Influence of Hydronium Ions in Zeolites on Sorption

Eckstein, Sebastian; Hintermeier, Peter H.; Zhao, Ruixue; Baráth, Eszter; Shi, Hui; Liu, Yue; Lercher, Johannes A.

doi:10.1002/anie.201812184

Cited by 98 publications

(194 citation statements)

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“…This maximum water loading at operating conditions was estimated using an in‐house developed thermodynamic model for the adsorption of guest species in nanoporous materials . Furthermore, there is quite some experimental work available on how the water loadings depend on the acid site density, water vapor pressure and temperature in H‐ZSM‐5 and for which some interesting analogies can be found with our work . Secondly, as there is a high probability to find two silicon atoms in the next nearest neighbor position in SAPO materials, we introduced a second acid site in the unit cell, as was done in our earlier work .…”

Section: Introductionmentioning

confidence: 99%

“…[13,68] Furthermore, there is quite some experimental work available on how the water loadings depend on the acid site density, water vapor pressure and temperature in H-ZSM-5 and for which some interesting analogies can be found with our work. [69][70][71][72][73] Secondly, as there is a high probability to find two silicon atoms in the next nearest neighbor position in SAPO materials, we introduced a second acid site in the unit cell, [74,75] as was done in our earlier work. [36,52] Note that the schematic representation shown in Figure 2 corresponds to starting structures.…”

Section: Introductionmentioning

confidence: 99%

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Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

et al. 2019

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The methylation of hexamethylbenzene with methanol is one of the key reactions in the methanol‐to‐olefins hydrocarbon pool reaction cycle taking place over the industrially relevant H‐SAPO‐34 zeolite. This methylation reaction can occur either via a concerted or via a stepwise mechanism, the latter being the preferred pathway at higher temperatures. Herein, we systematically investigate how a complex reaction environment with additional water molecules and higher concentrations of Brønsted acid sites in the zeolite impacts the reaction mechanism. To this end, first principle molecular dynamics simulations are performed using enhanced sampling methods to characterize the reactants and products in the catalyst pores and to construct the free energy profiles. The most prominent effect of the dynamic sampling of the reaction path is the stabilization of the product region where water is formed, which can either move freely in the pores of the zeolite or be stabilized through hydrogen bonding with the other protic molecules. These protic molecules also stabilize the deprotonated Brønsted acid site, created due to the formation of the heptamethylbenzenium cation, via a Grotthuss‐type mechanism. Our results provide fundamental insight in the experimental parameters that impact the methylation of hexamethylbenzene in H‐SAPO‐34, especially highlighting and rationalizing the crucial role of water in one of the main reactions of the aromatics‐based reaction cycle.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

et al. 2019

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“…Ah igher Brønsted acidity was found for protons associatedw ith Si-O-Al linkages compared to those located at Al-O-Al linkages. As ac onsequence, the Si-O-All inkages were found to be deprotonated in AIMD simulations of hydrated models, leadingt ot he formation of protonated water clusters (= hydratedh ydronium ions [12] )i n the pores. Framework deprotonation was not observed for non-Lçwenstein linkages.…”

Section: Introductionmentioning

confidence: 90%

Proton Acidity and Proton Mobility in ECR‐40, a Silicoaluminophosphate that Violates Löwenstein's Rule

Fischer

2019

Chemistry A European J

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The silicoaluminophosphate zeotype ECR-40 contains linkages of AlO 4 tetrahedra via ac ommon oxygen atom, therebyv iolating the famous" Lçwenstein'sr ule". In this work, ac ombinationo fs tatic density functional theory (DFT) calculations and DFT-based ab-initio molecular dynamics (AIMD) simulations were employed to study the acidity and mobility of protons associated with such unusual linkages. It was found that the Al-O-Al linkages are preferentially protonated, as deprotonationc auses al ocal accumulationo f negative charge. The protons at these linkages possess a somewhat lower Brønsted acidity than those at Si-O-All inks. AIMD simulations for fully hydrated ECR-40 predicted ap artial deprotonation of the Al-O-Al linkages, whereas Si-O-Al linkagesw ere fully deprotonated. Frequently,acoordination of water molecules to framework Al atomsw as observed in the vicinity of the Al-O-Al links. Hence, these linkages appear prone to break upon dehydration, potentially explaining why Lçwenstein's rule is mostly obeyed in materials formed in aqueous media.[a] Dr.

