The Application of Diffuse Reflectance Infrared Spectroscopy and Temperature-Programmed Desorption To Investigate the Interaction of Methanol on η-Alumina

McInroy, Alastair R.; Lundie, David T.; Winfield, John M.; Dudman, Chris C.; Jones, Peter N.; Lennon, David

doi:10.1021/la051429c

Cited by 46 publications

(76 citation statements)

References 43 publications

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“…At temperatures higher than 510 K, the methoxy groups can be converted into formates, in accordance with the mechanism that was discussed in Ref. [18] over h-Al 2 O 3 . As it was also substantiated by the results of our gas phase analysis with both IR and RGA (data not shown here), formate production is accompanied by gas phase methane and probably hydrogen formation.…”

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confidence: 86%

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NOx reduction on a transition metal-free γ-Al2O3 catalyst using dimethylether (DME)

2008

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NO 2 and dimethylether (DME) adsorption as well as DME and NO 2 co-adsorption on a transition metal-free g-alumina catalyst were investigated via in-situ transmission Fourier transform infrared spectroscopy (in-situ FTIR), residual gas analysis (RGA) and temperature programmed desorption (TPD) techniques. NO 2 adsorption at room temperature leads to the formation of surface nitrates and nitrites. DME adsorption on the alumina surface at 300 K leads to molecularly adsorbed DME, molecularly adsorbed methanol and surface methoxides. Upon heating the DME-exposed alumina to 500-600 K the surface is dominated by methoxide groups. At higher temperatures methoxide groups are converted into formates. At T > 510 K, formate decomposition takes place to form H 2 O(g) and CO(g). DME and NO 2 co-adsorption at 423 K does not indicate a significant reaction between DME and NO 2 . However, in similar experiments at 573 K, fast reaction occurs and the methoxides present at 573 K before the NO 2 adsorption are converted into formates, simultaneously with the formation of isocyanates. Under these conditions, NCO can further be hydrolyzed into isocyanic acid or ammonia with the help of water which is generated during the formate formation, decomposition and/or NCO formation steps. #

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confidence: 86%

“…On the other hand, the presence of a broad and a low frequency n(O-H) mode around 3278 cm À1 (see also inset of Fig. 2b) strongly indicates the presence of adsorbed methanol on the surface [18]. The feature at 1156 cm À1 can be attributed to molecularly adsorbed DME [40] or a coordinated methanol species [46].…”

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confidence: 92%

NOx reduction on a transition metal-free γ-Al2O3 catalyst using dimethylether (DME)

2008

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“…[51] A band at 1280 cm À1 due to OH deformation of the propan-2-ol molecule is hardly observable, which indicates the absence of non-dissociatively adsorbed propan-2-ol on the catalyst.…”

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confidence: 98%

Oxidant‐Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid–Base Sites on Alumina

Shimizu

Sugino

Sawabe

et al. 2009

Chemistry A European J

222

178

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A gamma-alumina-supported silver cluster catalyst--Ag/Al(2)O(3)--has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373 K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1 nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1) reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2) C-H activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3) H(2) desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid-base bifunctional support (Al(2)O(3)) than on basic (MgO and CeO(2)) and acidic to neutral (SiO(2)) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d(10) element--silver--through optimization of metal particle size and the acid-base natures of inorganic supports.

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“…[50][51][52][53] At around 1300 cm À1 À 1750 cm À1 , the two peaks can be related to asymmetric vibration modes of H-O-H; O-C-O, and C ¼ O. [54][55][56][57][58] The feature at 3000 cm À1 À 3800 cm À1 can be assigned to Si-OH and O-H stretching modes. 16,44 In Figure 3(b), the strong peak from the additional interfacial SiO 2 layer can be seen in the range of 900 cm À1 À 1300 cm À1 .…”

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confidence: 99%

A study on Si/Al2O3 paramagnetic point defects

Kühnhold-Pospischil

Saint‐Cast

Hofmann

et al. 2016

Journal of Applied Physics

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In this contribution, negative charges and electronic traps related to the Si=Al 2 O 3 interface were measured and related to paramagnetic point defects and molecular vibrations. To this end, contactless capacitance voltage measurements, X-band electron paramagnetic resonance (EPR), and infrared spectroscopy were carried out, and their results were compared. A change in the negative charge density and electron trap density at the Si=Al 2 O 3 interface was achieved by adding a thermally grown SiO 2 layer with varying thicknesses and conducting an additional temperature treatment. Using EPR, five paramagnetic moments were detected in Si=ðSiO 2 Þ=Al 2 O 3 samples with g values of g 1 ¼ 2:008160:0002; g 2 ¼ 2:005460:0002; g 3 ¼ 2:000360:0002; g 4 ¼ 2:002660:0002, and g 5 ¼ 2:002960:0002. Variation of the Al 2 O 3 layer thickness shows that paramagnetic species associated with g 1 , g 2 , and g 3 are located at the Si=Al 2 O 3 interface, and those with g 4 and g 5 are located within the bulk Al 2 O 3 . Furthermore, g 1 , g 2 , and g 3 were shown to originate from oxygen plasma exposure during Al 2 O 3 deposition. Comparing the g values and their location within the Si=Al 2 O 3 system, g 1 and g 3 can be attributed to P b0 centers, g 3 to Si dangling bonds (Si-dbs), and g 4 and g 5 to rotating methyl radicals. All paramagnetic moments observed in this contribution disappear after a 5-min temperature treatment at 450 C. The deposition of an additional thermal SiO 2 layer between the Si and the Al 2 O 3 decreases the negative fixed charge density and defect density by about one order of magnitude. In this contribution, these changes can be correlated with a decrease in amplitude of the Si-db signal. P b0 and the methyl radical signals were less affected by this additional SiO 2 layer. Based on these observations, microscopic models for the negative fixed charge density (Q tot ) and the interface trap density (D it ) and the connection between these values are proposed. Published by AIP Publishing. [http://dx

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The Application of Diffuse Reflectance Infrared Spectroscopy and Temperature-Programmed Desorption To Investigate the Interaction of Methanol on η-Alumina

Cited by 46 publications

References 43 publications

NOx reduction on a transition metal-free γ-Al2O3 catalyst using dimethylether (DME)

NOx reduction on a transition metal-free γ-Al2O3 catalyst using dimethylether (DME)

Oxidant‐Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid–Base Sites on Alumina

A study on Si/Al2O3 paramagnetic point defects

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