Investigation of Hydrogen Spillover on Metal Containing Catalysts by Isotopic Exchange

Dmitriev, R. V.; Detjuk, A. N.; Minachev, Ch. M.; Steinberg, K.-H.

doi:10.1016/s0167-2991(08)64658-3

Cited by 14 publications

(3 citation statements)

References 14 publications

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“…When metals were placed on Y zeolite, the exchange temperature decreased by 300 K, and exchange was faster for supported Pt and Pd than for Ni. 74 Steinberg et al found that hydroxyls on Pt/Y zeolite exchanged with D2 at room temperature, and the exchange was complete in 2 h.75,76 Even for mechanical mixtures, isotopic equilibrium was reached at 373 K. The authors concluded that spillover (and not surface diffusion of the spiltover D) was rate limiting for hydroxyl exchange. Similarly H-D exchange due to H spillover was observed in Pt-NaY/ H-NaY, and exchange of OH groups took place at of D2 by IR of the H-NaY acceptor surface, at a location 0.5 mm from the interface to the Pt-NaY source.…”

Section: A Isotope Exchangementioning

confidence: 99%

Spillover in Heterogeneous Catalysis

Conner¹,

Falconer²

1995

Chem. Rev.

1,200

795

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Section: A Isotope Exchangementioning

confidence: 99%

Spillover in Heterogeneous Catalysis

Conner¹,

Falconer²

1995

Chem. Rev.

1,200

795

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“…As for the study of hydrogen spillover on supported metal catalysts, two types of strategy can be employed. The first method consists in exchanging the hydrogen through small metal particles dispersed on the surface of the oxide, which implies a multitude of hydrogen species sources (each metal particle). ,,− In the second method, the hydrogen diffusing on the support issues from a single source: a grain of a supported metal catalyst deposited on, or in contact with, the oxide studied. − The above two methods lead to very different coefficients of hydrogen surface diffusion on the oxide surfaces. In this work, we used supported metal catalysts to determine the coefficients of hydrogen surface diffusion on the surface of oxides.…”

Section: Introductionmentioning

confidence: 99%

Mobility of Surface Species on Oxides. 2. Isotopic Exchange of D₂ with H of SiO₂, Al₂O₃, ZrO₂, MgO, and CeO₂: Activation by Rhodium and Effect of Chlorine

and

Duprez

1997

J. Phys. Chem. B

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Exchange of D2 with the OH groups of several oxides was carried out on the samples on which we investigated the 18O2/16OH exchange (part I, J. Phys. Chem. 1996, 100, 9429). Temperature-programmed isotopic exchange was first carried out on the bare oxides. In every case, the reaction follows a simple heteroexchange mechanism, with HD as a primary product. The maximal rates of exchange are obtained at the following temperature: CeO2 (prereduced), 100 °C > MgO, 120 °C > ZrO2, 145 °C > CeO2 (preoxidized), 160 °C > γ-Al2O3, 190 °C > Cl−Al2O3, 200 °C ≫ SiO2, 540 °C. The first two samples exchange their hydrogen at a significant rate at room temperature. Secondary peaks and shoulders show the multiplicity of the OH groups on most oxides. Compared to oxygen, hydrogen exchange occurs at much lower temperatures, the shift of the temperature ranges of O and H exchange being between 250 and 430 °C. Isothermal isotopic exchange was carried out between 25 and 100 °C over rhodium catalysts supported on these oxides. The presence of rhodium accelerates the hydrogen exchange, at least by 2 orders of magnitude. As with oxygen exchange, three main steps must be considered: (i) adsorption−desorption on the metal, (ii) transfer of D atoms onto the support (spillover), and (iii) hydrogen diffusion. Contrary to what was observed with O2 exchange, step i is never a rate-determining step (rds) for H2 exchange, the rate of H2 + D2 equilibration being much higher than the rate of exchange. The results are in accordance with a model where at T < 75 °C the rds of exchange would be the hydrogen transfer from the metal to the support (spillover step), while at T ≥ 75 °C, the rds would be the surface diffusion. This model is valid for all the supports except silica, for which most of the hydroxyl groups exchange at high temperatures. The rate of exchange depends linearly on the density of the hydroxyl groups and tends toward zero for a fully dehydroxylated support. Coefficients of surface diffusion give the following order for the hydrogen mobility at 75 °C (base 100 for γ-Al2O3): CeO2, 770 > MgO, 230 > γ-Al2O3, 100 > ZrO2, 23 ≫ SiO2, nd. There is no correlation between the hydrogen mobility and the surface acidity of the oxides, the highest hydrogen mobility being found on basic oxides with a very high oxygen mobility. A model of isotropic heterogeneous diffusion is proposed to explain certain discrepancies observed between the present isotopic exchange method and direct IR spectroscopic methods previously published.

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“…Diffusion distances in two-dimensions for H atoms on carbon surfaces have been reported to be 150 Å at 25 °C [21], 1000 Å at 200 °C and 5 mm at 350 °C [22]. A distance as large as 5 mm has also been reported by Dmitriev et al [23]. Counter to intuition, spilledover H atoms have been reported to diffuse even in empty space [17].…”

Section: Introductionmentioning

confidence: 65%

n-Hexane Isomerisation: Exploit Hydrogen Spillover to Reduce Catalyst Costs

Shinde

Chakraborty

Parikh

2017

Progress in Reaction Kinetics and Mechanism

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We report the role of hydrogen spillover in n-hexane isomerisation over carbon nanotubes or SiC mixed with hierarchical zeolite beta. Here we infer that: (1) hydrogen spillover is a necessary step; (2) spilled-over H hydrogenates isomerised olefin at Brønsted acid sites only; and (3) closeness between acid and metal sites at the nanoscale enhances the rate of reaction, though this is not a requirement for this reaction to proceed. The economic advantage of the spillover phenomenon (necessitating less Pt on the catalyst) has been highlighted.

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Investigation of Hydrogen Spillover on Metal Containing Catalysts by Isotopic Exchange

Cited by 14 publications

References 14 publications

Spillover in Heterogeneous Catalysis

Spillover in Heterogeneous Catalysis

Mobility of Surface Species on Oxides. 2. Isotopic Exchange of D₂ with H of SiO₂, Al₂O₃, ZrO₂, MgO, and CeO₂: Activation by Rhodium and Effect of Chlorine

n-Hexane Isomerisation: Exploit Hydrogen Spillover to Reduce Catalyst Costs

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Investigation of Hydrogen Spillover on Metal Containing Catalysts by Isotopic Exchange

Cited by 14 publications

References 14 publications

Spillover in Heterogeneous Catalysis

Spillover in Heterogeneous Catalysis

Mobility of Surface Species on Oxides. 2. Isotopic Exchange of D2 with H of SiO2, Al2O3, ZrO2, MgO, and CeO2: Activation by Rhodium and Effect of Chlorine

n-Hexane Isomerisation: Exploit Hydrogen Spillover to Reduce Catalyst Costs

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Mobility of Surface Species on Oxides. 2. Isotopic Exchange of D₂ with H of SiO₂, Al₂O₃, ZrO₂, MgO, and CeO₂: Activation by Rhodium and Effect of Chlorine