Role of potassium on the structure and activity of alumina-supported vanadium oxide catalysts for propane oxidative dehydrogenation

Cortez, G. G.; Fierro, J.L.G.; Bañares, Miguel Á.

doi:10.1016/s0920-5861(02)00341-3

Cited by 63 publications

(15 citation statements)

References 30 publications

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“…To the best of our knowledge, no conclusive evidence has been reported for propane ammoxidation. However, the initial activation of propane by vanadium is toward propylene. ,,,,− For alkane oxidative dehydrogenation, it has been shown that the terminal VO bond must be ruled out for oxidative dehydrogenation reactions 31,51 of ethane, , propane , and butane. , Thus, the active functionality must be a bridging oxygen connected to surface vanadium sites. Operando Raman-GC studies (i.e., simultaneous reaction in situ Raman spectroscopy and on-line catalytic measurement in a single experiment) illustrate that the presence of surface vanadia species proves critical to significantly increase total yield values to acrylonitrile and the specific rate of acrylonitrile formation per vanadium site. , But an increase in V/Sb ratio shifts the reaction pathway to oxidative dehydrogenation and nonselective oxidation. ,,, Thus, V sites promote propane activation, but need the cooperation of another site or phase to afford N-insertion.…”

Section: Discussionmentioning

confidence: 99%

A Study about the Propane Ammoxidation to Acrylonitrile with an Alumina-Supported Sb−V−O Catalyst

Guerrero‐Pérez

Peña

Fierro

et al. 2006

Ind. Eng. Chem. Res.

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The propane ammoxidation reaction is investigated on an alumina-supported Sb−V−O catalyst with an Sb/V atomic ratio of 1 at nominal Sb + V monolayer coverage on alumina support. The roles of reaction temperature and of the partial pressure of reactants in the reaction are evaluated. Fresh and used catalyst is characterized by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The effect of sudden changes in reaction feed is used to understand if the transient activation of the catalysts during the first hours on-stream is due to surface intermediates or to a change in the catalyst structure. A discussion is presented about the reaction network and the nature of the active phases.

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Section: Discussionmentioning

confidence: 99%

A Study about the Propane Ammoxidation to Acrylonitrile with an Alumina-Supported Sb−V−O Catalyst

Guerrero‐Pérez

Peña

Fierro

et al. 2006

Ind. Eng. Chem. Res.

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“…The oxidative dehydrogenation (ODH) of propane provides an attractive route for the synthesis of propene. − This reaction occurs on oxides of V, − Mo, ,,− and Cr, − with V-based catalysts typically providing higher rates and propene selectivities. , Supports influence rates and selectivities on dispersed VO x domains. , For example, VO x supported on ZrO 2 16,30,31 is highly active but gives low propene selectivities, while VO x /Al 2 O 3 gives lower rates but much higher alkene selectivities. , …”

Section: Introductionmentioning

confidence: 99%

Oxidative Dehydrogenation of Propane over V₂O₅/MoO₃/Al₂O₃ and V₂O₅/Cr₂O₃/Al₂O₃: Structural Characterization and Catalytic Function

