Reactions of laser-ablated tellurium atoms with oxygen molecules: Matrix isolation infrared and DFT studies

Sundararajan, K.; Sankaran, K.; Kavitha, V.

doi:10.1016/j.molstruc.2007.06.021

Cited by 11 publications

(8 citation statements)

References 20 publications

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“…These differences likely arise due to the fact that Torri et al13 utilized HF-level calculations, while we utilized DFT level of theory which was shown to produce more reliable results than HF in calculations of ground state properties, potential energies and especially vibrational frequencies 25,26. To some extent DFT is comparable in accuracy to high-level post-HF methods such as MP2, CASSCF and CIS 25-29…”

Section: Resultsmentioning

confidence: 99%

Dependence of Amide Vibrations on Hydrogen Bonding

2008

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The effect of hydrogen bonding on the amide group vibrational spectra has traditionally been rationalized by invoking a resonance model where hydrogen bonding impacts the amide functional group by stabilizing its [-O-C=NH+] structure over the [O=C-NH] structure. However, Triggs and Valentini’s UV-Raman study of solvation and hydrogen bonding effects on ε-caprolactum, N,N-dimethylacetamide (DMA) and N-methylacetamide (NMA) (J .Phys. Chem., 1992; 96, 6922-31) cast doubt on the validity of this model by demonstrating that contrary to the resonance model prediction, carbonyl hydrogen bonding does not impact the AmII’ frequency of DMA. In this study we utilize density functional theory (DFT) calculations to examine the impact of hydrogen bonding on the C=O and N-H functional groups of NMA, which is typically used as a simple model of the peptide bond. Our calculations indicate that, as expected, the hydrogen bonding frequency dependence of the AmI vibration predominantly derives from the C=O group, whereas the hydrogen bonding frequency dependence of the AmII vibration primarily derives from N-H hydrogen bonding. In contrast, the hydrogen bonding dependence of the conformation sensitive AmIII band derives equally from both C=O and N-H groups, and, thus, is equally responsive to hydrogen bonding at the C=O or N-H site. Our work shows that a clear understanding of the normal mode composition of the amide vibrations is crucial for an accurate interpretation of the hydrogen bonding dependence of amide vibrational frequencies.

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Section: Resultsmentioning

confidence: 99%

Dependence of Amide Vibrations on Hydrogen Bonding

2008

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“…830 cm -1 (Table 1). Although to the best of our knowledge experimental the vibrational signature of this surface species has not been identified, it is known that Te-O vibrational modes in amorphous or crystalline TeO 2 are at 780 cm -1 or less [54], whereas Ar matrix-isolated TeO and OTeO molecules exhibit Te-O and symmetric/asymmetric O-Te-O stretching modes at 783 and 823/841 cm -1 , respectively [55]. These experimental observations are in broad agreement with our theoretical results for the surface Te-O species.…”

Section: Cluster Modelsmentioning

confidence: 95%

Propane Ammoxidation Over the Mo–V–Te–Nb–O M1 Phase: Reactivity of Surface Cations in Hydrogen Abstraction Steps

Muthukumar

et al. 2011

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Density functional theory calculations (GGA-PBE) have been performed to investigate the adsorption of C 3 (propane, isopropyl, propene, and allyl) and H species on the proposed active center present in the surface ab planes of the bulk Mo-V-Te-Nb-O M1 phase in order to better understand the roles of the different surface cations in propane ammoxidation. Modified cluster models were employed to isolate the closely spaced V=O and Te=O from each other and to vary the oxidation state of the V cation. While propane and propene adsorb with nearly zero adsorption energy, the isopropyl and allyl radicals bind strongly to V=O and Te=O with adsorption energies, DE, being B-1.75 eV, but appreciably more weakly on other sites, such as Mo=O, bridging oxygen (Mo-O-V and Mo-O-Mo), and empty metal apical sites (DE [ -1 eV). Atomic H binds more strongly to Te=O (DE B -3 eV) than to all the other sites, including V=O (DE = -2.59 eV). The reduction of surface oxo groups by dissociated H and their removal as water are thermodynamically favorable except when both H atoms are bonded to the same Te=O. Consistent with the strong binding of H, Te=O is markedly more active at abstracting the methylene H from propane (E a B 1.01 eV) than V=O (E a = 1.70 eV on V 5? =O and 2.13 eV on V 4? =O). The higher-thanobserved activity and the loose binding of Te=O moieties to the mixed metal oxide lattice of M1 raise the question of whether active Te=O groups are in fact present in the surface ab planes of the M1 phase under propane ammoxidation conditions.

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“…Another possibility is that the Te centers are predominantly in a nitrided state instead of an oxo-terminated state under propane ammoxidation conditions, thus making active Te=O species for propane activation unavailable. Incidentally the reactivity of tellurium toward nitrogen has been noted before [34], while tellurium oxide is effective for propene ammoxidation [35].…”

Section: Adsorption Of Nh X Speciesmentioning

confidence: 99%

Propane Ammoxidation over Mo–V–Te–Nb–O M1 Phase Investigated by DFT: Elementary Steps of Ammonia Adsorption, Activation and NH Insertion into π-Allyl Intermediate

Guliants

2014

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The selective ammoxidation of propane into acrylonitrile catalyzed by the bulk Mo-V-Te-Nb-O system has received significant attention because it is more environmentally benign than the current process of propene ammoxidation and relies on more abundant propane feedstock. The reaction mechanism is proposed to consist of a series of elementary steps including propane oxidative dehydrogenation, ammonia and O 2 activation, and NH x insertion into C 3 intermediates. In this study density functional theory calculations have been performed to investigate the energetics of ammonia adsorption and activation in the proposed active center in the ab plane of the M1 phase. The formation of NH x (x = 0, 1, 2, 3) species is found to be highly favored on reduced, oxodepleted metal sites. The reduced Mo site is determined to be the most favorable site for ammonia activation by comparing the reaction energy profiles for the sequential dehydrogenation of ammonia on the various metal sites. The activation barrier for the initial H abstraction from ammonia was found to depend strongly on the surface sites that stabilize H and NH 2 , and is as low as 0.28 eV when NH 2 is stabilized by the reduced Mo site and H is abstracted by the telluryl oxo group. The subsequent step of surface NH insertion into a p-allyl gas intermediate was also found to have a low activation energy barrier of 0.03 eV on the reduced Mo site.

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Reactions of laser-ablated tellurium atoms with oxygen molecules: Matrix isolation infrared and DFT studies

Cited by 11 publications

References 20 publications

Dependence of Amide Vibrations on Hydrogen Bonding

Dependence of Amide Vibrations on Hydrogen Bonding

Propane Ammoxidation Over the Mo–V–Te–Nb–O M1 Phase: Reactivity of Surface Cations in Hydrogen Abstraction Steps

Propane Ammoxidation over Mo–V–Te–Nb–O M1 Phase Investigated by DFT: Elementary Steps of Ammonia Adsorption, Activation and NH Insertion into π-Allyl Intermediate

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