy Catalysts for Ethylene Hydrogenation