Catalytic Aluminas: Surface Models and Characterization of Surface Sites

Knözinger, Helmut; Ratnasamy, P.

doi:10.1080/03602457808080878

Cited by 1,804 publications

(1,078 citation statements)

References 65 publications

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“…The two bands at 3733 and 3753 cm À1 correspond to type II neutral hydroxyl groups (band at 3733 cm À1 : type IIa neutral hydroxyl groups, band at 3753 cm À1 : type IIb neutral hydroxyl group). The band at 3686 cm À1 is ascribed to type III Al VI -OH acid hydroxyl groups [46]. The broad and weakly intense band at 3600 cm À1 is due to hydrogen bond between hydroxyl groups.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties

Benkhaled

Morin

Pichon

et al. 2006

Applied Catalysis A: General

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Complexation with nitrite ions in aqueous medium was used to prepare highly dispersed Pd8 particles supported on alumina. It has been possible to obtain catalysts with different Pd loading keeping the particle size lower than 1 nm as shown by HRTEM, chemisorption, or extended X-ray absorption fine structure (EXAFS) characterizations, and as a consequence with different particle surface density. We observed that electronic properties measured by IR(CO) or X-ray photoelectron spectroscopy (XPS) measurements are strongly influenced by this last parameter and that the origin of these variations can be related to the different strengths of the interactions of the palladium precursor with the alumina surface sites as shown by low temperature CO adsorption followed by FTIR spectroscopy. On increasing Pd loading, saturation of unsaturated Lewis surface sites follows their acid strength: the more acidic ones are the first to react as germination sites, followed by the medium and finally the weaker sites. These different interactions may explain the variation of electronic properties of such small reduced particles which appears to be very sensitive to the chemical nature of their initial germination site on the oxide support. On the other hand, no such effects were observed on changing the type of alumina (d or g) support, in agreement with the principle of the synthesis method which tends to limit strong interaction with the support. Comparison with Pd8 particles with the same particle size and particle surface density but prepared with the well known grafting of acetylacetonate precursor shows marked differences in terms of electronic properties followed by CO FTIR. This result illustrates the possibility to prepare highly dispersed Pd particles with different physico-chemical properties. #

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Section: Resultsmentioning

confidence: 99%

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties

Benkhaled

Morin

Pichon

et al. 2006

Applied Catalysis A: General

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“…The surface hydroxyls are well pronounced in the spectrum at 7210, 7290, and 7360 cm -1 , assigned to the overtones of acidic, neutral, and basic hydroxyls, respectively. 24 The spectra of higher loaded (2-7 wt %) samples show comparable changes during calcination. The Mn band, observed in the range 20 900-22 000 cm -1 , is reflected at these loadings in the form of a shoulder of the band at 40 000 cm -1 .…”

Section: Methodsmentioning

confidence: 94%

“…14,18,[24][25][26][32][33][34] Wichterlová et al 34 report an ESR signal of Mn 2+ in a distorted tetrahedron at g ) 4.27. Literature data presented in Table 2 suggest the coordination of the Mn 2+ ions observed in the recorded ESR spectra to be most reasonably described as axially distorted octahedral.…”

Section: Oxidation State and Coordination Manganese Speciesmentioning

confidence: 99%

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Characterization of Al₂O₃-Supported Manganese Oxides by Electron Spin Resonance and Diffuse Reflectance Spectroscopy

Kijlstra¹,

Poels²,

Bliek³

et al. 1997

J. Phys. Chem. B

144

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Alumina-supported manganese oxides, used as catalysts for the selective catalytic reduction of NO, were characterized by combined electron spin resonance and diffuse reflectance spectroscopies. Upon impregnation of the acetate precursor solution, the [Mn(H 2 O) 6 ] 2+ complex interacts strongly with surface hydroxyls of the γ-Al 2 O 3 . Evidence was obtained that this anchoring reaction proceeds at a Mn/OH ) 1/2 ratio up to 4.5 wt % Mn loading, leading to a highly dispersed oxidic manganese layer. At higher loadings, the precursor complex is deposited on the surface concurrently. Upon drying at 383 K, part of the manganese is oxidized to higher oxidation states (Mn 3+ and Mn 4+ ), while a further increase in (average) oxidation state takes place upon calcination at 573 K. After calcination, the manganese species are present as a mixture of Mn 2+ , Mn 3+ , and Mn 4+ . At low loadings (<1 wt %), approximately equal amounts of these three oxidation states are present, whereas Mn 3+ becomes the predominant species at higher loadings. ESR reveals that at low loadings, almost all the manganese is present as isolated species, while at 4.5 wt % Mn loading, still more than 70% of the manganese is isolated. The decrease of the fraction of isolated manganese species at higher loadings is accompanied by a decreased selectivity toward N 2 production in the selective catalytic reduction of NO. The fraction Mn 2+ is present in an axially distorted octahedral coordination.

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“…This was also observed on loaded zirconia [16]. Analogous to alumina [40], it is very likely that on zirconia two chemisorbed hydroxyl groups recombine to form water. This means that both chemisorbed and physisorbed H 2 O may contribute to the slow removal of water out of the pores and, consequently, the re-oxidation of Fe 2+ .…”

Section: Re-oxidation In H 2 Of Reduced Fe/zromentioning

confidence: 73%

Reduction behaviour of Fe/ZrO2 and Fe/K/ZrO2 Fischer–Tropsch catalysts

Berg

Crajé

Kraan

et al. 2003

Applied Catalysis A: General

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The reduction behaviour (the activation process) of two iron-based Fischer-Tropsch catalysts viz. an unpromoted and a potassium-promoted zirconia-supported iron catalyst is investigated. The initial dispersion of both catalysts is very high. To establish the nature of the iron species under hydrogen atmosphere, experiments were performed at ambient pressure. It is demonstrated for both catalysts that during reduction the carbon originating from the citrate complex used in the preparation procedure is not completely removed, whereby the largest amount of the carbon species is encountered on the potassium-promoted catalyst. During reduction at ambient pressure this residual carbon reacts with metallic iron and forms cementite (θ-Fe 3 C). The iron oxide of the potassium-promoted catalyst turns out to reduce more easily than the oxide of the unpromoted catalyst. Upon formation of divalent iron, this divalent species readily reacts with the support to give a stable mixed oxide. This mixed oxide is suggested to be a prerequisite in maintaining a high dispersion of the metallic iron particles. Based on the analyses presented here, a reduction model is proposed.

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Catalytic Aluminas: Surface Models and Characterization of Surface Sites

Cited by 1,804 publications

References 65 publications

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties

Characterization of Al₂O₃-Supported Manganese Oxides by Electron Spin Resonance and Diffuse Reflectance Spectroscopy

Reduction behaviour of Fe/ZrO2 and Fe/K/ZrO2 Fischer–Tropsch catalysts

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Catalytic Aluminas: Surface Models and Characterization of Surface Sites

Cited by 1,804 publications

References 65 publications

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties

Synthesis of highly dispersed palladium alumina supported particles: Influence of the particle surface density on physico-chemical properties

Characterization of Al2O3-Supported Manganese Oxides by Electron Spin Resonance and Diffuse Reflectance Spectroscopy

Reduction behaviour of Fe/ZrO2 and Fe/K/ZrO2 Fischer–Tropsch catalysts

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Characterization of Al₂O₃-Supported Manganese Oxides by Electron Spin Resonance and Diffuse Reflectance Spectroscopy