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Stian Svelle - One of the best experts on this subject based on the ideXlab platform.
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Collective action of water molecules in zeolite Dealumination
Catalysis Science & Technology, 2019Co-Authors: Malte Nielsen, Pablo Beato, Anders Hafreager, Rasmus Y. Brogaard, Kristof De Wispelaere, Hanne Falsig, Veronique Van Speybroeck, Stian SvelleAbstract:When exposed to steam, zeolite catalysts are irreversibly deactivated by loss of acidity and framework degradation caused by Dealumination. Steaming typically occurs at elevated temperatures, making it challenging to investigate the mechanism with most approaches. Herein, we follow the dynamics of zeolite Dealumination in situ, in the presence of a realistic loading of water molecules by means of enhanced sampling molecular dynamics simulations. H-SSZ-13 zeolite is chosen as a target system. Monte Carlo simulations predict a loading of more than 3 water molecules per unit cell at representative steaming conditions (450 °C, 1 bar steam). Our results show that a higher water loading lowers the free energy barrier of Dealumination, as water molecules cooperate to facilitate hydrolysis of Al–O bonds. We find free energies of activation for Dealumination that agree well with the available experimental measurements. Clearly, the use of enhanced sampling molecular dynamics yields a major step forward in the molecular level understanding of the Dealumination; insight which is very hard to derive experimentally.
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On How Copper Mordenite Properties Govern the Framework Stability and Activity in the Methane-to-Methanol Conversion
2018Co-Authors: Michael Dyballa, Dimitrios K. Pappas, Karoline Kvande, Elisa Borfecchia, Bjørnar Arstad, Pablo Beato, Unni Olsbye, Stian SvelleAbstract:Herein we investigated the activity of copper mordenites in the methane-to-methanol conversion and the material de- and realumination. From four parent materials, a library of copper mordenites was synthesized by liquid- and solid-state ion-exchange techniques. Two key properties govern the activity of these materials in the methane conversion: the parent counterion and the copper ion-exchange procedure. H-form parents result in more active materials. The optimum stoichiometry between silicon, aluminum, and copper leads to a methanol productivity of up to 169 μmol/g. This equals a stoichiometry of up to 0.47 methanol molecules formed per copper atom. The methanol productivity is constant over up to three cycles. The stability of the mordenite framework was monitored by SEM, EDX, 27Al, and 29Si MAS NMR spectroscopy. No detectable copper nanoparticles formed. However, a Dealumination of the mordenite framework and the formation of extra-framework aluminum (EFAl) species in quantities of up to 12% were observed on H-form copper mordenites. The Dealumination is weak or completely inhibited if counterions like Na+ or Cu2+ are present. These ions stabilize the framework aluminum during the reaction steps and upon heat treatments. Notably, the most active materials have significant EFAl contents present
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kinetics of zeolite Dealumination insights from h ssz 13
ACS Catalysis, 2015Co-Authors: Malte Nielsen, Pablo Beato, Rasmus Y. Brogaard, Hanne Falsig, Ole Swang, Stian SvelleAbstract:When zeolite catalysts are subjected to steam at high temperatures, a permanent loss of activity happens, because of the loss of aluminum from the framework. This Dealumination is a complex process involving the hydrolysis of four Al–O bonds. This work addresses the Dealumination from a theoretical point of view, modeling the kinetics in zeolite H-SSZ-13 to gain insights that can extend to other zeolites. We employ periodic density functional theory (DFT) to obtain free-energy profiles, and we solve a microkinetic model to derive the rates of Dealumination. We argue that such modeling should consider water that has been physisorbed in the zeolite as the reference state and propose a scheme for deriving the free energy of this state. The results strongly suggest that the first of the four hydrolysis steps is insignificant for the kinetics of zeolite Dealumination. Furthermore, the results indicate that, in H-SSZ-13, it is sufficient to include only the fourth hydrolysis step when estimating the rate of dea...