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“…Ison and Gorte studied water adsorption on a HZSM‐5 with SAR = 70 via temperature programmed desorption (TPD), thermogravimetric analysis (TGA), and transmission infrared spectroscopy (IR), and found clusters of up to 5.3 waters per Al at 306 K. An adsorption energy of 12.1 kcal/mol and 8.2 kcal/mol was calculated for 0.7 and 2.0 waters per Al, respectively, leading to the conclusion that the first water forming a hydronium ion, H 3 O + , at the acid sites is more strongly held than subsequent waters that form clusters. Eckstein et al, also reported that water adsorption on HZSM‐5 is proportional to the Al content showing a maximum of 7 waters per Brønsted acid site …”

Section: Introductionmentioning

confidence: 99%

Quantification of Brønsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

et al. 2020

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The many studies that have been conducted on water adsorption on zeolites were carried out in "adsorption" mode, from adsorption isotherms or single-point measurements, with the samples being first degassed at high temperature, and then exposed to water vapor at variable partial pressure. Here, we report Thermogravimetric Analysis (TGA) studies of HZSM-5 saturated with water at room temperature, thus studying water adsorption in "desorption" mode. TGA was used to ascertain the amount of water remaining as a function of the pretreatment temperature, and to identify the temperature at which one water molecule per framework Al atom persists. 1860 Ison and Gorte studied water adsorption on a HZSM-5 with SAR = 70 via temperature programmed desorption (TPD), thermogravimetric analysis (TGA), and transmission infrared spectroscopy (IR), [8] and found clusters of up to 5.3 waters per Al at 306 K. An adsorption energy of 12.1 kcal/mol and 8.2 kcal/mol was calculated for 0.7 and 2.0 waters per Al, respectively, leading to the conclusion that the first water forming a hydronium ion, H 3 O + , at the acid sites is more strongly held than subsequent waters that form clusters. Eckstein et al., also reported that water adsorption on HZSM-5 is proportional to the Al content showing a maximum of 7 waters per Brønsted acid site. [9] All these previous works studied water in "adsorption" mode, from adsorption isotherms or single-point measurements whereby the samples were first degassed at high temperature and then exposed to water vapor at variable partial pressure. Herein, we report TGA studies of HZSM-5 samples of varying SAR saturated with water at room temperature using tempera-Carlos Bornes is a PhD student at CICECO -Aveiro Institute of Materials, University of Aveiro. He obtained his M. Sc. in 2017 from the Department of Chemistry, University of Aveiro, working on the characterization of zeolites by solid-state NMR spectroscopic methods. His current line of research is the characterization of the acid properties of zeolites using solid-state NMR and computational methods. Jeffrey Amelse received a B.Mark Peacock works at BP since 1998 in a range of catalysis development roles & focuses on advanced catalyst characterisation since 2008, primarily focusing on powder X-ray diffraction, In-situ pXRD as well as thermal analysis (TGA) and combustion elemental analysis. His experience covers a range of zeolite catalysts, binders as well and many heterogeneous metal/ metal oxide based systems. Christopher L. Marshall is a senior research chemist in the Catalysis Science Group of the Chemical Sciences and Engineering Division at Argonne. His research concentrates on the synthesis, testing and in situ characterization of refining, chemical and biomass conversion catalysts. Synthesis work has recently concentrated on the use of atomic layer deposition for stabilization and improved performance of supported catalysts. Michael M. Schwartz, now retired, obtained his Ph.D. (1970) at Florida State University. . His current research inter...

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Influence of Hydronium Ions in Zeolites on Sorption

Abstract: Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Cited by 98 publications

References 32 publications

Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

Insight into the Role of Water on the Methylation of Hexamethylbenzene in H‐SAPO‐34 from First Principle Molecular Dynamics Simulations

Proton Acidity and Proton Mobility in ECR‐40, a Silicoaluminophosphate that Violates Löwenstein's Rule

Quantification of Brønsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

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