Electronic structure of vanadyl pyrophosphate: cluster model studies

Witko, Małgorzata; Tokarz, R.; Haber, J.; Hermann, Klaus

doi:10.1016/s1381-1169(00)00470-2

Cited by 32 publications

(40 citation statements)

References 40 publications

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“…Moreover, as reported earlier higher amounts of surface lattice oxygen, which act as active species are also contributed in improving the catalyst activity [30]. The results revealed that the specific oxygen species was highly active for partial oxidation of n-butane and agreed with the electrical conductivity data obtained by Hermann and co-workers [31].…”

Section: Catalytic Oxidation Of N-butanesupporting

confidence: 89%

Influences of the Various Metal Dopants for the Nanosized Vanadium Phosphate Catalysts

2010

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In this study, undoped and doped nanosized vanadium phosphate (VPO) catalysts were prepared by using hemihydrate precursor, VOHPO 4 Á0.5H 2 O. Various metal dopants were used (Zr, Zn, Ni, Nb, Mo, Mn, Fe, Cu, Cr, Ce and Co) in the synthesizing step in order to prepare doped nanosized VPO catalysts. The effect of metal dopants on nanosized VPO catalyst was studied through XRD, BET, redox titration, ICP-AES, SEM, TEM and H 2 -TPR. Catalytic evaluation of the undoped and doped VPO catalysts was also carried out on fixed-bed microreactor. Particle sizes for all the doped nanosized VPO catalysts were produced in nano-scale range. Besides, from the TPR results it has shown that the certain metal dopants also induced the amount of oxygen removed from the V 4? and V 5? peaks. This interesting effect eventually caused a significant improvement in n-butane conversion and maleic anhydride (MA) selectivity at higher and lower temperatures (673, 643 and 623 K). The MA selectivity of all the doped nanosized VPO at lower temperatures, are comparable to the undoped nanosized VPO catalyst at higher temperature, 673 K.

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Section: Catalytic Oxidation Of N-butanesupporting

confidence: 89%

Influences of the Various Metal Dopants for the Nanosized Vanadium Phosphate Catalysts

2010

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“…Witko et al [151,152] reported about DFT calculations of the electronic structure for different clusters modelling a defective VPP (100) surface. It was found that neutral isolated oxygen vacancies may act as sources for enhancing the activity and selectivity of VPO.…”

Section: In-situ Investigation and Modelling On The Nature Of Vpp Actmentioning

confidence: 99%

VPO catalyst for n-butane oxidation to maleic anhydride: A goal achieved, or a still open challenge?

et al. 2006

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A Partner of Concorde CA and of Idecat NoE, 6FP of the EU) b Lonza SpA, via E. Fermi 51, 24020 Scanzorosciate (BG), ItalyThis review describes recent findings in the oxidation of n-butane to maleic anhydride. The process is commercial since the 80's, but yet the yield is far from being optimised. Therefore, it represents an emblematic example of how several scientific disciplines, from solid-state science to reactor technology, can contribute to the improvement of the process performance.KEY WORDS: Vanadyl pyrophosphate; n-butane; selective oxidation; maleic anhydride 1. The oxidation of n-butane catalysed by VPO: How to improve process performance?The activation of light alkanes by high-temperature contact with a redox catalyst represents one way to transform these hydrocarbons to valuable chemicals (a few reviews and books dealing with this topic, published after 1998, are refs [1-18]). The most successful example is the oxidation of n-butane to maleic anhydride (MA), catalysed by a V/P/O-based catalyst (VPO), which starting from the 80's has been replacing in part the commercial synthesis from benzene. This reaction, and the unique chemical-physical properties of the vanadyl pyrophosphate (VO) 2 P 2 O 7 (VPP), the active and selective phase for this reaction, are amongst the most studied topics in catalysis during the latest decades, initially with the aim of understanding which catalyst peculiarities make this complex transformation possible, and later on with the aim of improving the process performance.MA finds its major use in the production of unsaturated polyesters and of butanediol. The yearly world consumption exceeds 1.3 · 10 6 metric tons [19]. Approximately 70% is produced by n-butane oxidation, the remaining still being obtained from benzene. There are several reactor technologies available, including fixed-bed (Scientific Design, Huntsman, BASF, Pantochim), fluidised-bed (Lonza, BP, Mitsubishi), and transported-bed (DuPont). Best process performances reported in patent literature range from 53 to 65% molar yield to MA [20][21][22][23][24][25], with a conversion of the hydrocarbon not higher than 85-86%. An excellent result of more than 70% yield is reported [26], which however refers to a recycle process. In lab reactors best yields reported are lower than 50%.The best performance for a fixed-bed reactor does not exceed 65% per-pass yield, while that in a fluidised-bed is typically somewhat lower; in fact, back-mixing phenomena are responsible for the consecutive combustion of MA. Moreover, with fluidised-bed operation n-butane-richer conditions can be used (up to 5 molar % in feed); under the latter conditions, a worsening of selectivity is expected, which however is compensated by a considerable improvement in MA productivity. In the fluidised-bed process developed by Lonza and Lummus (shown in figure 1), the loss of selectivity is also compensated by the higher amount of high-pressure steam produced, due to the more efficient removal of the reaction heat and to the more CO x produced.The maximu...

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“…Among many examples in catalysis, the theoretical investigations on the structural and electronic surface properties and the catalytic reactions of transition-metal oxides, in particular based on vanadium and molybdenum, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] are especially important as they provided a deep insight into the structure-activity relationship of these compounds, used in a variety of applications.…”

Section: Introductionmentioning

confidence: 99%

On the asymmetry in molybdenum–oxygen bonding in the MoO3 structure: ETS–NOCV analysis

Mitoraj

Michalak

2012

Struct Chem

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In the present study, the analysis of natural orbitals for chemical valence (NOCV) combined with the extended-transition-state (ETS) bond-energy decomposition method (ETS-NOCV) was applied to characterize an asymmetry in Mo-O bonding in MoO 3 crystal. Considered were three non-equivalent oxygen sites (O1, O2, O3) in the Mo 7 O 30 H 18 cluster model of (010) surface of MoO 3 . The ETS-NOCV method leads to the conclusion that an increase in the Mo-O distances, from 1.68 Å (for Mo-O1), through 1.73 Å (for Mo-O2), up to 1.94 Å (for Mo-O3), is directly related to decrease in strength of both r-and p-contributions of Mo-O bond. Further, Mo-O connection appeared to exhibit both ionic (the charge transfer from 2p orbital of oxygen to molybdenum) and the covalent (charge accumulation in the region of Mo-O) components. Finally, the trend in the orbital energy stabilization (DE orb ) originating from the dominant r-and p-bond contributions appeared to correlate very well with the oxygen-vacancy formation energies published earlier by Tokarz-Sobieraj et al. (Surf Sci 489:107, 2001).

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Electronic structure of vanadyl pyrophosphate: cluster model studies

Cited by 32 publications

References 40 publications

Influences of the Various Metal Dopants for the Nanosized Vanadium Phosphate Catalysts

Influences of the Various Metal Dopants for the Nanosized Vanadium Phosphate Catalysts

VPO catalyst for n-butane oxidation to maleic anhydride: A goal achieved, or a still open challenge?

On the asymmetry in molybdenum–oxygen bonding in the MoO3 structure: ETS–NOCV analysis

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