Support effects on Brønsted acid site densities and alcohol dehydration turnover rates on tungsten oxide domains

Macht, Josef; Baertsch, Chelsey D.; May-Lozano, M.; Soled, S.; Wang, Yong; Iglesia, Enrique

doi:10.1016/j.jcat.2004.08.014

Cited by 163 publications

(169 citation statements)

References 24 publications

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“…Phys., 2008, 10, 5331-5343 | 5337 dehydration rates (per W atom). 33 These processes resemble those detected on WO x -ZrO 2 , indicating that temporary acid sites form via reduction of neutral WO x domains on all supports.…”

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 56%

“…This reflects either an overestimation of active Brønsted acid sites at low Brønsted acid densities or more reactive acid sites at high site densities. 33 For a given WO x surface density, however, the number of reduced centers and the density of Brønsted acid sites (but not their intrinsic reactivity) were sensitive to the identity of the support (Fig. 9).…”

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 97%

“…9). 33 The identity of the support can influence the reducibility and electronic properties of small oxide domains dispersed on their surfaces because of the intimate contact inherent in the stabilization of such small domains. Catalytic 2-butanol dehydration rates, Brønsted acid site densities, and the dynamics and extent of reduction were measured on WO x domains supported on ZrO 2 , Al 2 O 3 , SiO 2 , and SnO 2 .…”

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 99%

“…Catalytic 2-butanol dehydration rates, Brønsted acid site densities, and the dynamics and extent of reduction were measured on WO x domains supported on ZrO 2 , Al 2 O 3 , SiO 2 , and SnO 2 . 33 …”

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 99%

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Structure and function of oxide nanostructures: catalytic consequences of size and composition

Macht

Iglesia

2008

Phys. Chem. Chem. Phys.

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Redox and acid-base properties of dispersed oxide nanostructures change markedly as their local structure and electronic properties vary with domain size. These changes give rise to catalytic behavior, site structures, and reaction chemistries often unavailable on bulk crystalline oxides. Turnover rates for redox and acid catalysis vary as oxide domains evolve from isolated monomers to two-dimensional oligomers, and ultimately into clusters with bulk-like properties. These reactivity changes reflect the ability of oxide domains to accept or redistribute electron density in kinetically-relevant reduction steps, in the formation of temporary acid sites via reductive processes, and in the stabilization of cationic transition states. Reduction steps are favored by low-lying empty orbitals prevalent in larger clusters, which also favor electron delocalization, stable anions, and strong Brønsted acidity. Isomerization of xylenes and alkanes, elimination reactions of alkanols, and oxidation of alkanes to alkenes on V, Mo, Nb, and W oxide domains are used here to demonstrate the remarkable catalytic diversity made available by changes in domain size. The reactive and disordered nature of small catalytic domains introduces significant challenges in their synthesis and their structural and mechanistic characterization, which require in situ probes and detailed kinetic analysis. The local structure and electronic properties of these materials must be probed during catalysis and their catalytic function be related to specific kinetically-relevant steps. Structural uniformity can be imposed on oxide clusters by the use of polyoxometalate clusters with thermodynamically stable and well-defined size and connectivity. These clusters provide the compositional diversity and the structural fidelity required to develop composition-function relations from synergistic use of experiments and theory. In these clusters, the valence and electronegativity of the central atom affects the acid strength of the polyoxometalate clusters and the rate constants for acid catalyzed elementary steps via the specific stabilization of cationic transition states in isomerization and elimination reactions.

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Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 56%

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 97%

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 99%

Section: This Journal Is C the Owner Societies 2008mentioning

confidence: 99%

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Structure and function of oxide nanostructures: catalytic consequences of size and composition

Macht

Iglesia

2008

Phys. Chem. Chem. Phys.

