Active sites for reactions of olefin molecules at surfaces of molybdate catalysts

Brückman, K.; Haber, J.; Wiltowski, Tomasz

doi:10.1016/0021-9517(87)90223-5

Cited by 54 publications

(8 citation statements)

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“…Nevertheless, in view of the active site density in the (101) facets and the evaluated relative specific surface area corresponding to these facets (82 % of the total surface area), it is possible to compute the turnover frequency, under the reaction conditions used, which is found to be 1.2 10 -2 s -1 , or 2.4 10 -2 s -1 if only those sites with O4 pointing out of the plane are considered to be active. At 420°C this turnover frequency would be equal to 0.6 or 1.2 s -1 , which is of the same order of magnitude as that reported by Haber et al, for the case of Bi cations on supported bismuth molybdate, which is the only turnover reference for this type of material [47].…”

Section: Resultssupporting

confidence: 82%

“…The similarity between the catalytic sites identified on the surface of the (L)-Bi 2 Mo 2 O 9 and -Bi 2 Mo 3 O 12 phases could explain the very similar catalytic properties observed for these two phases. As pointed out by Haber et al, turnover frequencies have almost never been calculated for mild oxidation bulk-type catalysts, because active sites are generally difficult to identify, and even harder to count [47]. Nevertheless, in view of the active site density in the (101) facets and the evaluated relative specific surface area corresponding to these facets (82 % of the total surface area), it is possible to compute the turnover frequency, under the reaction conditions used, which is found to be 1.2 10 -2 s -1 , or 2.4 10 -2 s -1 if only those sites with O4 pointing out of the plane are considered to be active.…”

Section: Resultsmentioning

confidence: 99%

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β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

Guillou

Elkaı̈m

et al. 2022

Journal of Catalysis

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Section: Resultssupporting

confidence: 82%

Section: Resultsmentioning

confidence: 99%

β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

Guillou

Elkaı̈m

et al. 2022

Journal of Catalysis

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“…Grasselli and co-workers ,,, performed extensive studies of the oxidation of allyl iodide, azopropene, and a series of allyl alcohol isotopologues deuterated at various positions on bismuth molybdates; the facile oxidation of these probe molecules to acrolein and the isotopic content of the products demonstrated that surface allyl species are reaction intermediates in the oxidation of propylene to acrolein. The accepted route for acrolein synthesis on bismuth molybdates is a Mars–van Krevelen-like mechanism: propylene activation through abstraction of a methyl hydrogen, lattice oxygen incorporation in the surface propylene-derived allyl precursor, and catalyst surface regeneration with gas-phase oxygen. ,,,,− …”

Section: Introductionmentioning

confidence: 99%

Mechanistic Origins of Unselective Oxidation Products in the Conversion of Propylene to Acrolein on Bi₂Mo₃O₁₂

2016

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A reaction network detailing the formation and consumption of all C1–C3 products of propylene oxidation on Bi2Mo3O12 at 623 K is developed to show that acrolein, acetaldehyde, acetone, and acetic acid are direct oxidation products of propylene while acrylic acid and ethylene are secondary products. Coprocessing acetaldehyde, acetone, acrylic acid, and acetic acid, separately, with propylene, oxygen, and water revealed (i) the existence of overoxidation reactions of acrolein to acrylic acid and ethylene and oxidation pathways from acetone to acetaldehyde and acetic acid, (ii) the promotional effects of water on the synthesis rates of acetaldehyde from acrolein, acetone from propylene, and acetic acid from acetaldehyde and acrylic acid, and (iii) the inhibitory effects of water on the decomposition of acetic acid to CO x and acrylic acid to acetaldehyde and ethylene. A kinetic model is developed to quantitatively capture the kinetic behavior of all species using pseudo-first-order rate expressions in the organic reactant for all reaction pathways; additional promotional and inhibitory dependencies on water pressure were added to describe the kinetics of reaction rates affected by water. Based on the proposition that multiple types of active sites exist on the mixed metal oxide surface during propylene oxidation, a detailed mechanistic network is postulated that describes all molecular transformations with relevant surface intermediates and provides critical insights into the underlying pathways involved in overoxidation and C–C bond scission reactions.

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“…Reducible oxides have been extensively used as catalysts in the chemical industry for the synthesis of bulk chemicals such as aldehydes, − dimethyl ether, acrolein, − acrylonitrile, and butadiene because of their ability to selectively oxidize hydrocarbons. Most partial oxidation reactions on reducible oxides occur via a Mars–van Krevelen mechanism, which entails oxidation of the hydrocarbon with concomitant reduction of the oxide surface through loss of a surface oxygen.…”

Section: Introductionmentioning

confidence: 99%

Partial Oxidation of Methanol on MoO₃ (010): A DFT and Microkinetic Study

Choksi

Greeley

2016

ACS Catal.

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Methanol oxidation is employed as a probe reaction to evaluate the catalytic properties of the (010) facets of molybdenum trioxide (MoO3), a reducible oxide that exhibits a rich interplay of catalytic chemistry and structural transformations. The reaction mechanism is investigated with a combination of electronic structure calculations, using the BEEF-vdW and HSE06 functionals, and mean-field microkinetic modeling. Considered pathways include vacancy formation and oxidation, monomolecular dehydrogenation of methanol on reduced and nonreduced surfaces, bimolecular reactions between dehydrogenated intermediates, and precursor steps for hydrogen molybdenum phase (H y MoO3–x ) formation. Methanol dissociation begins with C–H or O–H scission, with the O–H route found to be kinetically and thermodynamically preferred. Dehydrogenation of CH2O* to CHO* is slow in comparison to desorption, leading to complete selectivity toward CH2O. C–H scission of CH3O* and recombination of dissociated OH* to form H2O* are kinetically significant steps exhibiting positive degrees of rate control, while oxidation of the reduced surface through adsorbed O2 has a negative degree of rate control. The energetics of the latter elementary step are somewhat sensitive to the choice of density functional, and although this does not affect the predicted reaction orders, the overall rate may change. To estimate the impact of the surface oxidation state on the kinetics, the external pressure of oxygen is varied in the microkinetic model, and the reaction rate is found to follow a volcano-like dependency, with the optimum rate located where surface oxidation neither promotes nor inhibits the overall rate. The methodology demonstrated in this study should be more broadly applicable to modeling catalytic kinetics on reducible oxide single-crystal surfaces.

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Active sites for reactions of olefin molecules at surfaces of molybdate catalysts

Cited by 54 publications

References 9 publications

β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

Mechanistic Origins of Unselective Oxidation Products in the Conversion of Propylene to Acrolein on Bi₂Mo₃O₁₂

Partial Oxidation of Methanol on MoO₃ (010): A DFT and Microkinetic Study

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Active sites for reactions of olefin molecules at surfaces of molybdate catalysts

Cited by 54 publications

References 9 publications

β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

β(L)-Bi2Mo2O9: A new, highly active and selective, mild oxidation bismuth molybdate catalyst

Mechanistic Origins of Unselective Oxidation Products in the Conversion of Propylene to Acrolein on Bi2Mo3O12

Partial Oxidation of Methanol on MoO3 (010): A DFT and Microkinetic Study

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Mechanistic Origins of Unselective Oxidation Products in the Conversion of Propylene to Acrolein on Bi₂Mo₃O₁₂

Partial Oxidation of Methanol on MoO₃ (010): A DFT and Microkinetic Study