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mechanistic comparison of the Dealumination in ssz 13 and the desilication in sapo 34
Journal of Physical Chemistry C, 2013Co-Authors: Torstein Fjermestad, Stian Svelle, Ole SwangAbstract:With the purpose of understanding the behavior of aluminosilicate zeolites and silicoaluminophosphates (SAPOs) in the presence of steam, we carried out a computational density functional theory (DFT) study on the desilication of SAPO-34. The mechanism studied was a stepwise hydrolysis of the four bonds to the Si heteroatom. An analogous process to the desilication of SAPO-34 is the Dealumination of SSZ-13. To investigate possible mechanistic differences between the two processes, we compared the results of this study with the results of a previous study on Dealumination in SSZ-13. We found that the intermediates along the Dealumination path of SSZ-13 have one of the protons bonded to a bridging oxygen atom. In the corresponding intermediates of the desilication path in SAPO-34, the same proton prefers to be part of an aqua ligand coordinated to an Al atom. The principal factor determining the different proton locations is the electronic requirement of the atoms surrounding the proton. The different proton...
Zhongmin Liu - One of the best experts on this subject based on the ideXlab platform.
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Influence of Al Coordinates on Hierarchical Structure and T Atoms Redistribution during Base Leaching of ZSM‑5
2018Co-Authors: Min Liu, Xinwen Guo, Yingxu Wei, Zhongmin Liu, Shu Zeng, Chunshan SongAbstract:Al coordinates in ZSM-5 showed significant effects on hierarchical structure and T atoms redistribution during NaOH/TPAOH treatment and different catalytic performances in the methanol-to-propylene reaction. NaOH treatment of parent ZSM-5 with a few extra-framework Al sites mainly involved the desilication process, while an additional alumination process was observed when some Al3+ was added into the NaOH solution, which resulted in mesoporous crystals with intact outer shells. Dealumination–realumination and desilication processes occurred with ZSM-5 with distorted four-coordinate, five-coordinate, or six-coordinate Al sites. For TPAOH treatment, the desilication–recrystallization process occurred with parent ZSM-5 and resulted in hollow crystals with ultrasilica shells via Si redistribution, consequently 2.5 times the lifetime of parent ZSM-5 by restricting external coke deposition. By comparison, desilication, Dealumination, and (Si, Al)-recystallization were observed for ZSM-5 with distorted four-coordinate Al sites, involving both Si and Al atoms redistribution processes resulting in abundant mesopores and a high-silica outer surface, which showed almost 5 times the lifetime of parent ZSM-5
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Interconnected Hierarchical ZSM-5 with Tunable Acidity Prepared by a Dealumination–Realumination Process: A Superior MTP Catalyst
ACS applied materials & interfaces, 2017Co-Authors: Min Liu, Xinwen Guo, Yingxu Wei, Zhongmin Liu, Chunshan SongAbstract:ZSM-5 that uses TPAOH as a template has an Al-rich exterior and defective Si-rich interior; thus, a simple base leaching selectively removed the Si-rich interior while the Al-rich exterior was protected. This catalyst showed no change in stability comparing with parent ZSM-5 during the MTP reaction that was attributed to the enclosed hollow structure and richly acidic outer shell. A preliminary fluorination, however, both removed defective Si-sites and caused distortion in tetrahedral aluminum that made the outer shell susceptible to alkaline treatment. These distorted tetrahedral Al were mostly leached out by NaOH in 1 min. Furthermore, aluminum in the filtrate was slowly redeposited onto the zeolite, serving as external pore-directing agents to control silicon dissolution from the Si-rich interior. This Dealumination-realumination alkaline treatment process led to a higher solid yield and a uniform opened-mesopore structure with mesopores around 13 nm in diameter. This material was characterized by SEM, TEM, N2 adsorption, and mercury porosimetry. In addition, NH3-TPD, OH-IR, 27Al MAS NMR, and 1H MAS NMR results demonstrated that the reinserted Al were unlike the framework Al, contributing less to acidity. The Dealumination-realumination process, therefore, was also capable of tuning the acidity of the mesoporous ZSM-5. This mesoporous catalyst exhibited a longer lifetime and a higher propylene selectivity than other catalysts with an enclosed mesopore structure.
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interconnected hierarchical zsm 5 with tunable acidity prepared by a Dealumination realumination process a superior mtp catalyst
ACS Applied Materials & Interfaces, 2017Co-Authors: Min Liu, Xinwen Guo, Yingxu Wei, Zhongmin Liu, Chunshan SongAbstract:ZSM-5 that uses TPAOH as a template has an Al-rich exterior and defective Si-rich interior; thus, a simple base leaching selectively removed the Si-rich interior while the Al-rich exterior was protected. This catalyst showed no change in stability comparing with parent ZSM-5 during the MTP reaction that was attributed to the enclosed hollow structure and richly acidic outer shell. A preliminary fluorination, however, both removed defective Si-sites and caused distortion in tetrahedral aluminum that made the outer shell susceptible to alkaline treatment. These distorted tetrahedral Al were mostly leached out by NaOH in 1 min. Furthermore, aluminum in the filtrate was slowly redeposited onto the zeolite, serving as external pore-directing agents to control silicon dissolution from the Si-rich interior. This Dealumination–realumination alkaline treatment process led to a higher solid yield and a uniform opened-mesopore structure with mesopores around 13 nm in diameter. This material was characterized by SEM,...
