Mechanism studies of the catalytic oxidation of propylene

Adams, Charles R.

doi:10.1016/0021-9517(64)90054-5

Cited by 126 publications

(38 citation statements)

References 1 publication

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“…Isotopic tracer studies for both catalysts show that the reaction proceeds by a Mars van Krevelen mechanism involving oxygen atoms of the lattice [29]. Moreover, the reaction kinetics suggests that the rate-limiting step involves cleavage of a C H bond in the methyl group of propene [30]. There are also further similarities in the catalytic properties of ␥-Bi 2 MoO 6 and ␣-Bi 2 Mo 3 O 12 .…”

Section: Catalystmentioning

confidence: 91%

Effects of catalyst crystal structure on the oxidation of propene to acrolein

et al. 2016

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Please cite this article in press as: Z. Zhai, et al., Effects of catalyst crystal structure on the oxidation of propene to acrolein, Catal. Today (2015), http://dx.a b s t r a c t Bismuth molybdate is known to be active for the oxidation of propene to acrolein and its activity can be altered by substitution of other elements (e.g. Fe, V, W) into the scheelite phase of ␣-Bi 2 Mo 3 O 12 . This work has further revealed that the apparent activation energy for acrolein formation correlates with the band gap of the catalyst measured at reaction temperature. It is, therefore, of interest to establish to how the crystal structure of the catalyst affects the activation energy. We report here an investigation of propene oxidation conducted over Bi, Mo, V oxides having the aurivillius structure with the composition Bi 4 V 2-x Mo x O 11+x/2 (x = 0−1) and compare them with oxides having the scheelite structure with the composition Bi 2-x/3 Mo x V 1-x O 12 (x = 0−1). The aurivillius-phase catalysts again show a correlation between the apparent activation energy and the band gap of the oxide, and the only difference being that for a given band gap, the apparent activation energy for the aurivillius-phase catalysts is 1.5 kcal/mol higher than that for the scheelite-phase catalysts. This difference is attributed to the lower heat of propene adsorption on the aurivillius-phase catalysts. A further finding is that for catalysts with band gaps greater than ∼2.1 eV, the acrolein selectivity is ∼75% for the conditions used and independent of the propene conversion. When the band gap falls below ∼2.1 eV, the intrinsic selectivity to acrolein decreases rapidly and then decreases further with increasing propene conversion. This pattern shows that when the activity of oxygen atoms at the catalyst surface becomes very high, two processes become more rapid -the oxidation of the intermediate from which acrolein is formed and the sequential combustion of acrolein to CO 2 .

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Section: Catalystmentioning

confidence: 91%

Effects of catalyst crystal structure on the oxidation of propene to acrolein

et al. 2016

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“…Oxygen insertion occurs via a σ bond formation between the lattice oxygen and the allylic intermediate. The oxygenated product desorbs and leaves an oxygen vacancy at the catalyst surface [5]. This vacancy is reoxidized via oxygen diffusion through either the near-surface layer or the bulk.…”

Section: Introductionmentioning

confidence: 99%

Structural characterization of high-performance catalysts for partial oxidation—the high-resolution and analytical electron microscopy approach

Wagner

Schunk

Hibst

et al. 2004

Journal of Catalysis

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A set of Mo, V, and W mixed-oxide samples with additives P and Cs showing high performance in selective partial oxidation of propene is studied by means of elemental mapping and crystal structure determination using scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) as supplement to XRD measurements which are insufficient for phase determination. The set is divided into two subsets of samples denoted A and B, where subset A samples show the highest performance in selective partial oxidation of propene.These high-performance catalysts are all predominated by structures of the Mo 5 O 14 type in contrast to a negligible amount of the orthorhombic MoO 3 , which is known to favor total oxidation.

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“…The second reaction step, the nucleophilic oxygen insertion, is thought to occur on the (010) surface via the formation of a p bond between the ''lattice oxygen'' and the allylic intermediate. The nucleophilic oxygen species is then inserted into the hydrocarbon to give the oxygenated product, which desorbs, leaving an oxygen vacancy at the catalyst surface [5]. This oxygen vacancy is reoxidized in the last step of the catalytic cycle and it is suggested that this occurs via oxygen bulk diffusion.…”

Section: Introductionmentioning

confidence: 99%

MoVW mixed metal oxides catalysts for acrylic acid production: from industrial catalysts to model studies

Mestl¹

2006

Top Catal

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MoVW) 5 O 14 -type oxides were identified as the active and selective components in industrial acrylic acid catalysts. Tungsten is suggested to play an important role as a structural promoter in the formation and stabilization of this oxide. Vanadium is responsible for high catalytic activities but is detrimental for the stability of this oxide at the necessary high concentrations for optimum catalytic performance. The activity of mixed MoVW oxide catalysts for methanol, propene, and acrolein partial oxidation could be considerably improved, when the amount of the (MoVW) 5 O 14 -type oxide was increased by thermal annealing. A model is proposed on the basis of the correlation between Raman wavenumber and bond order and degree of reduction, which explains the observed different selectivities of MoO 3)x and the (MoVW) 5 O 14 -type oxides in terms of metal-oxygen bond strengths, i.e. oxygen basicity and oxygen lability, respectively. According to this model, the (MoVW) 5 O 14 mixed oxide catalyses partial oxidation because of its intermediate C-H activation and oxygen releasing oxygen functionalities. However, these (MoVW) 5 O 14 -type industrial oxidation catalysts are heterogeneous and highly complex systems. Their physicochemical characterization also revealed that their chemical bulk and surface compositions vary with thermal activation and oxygen potential. A core-shell model is suggested to describe the active catalyst state, the shell providing a high number of active centers, the core high electronic conductivity and ion mobility. The fact that the surface composition of such catalysts is considerably different from their bulk compositions, most probably implies that the ''molecular structure'' at their surface differs too considerably from their bulk crystal structure. Hence, the posed question about the active catalyst structure and its relation to its catalytic performance cannot unambiguously be explained by the crystallographic structure, but still remains unsolved.

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Mechanism studies of the catalytic oxidation of propylene

Cited by 126 publications

References 1 publication

Effects of catalyst crystal structure on the oxidation of propene to acrolein

Effects of catalyst crystal structure on the oxidation of propene to acrolein

Structural characterization of high-performance catalysts for partial oxidation—the high-resolution and analytical electron microscopy approach

MoVW mixed metal oxides catalysts for acrylic acid production: from industrial catalysts to model studies

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