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45 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I11-High Resolution Powder Diffraction	Rational design of synergistic active sites for catalytic ethene/2-butene cross-metathesis in a rhenium-doped Y zeolite catalyst 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 Acs Catalysis DOI: 10.1021/acscatal.1c00524 Show Abstract ▼ 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.	Mar 2021
I11-High Resolution Powder Diffraction	Responses of defect-rich Zr-based metal–organic frameworks toward NH3 adsorption 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 Journal Of The American Chemical Society DOI: 10.1021/jacs.0c12483 Show Abstract ▼ 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.	Feb 2021
I11-High Resolution Powder Diffraction	Characterisation of oxygen defects and nitrogen impurities in TiO2 photocatalysts using variable-temperature X-ray powder diffraction Christopher Foo , Yiyang Li , Konstantin Lebedev , Tianyi Chen , Sarah Day , Chiu Tang , Chi Edman Tsang Nature Communications 12 DOI: 10.1038/s41467-021-20977-z Open Access Show Abstract ▼ Abstract: TiO2-based powder materials have been widely studied as efficient photocatalysts for water splitting due to their low cost, photo-responsivity, earthly abundance, chemical and thermal stability, etc. In particular, the recent breakthrough of nitrogen-doped TiO2, which enhances the presence of structural defects and dopant impurities at elevated temperatures, exhibits an impressive visible-light absorption for photocatalytic activity. Although their electronic and optical properties have been extensively studied, the structure-activity relationship and photocatalytic mechanism remain ambiguous. Herein, we report an in-depth structural study of rutile, anatase and mixed phases (commercial P25) with and without nitrogen-doping by variable-temperature synchrotron X-ray powder diffraction. We report that an unusual anisotropic thermal expansion of the anatase phase can reveal the intimate relationship between sub-surface oxygen vacancies, nitrogen-doping level and photocatalytic activity. For highly doped anatase, a new cubic titanium oxynitride phase is also identified which provides important information on the fundamental shift in absorption wavelength, leading to excellent photocatalysis using visible light.	Jan 2021
B18-Core EXAFS	Structural insight into [Fe–S2–Mo] motif in electrochemical reduction of N2 over Fe1-supported molecular MoS2 Jianwei Zheng , Simson Wu , Lilin Lu , Chen Huang , Ping-luen Ho , Angus Kirkland , Tim Sudmeier , Rosa Arrigo , Diego Gianolio , Shik Chi Edman Tsang Chemical Science 12, 688 - 695 DOI: 10.1039/D0SC04575F Diamond Proposal Number(s): [20856] Open Access Show Abstract ▼ Abstract: The catalytic synthesis of NH3 from the thermodynamically challenging N2 reduction reaction under mild conditions is currently a significant problem for scientists. Accordingly, herein, we report the development of a nitrogenase-inspired inorganic-based chalcogenide system for the efficient electrochemical conversion of N2 to NH3, which is comprised of the basic structure of [Fe–S2–Mo]. This material showed high activity of 8.7 mgNH3 mgFe−1 h−1 (24 μgNH3 cm−2 h−1) with an excellent faradaic efficiency of 27% for the conversion of N2 to NH3 in aqueous medium. It was demonstrated that the Fe1 single atom on [Fe–S2–Mo] under the optimal negative potential favors the reduction of N2 to NH3 over the competitive proton reduction to H2. Operando X-ray absorption and simulations combined with theoretical DFT calculations provided the first and important insights on the particular electron-mediating and catalytic roles of the [Fe–S2–Mo] motifs and Fe1, respectively, on this two-dimensional (2D) molecular layer slab.	Jan 2021
I11-High Resolution Powder Diffraction	Cooperative catalytically active sites for methanol activation by single metal ion-doped H-ZSM-5 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 Chemical Science 3 DOI: 10.1039/D0SC04058D Diamond Proposal Number(s): [16358] Open Access Show Abstract ▼ 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.	Oct 2020
I11-High Resolution Powder Diffraction	In situ phase transformation on nickel-based selenides for enhanced hydrogen evolution reaction in alkaline medium Lingling Zhai , Tsz Woon Benedict Lo , Zheng-long Xu , Jonathan Potter , Jiaying Mo , Xuyun Guo , Chiu Chung Tang , Shik Chi Edman Tsang , Shu Ping Lau Acs Energy Letters DOI: 10.1021/acsenergylett.0c01385 Diamond Proposal Number(s): [23230] Show Abstract ▼ Abstract: Identification of the active species in electrocatalysts toward hydrogen evolution reaction (HER) is of great significance for the development of the catalytic industry; however, it is still the subject of considerable controversy. Herein, we applied operando synchrotron X-ray powder diffraction (SXRD) in the NiSe2 electrocatalyst system, and an in situ phase transformation from cubic NiSe2 to hexagonal NiSe was revealed. The NiSe phase showed an enhanced catalytic activity. Operando Raman spectroscopy verified the decomposition of NiSe2 during HER. Theoretical calculations suggested that the charge transfers from the Se site to Ni site during this evolution process, leading to an increased conductivity and a shifting up of d-band center, which is attributed to the enhanced activity. The generated NiSe phase acts as the “real” active species. Our work unravels the underlying phase transition of the electrocatalyst on reductive conditions in alkaline medium and highlights the significance of identifying the intrinsic active sites under realistic reaction conditions.	Jul 2020
