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

Yang, Shangbin; Iglesia, Enrique; Bell, Alexis T.

doi:10.1021/jp0582538

Cited by 15 publications

(8 citation statements)

References 54 publications

(104 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…If the support is a non-reducible oxide and no phase formation occurs at the interface, then no charges can be exchanged between support and active phase. Consequently the support is electronically ''innocent'' and the catalytic properties are given by the structure of the isolated grafted species much in accord to the ''site isolation'' concept from Table 1 and in agreement with experimental [130,133] and theoretical treatments [102,[136][137][138] of the problem. The genesis of active sites for metathesis of propene over grafted MoO x catalysts through sacrificial formation of carbene ligands in situ [139] is an illustrative example of the local character of an active site.…”

Section: On the Electronic Structure Of Oxidation Catalystssupporting

confidence: 65%

“…One puzzling aspect in selective oxidation is the dominating influence of the catalyst bulk [126][127][128][129] for achieving performance in selective oxygen transfer reactions. Surface-only species such as grafted systems [130][131][132][133] are poorly active in selective oxygen transfer but can well combust olefins. When for example vanadia species form the termination layer of bulk reducible oxides such as VPP and M1, they are well capable to transfer oxygen without combusting the substrate.…”

Section: On the Electronic Structure Of Oxidation Catalystsmentioning

confidence: 99%

See 1 more Smart Citation

Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

Schlögl

2016

Top Catal

View full text Add to dashboard Cite

The design of heterogeneous selective oxidation catalysts based upon complex metal oxides is governed at present by a set of empirical rules known as “pillars of oxidation catalysis”. They serve as practical guidelines for catalyst development and guide the reasoning about the catalyst role in the process. These rules are, however, not based upon atomistic concepts and thus preclude their immediate application in for example computer-aided search strategies. The present work extends the ideas of the pillar rules and develops the concept of considering a selective oxidation catalyst as enabler for the execution of a reaction network. The enabling function is controlled by mutual interactions between catalyst and reactants. The electronic structure of the catalyst is defined as a bulk semiconductor with a surface state arising form a terminating over layer being different from the structure of the bulk. These components that can be identified by in situ analytical methods form a chemical system with feedback loops, which is responsible for generating selectivity during execution of the reaction network. This concept is based upon physical observables and could allow for a design strategy based upon a kinetic description that combines the processes between reactants with the processes between catalyst and reactants. Such kinetics is not available at present. Few of the constants required are known but many of them are accessible to experimental determination with in situ techniques

show abstract

Section: On the Electronic Structure Of Oxidation Catalystssupporting

confidence: 65%

Section: On the Electronic Structure Of Oxidation Catalystsmentioning

confidence: 99%

Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

Schlögl

2016

Top Catal

View full text Add to dashboard Cite

show abstract

“…Likewise, the concept of a functional heterodimer [63,64] would help to simplify the reaction; the redox equivalents may be stored onto the redox-active ''support''. Silica or alumina are thus no optimal supports for partial oxidation catalysts but molybdenum oxide (in the form of the M1 phase) or other reducible mixed oxides with a stable geometric structure [65][66][67][68][69][70][71][72] are suitable choices for reactions involving both C-H activation and oxygen transfer.…”

Section: Size and Functions Of Active Sitesmentioning

confidence: 99%

Active Sites for Propane Oxidation: Some Generic Considerations

Schlögl

2011

Top Catal

View full text Add to dashboard Cite

Based on experimental observations about structure and dynamics of the reactive surface of the M1 phase some considerations are made about the nature and size of active sites. In analyzing the stoichiometry of the reactions following activation of propane it occurs that for dehydrogenation small sites are desirable being just sufficient to re-activate oxygen without kinetic hindrance. For deeper oxidation to acrylic acid (AA) the sites should be larger to accommodate all redox equivalents and oxygen species required for one transformation. A qualitative model for size and composition of the active site is made. It is likely that the active site consists on a VxOy species of strictly 2-D nature. This follows the structural suggestion for the active site on the a-b-plane of the M1 structure. The role of Te in moderating the active site is discussed. The suggestions are discussed in comparing requirements for oxidative dehydrogenation of propane (ODP) with those for AA synthesis.

show abstract

“…The X-ray diffraction (XRD) pattern of the V–Cr catalyst is shown in Figure a, a monoclinic CrVO 4 phase (PDF 83–0761) can be observed, and V–Cr–O mixed oxide is believed to perform ideal ammoxidation reactivity. , The Raman spectra in Figure b confirms the existing of CrVO 4 phase, as the strongest peak at 923 cm –1 is assigned to the stretch of V–O–Cr bond of crystalline CrVO 4 , while the 785 cm –1 peak is assigned to the vibration of dichromates, both peaks can be observed in a CrVO 4 sample. , The transmission electron microscope (TEM) image is shown in Figure c, the d -spacing of the observed planes is measured to be 0.330 nm, which is similar to the estimated values of (2 2 0) plane of CrVO 4 obtained by XRD pattern. The surface area of the catalyst determined by Brunauer–Emmett–Teller (BET) model based on N 2 physisorptionis is 57.0 m 2 g –1 , which is suitable for the oxidation reaction.…”

Section: Resultsmentioning

confidence: 78%

Kinetic Study of Meta-Xylene Ammoxidation Reaction over a Commercial V–Cr Mixed Oxide Catalyst

Feng

et al. 2021

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

The reaction behavior of meta-xylene ammoxidation on a commercial V−Cr mixed oxide catalyst (NC-IV) were studied in a fixed bed reactor, by kinetic modeling of experimental data of designed conditions. Specially, the oxidation of NH 3 to N 2 was also involved in the kinetic model, which is vital in the ammoxidation reaction. The catalyst showed monoclinic CrVO 4 phase and spherical morphology with an average particle diameter of 45 μm. Nonlinear regression analysis of the evaluation data has been employed to determine the rate constant and the order of reaction. The results indicated that m-xylene, oxygen, and ammonia share similar kinetic reaction orders for the production of isophthalonitrile (IPN) and m-tolunitrile (MTN), while the NH 3 oxidation reaction shows the highest reaction order, indicating that the partial pressure of ammonia and O 2 requires a precise control. The calculation of activation energies implies that selective ammoxidation to IPN has the highest activation energy (170.6 kJ mol −1 ), which is higher than MTN formation (117.5 kJ mol −1 ). The oxidation of m-xylene to CO 2 has slightly higher activation energy (122.9 kJ mol −1 ) than MTN production, implying the production of mtolunitrile is the dominant reaction under high reaction WHSV. The NH 3 oxidation shows the lowest activation energy (58.2 kJ mol −1 ) than the m-xylene participated reactions demonstrating a relatively easy NH 3 oxidation. These kinetic analyses are useful for a better understanding of the catalytic ammoxidation reaction of alkyl substituted aromatics over V−Cr mixed oxide catalysts.

show abstract

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

Cited by 15 publications

References 54 publications

Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

Selective Oxidation: From a Still Immature Technology to the Roots of Catalysis Science

Active Sites for Propane Oxidation: Some Generic Considerations

Kinetic Study of Meta-Xylene Ammoxidation Reaction over a Commercial V–Cr Mixed Oxide Catalyst

Contact Info

Product

Resources

About