Spreading and Wetting

Knözinger, Helmut; Taglauer, E.

doi:10.1002/9783527610044.hetcat0027

Cited by 7 publications

(3 citation statements)

References 105 publications

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“…Therefore, the observed increase of the DMO conversion during the induction period and the decreased byproducts yield over time were related to the slow oxidation and spreading of highly dispersed Cu nanoparticles, increasing the metal-support interface, and leading to an increase of the DMO chemisorption and its hydrogenation rate to MG and EG. Such a behavior has been previously reported on Pd/Al2O3 catalysts after calcination [53,54] and could effectively decrease the density of vicinal metallic and acidic/basic sites and the rates of Guerbet and hydrodeoxygenation routes (Error! Reference source not found.).…”

Section: Figure 10 Here Figure 11 Here Figure 12 Heresupporting

confidence: 62%

Hydrogenation of dimethyl oxalate to ethylene glycol on Cu/SiO2 catalysts prepared by a deposition-decomposition method: Optimization of the operating conditions and pre-reduction procedure

et al. 2022

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Section: Figure 10 Here Figure 11 Here Figure 12 Heresupporting

confidence: 62%

Hydrogenation of dimethyl oxalate to ethylene glycol on Cu/SiO2 catalysts prepared by a deposition-decomposition method: Optimization of the operating conditions and pre-reduction procedure

et al. 2022

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“…Numerous experimental studies of MoO3 thermally induced dispergation over supports surface were undertaken [11]. They were focused on individual well defined SiO2 [12,13], Al2O3 [13][14][15][16] or mixed SiO2−Al2O3 [17,18] supports, siliceous [19][20][21] and aluminosilicate [15,16,22] molecular sieves.…”

Section: Introductionmentioning

confidence: 99%

“…The driving force for the bulk MoO3 spreading is the surface free energy which is lower for surface-dispersed species. Stabilisation of molybdena surface species occurs due to interaction with surface hydroxyl groups [11], In the case of dispersed supports like Al2O3, SiO2 or TiO2 the gas phase diffusion mechanism where Mo oxide clusters are evaporated from MoO3 crystallites with subsequent dispergation in monomeric state on the support surface was proposed [26,27]. The diffusion process of MoO3 on oxide thin films (Al2O3, SiO2, TiO2) was also investigated.…”

