Density Functional Theory Study of Nitrous Oxide Decomposition over Fe- and Co-ZSM-5

Ryder, Jason A.; Chakraborty, Arup K.; Bell, Alexis T.

doi:10.1021/jp014705e

Cited by 104 publications

(144 citation statements)

References 37 publications

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“…The adsorption energies are quite small and within the range of À2.8 to 8.4 kJ mol À1 (Table 5 and Supporting Information Table S1). Previous studies [45][46][47][48] indicate that the adsorption energies may be underestimated because DFT is not accurate enough to describe weak interactions. Generally, more methyl groups in alkanes corre- [a] The two types of O12 atoms are distinguished by a prime sign (see Figures 4 and 6).…”

Section: Resultsmentioning

confidence: 99%

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Yang

Zhou

Liu

et al. 2011

Chemistry A European J

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Isolated Ti species in zeolites show unique catalytic activities for a variety of chemical reactions. In this work, density functional calculations were used to explore three current concerns: 1) the distributions of TiIV and TiIII ions in the MCM‐22 zeolite; 2) the Lewis acidity of the TiIV and TiIII sites; and 3) activation of alkane CH bonds by photocatalysis with Ti‐doped zeolites. Neither the TiIV nor TiIII ions are randomly distributed in the MCM‐22 zeolite. The orders of relative stability are very close for the eight TiIV and TiIII sites, and the T3 site is the most probable in both cases. The wavelengths for TiIV–TiIII excitations were calculated to lie in the range λ=246.9–290.2 nm. The Ti3IV site shows Lewis acidity toward NH3 in two different modes, and these two modes can coexist with each other. The calculated TiIV coordination numbers, TiIVO bond elongations, and charge transfers caused by NH3 adsorption are in good agreement with previous results. Similarly, two different NH3 adsorption modes exist for the Ti3III site; the site that exhibits radical transfer from the lattice O to N atoms is preferred due to the higher adsorption energy. This indicates that the Ti3III site does not show Lewis acidity, in contrast to the Ti3IV site. At the Ti3III site, the energy barrier for activating the methane CH bond was calculated to be 33.3 kJ mol−1 and is greatly reduced by replacing the hydrogen atoms with methyl groups. In addition, the reactivity is improved when switching from MCM‐22 to TS‐1 zeolite. The studies on the various Ti species reveal that lattice O atoms rather than TiIII radicals are crucial to the activation of alkane CH bonds. This work provides new insights into and aids understanding of the catalysis by isolated Ti species in zeolites.

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Section: Resultsmentioning

confidence: 99%

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Yang

Zhou

Liu

et al. 2011

Chemistry A European J

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“…The exframework Fe center consists of a single metal oxo-cations ([FeO] + , or [Fe(OH) 2 ] + , as proposed by Bell and coworkers [30] and Sachtler and co-workers [17]. The steaming and calcination seem to induce surface migration forming a binuclear Fe center I (see Scheme 2).…”

Section: Discussionmentioning

confidence: 99%

Active sites in HZSM-5 with low Fe content for the formation of surface oxygen by decomposing N2O: is every deposited oxygen active?

Kiwi‐Minsker

2003

Journal of Catalysis

131

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Surface-active centers were detected in HZSM-5 with a low content of iron (< 1000 ppm) activated by steaming and high-temperature calcination in inert atmospheres (up to 1323 K). These centers lead to the formation of surface oxygen (O) ad species from N 2 O and were characterized quantitatively by the transient response method. The total amount of active centers was proportional to the content of iron in the zeolites. Only a part of (O) ad deposited by decomposing N 2 O was active in CO oxidation at 523 K and appeared as sharp O 2 peaks at 666 K during the TPD measurements. A binuclear Fe center is suggested featuring a "diamond core" structure, similar to that of the monooxygenase enzyme, as an active center. The active O atoms were assigned to the paired terminal oxygen atoms each bonded to one Fe site (ferryl groups) in the diferric [Fe 2 O 2 H] + cluster. Oxygen pretreatment at 823 K decreases somewhat the total amount of active sites but does not affect the ratio of active/inactive oxygen. Zeolite presaturated by water vapor at 473-523 K generates (O) ad species from N 2 O completely inactive in the CO oxidation. Part of it appears as a broad peak at 940 K in the TPD profile. The total amount of the deposited oxygen corresponds to half of the stoichiometric amount of the surface Fe atoms and suggests that water blocks a half of the binuclear [Fe 2 O 2 H] + center, the remaining acting as a single Fe site.

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“…2). Water [10,11]. Surface migration of iron may lead to the binuclear Fe-center I (see Scheme 1), and its presence in FeZSM-5 has been proven experimentally [12].…”

Section: Effect Of the Catalyst Pre-treatment On The Formation Of Actmentioning

confidence: 95%

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

2004

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The surface active Fe-sites in HZSM-5 with low content of iron (<1000 ppm) activated by steaming and high temperature (up to 1323 K) calcination in inert lead to the formation of surface oxygen (O) ad species from N 2 O and were characterized quantitatively by transient response method. Only a part of (O) ad deposited on zeolite by decomposing N 2 O was active in CO oxidation at 523 K. A binuclear Fe-center is suggested as an active center, featuring a "diamond core" structure, similar to that of the monooxygenase enzyme. The active O-atoms were assigned to the paired terminal oxygen atoms each bound to one Fe-site in the binuclear [Fe 2 O 2 H] + -cluster.Zeolite pre-saturated by water vapor at 473-523 K generates (O) ad species from N 2 O completely inactive in the CO oxidation. The total amount of the oxygen, (O) ad , deposited on the pre-saturated by water zeolite corresponds to a half of stoichiometric amount of the surface Fe-atoms and suggests that water blocks a half of the binuclear [Fe 2 O 2 H] + -center, the remaining acting as a single Fe-site.

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Density Functional Theory Study of Nitrous Oxide Decomposition over Fe- and Co-ZSM-5

Cited by 104 publications

References 37 publications

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Active sites in HZSM-5 with low Fe content for the formation of surface oxygen by decomposing N2O: is every deposited oxygen active?

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

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Density Functional Theory Study of Nitrous Oxide Decomposition over Fe- and Co-ZSM-5

Cited by 104 publications

References 37 publications

Density Functional Calculations on the Distribution, Acidity, and Catalysis of TiIV and TiIII Ions in MCM‐22 Zeolite

Density Functional Calculations on the Distribution, Acidity, and Catalysis of TiIV and TiIII Ions in MCM‐22 Zeolite

Active sites in HZSM-5 with low Fe content for the formation of surface oxygen by decomposing N2O: is every deposited oxygen active?

Transient response method for characterization of active sites in HZSM-5 with low content of iron during N2O decomposition

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Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite