The structure–function relationships in selective oxidation reactions over metal oxides

Ozkan, Umit S.; Watson, Rick B.

doi:10.1016/j.cattod.2004.12.018

Cited by 47 publications

(50 citation statements)

References 90 publications

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“…Furthermore, the difference in the NO x adsorption properties of the mixed oxide support materials can also be ascribed to the different number of oxygen defect sites and the nature of the surface hydroxyl groups exposed on the surface. 43 A detailed analysis of the spectral region within 1300-1100 cm -1 (the spectra marked in red) in Figure 3a,b during the very initial NO 2 doses reveals that the NO x uptake process starts to occur with the formation of nitrites. As discussed above, the nitrite species on the Al 3+ and Ti 4+ adsorption sites with the corresponding IR bands were detected at 1230 and 1185 cm -1 , respectively.…”

Section: No X Adsorption On Ti/al Support Materials Via Ftir Spectrosmentioning

confidence: 99%

“…In other words, in Figure 3, the initial nitrite formation is observed to a greater extent on pure γ-Al 2 O 3 ( Figure 3a) and decreases as the number of exposed Al 2 O 3 surface sites decreases (i.e., γ-Al 2 O 3 > Ti/Al(P1) > Ti/ Al(P2) > TiO 2 -anatase). This relative decrease in the initial nitrite formation could be ascribed to the presence of reactive oxygen species on the TiO 2 domains in the form of uncoordinated oxygen defects, 43 or as transient oxygen species like O -, O 2-providing an efficient and rapid oxidation of nitrites into nitrates. 43 Further insight regarding the structure and the NO x uptake properties of the synthesized mixed oxide systems can be obtained by analyzing the vibrational spectral changes in the hydroxyl stretching region of the FTIR data.…”

Section: No X Adsorption On Ti/al Support Materials Via Ftir Spectrosmentioning

confidence: 99%

“…This relative decrease in the initial nitrite formation could be ascribed to the presence of reactive oxygen species on the TiO 2 domains in the form of uncoordinated oxygen defects, 43 or as transient oxygen species like O -, O 2-providing an efficient and rapid oxidation of nitrites into nitrates. 43 Further insight regarding the structure and the NO x uptake properties of the synthesized mixed oxide systems can be obtained by analyzing the vibrational spectral changes in the hydroxyl stretching region of the FTIR data. Figure 4 presents the series of IR spectra that were acquired during the identical set of NO 2 adsorption experiments described for the data given in Figure 3.…”

Section: No X Adsorption On Ti/al Support Materials Via Ftir Spectrosmentioning

confidence: 99%

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Fine-Tuning the Dispersion and the Mobility of BaO Domains on NO_x Storage Materials via TiO₂ Anchoring Sites

2010

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In an attempt to control the surface dispersion and the mobility of BaO domains on NO x storage materials, TiO 2 /TiO x anchoring sites were introduced on/inside the conventional γ-Al 2 O 3 support matrix. BaO/TiO 2 / Al 2 O 3 ternary oxide materials were synthesized via two different sol-gel preparation techniques, with varying surface compositions and morphologies. The synthesized NO x storage materials were studied via XRD, Raman spectroscopy, BET surface area analysis, TPD, XPS, SEM, EDX-mapping, and in situ FTIR spectroscopy of adsorbed NO 2 . NO x uptake properties of the BaO/TiO 2 /Al 2 O 3 materials were found to be strongly influenced by the morphology and the surface structure of the TiO 2 /TiO x domains. An improved Ba surface dispersion was observed for the BaO/TiO 2 /Al 2 O 3 materials synthesized via the coprecipitation of alkoxide precursors, which was found to originate mostly from the increased fraction of accessible TiO 2 /TiO x sites on the surface. These TiO 2 /TiO x sites function as strong anchoring sites for surface BaO domains and can be tailored to enhance surface dispersion of BaO. TPD experiments suggested the presence of at least two different types of NO x species adsorbed on the TiO 2 /TiO x sites, with distinctively different thermal stabilities. The relative stability of the NO x species adsorbed on the BaO/TiO 2 /Al 2 O 3 system was found to increase in the following order: NO + /N 2 O 3 on alumina , nitrates on alumina < surface nitrates on BaO < bridged/bidentate nitrates on large/isolated TiO 2 clusters < bulk nitrates on BaO on alumina surface and bridged/bidentate nitrates on TiO 2 crystallites homogenously distributed on the surface < bulk nitrates on the BaO sites located on the TiO 2 domains.

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Section: No X Adsorption On Ti/al Support Materials Via Ftir Spectrosmentioning

confidence: 99%

Section: No X Adsorption On Ti/al Support Materials Via Ftir Spectrosmentioning

confidence: 99%

Section: No X Adsorption On Ti/al Support Materials Via Ftir Spectrosmentioning

confidence: 99%

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Fine-Tuning the Dispersion and the Mobility of BaO Domains on NO_x Storage Materials via TiO₂ Anchoring Sites

2010

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“…However, catalysts applied in selective oxidation reactions are highly complex and seem to become more complex with increasing efficiency. Rational catalyst design constitutes a promising alternative to conventional trial‐and‐error approach in developing optimized catalysts . Rational catalyst design requires an in‐depth understanding of reliable structure‐activity correlations.…”

