1
|
Bae J, Dusselier M. Synthesis strategies to control the Al distribution in zeolites: thermodynamic and kinetic aspects. Chem Commun (Camb) 2023; 59:852-867. [PMID: 36598011 DOI: 10.1039/d2cc05370e] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The activity and selectivity of acid-catalyzed chemistry is highly dependent on the Brønsted and Lewis acid sites generated by Al substitutions in a zeolite framework with the desired pore architecture. The siting of two Al atoms in close proximity in the framework of high-silica zeolites can also play a decisive role in improving the performance of redox catalysts by producing exchangeable positions for extra-framework multivalent cations. Thus, considerable attention has been devoted to controlling the Al incorporation through direct synthesis approaches and post-synthesis treatments to optimize the performance as (industrial) solid catalysts and to develop new acid- and redox-catalyzed reactions. This Feature Article highlights bottom-up synthetic strategies to fine-tune the Al incorporation in zeolites, interpreted with respect to thermodynamic and kinetic aspects. They include (i) variation in extra-framework components in zeolite synthesis, (ii) isomorphous substitution of other heteroatoms in the zeolite framework, and (iii) control over the (alumino)silicate network in the initial synthesis mixture via in situ and ex situ methods. Most synthetic approaches introduced here tentatively showed that the energy barriers associated with Al incorporation in zeolites can be variable during zeolite crystallization processes, occurring in complex media with multiple chemical interactions. Although the generic interpretation of each strategy and underlying crystallization mechanism remains largely unknown (and often limited to a specific framework), this review will provide guidance on more efficient methods to prepare fine-tuned zeolites with desired chemical properties.
Collapse
Affiliation(s)
- Juna Bae
- Center for Sustainable Catalysis and Engineering (CSCE), KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium.
| | - Michiel Dusselier
- Center for Sustainable Catalysis and Engineering (CSCE), KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium.
| |
Collapse
|
2
|
Ke Q, Khalil I, Smeyers B, Li Z, de Oliveira-Silva R, Sels B, Sakellariou D, Dusselier M. A Cooperative OSDA Blueprint for Highly Siliceous Faujasite Zeolite Catalysts with Enhanced Acidity Accessibility. Angew Chem Int Ed Engl 2021; 60:24189-24197. [PMID: 34478216 DOI: 10.1002/anie.202109163] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 08/31/2021] [Indexed: 11/10/2022]
Abstract
A cooperative OSDA strategy is demonstrated, leading to novel high-silica FAU zeolites with a large potential for disruptive acid catalysis. In bottom-up synthesis, the symbiosis of choline ion (Ch+ ) and 15-crown-5 (CE) was evidenced, in a form of full occupation of the sodalite (sod) cages with the trans Ch+ conformer, induced by the CE presence. CE itself occupied the supercages along with additional gauche Ch+ , but in synthesis without CE, no trans was found. The cooperation, and thus the fraction of trans Ch+ , was closely related to the Si/Al ratio, a key measure for FAU stability and acidity. As such, a bottom-up handle for lowering the Al-content of FAU and tuning its acid site distribution is shown. A mechanistic study demonstrated that forming sod cages with trans Ch+ is key to the nucleation of high-silica FAU zeolites. The materials showed superior performances to commercial FAU zeolites and those synthesized without cooperation, in the catalytic degradation of polyethylene.
