I15-1-X-ray Pair Distribution Function (XPDF)
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Chirui
Xu
,
William
Orbell
,
Guilian
Wang
,
Boye
Li
,
Bryan K. Y.
Ng
,
Tai-Sing
Wu
,
Yun-Liang
Soo
,
Zhao-Xue
Luan
,
Kangjian
Tang
,
Xin-Ping
Wu
,
S. C. Edman
Tsang
,
Pu
Zhao
Abstract: Improving the efficiency of catalytic materials is vital to chemical and energy industries. Constructing neighbouring active sites in metal−organic framework (MOF) materials for cooperative catalysis is a promising way to achieve the above goal. However, it is difficult to fine-tune active sites at the atomic level due to the challenge of visualising their local structures and their interaction with substrates. In this article, we report the direct visualisation of metal and defect active sites and binding of phenol substrate in a Ru-doped defective MOF-808. X-ray absorption spectroscopy, X-ray pair distribution function analysis, X-ray powder diffraction, and infrared spectroscopy reveal that the enhanced selective hydrogenation originates from the specific adsorption geometry of phenol over 7-centred Ru clusters and hydroxyl or water of defect sites. This mechanism also well explains the high catalytic activity in CO2 reduction. This work represents the first example of structural elucidation of metal−defect cooperative catalysis in MOFs and will lead to the rational design of new superactive MOF catalysts.
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Jun 2024
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Kwan Chee
Leung
,
Sungil
Hong
,
Guangchao
Li
,
Youdong
Xing
,
Bryan Kit Yue
Ng
,
Ping-Luen
Ho
,
Dongpei
Ye
,
Pu
Zhao
,
Ephraem
Tan
,
Olga
Safonova
,
Tai-Sing
Wu
,
Molly Meng-Jung
Li
,
Giannis
Mpourmpakis
,
Shik Chi Edman
Tsang
Open Access
Abstract: Catalytic NH3 synthesis and decomposition offer a new promising way to store and transport renewable energy in the form of NH3 from remote or offshore sites to industrial plants. To use NH3 as a hydrogen carrier, it is important to understand the catalytic functionality of NH3 decomposition reactions at an atomic level. Here, we report for the first time that Ru species confined in a 13X zeolite cavity display the highest specific catalytic activity of over 4000 h–1 for the NH3 decomposition with a lower activation barrier, compared to most reported catalytic materials in the literature. Mechanistic and modeling studies clearly indicate that the N–H bond of NH3 is ruptured heterolytically by the frustrated Lewis pair of Ruδ+–Oδ− in the zeolite identified by synchrotron X-rays and neutron powder diffraction with Rietveld refinement as well as other characterization techniques including solid-state nuclear magnetic resonance spectroscopy, in situ diffuse reflectance infrared transform spectroscopy, and temperature-programmed analysis. This contrasts with the homolytic cleavage of N–H displayed by metal nanoparticles. Our work reveals the unprecedented unique behavior of cooperative frustrated Lewis pairs created by the metal species on the internal zeolite surface, resulting in a dynamic hydrogen shuttling from NH3 to regenerate framework Brønsted acid sites that eventually are converted to molecular hydrogen.
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Jun 2023
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I11-High Resolution Powder Diffraction
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Guangchao
Li
,
Christopher
Foo
,
Xianfeng
Yi
,
Wei
Chen
,
Pu
Zhao
,
Pan
Gao
,
Tatchamapan
Yoskamtorn
,
Yao
Xiao
,
Sarah
Day
,
Chiu C.