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On the acid-Dealumination of USY zeolite: a solid state NMR investigation
Journal of Molecular Catalysis A-chemical, 2002Co-Authors: Zhimin Yan, Jianqin Zhuang, Xianchun Liu, Xiumei Liu, Xiuwen Han, Xinhe Bao, Fuxiang Chang, Zhongmin LiuAbstract:The Dealumination of USY (ultrastable Y) zeolites by nitric acid and oxalic acid treatment was systematically investigated by multinuclear solid-state NMR and MQ MAS NMR experiments. The results show that both acids are very effective in removing non-framework Al as well as framework Al but that aluminum is extracted from the lattice at a higher rate by oxalic acid even at low concentrations. The presence of different species (e.g. silanol nest, Al–OH, four-coordinated framework Al, six-coordinated framework Al, six-coordinated non-framework Al and five-coordinated non-framework Al) was detected, and their changes were followed during the Dealumination. The investigation gives evidence that the breakdown of the parent USY zeolite mainly depends on the degree of Dealumination and that non-framework Al exerts a great effect on the acidity of the USY zeolite. Leaching-induced increase in the Bronsted acidity of the USY zeolite was also observed by 1 H MAS NMR spectroscopy. The different distribution of Al species in these samples accounted for the different catalytic performance of n-dodecane cracking. © 2002 Published by Elsevier Science B.V.
Roel Prins - One of the best experts on this subject based on the ideXlab platform.
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Dealumination and realumination of microcrystalline zeolite beta an xrd ftir and quantitative multinuclear mq mas nmr study
Physical Chemistry Chemical Physics, 2004Co-Authors: Anna Omegna, Milena Vasic, Jeroen A Van Bokhoven, Gerhard D Pirngruber, Roel PrinsAbstract:Zeolite beta was dealuminated by treatment with hydrochloric acid and realuminated by reaction of the dealuminated zeolite beta with aluminium isopropoxide at room temperature. FTIR and 1H MAS NMR spectroscopy showed that the extent of the generated Bronsted acidity was similar to that of the parent material before Dealumination. The distribution of aluminium in zeolite beta and in dealuminated and realuminated zeolite beta was investigated by means of multiple quantum (MQ) 27Al MAS NMR spectroscopy. Dealumination occurred preferentially at specific T-sites. Subsequent reaction with aluminium isopropoxide led to the preferential insertion of aluminium into the same crystallographic sites by the occupancy of the structural vacancies. The controlled amount of aluminium isopropoxide and dry conditions, under which the reaction took place, limited the formation of extraframework material to some extent.
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comparison of the Dealumination of zeolites beta mordenite zsm 5 and ferrierite by thermal treatment leaching with oxalic acid and treatment with sicl4 by 1h 29si and 27al mas nmr
Microporous and Mesoporous Materials, 2000Co-Authors: Melanie Muller, G Harvey, Roel PrinsAbstract:Abstract The Si/Al ratio of the framework and the number of defect sites in the framework of zeolites were investigated by means of solid state NMR investigations and elemental analysis before and after Dealumination of zeolites beta, ferrierite, mordenite and ZSM-5. Dealumination was performed by thermal treatment, complexation by oxalic acid and direct replacement of aluminum by silicon with gaseous silicon tetrachloride. The extent of Dealumination decreased in the same order as the number of T-sites in four-rings: beta>mordenite>ZSM-5>ferrierite. Considerable differences arising from the synthesis conditions for samples of the same zeolite type were also observed. 1 H MAS NMR showed that the extent of Dealumination increased with the number of Bronsted acid sites interacting with the zeolite framework, and 29 Si MAS NMR showed that at the same time the number of defect sites in the samples increased. Depending on the synthesis conditions, the framework is interrupted to different extents and, as a result, the framework becomes more flexible, thereby enabling interaction between Bronsted protons and oxygen atoms in the framework. Factors such as the zeolite structure type, the Si/Al ratio of the framework, the crystal size, and the number of Bronsted acid sites interacting with the framework or the number of defect sites influence the Dealumination behavior of an individual zeolite sample.
