Dehydration of methanol to dimethyl ether over Nb2O5 and NbOPO4 catalysts: Microcalorimetric and FT-IR studies

Sun, Qizhen; Fu, Yuchuan; Yang, Hengquan; Auroux, A.; Shen, Jianyi

doi:10.1016/j.molcata.2007.06.008

Cited by 71 publications

(32 citation statements)

References 41 publications

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“…The adsorption of water on undercoordinated sites in metal oxides is a generally accepted phenomenon, 75 and water adsorption specifically on Nb 5+ sites has also been suggested in previous literature. 70,72 From the correlation between the XPS and TPD results discussed above, we propose that the water molecules initially adsorb and dissociate on Nb 5+ cation sites which are doubly bonded to a terminal oxygen atom, i.e., Lewis acid sites. Water dissociation results in the formation of two OH groups which, according to the DFT calculations described below, are located at the original terminal oxygen site and a nearby bridging oxygen.…”

Section: Resultsmentioning

confidence: 95%

Influence of Cluster–Support Interactions on Reactivity of Size-Selected Nb_xO_y Clusters

Nakayama

Xue

et al. 2015

J. Phys. Chem. C

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Size-selected niobium oxide nanoclusters (Nb 3 O 5 , Nb 3 O 7 , Nb 4 O 7 , and Nb 4 O 10 ) were deposited at room temperature onto a Cu(111) surface and a thin film of Cu 2 O on Cu(111), and their interfacial electronic interactions and reactivity toward water dissociation were examined. These clusters were specifically chosen to elucidate the effects of the oxidation state of the metal centers; Nb 3 O 5 and Nb 4 O 7 are the reduced counterparts of Nb 3 O 7 and Nb 4 O 10 , respectively. From twophoton photoemission spectroscopy (2PPE) measurements, we found that the work function increases upon cluster adsorption in all cases, indicating a negative interfacial dipole moment with the positive end pointing into the surface. The amount of increase was greater for the clusters with more metal centers and higher oxidation state. Further analysis with DFT calculations of the clusters on Cu (111) indicated that the reduced clusters donate electrons to the substrate, indicating that the intrinsic cluster dipole moment makes a larger contribution to the overall interfacial dipole moment than charge transfer. X-ray photoelectron spectroscopy (XPS) measurements showed that the Nb atoms of Nb 3 O 7 and Nb 4 O 10 are primarily Nb 5+ on Cu(111), while for the reduced Nb 3 O 5 and Nb 4 O 7 clusters, a mixture of oxidation states was observed on Cu(111). Temperature-programmed desorption (TPD) experiments with D 2 O showed that water dissociation occurred on all systems except for the oxidized Nb 3 O 7 and Nb 4 O 10 clusters on the Cu 2 O film. A comparison of our XPS and TPD results suggests that Nb 5+ cations associated with NbO terminal groups act as Lewis acid sites which are key for water binding and subsequent dissociation. TPD measurements of 2-propanol dehydration also show that the clusters active toward water dissociation are indeed acidic. DFT calculations of water dissociation on Nb 3 O 7 support our TPD results, but the use of bulk Cu 2 O(111) as a model for the Cu 2 O film merits future scrutiny in terms of interfacial charge transfer. The combination of our experimental and theoretical results suggests that both Lewis acidity and metal reducibility are important for water dissociation.

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Section: Resultsmentioning

confidence: 95%

Influence of Cluster–Support Interactions on Reactivity of Size-Selected Nb_xO_y Clusters

Nakayama

Xue

et al. 2015

J. Phys. Chem. C

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“…This family of catalysts has been reported in the literature to posses mesoporosity, showing an average pore size which ranges from 2.5 nm to 4 nm ca (see for instance Ref. [2]). …”

Section: Methodsmentioning

confidence: 87%

“…Lewis acidity is also present in this catalyst and it is assigned to co-ordinatively unsaturated Nb +5 sites as revealed by acetonitrile (AN) adsorption followed by FT spectrocopy [16]. FT IR spectroscopy has also been applied, together with microcalorimetry, to analyze adsorption of probe molecule such as methanol, dimethylether and ammonia over NbOPO 4 catalyst, the strong interaction of such probe molecules evidencing that NbOPO 4 is more acidic than pure Niobia [2]. Pyridine adsorption/desorption experiments allow quantification of Brønsted and Lewis acidic sites [17,18], however its diagnostic bands fall in a spectral region which can be strongly perturbed by the signal of adsorbed organic species, i.e., heavy reaction by products over the spent catalyst.…”