Tang
,
Guangjin
Hou
,
Anmin
Zheng
,
Shik Chi Edman
Tsang
Abstract: There has been a long debate on how and where active sites are created for molecular adsorption and catalysis in zeolites, which underpin many important industrial applications. It is well accepted that Lewis acidic sites (LASs) and basic sites (LBSs) as active sites in pristine zeolites are generally believed to be the extra-framework Al species and residue anion (OH–) species formed at fixed crystallographic positions after their synthesis. However, the dynamic interactions of adsorbates/reactants with pristine zeotype materials to “create” sites during real conditions remain largely unexplored. Herein, direct experimental observation of the establishment of induced active sites in silicoaluminophosphate (SAPO) by an adsorbate is for the first time made, which contradicts the traditional view of the fixed active sites in zeotype materials. Evidence shows that an induced frustrated Lewis pair (FLP, three-coordinated framework Al as LAS and SiO (H) as LBS) can be transiently favored for heterolytic molecular binding/reactions of competitive polar adsorbates due to their ineffective orbital overlap in the rigid framework. High-resolution magic-angle-spinning solid-state NMR, synchrotron X-ray diffraction, neutron powder diffraction, in situ diffuse reflectance infrared Fourier transform spectroscopy, and ab initio molecular dynamics demonstrate the transformation of a typical Brønsted acid site (Al(OH)Si) in SAPO zeolites to new induced FLP structure for hetereolytic binding upon adsorption of a strong polar adsorbate. Our unprecedented finding opens up a new avenue to understanding the dynamic establishment of active sites for adsorption or chemical reactions under molecular bombardment of zeolitic structures.
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Jun 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Jianwei
Zheng
,
Lilin
Lu
,
Konstantin
Lebedev
,
Simson
Wu
,
Pu
Zhao
,
Ian J.
Mcpherson
,
Tai-Sing
Wu
,
Ryuichi
Kato
,
Yiyang
Li
,
Ping-Luen
Ho
,
Guangchao
Li
,
Linlu
Bai
,
Jianhui
Sun
,
Dharmalingam
Prabhakaran
,
Robert A.
Taylor
,
Yun-Liang
Soo
,
Kazu
Suenaga
,
Shik Chi Edman
Tsang
Abstract: Current industrial production of ammonia from the Haber-Bosch process and its transport concomitantly produces a large quantity of CO2. Herein, we successfully synthesize inorganic-structure-based catalysts with [Fe-S2-Mo] motifs with a connecting structure similar to that of FeMoco (a cofactor of nitrogenase) by placing iron atoms on a single molecular layer of MoS2 at various loadings. This type of new catalytic material functionally mimics the nitrogenase to convert N2 to ammonia and hydrogen in water without adding any sacrificial agent under visible-light illumination. Using the elevated temperature boosts the ammonia yield and the energy efficiency by one order of magnitude. The solar-to-NH3 energy-conversion efficiency can be up to 0.24% at 270°C, which is the highest efficiency among all reported photocatalytic systems. This method of ammonia production and the photocatalytic materials may open up an exciting possibility for the decentralization of ammonia production for fertilizer provision to local farmlands using solar illumination.
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Apr 2021
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Pu
Zhao
,
Lin
Ye
,
Guangchao
Li
,
Chen
Huang
,
Simson
Wu
,
Ping-Luen
Ho
,
Haokun
Wang
,
Tatchamapan
Yoskamtorn
,
Denis
Sheptyakov
,
Giannantonio
Cibin
,
Angus I.
Kirkland
,
Chiu C.
Tang
,
Anmin
Zheng
,
Wenjuan
Xue
,
Donghai
Mei
,
Kongkiat
Suriye
,
Shik Chi Edman
Tsang
Abstract: Synthesizing atomically dispersed synergistic active pairs is crucial yet challenging in developing highly active heterogeneous catalysts for various industrially important reactions. Here, a single molecular Re species is immobilized on the inner surface of a Y zeolite with Brønsted acid sites (BASs) within atomic proximity to form Re OMS–BAS active pairs for the efficient catalysis of olefin metathesis reactions (OMS: olefin metathesis site). The synergy within the active pairs is revealed by studying the coadsorption geometry of the olefin substrates over the active pairs by synchrotron X-ray and neutron powder diffraction. It is shown that the BAS not only facilitates olefin adsorption but also aligns the olefin molecule to the Re OMS for efficient intermediate formation. Consequently, for the cross-metathesis of ethene and trans-2-butene to propene, this catalyst shows high activity under mild reaction conditions without observable deactivation. The catalyst outperforms not only traditional ReOx-based catalysts but also the best industrially applicable WOx-based catalyst thus far that we discovered previously. The concept of using two isolated active sites of different functionalities within atomic proximity in a confined cavity can provide opportunities for designing synergistically catalytic materials.
