DFT+U Investigation of Propene Oxidation over Bismuth Molybdate: Active Sites, Reaction Intermediates, and the Role of Bismuth

Getsoian, Andrew “Bean”; Shapovalov, Vladimir; Bell, Alexis T.

doi:10.1021/jp400440p

Cited by 74 publications

(133 citation statements)

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“…Jung et al [60] tested the influence of the pH value during co-precipitation of γ-Bi2MoO6 (initial ratio Bi/Mo = 2/1) on the oxidative dehydrogenation of n-butylene and discovered that the sample synthesized at pH = 3 showed both the highest butylene conversion and 1,3-butadiene yield due to a high oxygen mobility of this sample. According to the group of Keulks [8,20], re-oxidation of the catalyst is the rate-determining step in propylene oxidation at temperatures below 400 °C, whereas abstraction of an α-hydrogen atom to form an allylic intermediate is the rate determining step at higher temperatures (>400 °C), in agreement with theory [14]. Recently, it was further reported that the reaction order in oxygen was zero at 340 °C and 400 °C for Bi2Mo3O12 catalysts, i.e., the reaction rate for acrolein formation, was independent of the partial pressure of oxygen, indicating that the transition temperature where re-oxidation of the catalyst becomes the rate determining step was lower than 340 °C [61,62].…”

Section: Catalytic Performance In Propylene Oxidation To Acroleinsupporting

confidence: 70%

“…Nevertheless, the surface layer of these multicomponent catalysts consists of mixed oxides based on Bi and Mo, and these two metals seem to form the key active sites [13]. The rate-determining step is the abstraction of hydrogen from propylene on bismuth or bismuth connected to molybdyl groups [14]. The addition of other transition metals and main group metals helps to increase the specific surface area of the catalyst [15], the extent of lattice oxygen participation [15,16] and the electronic conductivity [17].…”

Section: Introductionmentioning

confidence: 99%

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Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

et al. 2015

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A series of bismuth molybdate catalysts with relatively high surface area was prepared via mild hydrothermal synthesis. Variation of the pH value and Bi/Mo ratio during the synthesis allowed tuning of the crystalline Bi-Mo oxide phases, as determined by X-ray diffraction (XRD) and Raman spectroscopy. The pH value during synthesis had a strong influence on the catalytic performance. Synthesis using a Bi/Mo ratio of 1/1 at pH ≥ 6 resulted in γ-Bi2MoO6, which exhibited a better catalytic performance than phase mixtures obtained at lower pH values. However, a significantly lower catalytic activity was observed at pH = 9 due to the low specific surface area. γ-Bi2MoO6 synthesized with Bi/Mo = 1/1 at pH = 6 and 7 exhibited relatively high surface areas and the best catalytic performance. All OPEN ACCESSCatalysts 2015, 5 1555 samples prepared with Bi/Mo = 1/1, except samples synthesized at pH = 1 and 9, showed better catalytic performance than samples synthesized with Bi/Mo = 2/3 at pH = 4 and 9 and γ-Bi2MoO6 synthesized by co-precipitation at pH = 7. At temperatures above 440 °C, the catalytic activity of the hydrothermally synthesized bismuth molybdates started to decrease due to sintering and loss of surface area. These results support that a combination of the required bismuth molybdate phase and a high specific surface area is crucial for a good performance in the selective oxidation of propylene.

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Section: Catalytic Performance In Propylene Oxidation To Acroleinsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

et al. 2015

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“…This conclusion is supported by DFT studies, which reveal further that the most reactive O atoms are those in Mo O bonds that interact with the lone pair of proximal Bi atoms (e.g. equatorial Mo O bonds) [15,16]. This interaction destabilizes the HOMO and stabilizes the LUMO of the molybdate species, thereby facilitating the transfer of an electron into a Mo O p* orbital.…”

Section: Catalystmentioning

confidence: 74%

“…The principle catalysts used to promote this reaction are bismuth molybdates in which a part of the molybdenum is substituted by one or more other metals in order to enhance the catalyst activity and selectivity [3][4][5][6][7][8][9][10]. A number of groups have investigated the mechanism of propene oxidation on ␣-Bi 2 Mo 3 O 12 with the aim of understanding the elementary processes leading to acrolein and the influence of added elements on these processes [11][12][13][14][15][16]. These efforts have led to the following findings.…”

Section: Introductionmentioning

confidence: 99%

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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“…Experimental and computational results have indicated that the critical alkene activation step occurs at the methyl group of propene by a Bi-O function in the bismuth-molybdate catalysts [4][5][6][7][8][9]. Supported catalysts incorporating bismuth have also been shown to catalyze the oxidation of different aromatic and alkane compounds [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Ammoxidation of propane to acrylonitrile over silica-supported Fe-Bi nanocatalysts

Adams

Elpitiya

Khivantsev

et al. 2015

Applied Catalysis A: General

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a b s t r a c tAmmoxidation of propane to acrylonitrile was examined over a Fe 3 BiO x /SiO 2 sample prepared by thermal decarbonylation of [Et 4 N][Fe 3 (CO) 10 ( 3 -Bi)] on the surface of mesoporous silica. Catalytic measurements performed at 500 • C showed that this sample yields 49% acrylonitrile selectivity at 36% propane conversion when a 5.5%C 3 H 8 /30%O 2 /11%NH 3 /He balance reaction mixture was used at a GHSV of 1360 h −1 . HRSTEM, EDS, and XPS measurements indicate that mixed Fe 3 BiO 6 oxide particles less than 2 nm in size were formed on the surface of this material under reaction conditions. A Fe/Bi atomic ratio in these particles is approximately 3:1 and the Fe and Bi ions both are in the +3 oxidation state. A Fe-Bi/SiO 2 sample prepared by co-impregnation of individual Fe and Bi salts had very low activity and low selectivity for acrylonitrile formation from propane under similar experimental conditions due to larger sizes of particles formed under reaction conditions and enrichment of their surface with Fe.

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DFT+U Investigation of Propene Oxidation over Bismuth Molybdate: Active Sites, Reaction Intermediates, and the Role of Bismuth

Cited by 74 publications

References 94 publications

Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

Bismuth Molybdate Catalysts Prepared by Mild Hydrothermal Synthesis: Influence of pH on the Selective Oxidation of Propylene

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

Ammoxidation of propane to acrylonitrile over silica-supported Fe-Bi nanocatalysts

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