ESR evidence of hydrogen migration on supported metal catalysts

doi:10.1016/0021-9517(68)90020-1

Journal of Catalysis

Volume 11, Issue 2, June 1968, Pages 135-142

https://doi.org/10.1016/0021-9517(68)90020-1 Get rights and content

Abstract

The ESR investigation has provided evidence that the resonance at g = 2.10, developed upon heating of noble-metal-supported catalysts in hydrogen, results from the reduction of iron oxide to metallic iron also present on the supported catalyst. The mechanism of the oxide reduction evidently occurs by a sequence of events including hydrogen chemisorption on a metal such as palladium, hydrogen atom transfer to the support and then to iron oxide sites, and subsequent coalescing of iron to form ferromagnetic domains. The relative effectiveness of iron oxide reduction resulting from the presence of various supported metals and supports appears to depend on the relative heats of hydrogen atom sorption compared with the activation energy required for the atom transfer from the metal to the support.

References (19)

E.J. Nowak et al.
J. Catalysis
(1967)
J.E. Benson et al.
J. Catalysis
(1966)
P.B. Wells et al.
J. Catalysis
(1967)
P.A. Berger et al.
J. Catalysis
(1965)
L.S. Singer et al.
J. Chem. Phys.
(1965)
I.I. Levitskii et al.
Izv. Akad. Nauk. SSSR, Ser. Khim.
(1966)
J.A. Rabo et al.
Preprint of the Faraday Society
(1966)
H.L. Gruber et al.
Kolloid-Z. and Z. Polymere
(1966)
J.L. Carter et al.
J. Phys. Chem.
(1965)

There are more references available in the full text version of this article.