Collapse
Affiliation(s)
- Quanli Ke
- Center for Sustainable Catalysis and Engineering, KU Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium.,Institute of Catalytic Reaction Engineering, College of Chemical Engineering, Zhejiang University of Technology, Chaowang Road 18, 310014, Hangzhou, China
| | - Ibrahim Khalil
- Center for Sustainable Catalysis and Engineering, KU Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium
| | - Brent Smeyers
- Center for Sustainable Catalysis and Engineering, KU Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium
| | - Zheng Li
- Department of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium
| | - Rodrigo de Oliveira-Silva
- Centre For Membrane Separations, Adsorption, Catalysis and Spectroscopy for Sustainable Solutions (cMACS), KU Leuven, Celestijnenlaan 200F, p.o. box 2454, 3001, Heverlee, Belgium
| | - Bert Sels
- Center for Sustainable Catalysis and Engineering, KU Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium
| | - Dimitrios Sakellariou
- Centre For Membrane Separations, Adsorption, Catalysis and Spectroscopy for Sustainable Solutions (cMACS), KU Leuven, Celestijnenlaan 200F, p.o. box 2454, 3001, Heverlee, Belgium
| | - Michiel Dusselier
- Center for Sustainable Catalysis and Engineering, KU Leuven, Celestijnenlaan 200F, 3001, Heverlee, Belgium
| |
Collapse
|
3
|
Raman G. Study of the Relationship between Synthesis Descriptors and the Type of Zeolite Phase Formed in ZSM‐43 Synthesis by Using Machine Learning. ChemistrySelect 2021. [DOI: 10.1002/slct.202102890] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Ganesan Raman
- Reliance Research & Development Center Reliance Corporate Park, Reliance Industries Limited Thane-Belapur Road, Ghansoli Navi Mumbai India 400701
| |
Collapse
|
4
|
Ke Q, Khalil I, Smeyers B, Li Z, Oliveira‐Silva R, Sels B, Sakellariou D, Dusselier M. A Cooperative OSDA Blueprint for Highly Siliceous Faujasite Zeolite Catalysts with Enhanced Acidity Accessibility. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202109163] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Quanli Ke
- Center for Sustainable Catalysis and Engineering KU Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
- Institute of Catalytic Reaction Engineering College of Chemical Engineering Zhejiang University of Technology Chaowang Road 18 310014 Hangzhou China
| | - Ibrahim Khalil
- Center for Sustainable Catalysis and Engineering KU Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Brent Smeyers
- Center for Sustainable Catalysis and Engineering KU Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Zheng Li
- Department of Chemistry KU Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Rodrigo Oliveira‐Silva
- Centre For Membrane Separations, Adsorption, Catalysis and Spectroscopy for Sustainable Solutions (cMACS) KU Leuven Celestijnenlaan 200F, p.o. box 2454 3001 Heverlee Belgium
| | - Bert Sels
- Center for Sustainable Catalysis and Engineering KU Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| | - Dimitrios Sakellariou
- Centre For Membrane Separations, Adsorption, Catalysis and Spectroscopy for Sustainable Solutions (cMACS) KU Leuven Celestijnenlaan 200F, p.o. box 2454 3001 Heverlee Belgium
| | - Michiel Dusselier
- Center for Sustainable Catalysis and Engineering KU Leuven Celestijnenlaan 200F 3001 Heverlee Belgium
| |
Collapse
|
5
|
Wang Z, Chu W, Zhao Z, Liu Z, Chen H, Xiao D, Gong K, Li F, Li X, Hou G. The Role of Organic and Inorganic Structure-Directing Agents in Selective Al Substitution of Zeolite. J Phys Chem Lett 2021; 12:9398-9406. [PMID: 34553943 DOI: 10.1021/acs.jpclett.1c01448] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Organic and inorganic structure-directing agents (SDAs) impact Al distributions in zeolite, but the insights into how SDAs manipulate Al distribution have not been elucidated yet. Herein, the roles of different SDAs such as cyclohexylamine (CHA), hexamethylenimine (HMI), and Na+ in selective Al substitution of MCM-49 zeolite are investigated comprehensively by multinuclear solid-state NMR. The results demonstrate that MCM-49 synthesized with HMI shows relatively more T6 and T7 Al, while more T2 Al is observed using CHA. The formation of T2 Al in both MCM-49(HMI) and MCM-49(CHA) is derived from Na+, while protonated HMIs show bias in incorporation of T6 and T7 Al. Most HMIs are occluded in protonated status, and about half of CHAs are occluded in nonprotonated status. The close spatial proximity between nonprotonated CHAs and Na+ synergistically promotes the formation of zeolite structure, leading to more Na+ ions occluded in the zeolite channel with preferential T2 Al substitution.