Section: Introductionmentioning

confidence: 99%

Influence of Adding Molybdenum on Structure and Performance of Fe_xO_y/SBA‐15 Catalysts in Selective Oxidation of Propene

Genz

Ressler

2019

ChemistryOpen

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Mixed iron and molybdenum oxide catalysts supported on nanostructured silica, SBA‐15, were synthesized with various Mo/Fe atomic ratios ranging from 0.07/1.0 to 0.57/1.0. Structural characterization of as‐prepared Mo x O y _Fe x O y /SBA‐15 samples was performed by nitrogen physisorption, X‐ray diffraction, and DR‐UV‐Vis spectroscopy. Adding molybdenum resulted in a pronounced dispersion effect on supported iron oxidic species. Increasing atomic ratio up to 0.21Mo/1.0Fe was accompanied by decreasing species sizes. Strong interactions between iron and molybdenum during the synthesis resulted in the formation of Fe−O−Mo structure units, possibly Fe 2 (MoO 4 ) 3 ‐like species. Reducibility of Mo x O y _Fe x O y /SBA‐15 catalysts was investigated by temperature‐programmed reduction experiments with hydrogen as reducing agent. The lower reducibility obtained when adding molybdenum was ascribed to both dispersion and electronic effect of molybdenum. Catalytic performance of Mo x O y _Fe x O y /SBA‐15 samples was studied in selective gas‐phase oxidation of propene with O 2 as oxidant. Adding molybdenum resulted in an increased acrolein selectivity and a decreased selectivity towards total oxidation products.

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“…[6,7] The molecular structure and reactivity of active sites on metal-oxide catalysts has been a particular focus. [1][2][3][4][5][8][9][10][11] However, detailed mechanistic studies are often hampered by factors such as the dynamic nature of the catalyst surface and its inhomogeneity. Furthermore, important reactions appear to occur at localized reaction sites (such as surface defects or adsorbed reactant molecules), and such sites might exhibit significantly different reactivity from that of the bulk oxide.…”

Section: Introductionmentioning

confidence: 99%

Gas‐Phase Reactivity of Metavanadate [VO₃]⁻ towards Methanol and Ethanol: Experiment and Theory

Waters¹,

Wedd²,

O’Hair³

2007

Chemistry A European J

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The gas-phase reactivity of the metavanadate anion [VO3]- towards methanol and ethanol was examined by a combination of ion-molecule reaction and isotope labelling experiments in a quadrupole ion-trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations. [VO3]- dehydrated methanol to eliminate water and form [VO2(eta2-OCH2)]-, which features an [eta2-C,O-OCH2]2- ligand formed by formal removal of two protons from methanol and which is isoelectronic with peroxide. [VO3]- reacted with ethanol in an analogous manner to form [VO2(eta2-OCHCH3)]-, as well as by loss of ethene to form [VO2(OH)2]-. The calculations predicted that important intermediates in these reactions were the hydroxo alkoxo anions [VO2(OH)(OCH2R)]- (R: H, CH3). These were predicted to undergo intramolecular hydrogen-atom transfer to form [VO(OH)2(eta1-OCHR)]- followed by eta1-O-->eta2-C,O rearrangements to form [VO(OH)2(eta2-OCHR)]-. The latter reacted further to eliminate water and generate the product [VO2(eta2-OCHR)]-. This major product observed for [VO3]- is markedly different from that observed previously for [NbO3]- containing the heavier Group 5 congener niobium. In that case, the major product of the reaction was an ion of stoichiometry [Nb, O3, H2]- arising from the formal dehydrogenation of methanol to formaldehyde. The origin of this difference was examined theoretically and attributed to the intermediate alkoxo anion [NbO2(OH)(OCH3)]- preferring hydride transfer to form [HNbO2(OH)]- with loss of formaldehyde. This contrasts with the hydrogen-atom-transfer pathway observed for [VO2(OH)(OCH3)]-.

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The structure–function relationships in selective oxidation reactions over metal oxides

Cited by 47 publications

References 90 publications

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NO_x Storage Materials via TiO₂ Anchoring Sites

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NO_x Storage Materials via TiO₂ Anchoring Sites

Influence of Adding Molybdenum on Structure and Performance of Fe_xO_y/SBA‐15 Catalysts in Selective Oxidation of Propene

Gas‐Phase Reactivity of Metavanadate [VO₃]⁻ towards Methanol and Ethanol: Experiment and Theory

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The structure–function relationships in selective oxidation reactions over metal oxides

Cited by 47 publications

References 90 publications

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NOx Storage Materials via TiO2 Anchoring Sites

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NOx Storage Materials via TiO2 Anchoring Sites

Influence of Adding Molybdenum on Structure and Performance of FexOy/SBA‐15 Catalysts in Selective Oxidation of Propene

Gas‐Phase Reactivity of Metavanadate [VO3]− towards Methanol and Ethanol: Experiment and Theory

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About

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NO_x Storage Materials via TiO₂ Anchoring Sites

Fine-Tuning the Dispersion and the Mobility of BaO Domains on NO_x Storage Materials via TiO₂ Anchoring Sites

Influence of Adding Molybdenum on Structure and Performance of Fe_xO_y/SBA‐15 Catalysts in Selective Oxidation of Propene

Gas‐Phase Reactivity of Metavanadate [VO₃]⁻ towards Methanol and Ethanol: Experiment and Theory