Kinetics of the bimolecular ether formation from alcohols over alumina*1

Knözinger, Helmut; Kochloefl, K.; Meye, Wolfgang

doi:10.1016/0021-9517(73)90180-2

Cited by 59 publications

(11 citation statements)

References 6 publications

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“…The influence of water on dehydration reactions was shown to be decisive in many previous publications and is often considered as a poison 34 or as an inhibitor of the reaction. 15,25,71,72 Our study suggests that two effects of water can be expected:…”

Section: Discussionmentioning

confidence: 87%

Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production

et al. 2015

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Alcohol dehydration is of prominent relevance in the context of biomass conversion. This reaction can be efficiently catalyzed by alumina surfaces, but the nature of active sites, the mechanisms involved, and the key parameters to tune both the activity and the alkene/ether selectivity remain a matter of debate. In the present paper, isopropanol dehydration to propene and diisopropylether over γ-alumina, δ-alumina, and sodium-poisoned γ-alumina was investigated through a combined experimental and theoretical study. The experimental kinetic study shows that dehydration occurs following the same reaction mechanism on all materials, although γ-alumina activated above 450°C exhibits the highest density of active sites and the highest global activity. Results suggest that all the reaction pathways involved in dehydration require the same set of adjacent active sites located on the (100) facets of γ-alumina. DFT transition-state calculations of the formation of propene and diisopropylether on the main terminations of alumina, (110) and (100), were also performed. The less activated pathways for both the formation of the olefin (E2 mechanism) and the formation of the ether (S N 2 mechanism) were found on a Al V Lewis acidic site of the (100) termination, with calculated activation enthalpies (125 and 112 kJ·mol −1 for propene and diisopropylether formation, respectively) in good agreement with the experimental values (128 and 118 kJ·mol −1 , respectively). The higher or lesser selectivity toward propene or ether appears to originate from significantly different activation entropies. The effect of coadsorbed sodium on the reaction is linked to the poisoning of Al sites by neighboring, Na-stabilized OH groups, but no influence of sodium on distant sites is evidenced. Reaction temperature is identified as the main key parameter to tune alkene/ ether selectivity rather than morphology effects, which in turn affect drastically the number of available active sites, and thus catalytic activity.

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Section: Discussionmentioning

confidence: 87%

Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production

et al. 2015

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“…9a). While the former feature has been assigned to linear (type-I) OH species, the latter one is characteristics for three-fold (type-III) hydroxyls [35][36][37][38][39][40][41][42] which disappear from the surface upon interaction/coordination with adsorbed nitrates and nitrites. Another broad and highly convoluted feature centered at 3512 cm −1 can be attributed to H-bonded surface hydroxyl species [38,39].…”

Section: No X Reduction On Binary and Ternary Oxide Systems Via H 2 (G)mentioning

confidence: 99%

NOx storage and reduction pathways on zirconia and titania functionalized binary and ternary oxides as NOx storage and reduction (NSR) systems

2014

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a b s t r a c tBinary and ternary oxide materials, ZrO 2 /TiO 2 (ZT) and Al 2 O 3 /ZrO 2 /TiO 2 (AZT), as well as their Ptfunctionalized counterparts were synthesized and characterized via XRD, Raman spectroscopy, BET, in situ FTIR and TPD techniques. In the ZT system, a strong interaction between TiO 2 and ZrO 2 domains at high temperatures (>973 K) resulted in the formation of a low specific surface area (i.e. 26 m 2 /g at 973 K) ZT material containing a highly ordered crystalline ZrTiO 4 phase. Incorporation of Al 2 O 3 in the AZT structure renders the material highly resilient toward crystallization and ordering. Alumina acts as a diffusion barrier in the AZT structure, preventing the formation of ZrTiO 4 and leading to a high specific surface area (i.e. 264 m 2 /g at 973 K). NO x adsorption on the AZT system was found to be significantly greater than that of ZT, due to almost ten-fold greater SSA of the former surface. While Pt incorporation did not alter the type of the adsorbed nitrate species, it significantly boosted the NO x adsorption on both Pt/ZT and Pt/AZT systems. Thermal stability of nitrates was higher on the AZT compared to ZT, most likely due to the defective structure and the presence of coordinatively unsaturated sites on the former surface. Pt sites also facilitate the decomposition of nitrates in the absence of an external reducing agent by shifting the decomposition temperatures to lower values. Presence of Pt also enhances partial/complete NO x reduction in the absence of an external reducing agent and the formation of N 2 and N 2 O. In the presence of H 2 (g), reduction of surface nitrates was completed at 623 K on ZT, while this was achieved at 723 K for AZT. Nitrate reduction over Pt/ZT and Pt/AZT via H 2 (g) under mild conditions initially leads to conversion of bridging nitrates into monodentate nitrates/nitrites and the formation of surface OH and NH x functionalities. N 2 O(g) was also continuously generated during the reduction process as an intermediate/byproduct.