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“…[1][2][3][4][5][6][7][8][9][10][11] These previous studies have established a good understanding of the performance of these catalysts as a function of WO 3 domain size and support effects. The acid site reactivity of WO 3 catalysts is commonly probed using the selective transformation of methanol (MeOH) to dimethyl ether (DME).…”

Section: Introductionmentioning

confidence: 99%

Investigating the Influence of Au Nanoparticles on Porous SiO₂–WO₃ and WO₃ Methanol Transformation Catalysts

et al. 2016

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American Chemical SocietyDepuccio, DP.; Ruiz-Rodríguez, L.; Rodriguez-Castellon, E.; Botella Asuncion, P.; López Nieto, JM.; Landry, CC. (2016) AbstractAnalyzing the structural and chemical properties of materials at the interface of metal nanoparticles and metal oxide supports is important for catalytic applications. Tungsten oxide (WO 3 ) is a widely studied catalyst, but changing the catalytic reactivity at the surface of this oxide with metal nanoparticles is of interest. In this work, we sought to modify the redox properties of porous WO 3 and SiO 2 -WO 3 catalysts with sonochemically deposited gold nanoparticles (Au NPs) in order to access and study this reaction pathway. Characterization using powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and inductively-coupled plasma optical emission spectroscopy (ICP-OES) confirmed that crystalline Au NPs with diameters of 5 -12 nm were distributed throughout the catalysts. Temperature-programmed desorption (TPD) was used to probe the surface acidity of the catalysts. The physic-chemical characteristics of catalysts have been also discussed by considering the catalytic performance of these materials in the aerobic transformation of methanol. Catalysts containing nanocrystalline WO 3 but no Au NPs displayed very high selectivity to DME (> 60%) at all conversions with minor oxidation reactivity, which highlighted the acidic nature of these catalysts. No effect on the acidity of the catalysts was observed by TPD when Au NPs were loaded in the catalysts. The reducibility of the crystalline WO 3 species, however, increased significantly due to the interaction with Au NPs, as observed by temperature-programmed reduction (TPR). In the gas-phase transformation of MeOH under aerobic conditions, catalysts modified with Au NPs showed greater activity compared to non-modified catalysts. In addition, oxidation selectivity to products such as methyl formate as well as formaldehyde, dimethoxymethane, and carbon oxides became heavily favored with only minor dehydration selectivity. The redox properties of these WO 3 catalysts could be tuned by changing the Au loading. More labile lattice oxygen and enhanced redox properties at the surface of WO 3 modified with Au NPs clearly altered these traditional dehydration catalysts to potential oxidation catalysts. Thus, modification of WO 3 with Au is an effective way to expand the MeOH transformation product distribution beyond DME to other useful, oxidized products not typically observed over pure WO 3 .

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Role of Mixed Metal Oxides in Heterogeneous Catalysis

Burange¹,

Gawande

2016

Encyclopedia of Inorganic and Bioinorganic Chemistry

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In this article, we include numerous types of mixed metal oxides (MMOs) including their properties and catalytic applications for several types of reactions, focusing on their active sites (acidic and basic). Owing to the acid–base and redox properties of MMOs, they establish a largest family of catalysts in heterogeneous catalysis. Generally, in most of the examples, MMOs have superior properties in terms of acidic or basic sites and surface area than single oxide. In addition, some examples of mixed metal ratio are also discussed on specific catalytic applications.

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Support effects on Brønsted acid site densities and alcohol dehydration turnover rates on tungsten oxide domains

Cited by 163 publications

References 24 publications

Structure and function of oxide nanostructures: catalytic consequences of size and composition

Structure and function of oxide nanostructures: catalytic consequences of size and composition

Investigating the Influence of Au Nanoparticles on Porous SiO₂–WO₃ and WO₃ Methanol Transformation Catalysts

Role of Mixed Metal Oxides in Heterogeneous Catalysis

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Support effects on Brønsted acid site densities and alcohol dehydration turnover rates on tungsten oxide domains

Cited by 163 publications

References 24 publications

Structure and function of oxide nanostructures: catalytic consequences of size and composition

Structure and function of oxide nanostructures: catalytic consequences of size and composition

Investigating the Influence of Au Nanoparticles on Porous SiO2–WO3 and WO3 Methanol Transformation Catalysts

Role of Mixed Metal Oxides in Heterogeneous Catalysis

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Investigating the Influence of Au Nanoparticles on Porous SiO₂–WO₃ and WO₃ Methanol Transformation Catalysts