H2 adsorption and H/D exchange on Au/TS-1 and Au/S-1 catalysts

Joshi, Ajay M.; Delgass, W. Nicholas; Thomson, Kendall T.

doi:10.1007/s11244-007-0275-y

Cited by 14 publications

(16 citation statements)

References 92 publications

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“…2 As for the case of 2 synthesized with NH 3 , a shift of the NH 2 bending modes could not be observed since d(ND 2 ) are expected to appear at 1131 and 1110 cm -1 which is an opaque region of silica. The appearance of a band at 2760 cm -1 is similar to the one described above and corresponds to the formation of Si-OD by H/D exchange with residual isolated silanols [24]. The IR spectrum of the deuterated amido imido complex thus obtained is equivalent to the spectrum of 2-d obtained by H/D exchange with D 2 (see Fig.…”

Section: In Situ Infrared Spectroscopysupporting

confidence: 67%

“…A broad and weak band raises the baseline at 3200 cm -1 . This effect and the shift of the silanol stretching frequency are explained by the interaction of ammonia with the silanols of silica via van der Waals interactions [24], and was confirmed by blank experiments.…”

Section: In Situ Infrared Spectroscopysupporting

confidence: 60%

“…Finally, the m(OH) band of the silanol groups, which appears at 3750 cm -1 was replaced by a novel band at 2757 cm -1 . This value corresponds to the formation of Si-OD by H/D exchange with residual isolated silanols [24]. Table 1 summarizes all these data.…”

Section: In Situ Infrared Spectroscopymentioning

confidence: 89%

“…A classical way to start probing the reactivity of a new complex is the investigation of its H/D exchange reactions: such a longstanding approach in the study of C-H and H-H bond activation and reaction mechanisms [17][18][19][20][21][22][23][24] is being extended, given the renewed interest in catalytic C-H activation [25][26][27] and novel applications of deuterium tags in biocatalysis [28][29][30][31] and analytical chemistry [32,33], leading to the current renaissance of the topic [34,35].…”

Section: Introductionmentioning

confidence: 99%

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H/D Exchange on Silica-Grafted Tantalum(V) Imido Amido [(≡SiO)2Ta(V)(NH)(NH2)] Synthesized from Either Ammonia or Dinitrogen: IR and DFT Evidence for Heterolytic Splitting of D2

et al. 2009

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The silica-grafted Ta (V) imido amido complex [(:SiO) 2 Ta(NH)(NH 2 )], 2, obtained from the reaction of either ammonia or dinitrogen plus hydrogen with the silicagrafted hydrides [(:SiO) 2 Ta (III) H], 1a, and [(:SiO) 2-Ta (V) H 3 ], 1b, undergoes H/D exchange with D 2 . In situ IR spectroscopy shows that the fully labelled compound [(:SiO) 2 Ta(ND)(ND 2 )], 2-d, can be obtained by moderate heating (60°C, 3 h) under D 2 atmosphere (550 torr, 300 eq. with respect to Ta), and that the exchange is reversible. The observed stretching and bending frequencies of 2-d are in agreement with the expected isotopic shift upon H/D replacement with respect to literature values reported for 2 and have been corroborated by the independent synthesis of 2-d by reaction of deuterated 1a and 1b with N 2 and D 2 . Density functional theory (DFT) calculations, performed using a periodic or a cluster model, explored the structures and energetics of all minima involved in the reaction with H 2 and showed that among the explored pathways the energetically preferred mechanisms for H 2 reaction with [{(l-O)[(HO) 2 SiO] 2 }Ta (V) (NH) (NH 2 )], 2q, is the heterolytic cleavage of either the imido Ta=N or the amido Ta-N bonds, to yield respectively [{(l-O)[(HO) 2 SiO] 2 }TaH(NH 2 ) 2 ], 3q (DE = -9.5 kcal mol -1 and DG 298K = ?2.6 kcal mol -1 with respect to 2q) and [{(l-O)[(HO) 2 SiO] 2 }Ta(NH) (NH 3 )], 4q (DE = -6.0 kcal mol -1 and DG 298K = ?7.9 kcal mol -1 with respect to 2q). All activation barriers are moderate (between 17.7 and 30.2 kcal mol -1 ) in agreement with the observed mild heating conditions necessary for the reaction to occur.

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Section: In Situ Infrared Spectroscopysupporting

confidence: 67%

Section: In Situ Infrared Spectroscopysupporting

confidence: 60%

Section: In Situ Infrared Spectroscopymentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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H/D Exchange on Silica-Grafted Tantalum(V) Imido Amido [(≡SiO)2Ta(V)(NH)(NH2)] Synthesized from Either Ammonia or Dinitrogen: IR and DFT Evidence for Heterolytic Splitting of D2

et al. 2009

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“…In their studies, both metadynamics and constrained molecular dynamics (MD) simulations highlight important fluctuations of the Au cluster during the reaction process, which is consistent with the geometric fluxionality of Au particles aforementioned [69]. Later, Thomson et al compared the catalytic activity of Au3, Au 4 + , Au5, and Au 5  clusters in the gas-phase reaction of H2 and O2 to form H2O2 [85]. It was found that both neutral and charged Au clusters are active in the peroxide formation reaction, but Au 4 + is the most active one for H2O2 formation based on the Gibbs free energy of activation.…”

Section: The Synthesis Of H 2 O 2 From O 2 and Hmentioning

confidence: 82%

Theoretical Studies on the Direct Propylene Epoxidation Using Gold-Based Catalysts: A Mini-Review

Lü

et al. 2018

Catalysts

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Direct propylene epoxidation using Au-based catalysts is an important gas-phase reaction and is clearly a promising route for the future industrial production of propylene oxide (PO). For instance, gold nanoparticles or clusters that consist of a small number of atoms demonstrate unique and even unexpected properties, since the high ratio of surface to bulk atoms can provide new reaction pathways with lower activation barriers. Support materials can have a remarkable effect on Au nanoparticles or clusters due to charge transfer. Moreover, Au (or Au-based alloy, such as Au–Pd) can be loaded on supports to form active interfacial sites (or multiple interfaces). Model studies are needed to help probe the underlying mechanistic aspects and identify key factors controlling the activity and selectivity. The current theoretical/computational progress on this system is reviewed with respect to the molecular- and catalyst-level aspects (e.g., first-principles calculations and kinetic modeling) of propylene epoxidation over Au-based catalysts. This includes an analysis of H2 and O2 adsorption, H2O2 (OOH) species formation, epoxidation of propylene into PO, as well as possible byproduct formation. These studies have provided a better understanding of the nature of the active centers and the dominant reaction mechanisms, and thus, could potentially be used to design novel catalysts with improved efficiency.

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