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“…The 6-311+G* basis set was used for H, C, O, and Al atoms, and the 6-31G* basis set was used for Si. The reactive site of the TMA-saturated Al 2 O 3 surface was modeled with a −CH 3 group bound to a trivalent Al on a hydroxyl-terminated Si(100)-like Si 15 H 16 cluster (Si 15 H 18 O 2 AlCH 3 ). , The transition state geometries were optimized using the synchronous transit-guided quasi-Newton (QST3) method as implemented in Gaussian 09, and then they were confirmed after optimization to obtain an imaginary vibrational frequency along the reaction coordinate.…”

Section: Methodsmentioning

confidence: 99%

“…In addition to Si technology, the oxidation of the channel layer during the ALD process can be a critical issue for two-dimensional (2D) transition-metal dichalcogenide (TMDC)-based field effect transistors (FETs) because of its atomic thickness. To obtain high-performance 2D FETs, ALD high- k dielectrics have been widely adopted because ALD provides ultrathin films with high density and free of pinholes on the 2D channel layer. − However, in previous results, oxidation of the 2D channel layer was observed in ALD oxidants such as H 2 O and O 3 , which considerably degraded device performance. , Furthermore, some previous studies have shown that H 2 O vapor under ambient conditions can degrade the long-term stability of organic–inorganic hybrid-based perovskite solar cells (PSCs) and organic light-emitting diodes (OLEDs) . To impede the degradation of PSCs and OLEDs, an ALD-deposited passivation layer was adopted, and the long-term stability of the PSCs and OLEDs with an ALD passivation layer was improved. − However, the exposed H 2 O molecules during the thermal ALD process can cause degradation due to undesirable reactions with PSCs and OLEDs.…”

Section: Introductionmentioning

confidence: 99%

Reaction Mechanisms of Non-hydrolytic Atomic Layer Deposition of Al₂O₃ with a Series of Alcohol Oxidants

et al. 2021

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Atomic layer deposition (ALD) of Al 2 O 3 using trimethylaluminum (TMA) and H 2 O is the most widely and deeply studied ALD process owing to the superior properties of the deposited Al 2 O 3 thin films and usability of TMA and H 2 O. However, H 2 O can cause undesirable substrate oxidation during ALD. While previous studies have shown that alcohol oxidants can be used to deposit Al 2 O 3 thin films with less substrate oxidation, the reaction mechanism of ALD Al 2 O 3 with alcohol oxidants has not been elucidated yet. In this study, the reaction mechanism of ALD of Al 2 O 3 thin films using various alcohol oxidants was systematically investigated by computational and experimental methods. Various possible reaction pathways are considered for the oxidation of Al−CH 3 with methanol (MeOH), ethanol (EtOH), and propanol (n-PrOH). It is found that the feasible reaction mechanism for removal of the surface-adsorbed alkoxy group is autocatalytic liberation of alkene through β-hydrogen transfer. ALD processes were developed using the alcohol oxidants. Our process using EtOH showed a growth rate of 0.96 Å/cycle and a moderate level of carbon impurities (2.6%). In addition, we investigated the properties of ALD-deposited Al 2 O 3 thin films with alcohol oxidants, which indicated superior electrical properties and decreased formation of interfacial oxide on the Si substrate.

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Kinetics of the bimolecular ether formation from alcohols over alumina*1

Cited by 59 publications

References 6 publications

Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production

Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production

NOx storage and reduction pathways on zirconia and titania functionalized binary and ternary oxides as NOx storage and reduction (NSR) systems

Reaction Mechanisms of Non-hydrolytic Atomic Layer Deposition of Al₂O₃ with a Series of Alcohol Oxidants

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Kinetics of the bimolecular ether formation from alcohols over alumina*1

Cited by 59 publications

References 6 publications

Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production

Mechanistic Investigation of Isopropanol Conversion on Alumina Catalysts: Location of Active Sites for Alkene/Ether Production

NOx storage and reduction pathways on zirconia and titania functionalized binary and ternary oxides as NOx storage and reduction (NSR) systems

Reaction Mechanisms of Non-hydrolytic Atomic Layer Deposition of Al2O3 with a Series of Alcohol Oxidants

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Reaction Mechanisms of Non-hydrolytic Atomic Layer Deposition of Al₂O₃ with a Series of Alcohol Oxidants