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Mar 2021
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I11-High Resolution Powder Diffraction
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Tatchamapan
Yoskamtorn
,
Pu
Zhao
,
Xin-Ping
Wu
,
Kirsty
Purchase
,
Fabio
Orlandi
,
Pascal
Manuel
,
James
Taylor
,
Yiyang
Li
,
Sarah
Day
,
Lin
Ye
,
Chiu C.
Tang
,
Yufei
Zhao
,
S. C. Edman
Tsang
Abstract: Understanding structural responses of metal–organic frameworks (MOFs) to external stimuli such as the inclusion of guest molecules and temperature/pressure has gained increasing attention in many applications, for example, manipulation and manifesto smart materials for gas storage, energy storage, controlled drug delivery, tunable mechanical properties, and molecular sensing, to name but a few. Herein, neutron and synchrotron diffractions along with Rietveld refinement and density functional theory calculations have been used to elucidate the responsive adsorption behaviors of defect-rich Zr-based MOFs upon the progressive incorporation of ammonia (NH3) and variable temperature. UiO-67 and UiO-bpydc containing biphenyl dicarboxylate and bipyridine dicarboxylate linkers, respectively, were selected, and the results establish the paramount influence of the functional linkers on their NH3 affinity, which leads to stimulus-tailoring properties such as gate-controlled porosity by dynamic linker flipping, disorder, and structural rigidity. Despite their structural similarities, we show for the first time the dramatic alteration of NH3 adsorption profiles when the phenyl groups are replaced by the bipyridine in the organic linker. These molecular controls stem from controlling the degree of H-bonding networks/distortions between the bipyridine scaffold and the adsorbed NH3 without significant change in pore volume and unit cell parameters. Temperature-dependent neutron diffraction also reveals the NH3-induced rotational motions of the organic linkers. We also demonstrate that the degree of structural flexibility of the functional linkers can critically be affected by the type and quantity of the small guest molecules. This strikes a delicate control in material properties at the molecular level.
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Feb 2021
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I11-High Resolution Powder Diffraction
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Wei-Che
Lin
,
Simson
Wu
,
Guangchao
Li
,
Ping-Luen
Ho
,
Yichen
Ye
,
Pu
Zhao
,
Sarah
Day
,
Chiu
Tang
,
Wei
Chen
,
Anmin
Zheng
,
Benedict T. W.
Lo
,
Shik Chi Edman
Tsang
Diamond Proposal Number(s):
[16358]
Open Access
Abstract: Catalytic conversion of methanol to aromatics and hydrocarbons is regarded as a key alternative technology to oil processing. Although the inclusion of foreign metal species in H-ZSM-5 containing Brønsted acid site (BAS) is commonly found to enhance product yields, the nature of catalytically active sites and the rationalization for catalytic performance still remain obscure. Herein, by acquiring comparable structural parameters by both X-ray and neutron powder diffractions over a number of metal-modified ZSM-5 zeolites, it is demonstrated for the first time that active pairs of metal site-BAS within molecular distance is created when single and isolated transition metal cation is ion-exchanged with the zeolites. According to our DFT model, this could lead to the initial heterolytic cleavage of small molecules such as water and methanol by the pair with subsequent reactions to form products at high selectivity as that observed experimentally. It may account for their active and selective catalytic routes of small molecule activations.