Chunshan Song - One of the best experts on this subject based on the ideXlab platform.
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Influence of Al Coordinates on Hierarchical Structure and T Atoms Redistribution during Base Leaching of ZSM‑5
2018Co-Authors: Min Liu, Xinwen Guo, Yingxu Wei, Zhongmin Liu, Shu Zeng, Chunshan SongAbstract:Al coordinates in ZSM-5 showed significant effects on hierarchical structure and T atoms redistribution during NaOH/TPAOH treatment and different catalytic performances in the methanol-to-propylene reaction. NaOH treatment of parent ZSM-5 with a few extra-framework Al sites mainly involved the desilication process, while an additional alumination process was observed when some Al3+ was added into the NaOH solution, which resulted in mesoporous crystals with intact outer shells. Dealumination–realumination and desilication processes occurred with ZSM-5 with distorted four-coordinate, five-coordinate, or six-coordinate Al sites. For TPAOH treatment, the desilication–recrystallization process occurred with parent ZSM-5 and resulted in hollow crystals with ultrasilica shells via Si redistribution, consequently 2.5 times the lifetime of parent ZSM-5 by restricting external coke deposition. By comparison, desilication, Dealumination, and (Si, Al)-recystallization were observed for ZSM-5 with distorted four-coordinate Al sites, involving both Si and Al atoms redistribution processes resulting in abundant mesopores and a high-silica outer surface, which showed almost 5 times the lifetime of parent ZSM-5
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Interconnected Hierarchical ZSM-5 with Tunable Acidity Prepared by a Dealumination–Realumination Process: A Superior MTP Catalyst
ACS applied materials & interfaces, 2017Co-Authors: Min Liu, Xinwen Guo, Yingxu Wei, Zhongmin Liu, Chunshan SongAbstract:ZSM-5 that uses TPAOH as a template has an Al-rich exterior and defective Si-rich interior; thus, a simple base leaching selectively removed the Si-rich interior while the Al-rich exterior was protected. This catalyst showed no change in stability comparing with parent ZSM-5 during the MTP reaction that was attributed to the enclosed hollow structure and richly acidic outer shell. A preliminary fluorination, however, both removed defective Si-sites and caused distortion in tetrahedral aluminum that made the outer shell susceptible to alkaline treatment. These distorted tetrahedral Al were mostly leached out by NaOH in 1 min. Furthermore, aluminum in the filtrate was slowly redeposited onto the zeolite, serving as external pore-directing agents to control silicon dissolution from the Si-rich interior. This Dealumination-realumination alkaline treatment process led to a higher solid yield and a uniform opened-mesopore structure with mesopores around 13 nm in diameter. This material was characterized by SEM, TEM, N2 adsorption, and mercury porosimetry. In addition, NH3-TPD, OH-IR, 27Al MAS NMR, and 1H MAS NMR results demonstrated that the reinserted Al were unlike the framework Al, contributing less to acidity. The Dealumination-realumination process, therefore, was also capable of tuning the acidity of the mesoporous ZSM-5. This mesoporous catalyst exhibited a longer lifetime and a higher propylene selectivity than other catalysts with an enclosed mesopore structure.
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interconnected hierarchical zsm 5 with tunable acidity prepared by a Dealumination realumination process a superior mtp catalyst
ACS Applied Materials & Interfaces, 2017Co-Authors: Min Liu, Xinwen Guo, Yingxu Wei, Zhongmin Liu, Chunshan SongAbstract:ZSM-5 that uses TPAOH as a template has an Al-rich exterior and defective Si-rich interior; thus, a simple base leaching selectively removed the Si-rich interior while the Al-rich exterior was protected. This catalyst showed no change in stability comparing with parent ZSM-5 during the MTP reaction that was attributed to the enclosed hollow structure and richly acidic outer shell. A preliminary fluorination, however, both removed defective Si-sites and caused distortion in tetrahedral aluminum that made the outer shell susceptible to alkaline treatment. These distorted tetrahedral Al were mostly leached out by NaOH in 1 min. Furthermore, aluminum in the filtrate was slowly redeposited onto the zeolite, serving as external pore-directing agents to control silicon dissolution from the Si-rich interior. This Dealumination–realumination alkaline treatment process led to a higher solid yield and a uniform opened-mesopore structure with mesopores around 13 nm in diameter. This material was characterized by SEM,...