Collapse
Affiliation(s)
- Zhili Wang
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Weifeng Chu
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
| | - Zhenchao Zhao
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
| | - Zhengmao Liu
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hongyu Chen
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Dong Xiao
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
| | - Ke Gong
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fan Li
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiujie Li
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
| | - Guangjin Hou
- State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
| |
Collapse
|
6
|
Ghanbari B, Kazemi Zangeneh F, Sastre G, Moeinian M, Marhabaie S, Taheri Rizi Z. Computational elucidation of the aging time effect on zeolite synthesis selectivity in the presence of water and diquaternary ammonium iodide. Phys Chem Chem Phys 2021; 23:21240-21248. [PMID: 34542551 DOI: 10.1039/d1cp01921j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An example of zeolite selectivity (MFI → MOR) driven by synthesis aging time has been studied. Using N,N,N',N'-tetramethyl-N,N'-dipropyl-ethylenediammonium diiodide (TMDP) as an organic structure-directing agent (OSDA), the zeolite phases obtained at 2 h (MFI 97%), 8 h (MFI 84%, MOR 16%) and 24 h (MFI 43%, MOR 57%) have been characterized by powder X-ray diffraction. The results suggest that at intermediate aging time, namely 8 h and 24 h, the dominant phase (MFI) is displaced by MOR. Different techniques (FT-IR, Raman, 13C MAS NMR, TGA/DTG and HC microanalysis) have been employed to verify the OSDA integrity and occlusion inside the zeolite micropores as well as to quantify the water and OSDA loading. The 1H MAS NMR of the as-made occluded zeolite was compared with the spectra of TMDP and the recovered OSDA from the sample by extraction with water. The comparison indicated that TMDP was not structurally intact, indicating the chemical transformation of TMDP to imidazolinium homologues through the Hofmann degradation process. Furthermore, careful acidic breakdown of the aluminosilicate shell, covered on the zeolite samples by hydrofluoric acid, revealed that the remaining OSDA had been partially degraded to lower molecular weight ammonium salt, confirmed by 1H NMR and mass spectrometry measurements. A computational study was performed by using a force field based methodology, including accurate loading of water and OSDA in the zeolite (MFI and MOR) unit cells. The results show an important contribution of the presence of water. The samples with larger aging time (8 h and 24 h) incorporate less water and show partial TMDP degradation, whilst at the shortest aging time (2 h), there is a larger water content and TMDP remains intact. The larger accessible volume of MFI justifies that this is the dominant phase at short aging times (large water content) since it can accommodate a larger number of water molecules than MOR. The OSDA partial degradation also plays a role. At longer aging times the partial OSDA decomposition has been considered in the models by including TMDP + Imidaz, which is more stabilized by MOR, whilst at shorter aging times the only OSDA present, TMDP, is better stabilized by MFI.
Collapse
Affiliation(s)
- Bahram Ghanbari
- Department of Chemistry, Sharif University of Technology, PO Box 11155-3516, Tehran, Iran.
| | | | - German Sastre
- Instituto de Tecnologia Quimica U.P.V.-C.S.I.C., Universidad Politecnica de Valencia, Avenida Los Naranjos s/n, 46022 Valencia, Spain
| | - Maryam Moeinian
- Department of Chemistry, Sharif University of Technology, PO Box 11155-3516, Tehran, Iran.
| | - Sina Marhabaie
- Laboratoire des biomolécules, LBM, Département de chimie, École normale supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Zahra Taheri Rizi
- Research Institute of Petroleum Industry, West Blvd. of Azadi Complex, Tehran 1485733111, Iran
| |
Collapse
|
7
|
Dong L, Zhai D, Chen Z, Zheng G, Wang Y, Hong M, Yang S. A dramatic conformational effect of multifunctional zwitterions on zeolite crystallization. Chem Commun (Camb) 2020; 56:14693-14696. [PMID: 33165479 DOI: 10.1039/d0cc04965d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Carnitine functions as a mesoporogen in LTA zeolite synthesis whereas its structural analogue acetylcarnitine acts as a crystal growth modifier. An array of experimental and theoretical studies reveal a remarkable effect of molecular conformation on the actual roles of organic functional groups during zeolite crystallization.