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Oct 2020
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I11-High Resolution Powder Diffraction
I15-1-X-ray Pair Distribution Function (XPDF)
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Tianyi
Chen
,
Ieuan
Ellis
,
Thomas
Hooper
,
Emanuela
Liberti
,
Lin
Ye
,
Tsz Woon Benedict
Lo
,
Colum
O'Leary
,
Alexandra A.
Sheader
,
Gerardo T.
Martinez
,
Lewys
Jones
,
Ping-Luen
Ho
,
Pu
Zhao
,
James
Cookson
,
Peter T
Bishop
,
Philip A.
Chater
,
John V.
Hanna
,
Peter D.
Nellist
,
Shik Chi Edman
Tsang
Diamond Proposal Number(s):
[15452]
Abstract: It is well established that the inclusion of small atomic species such as boron (B) in powder metal catalysts can subtly modify catalytic properties, and the associated changes in the metal lattice implies that the B atoms are located in the interstitial sites. However, there is no compelling evidence for the occurrence of interstitial B atoms, and there is a concomitant lack of detailed structural information describing the nature of this occupancy and its effects on the metal host. In this work, we use an innovative combination of high-resolution 11B magic-angle-spinning (MAS) and 105Pd static solid state NMR nuclear magnetic resonance (NMR), synchrotron X-ray diffraction (SXRD), in-situ X-ray pair distribution function (XPDF), scanning transmission electron microscopy-annular dark field imaging (STEM-ADF), electron ptychography and electron energy loss spectroscopy (EELS) to investigate the B atom positions, properties and structural modifications to the palladium lattice of an industrial type interstitial boron doped palladium nanoparticle catalyst system (Pd-intB/C NPs). In this study we report that upon B incorporation into the Pd lattice, the overall face centered cubic (FCC) lattice is maintained, however short range disorder is introduced. The 105Pd static solid-state NMR illustrates how different types (and levels) of structural strain and disorder are introduced in the nanoparticle history. These structural distortions can lead to the appearance of small amounts of local hexagonal close packed (HCP) structured material in localized regions. The short range lattice tailoring of the Pd framework to accommodate interstitial B dopants in the octahedral sites of the distorted FCC structure can be imaged by electron ptychography. This study describes new toolsets that enables the characterization of industrial metal nanocatalysts across length scales from macro-analysis to micro-analysis, which gives important guidance to structure-activity relationship of the system.
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Nov 2019
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I11-High Resolution Powder Diffraction
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Open Access
Abstract: Stimuli-responsive behaviors of flexible metal–organic frameworks (MOFs) make these materials promising in a wide variety of applications such as gas separation, drug delivery, and molecular sensing. Considerable efforts have been made over the last decade to understand the structural changes of flexible MOFs in response to external stimuli. Uniform pore deformation has been used as the general description. However, recent advances in synthesizing MOFs with non-uniform porous structures, i.e. with multiple types of pores which vary in size, shape, and environment, challenge the adequacy of this description. Here, we demonstrate that the CO2-adsorption-stimulated structural change of a flexible MOF, ZIF-7, is induced by CO2 migration in its non-uniform porous structure rather than by the proactive opening of one type of its guest-hosting pores. Structural dynamics induced by guest migration in non-uniform porous structures is rare among the enormous number of MOFs discovered and detailed characterization is very limited in the literature. The concept presented in this work provides new insights into MOF flexibility.
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Mar 2019
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I11-High Resolution Powder Diffraction
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Abstract: Gamma‐valerolactone (GVL) is regarded as a key platform molecule in the production of fine chemicals such as pentenoic acid (PA) from biomass. Although PA is believed to be the key intermediate in solid acid catalyzed reactions of GVL, due to subsequent facile decarboxylation reactions, further alkene products were formed. Here, by tailoring the acidity of Brønsted acid sites in an alumino‐phosphate (AlPO) molecular sieve via incorporation of Zn2+ into the framework, we access a new selective, high yield catalytic route for GVL conversion to PA.
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Oct 2018
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