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Citation Excerpt :
However, preparation of well-homogenized bimetallic system remains a real challenge. Impregnation methods resulted in insufficient bimetal homogeneity (Juszczyk et al., 1995) and require high temperature (up to 1173 K) to alloy the metals (Sancier and Inami, 1968; Inami and Wise, 1972). Such temperature led to undesirable metal sintering and/or formation of strong metal-support interactions.
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Characterisation of Mg/Al hydrotalcite with interlayer palladium complex for catalytic oxidation of toluene
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The synthesis, characterisation and catalytic behaviour of palladium compound derived from Mg/Al hydrotalcite were investigated in the toluene total oxidation. The hydrotalcite sample was prepared by co-precipitation of the corresponding chlorides (MgCl₂, AlCl₃ and H₂PdCl₄) with boiled fresh water and under N₂ atmosphere. Under these conditions, the layered double hydroxide [Mg_0.75Al_0.25(OH)₂]^0.25+ $PdCl_{2} (OH)_{2}_{0.125−x}^{2−}$ (CO₃)_x²⁻·nH₂O was formed. Palladium species were inserted as [PdCl₂(OH)₂]²⁻ complex coming from the partial substitution of Cl with OH. The space interlayer was imposed by CO₃²⁻ present also as balancing anion. This new hydrotalcite is less stable than classical hydrotalcite Mg/Al without Pd since its destruction took place at a lower temperature. The palladium hydrotalcite calcined at 290 °C exhibited the best catalytic behaviour (activity and selectivity) in the total oxidation of toluene compared with a conventional palladium catalyst.
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The influence of Fe as a second metal component on the decomposition, dispersion and catalysis of the platinum amine complex in KL zeolite has been investigated. TG-DTA was used to measure the decomposition of the complex in KL and Fe/KL zeolites. XPS showed that Pt²⁺ and in particular Fe³⁺ ions show strong surface enrichment after calcination. Partial reduction of Fe³⁺ was found to occur both under calcination (autoreduction) and reduction (in a hydrogen atmosphere) treatments, as evidenced by an increase of the ESR signal at g=2.3. Both, ESR and TPR results revealed that platinum catalyzes the reduction of Fe³⁺, leading to a nearly 100 K decrease of the reduction temperature. Bimetallic Pt–Fe particles were thus produced, exhibiting better dispersion than mono-metallic Pt/KL zeolite, as determined by TEM. The catalytic properties of Pt–Fe/KL zeolite varied with the amount of Fe. At 0.3 wt.% Fe, the catalyst was found to show both excellent n-hexane aromatization reactivity and higher sulfur-resistance. An interpretation of the differences in the catalytic performance based on the particle size and electronic state of active platinum by Pt–Fe interaction is discussed.
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Two series of Pd–Au/SiO₂ catalysts, differing widely in metal particle size distribution, were prepared by a direct redox method, which involves reductive deposition of gold onto prereduced palladium particles. The method yields good results; i.e., a significant Pd–Au alloying was achieved in reduced bimetallic catalysts. The catalysts were investigated at various stages of their preparation by X-ray diffraction and temperature-programmed hydride decomposition. These techniques appear valuable in assessing the degree of alloying. Being sensitive to palladium particle size, the temperature-programmed hydride decomposition could also be applied to estimate the palladium dispersion. 2,2-Dimethylpropane conversion carried out on Pd–Au/SiO₂ also appeared to be a useful probe. Apparent activation energy decreased considerably with gold addition. This result is contrary to a relative constancy of the activation energy observed earlier for Pd–Au/SiO₂ catalysts, which were prepared by an incipient wetness coimpregnation when the resulting bimetallic samples were not satisfactorily homogenized.
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Nickel or molybdenum were supported on niobium oxide, both pure and modified with phosphate. The catalysts and supports were sulphided at 673 K under a 15 mol% H₂S in H₂ mixture. It was observed by X-ray photoelectron spectroscopy (XPS) that the sulphur uptake of the catalysts was much in excess to the amount necessary for complete sulphidation of nickel and molybdenum and occurred even with the non-impregnated supports. Simultaneously, a peak attributable to niobium in an oxidation state lower than +5 appeared in the XPS spectra. A good linear correlation was found between the atomic percentage of sulphur, above the one necessary to sulphide the supported metals, and the atomic percentage of niobium in the reduced state, showing that partial reduction–sulphidation of the support occurred during the sulphidation treatment. The slope of the best line through the experimental points was 1.99, indicating that a surface niobium sulphide with stoichiometry close to NbS₂ was formed during the treatment. While the reduction–sulphidation of niobium was enhanced by the presence of supported nickel and especially molybdenum, it was inhibited by phosphate.
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Journal of Catalysis

Abstract

References (19)

J. Catalysis

J. Catalysis

J. Catalysis

J. Catalysis

J. Chem. Phys.

Izv. Akad. Nauk. SSSR, Ser. Khim.

Preprint of the Faraday Society

Kolloid-Z. and Z. Polymere

J. Phys. Chem.

Cited by (44)

Application of silica-supported Ir and Ir-M (M = Pt, Pd, Au) catalysts for low-temperature hydrodechlorination of tetrachloromethane

Characterisation of Mg/Al hydrotalcite with interlayer palladium complex for catalytic oxidation of toluene

Properties of alumina supported Pd-Fe and Pt-Fe catalysts prepared using surface organometallic chemistry

The influence of Fe on the dispersion, electronic state, sulfur-resistance and catalysis of platinum supported on KL zeolite

Characterization of Pd-Au/SiO<inf>2</inf> catalysts by X-ray diffraction, temperature-programmed hydride decomposition, and catalytic probes

Effect of support sulphidation on the hydrocracking activity of niobia-supported nickel and molybdenum catalysts

ESR evidence of hydrogen migration on supported metal catalysts☆

Abstract

J. Catalysis

J. Catalysis

J. Catalysis

J. Catalysis

J. Chem. Phys.

Izv. Akad. Nauk. SSSR, Ser. Khim.

Preprint of the Faraday Society

Kolloid-Z. and Z. Polymere

J. Phys. Chem.