Collapse
Affiliation(s)
- Lei Dong
- State Key Laboratory of Chemical Oncogenomics, Guangdong Provincial Key Laboratory of Nano-Micro Materials Research, School of Chemical Biology & Biotechnology, Peking University Shenzhen Graduate School (PKUSZ), Shenzhen 518055, P. R. China.
| | | | | | | | | | | | | |
Collapse
|
8
|
Bae J, Cichocka MO, Zhang Y, Bacsik Z, Bals S, Zou X, Willhammar T, Hong SB. Phase Transformation Behavior of a Two‐Dimensional Zeolite. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201904825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Juna Bae
- Center for Ordered Nanoporous Materials SynthesisDivision of Environmental Science and EngineeringPOSTECH Pohang 37673 Korea
| | - Magdalena O. Cichocka
- Berzelii Center EXSELENT on Porous MaterialsDepartment of Materials and Environmental ChemistryStockholm University 106 91 Stockholm Sweden
| | - Yi Zhang
- Berzelii Center EXSELENT on Porous MaterialsDepartment of Materials and Environmental ChemistryStockholm University 106 91 Stockholm Sweden
| | - Zoltán Bacsik
- Berzelii Center EXSELENT on Porous MaterialsDepartment of Materials and Environmental ChemistryStockholm University 106 91 Stockholm Sweden
| | - Sara Bals
- Electron Microscopy for Materials Science (EMAT)University of Antwerp Groenenborgerlaan 171 2020 Antwerp Belgium
| | - Xiaodong Zou
- Berzelii Center EXSELENT on Porous MaterialsDepartment of Materials and Environmental ChemistryStockholm University 106 91 Stockholm Sweden
| | - Tom Willhammar
- Berzelii Center EXSELENT on Porous MaterialsDepartment of Materials and Environmental ChemistryStockholm University 106 91 Stockholm Sweden
| | - Suk Bong Hong
- Center for Ordered Nanoporous Materials SynthesisDivision of Environmental Science and EngineeringPOSTECH Pohang 37673 Korea
| |
Collapse
|
9
|
Bae J, Cichocka MO, Zhang Y, Bacsik Z, Bals S, Zou X, Willhammar T, Hong SB. Phase Transformation Behavior of a Two-Dimensional Zeolite. Angew Chem Int Ed Engl 2019; 58:10230-10235. [PMID: 31116498 DOI: 10.1002/anie.201904825] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Indexed: 11/08/2022]
Abstract
Understanding the molecular-level mechanisms of phase transformation in solids is of fundamental interest for functional materials such as zeolites. Two-dimensional (2D) zeolites, when used as shape-selective catalysts, can offer improved access to the catalytically active sites and a shortened diffusion length in comparison with their 3D analogues. However, few materials are known to maintain both their intralayer microporosity and structure during calcination for organic structure-directing agent (SDA) removal. Herein we report that PST-9, a new 2D zeolite which has been synthesized via the multiple inorganic cation approach and fulfills the requirements for true layered zeolites, can be transformed into the small-pore zeolite EU-12 under its crystallization conditions through the single-layer folding process, but not through the traditional dissolution/recrystallization route. We also show that zeolite crystal growth pathway can differ according to the type of organic SDAs employed.