Section: Introductionmentioning

confidence: 98%

“…Nb oxide can be effectively supported over several oxidic materials, such as alumina, titania, silica, thus modulating their acidity and leading to catalysts very active in dehydration reactions (for instance, dehydration of methanol to diethylether, dehydration of butanol, dehydration of glycerol to acrolein [1][2][3]). Combination of niobium oxide and phosphoric acid, i.e., niobium phosphate and phosphoric acid-treated niobic acid are also potentially useful in any application requiring heterogeneous acid catalysts.…”

Section: Introductionmentioning

confidence: 99%

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NbP catalyst for furfural production: FT IR studies of surface properties

Gómez-Bernal

Galletti

Garbarino

et al. 2015

Applied Catalysis A: General

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“…En la fig. 3 se presenta el espectro FT-IR de los catalizadores estudiados, se registró una banda de absorción amplia alrededor de 3200 cm −1 -3500 cm −1 , asignadas al modo de estiramiento del grupo OH pertenecientes a enlaces N b − OH libres y H enlazados a grupos OH del agua [35] más acentuadas que el T iO 2 por su condición de oxido hidratado, habido se adsorber humedad. El análisis de la región a bajas frecuencias mostró una banda presente entre 1600 cm −1 -1650 cm −1 , debido al modo tijereteo de las moléculas de H 2 O absorbidas, que no se observó para el T iO 2 , las bandas entre 500 cm −1 y 750 cm −1 , fueron asignadas al modo de estiramiento N b − O − N b [35].…”

Section: Caracterización De Los Catalizadoresunclassified

Estudio catalítico comparativo de los sistemas TiO2 y Nb2O5 en la degradación de cianuro en función del tipo de oxidante

López

Sierra

2012

ing.cienc.

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La viabilidad del uso de otros agentes fotocatalizadores como el niobio, radicaen disminuir las energías altas de la banda prohibida para hacerlo competitivo frente al TiO2, sin embargo la presencia de coayudantes de oxidación, talescomo H2O2 y O3 podrían presentar resultados sorprendentes en el desempeño catalítico, debido a una mayor generación del radicales OH. La obtención de óxidos de mayor área y propiedades texturales diferentes al oxido de niobio comercial, mejoran su actividad catalítica en la remoción de cianuro libre. El trabajo presenta resultados experimentales de fotodegradación de cianuro 100mg=l sobre TiO2 Degussa P- 25 y Nb2O5 · 3H2O, usando un fotorreactor CPC con una capacidad de 4L de solución, usando como fuente de radiación la luz solar, tomando una inclinación igual a la latitud de Cartagena 10.45°, los resultados indicaron un claro efecto del pH, el tipo de catalizador y el coayudante de oxidación. La reducción de ion cianuro del efluente contaminado aumento por la adición del agente oxidante (O3 y H2O2). Sugiriendo una mayor susceptibilidad del cianuro libre, para oxidarse a cianato de forma indirecta, por una mayor generación de radicales hidroxilos, inducidos por la presencia de H2O2 o del O3 bajo radiación solar. Se obtuvo porcentajes de oxidación fotocatalítica de cianuro libre, entre el 64% y 72% usando Nb2O5 · 3H2O y un rango entre 67% y 71% usando TiO2 Degussa P - 25. Los catalizadores fueron caracterizados estructuralmente usando DRX, BET,Raman e FT-IR, con la finalidad de correlacionar los cambios morfológicos con el desempeño catalítico.

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Dehydration of methanol to dimethyl ether over Nb2O5 and NbOPO4 catalysts: Microcalorimetric and FT-IR studies

Cited by 71 publications

References 41 publications

Influence of Cluster–Support Interactions on Reactivity of Size-Selected Nb_xO_y Clusters

Influence of Cluster–Support Interactions on Reactivity of Size-Selected Nb_xO_y Clusters

NbP catalyst for furfural production: FT IR studies of surface properties

Estudio catalítico comparativo de los sistemas TiO2 y Nb2O5 en la degradación de cianuro en función del tipo de oxidante

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Dehydration of methanol to dimethyl ether over Nb2O5 and NbOPO4 catalysts: Microcalorimetric and FT-IR studies

Cited by 71 publications

References 41 publications

Influence of Cluster–Support Interactions on Reactivity of Size-Selected NbxOy Clusters

Influence of Cluster–Support Interactions on Reactivity of Size-Selected NbxOy Clusters

NbP catalyst for furfural production: FT IR studies of surface properties

Estudio catalítico comparativo de los sistemas TiO2 y Nb2O5 en la degradación de cianuro en función del tipo de oxidante

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Influence of Cluster–Support Interactions on Reactivity of Size-Selected Nb_xO_y Clusters

Influence of Cluster–Support Interactions on Reactivity of Size-Selected Nb_xO_y Clusters