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Methanol synthesis at a wide range of H2/CO2 ratios over Rh‐In bimetallic catalyst Molly Meng-jung Li , Hanbo Zou , Jianwei Zheng , Tai-sing Wu , Ting-shan Chan , Yun-liang Soo , Xin-ping Wu , Xueqing Gong , Tianyi Chen , Kanak Roy , Georg Held , Edman Shik Chi Tsang Angewandte Chemie International Edition DOI: 10.1002/anie.202000841 Show Abstract ▼ Abstract: Recent years have seen an increasing interest in capturing hydrogen generated from renewables with CO 2 to produce methanol. However, renewable hydrogen production is currently expensive and in limited quantity as compared to CO 2 . Excess CO 2 and limited H 2 in the feedstock gas mixture is not favourable for the CO 2 hydrogenation to methanol reaction, which causes low activity and poor methanol selectivity. Here we report a new class of Rh‐In catalysts with optimal adsorption property to the intermediates of methanol production. The Rh‐In catalyst can effectively catalyse methanol synthesis but inhibit reverse water‐gas shift reaction under H 2 ‐deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with the literature reported values. This work demonstrates a strong potential of Rh‐In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (e.g. H 2 /CO 2 from biomass derivatives) with lower energy cost can be established.	May 2020
I11-High Resolution Powder Diffraction	Evaluation of Brønsted and Lewis acid sites in H-ZSM-5 and H-USY with or without metal modification using probe molecule-synchrotron X-ray powder diffraction Benedict T. W. Lo , Wei-che Lin , Molly Meng Jung Li , Sarah Day , Chiu Tang , Shik Chi Edman Tsang Applied Catalysis A: General 596 DOI: 10.1016/j.apcata.2020.117528 Show Abstract ▼ Abstract: The adsorbate interactions of furans as probe molecules in H-ZSM-5 and H-USY with and without metal ion modification have been revealed by synchrotron X-ray powder diffraction (SXRD). The Rietveld refinements give both qualitatively and quantitatively the spatial arrangements and adsorption geometries of furan and 2,5-dimethylfuran (DMF) on the Brønsted acid sites (BAS) and metal Lewis acid sites (LAS). The bonding information between the adsorbate-framework can also be correlated with thermogravimetric findings. The use of probe molecule-SXRD can be used as a new characterisation tool which can spatially interrogate the acidity of crystalline porous catalysts, leading to molecular engineering of new catalytic systems.	Apr 2020
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Removal of hydrogen poisoning by electrostatically polar MgO support for low pressure NH3 synthesis at high rate over Ru catalyst Simson Wu , Yung-kang Peng , Tianyi Chen , Jiaying Mo , Alex Large , Ian Mcpherson , Hung-lung Chou , Ian Wilkinson , Federica Venturini , David Grinter , Pilar Ferrer Escorihuela , Georg Held , Shik Chi Edman Tsang Acs Catalysis DOI: 10.1021/acscatal.0c00954 Show Abstract ▼ Abstract: The increasing availability of low-cost and low pressure, renewable H2 from wind and solar means has triggered tremendous interest in developing low pressure ammonia synthesis with N2 as energy carrier as well as green fertilizer. As such Cs-promoted Ru/MgO catalysts used in Kellogg process show superiority to Fe-based catalysts at milder conditions, however, as known, the surface poisoning of Ru sites by competitive strong H2 dissociative adsorption limits the overall rate. It is demonstrated for the first time that the use of simple polar MgO(111) to replace non-polar MgO as support can significantly alleviate the hydrogen poisoning and facilitate an unprecedented ammonia production rate by its high intrinsic proton capture ability.	Apr 2020
I11-High Resolution Powder Diffraction	Differential adsorption of L- and D-lysine on achiral MFI zeolites as determined by synchrotron X-ray powder diffraction and thermogravimetric analysis Tianxiang Chen , Bolong Huang , Sarah Day , Chiu Chung Tang , Shik Chi Edman Tsang , Kwok-yin Wong , Tsz Woon Benedict Lo Angewandte Chemie International Edition DOI: 10.1002/anie.201909352 Diamond Proposal Number(s): [23230] Show Abstract ▼ Abstract: We report the first crystallographic observation of stereospecific bindings of L‐ and D‐lysine in achiral MFI zeolites. The MFI structure has offered inherent geometric and internal confinement effects for the enantiomeric difference in L‐ and D‐lysine adsorption. Notable difference over the sorption properties has been observed by circular dichroism (CD) spectroscopy and thermogravimetric analysis (TGA). Distinct L‐ and D‐lysine adsorption behaviours on the H‐ZSM‐5 framework have been revealed by the Rietveld refinement of high‐resolution synchrotron X‐ray powder diffraction (SXRD) data and the density functional theory (DFT) calculation. Despite only demonstrated in L‐ and D‐lysine over MFI zeolites, the differential adsorption study sheds light towards the rational engineering of molecular interactions(s) with achiral microporous materials for chiral separation purposes.	Nov 2019

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