Section: Introductionmentioning

confidence: 99%

Quantum chemical simulation of MoO3 dispergation on hydroxylated SiO2 surface

et al. 2021

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Метою даної роботи є оцінка енергетичної сприятливості утворення різних молібдатних груп (≡Si‑O‑)2Mo(=O)2 та =Si(‑O‑)2Mo(=O)2 під час термічно ініційованого диспергування MoO3 на гідроксильованій поверхні SiO2. Для цього було здійснено квантовохімічне моделювання реакції O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O в температурному інтервалі 300–1100 K із використанням обмеженого методу Хартрі-Фока (наближення ЛКАО) з валентним базисом SBKJC (Stevens-Basch-Krauss-Jasien-Cundari). Кластер O12Si10(OH)16, який являє собою структурний фрагмент кристала β‑кристобаліту, був використаний як модель високогідроксильованої поверхні кремнезему. Ми розглянули дві структури молібдатних груп (≡Si‑O‑)2Mo(=O)2, прикріплених до кремнеземного кластера O12Si10(OH)16 через силанольні групи. Молібдатні групи (Etot ‑584.60147 Hartree), прикріплені до кремнеземного кластера через віддалені силанольні групи, виявляються більш енергетично вигідними, ніж молібдатні групи (Etot ‑584.56565 Hartree), прикріплені до кремнеземного кластера через сусідні силанольні групи. Енергія молібдатних груп =Si(‑O‑)2Mo(=O)2 (Etot ‑584.48399 Hartree), прикріплених до кремнеземного кластера O12Si10(OH)16 через силандіольні групи, менш енергетично вигідні в порівнянні з подібними групами, прикріпленими через силанольні групи, через більше напруження кута між зв’язками. Знайдено, що реакція O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O в температурному інтервалі 300–1100 K, змодельована шляхом квантовохімічних розрахунків, свідчить, що процес диспергування MoO3 на гідроксильованій поверхні SiO2 є енергетично вигідним. Експ The aim of the present work is to evaluate the energetic favourability of the formation of different molybdate species (≡Si‑O‑)2Mo(=O)2 and =Si(‑O‑)2Mo(=O)2 during the thermally induced MoO3 dispergation on hydroxylated SiO2 surface. In order to do this a quantum chemical modelling of the reaction O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O within the temperature interval of 300–1100 K was undertaken using the Restricted Hartree-Fock method (the LCAO approximation) with the SBKJC (Stevens-Basch-Krauss-Jasien-Cundari) valence basis set. The cluster O12Si10(OH)16 which represents a structural fragment of a β‑cristobalite crystal was used in this work as a model of highly hydroxylated silica surface. We considered two structures of molybdate (≡Si‑O‑)2Mo(=O)2 species attached to O12Si10(OH)16 silica cluster via silanol groups. Molybdate species (Etot ‑584.60147 Hartree) attached to silica cluster via distant silanols appeared more energetically favourable than molybdate species (Etot ‑584.56565 Hartree) attached to silica cluster via nearby silanols. The energy of molybdate =Si(‑O‑)2Mo(=O)2 species (Etot ‑584.48399 Hartree) attached to O12Si10(OH)16 silica cluster via silanediol group is less favourable energetically in comparison with those attached via silanol groups because of higher bond angle straining. The reaction O12Si10(OH)16 + MoO3 = O12Si10(OH)14O2MoO2 + H2O in the temperature interval of 300–1100 K which simulates by quantum chemical calculations the dispergation of MoO3 on hydroxylated SiO2 surface was found to be energetically favourable. The experimentally optimised temperature of ca. 800 K required for dispergation of MoO3 on hydroxylated SiO2 surface is determined by MoO3 evaporation and transportation via the gas phase. ериментальна оптимальна температура (близько 800 K), потрібна для диспергування MoO3 на гідроксильованій поверхні SiO2, визначається випаровуванням та перенесенням MoO3 в газовій фазі.

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Impact of Calcination Temperature on Tungsten‐based Composite Catalysts for Olefins Metathesis

Wei,

Zhang,

Zhang

et al. 2023

ChemCatChem

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The thermal treatment is one of the key procedures for the distribution and transformation of active sites for the supported metal oxide catalysts. However, the underlying impacts of thermal treatment on composite supported catalysts receives limited attention due to the additional complexity of the composite support. In this work, the progressive gradient in the metathesis activity, as the function of enhanced calcination temperature, has been observed for the tungsten‐based catalysts supported on the hierarchical ZSM‐5 zeolite‐alumina composite. The metathesis activity, reflected by ethene conversion, undergoes a stepwise growth from 24.2% to 38.9% along with the enhanced calcination temperature from 723 K to 923 K. The supported W‐oxo species share high similarity in structural states except their interaction with the Brønsted acidic bridge hydroxyl groups in zeolite. The density of bridge hydroxyl groups is reduced as the function of enhanced calcination temperatures, which reflects the intensified anchoring of surface W‐oxo species. It should be noted that such dependence is not observed for their counterparts based on microporous ZSM‐5 zeolite‐alumina. These sharp comparisons highlight the critical routes of thermal migration of W‐oxo species along the intrazeolite‐alumina interface in the evolution of active sites for the olefins cross‐metathesis reaction.

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Spreading and Wetting

Abstract: The sections in this article are Introduction Theoretical Considerations Thermodynamics of Wetting and Spreading Qualitative Discussion of the Dynamics of Interfacial Processes Supported Metal Catalysts Sintering and Redispersion Strong Metal Support Interacti… Show more

Cited by 7 publications

References 105 publications

Hydrogenation of dimethyl oxalate to ethylene glycol on Cu/SiO2 catalysts prepared by a deposition-decomposition method: Optimization of the operating conditions and pre-reduction procedure

Hydrogenation of dimethyl oxalate to ethylene glycol on Cu/SiO2 catalysts prepared by a deposition-decomposition method: Optimization of the operating conditions and pre-reduction procedure

Quantum chemical simulation of MoO3 dispergation on hydroxylated SiO2 surface

Impact of Calcination Temperature on Tungsten‐based Composite Catalysts for Olefins Metathesis

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