2005

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The structure and catalytic properties of binary dispersed oxide structures prepared by sequential deposition of VO x and MoO x or VO x and CrO x on Al 2 O 3 were examined using Raman and UV-visible spectroscopies, the dynamics of stoichiometric reduction in H 2 , and the oxidative dehydrogenation of propane. VO x domains on Al 2 O 3 modified by an equivalent MoO x monolayer led to dispersed binary structures at all surface densities. MoO x layers led to higher reactivity for VO x domains present at low VO x surface densities by replacing V-O-Al structures with more reactive V-O-Mo species. At higher surface densities, V-O-V structures in prevalent polyvanadates were replaced with less reactive V-O-Mo, leading to lower reducibility and oxidative dehydrogenation rates. Raman, reduction, and UV-visible data indicate that polyvanadates predominant on Al 2 O 3 convert to dispersed binary oxide structures when MoO x is deposited before or after VO x deposition; these structures are less reducible and show higher UV-visible absorption energies than polyvanadate structures on Al 2 O 3 . The deposition sequence in binary Mo-V catalysts did not lead to significant differences in structure or catalytic rates, suggesting that the two active oxide components become intimately mixed. The deposition of CrO x on Al 2 O 3 led to more reactive VO x domains than those deposited on pure Al 2 O 3 at similar VO x surface densities. At all surface densities, the replacement of V-O-Al or V-O-V structures with V-O-Cr increased the reducibility and catalytic reactivity of VO x domains; it also led to higher propene selectivities via the selective inhibition of secondary C 3 H 6 combustion pathways, prevalent in VO x -Al 2 O 3 , and of C 3 H 8 combustion routes that lead to low alkene selectivities on CrO x -Al 2 O 3 . VO x and CrO x mix significantly during synthesis or thermal treatment to form CrVO 4 domains. The deposition sequence, however, influences catalytic selectivities and reduction rates, suggesting the retention of some of the component deposited last as unmixed domains exposed at catalyst surfaces. These findings suggest that the reduction and catalytic properties of active VO x domains can be modified significantly by the formation of binary dispersed structures. VO x -CrO x structures, in particular, lead to higher oxidative dehydrogenation rates and selectivities than do VO x domains present at similar surface densities on pure Al 2 O 3 supports.

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“…VO x /Al 2 O 3 is one of the most active and selective catalysts reported for the oxidative dehydrogenation (ODH) of propane to propene, − but reaction rates and selectivities remain too low for industrial practice. V−O−Al linkages present in VO x /Al 2 O 3 are relatively inactive for ODH reactions but favor secondary combustion of propene to CO and CO 2 . , These undesired V−O−Al linkages can be minimized by placing an intervening layer of another reducible oxide between VO x and Al 2 O 3 . , Specific promotional effects were detected when CrO x was used as the intervening layer .…”

Section: Introductionmentioning

confidence: 99%

Nature, Density, and Catalytic Role of Exposed Species on Dispersed VO_x/CrO_x/Al₂O₃ Catalysts

2006

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The structure and surface composition of binary oxides consisting of CrO x and VO x dispersed on alumina and their effects on the rate and selectivity of oxidative dehydrogenation (ODH) of propane were examined and compared with those for CrO x and VO x dispersed on alumina. VO x deposition on an equivalent CrO x monolayer on alumina and deposition of CrO x on an equivalent monolayer of VO x deposited on alumina led to CrVO 4 species during thermal treatment with concomitant reduction of Cr 6+ to Cr 3+ .

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Role of potassium on the structure and activity of alumina-supported vanadium oxide catalysts for propane oxidative dehydrogenation

Cited by 63 publications

References 30 publications

A Study about the Propane Ammoxidation to Acrylonitrile with an Alumina-Supported Sb−V−O Catalyst

A Study about the Propane Ammoxidation to Acrylonitrile with an Alumina-Supported Sb−V−O Catalyst

Oxidative Dehydrogenation of Propane over V₂O₅/MoO₃/Al₂O₃ and V₂O₅/Cr₂O₃/Al₂O₃: Structural Characterization and Catalytic Function

Nature, Density, and Catalytic Role of Exposed Species on Dispersed VO_x/CrO_x/Al₂O₃ Catalysts

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Role of potassium on the structure and activity of alumina-supported vanadium oxide catalysts for propane oxidative dehydrogenation

Cited by 63 publications

References 30 publications

A Study about the Propane Ammoxidation to Acrylonitrile with an Alumina-Supported Sb−V−O Catalyst

A Study about the Propane Ammoxidation to Acrylonitrile with an Alumina-Supported Sb−V−O Catalyst

Oxidative Dehydrogenation of Propane over V2O5/MoO3/Al2O3 and V2O5/Cr2O3/Al2O3: Structural Characterization and Catalytic Function

Nature, Density, and Catalytic Role of Exposed Species on Dispersed VOx/CrOx/Al2O3 Catalysts

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Oxidative Dehydrogenation of Propane over V₂O₅/MoO₃/Al₂O₃ and V₂O₅/Cr₂O₃/Al₂O₃: Structural Characterization and Catalytic Function

Nature, Density, and Catalytic Role of Exposed Species on Dispersed VO_x/CrO_x/Al₂O₃ Catalysts