Baojie Wang - One of the best experts on this subject based on the ideXlab platform.
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Desilication by Alkaline Treatment and Increasing the Silica to Alumina Ratio of Zeolite Y
Chinese Journal of Catalysis, 2012Co-Authors: Baojian Shen, Zhengxing Qin, Xionghou Gao, Feng Lin, Shuge Zhou, Shen Wen, Baojie Wang, Hongjuan Zhao, Honghai LiuAbstract:The framework silica to alumina ratio, the porosity, and the acidity properties of ultrastable Y zeolites prepared by ‘steaming’ and by the ‘sequential alkaline treatment and steaming’ of NaY zeolites are compared. The adaptability of the combined alkaline treatment method and steaming toward the type of starting NaY zeolites was studied. By comparison with single steaming treatment the combination of sequential alkaline treatment and steaming affords products with an obviously increased mesopore volume. The level of framework ultrastabilization and acidity of the final products were not affected. The mesopore volume of the ultrastable Y zeolite prepared by steaming Dealumination only was no more than 0.14 cm3/g. The mesopore volume of the final product prepared by sequential desilication and Dealumination was 0.22 cm3/g. The sequential desilication and Dealumination method is suitable for the NaY zeolite with a high framework silica to alumina ratio. A small increase in the mesopore volume and severe micropore damage were evident when the NaY zeolite with a relatively low silica to alumina ratio (SiO2/Al2O3 = 4.8, determined by nuclear magnetic resonance) was used as the starting material for the combined desilication and Dealumination treatment.
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Mesoporous Y zeolite with homogeneous aluminum distribution obtained by sequential desilication–Dealumination and its performance in the catalytic cracking of cumene and 1,3,5-triisopropylbenzene
Journal of Catalysis, 2011Co-Authors: Zhengxing Qin, Baojian Shen, Xionghou Gao, Feng Lin, Baojie WangAbstract:Abstract The aluminum–silicon distribution and mesoporosity of Y zeolites prepared by sequential NaOH desilication and ammonium hexafluorosilicate (AHFS) Dealumination are compared with that of Y samples prepared via AHFS Dealumination only. AHFS treatment led to severe non-uniform Dealumination and substantial surface silicon deposition. Y samples obtained by sequential desilication and Dealumination had substantially better Dealumination uniformity and aluminum–silicon distribution. The mesopore formation in these zeolites is discussed in detail. The desilication creates defects in the framework of the parent NaY zeolite. These defects improve the intra-crystalline transport and induce mesopore formation during Dealumination. The desilication- plus Dealumination-treated zeolites showed higher initial activity and lower deactivation tendency in the case of 1,3,5-triisopropylbenzene cracking, and higher conversion rate of cumene than those zeolites modified by AHFS treatment only. These catalytic data indicate that the former could be a viable catalyst in the catalytic cracking of heavy hydrocarbons.
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mesoporous y zeolite with homogeneous aluminum distribution obtained by sequential desilication Dealumination and its performance in the catalytic cracking of cumene and 1 3 5 triisopropylbenzene
Journal of Catalysis, 2011Co-Authors: Zhengxing Qin, Baojian Shen, Xionghou Gao, Feng Lin, Baojie WangAbstract:Abstract The aluminum–silicon distribution and mesoporosity of Y zeolites prepared by sequential NaOH desilication and ammonium hexafluorosilicate (AHFS) Dealumination are compared with that of Y samples prepared via AHFS Dealumination only. AHFS treatment led to severe non-uniform Dealumination and substantial surface silicon deposition. Y samples obtained by sequential desilication and Dealumination had substantially better Dealumination uniformity and aluminum–silicon distribution. The mesopore formation in these zeolites is discussed in detail. The desilication creates defects in the framework of the parent NaY zeolite. These defects improve the intra-crystalline transport and induce mesopore formation during Dealumination. The desilication- plus Dealumination-treated zeolites showed higher initial activity and lower deactivation tendency in the case of 1,3,5-triisopropylbenzene cracking, and higher conversion rate of cumene than those zeolites modified by AHFS treatment only. These catalytic data indicate that the former could be a viable catalyst in the catalytic cracking of heavy hydrocarbons.