Collapse
Affiliation(s)
- Juna Bae
- Center for Ordered Nanoporous Materials Synthesis, Division of Environmental Science and Engineering, POSTECH, Pohang, 37673, Korea
| | - Magdalena O Cichocka
- Berzelii Center EXSELENT on Porous Materials, Department of Materials and Environmental Chemistry, Stockholm University, 106 91, Stockholm, Sweden
| | - Yi Zhang
- Berzelii Center EXSELENT on Porous Materials, Department of Materials and Environmental Chemistry, Stockholm University, 106 91, Stockholm, Sweden
| | - Zoltán Bacsik
- Berzelii Center EXSELENT on Porous Materials, Department of Materials and Environmental Chemistry, Stockholm University, 106 91, Stockholm, Sweden
| | - Sara Bals
- Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020, Antwerp, Belgium
| | - Xiaodong Zou
- Berzelii Center EXSELENT on Porous Materials, Department of Materials and Environmental Chemistry, Stockholm University, 106 91, Stockholm, Sweden
| | - Tom Willhammar
- Berzelii Center EXSELENT on Porous Materials, Department of Materials and Environmental Chemistry, Stockholm University, 106 91, Stockholm, Sweden
| | - Suk Bong Hong
- Center for Ordered Nanoporous Materials Synthesis, Division of Environmental Science and Engineering, POSTECH, Pohang, 37673, Korea
| |
Collapse
|
10
|
Shin J, Jo D, Hong SB. Rediscovery of the Importance of Inorganic Synthesis Parameters in the Search for New Zeolites. Acc Chem Res 2019; 52:1419-1427. [PMID: 31013053 DOI: 10.1021/acs.accounts.9b00073] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Zeolites and related crystalline microporous materials with cavities and channels of molecular dimensions are of major importance for applications ranging from ion-exchange to adsorption and to catalysis. Because their unique shape-selective properties are closely related to the size, shape, and dimensionality of the intracrystalline channels and cavities, much interest has been devoted to the discovery of novel zeolitic materials over the last several decades. As a result, a dramatic expansion in the structural domain of crystalline microporous materials, as well as in their compositional range, has been achieved. This is largely due to the development of innovative synthetic strategies, for example, organic structure-directing agent (OSDA) design, introduction of heteroatoms like Ge in OSDA-mediated zeolite synthesis, topotactic transformation of two-dimensional layered zeolite precursors, assembly-disassembly-organization-reassembly method, etc. However, although many of these methodologies are quite successful in finding unprecedented zeolite structures, the resulting materials tend to be (hydro)thermally unstable and are often commercially impractical from a manufacturing perspective because of the high cost of the OSDA and/or heteroatom employed. Therefore, we focused on inorganic synthesis parameters as the key phase selectivity factor that has received relatively little attention in the search for new industrially relevant zeolites. This Account describes our recent efforts to find previously undiscovered aluminosilicate zeolites by boosting the roles of inorganic structure-directing agents (ISDAs) in the presence of OSDAs. They include the multiple inorganic cation and excess fluoride approaches, which aim to promote a synergistic cooperation between ISDAs and/or OSDAs and thus to hold a rational design concept, although the latter is not friendly to the practical zeolite manufacturing process due to the toxicity of fluoride. Using these two approaches, we were able to synthesize not only the second generation (PST-29) and four higher generations (PST-20 (RHO-G5), PST-25 (RHO-G6), PST-26 (RHO-G7), and PST-28 (RHO-G8)) of the RHO family of embedded isoreticular zeolites but also three other novel zeolite structures (EU-12, PST-21, and PST-22). We also explored the synthesis of a number of heteroatom-containing aluminophosphate (AlPO4) molecular sieves with different framework structures and unusually high framework charge density through the cooperative structure direction of alkali metal and small OSDA cations or under wholly inorganic conditions. Although we need to clarify the nature and extent of interactions between the inorganic cations and framework components in synthesis mixtures, we believe that our synthetic concepts, shedding new light on the importance of inorganic synthesis parameters, will open a door for achieving many other novel zeolite structures and compositions.
Collapse
Affiliation(s)
- Jiho Shin
- Center for Ordered Nanoporous Materials Synthesis, Division of Environmental Science and Engineering, POSTECH, Pohang 37673, Korea
| | - Donghui Jo
- Center for Ordered Nanoporous Materials Synthesis, Division of Environmental Science and Engineering, POSTECH, Pohang 37673, Korea
| | - Suk Bong Hong
- Center for Ordered Nanoporous Materials Synthesis, Division of Environmental Science and Engineering, POSTECH, Pohang 37673, Korea
| |
Collapse
|