I11-High Resolution Powder Diffraction
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Zhenping
Cai
,
Jinxing
Long
,
Yingwen
Li
,
Lin
Ye
,
Biaolin
Yin
,
Liam John
France
,
Juncai
Dong
,
Lirong
Zheng
,
Hongyan
He
,
Sijie
Liu
,
Shik Chi Edman
Tsang
,
Xuehui
Li
Abstract: Green production of bulk chemicals traditionally obtained from fossil resources is of great importance. One potential route toward realizing this goal is through the utilization of renewable lignin; however, current techniques generally lead to low product specificity because of the structural diversity of this recalcitrant biopolymer. Herein, we devised a new catalytic system to promote selectively oxidative lignin in air, and diethyl maleate was formed at impressively high yield of 404.8 mg g−1 and selectivity of 72.7% over the polyoxometalate ionic liquid of [BSmim]CuPW12O40. This high catalytic activity is ascribed to a five-coordinated Cu+ species, which, through the formation of end-on dioxygen species in vacant orbitals, facilitates the selective oxidation of basic lignin aromatic units (phenylpropane C9 units). Therefore, these results represent significant progress toward the realization of an industrially applicable and highly selective lignin oxidation process for the generation of value-added and bulk chemicals.
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Jun 2019
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Lin
Ye
,
A. A. Hanif
Mahadi
,
Chalathan
Saengruengrit
,
Jin
Qu
,
Feng
Xu
,
Simon
Fairclough
,
Neil
Young
,
Ping-luen
Ho
,
Junjun
Shan
,
Luan
Nguyen
,
Franklin F.
Tao
,
Karaked
Tedsree
,
Shik Chi Edman
Tsang
Abstract: Ceria has been widely used as support in electrocatalysis for its high degree of oxygen storage, fast oxygen mobility and reduction and oxidation properties at mild conditions. However, it is unclear what are the underlying principles and the nature of surface involved. By controlling the growth of various morphologies of ceria nanoparticles, it is demonstrated that the cubic-form of ceria, predominantly covered with higher energy polar surface (100), as support for Pd gives much higher activity in the electrocatalytic oxidation of formic acid than ceria of other morphologies (rods and spheres) with low indexed facets ((110) and (111)). High resolution TEM confirms the alternating layer-to-layer of cations and anions in (100) surface, the electrostatic repulsion of oxygen anions within the same layers gives intrinsically higher oxygen vacancies on this redox active surface in order to reduce surface polarity. DFT calculations suggest that the properties of fast oxygen mobility to re-oxidize the CO-poisoned Pd may arise from the overdosed oxygens on these ceria surface layers during electro-oxidation hence sustaining higher activity.
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Apr 2019
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B18-Core EXAFS
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Abstract: The direct hydrogenation of CO2 to methanol has become a very active research field because CO2 can be prospectively recycled to mitigate greenhouse effect and store clean synthetic fuels. This reaction can be catalyzed by supported Cu catalysts and the catalysts display strong support or promoter effects. Sintering of Cu species accelerates the separation of Cu–oxide interfaces, reduces the active component, and diminishes the methanol selectivity. In this work, we report a Cu catalyst supported on La-modified SBA-15, where the Cu–LaOx interface is generated through the interaction of highly dispersed Cu nanoparticles with LaOx species bedded into the SBA-15 pore wall. The optimized Cu1La0.2/SBA-15 catalyst can achieve methanol selectivity up to 81.2% with no deterioration in activity over 100 h on stream compared with the La-free catalyst. A thorough study reveals that La species not only significantly improve the CO2 adsorption but also enhance Cu dispersion to produce well-dispersed active sites. The H/D exchange experiments show that the methanol synthesis displays a strong thermodynamic isotope effect and the Cu–LaOx interface plays a crucial role for the methanol synthesis rate in CO2/D2 feed. In situ DRIFTS studies reveal that *HCOO and *OCH3 species are the key intermediates formed during the activation of CO2 and methanol synthesis over the Cu1La0.2/SBA-15 catalyst.
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Mar 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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Lin
Ye
,
Xinping
Duan
,
Simson
Wu
,
Tai-sing
Wu
,
Yuxin
Zhao
,
Alex W.
Robertson
,
Hung-lung
Chou
,
Jianwei
Zheng
,
Tugce
Ayvali
,
Sarah
Day
,
Chiu
Tang
,
Yun-liang
Soo
,
Youzhu
Yuan
,
Shik Chi Edman
Tsang
Open Access
Abstract: Replacement of Hg with non-toxic Au based catalysts for industrial hydrochlorination of acetylene to vinyl chloride is urgently required. However Au catalysts suffer from progressive deactivation caused by auto-reduction of Au(I) and Au(III) active sites and irreversible aggregation of Au(0) inactive sites. Here we show from synchrotron X-ray absorption, STEM imaging and DFT modelling that the availability of ceria(110) surface renders Au(0)/Au(I) as active pairs. Thus, Au(0) is directly involved in the catalysis. Owing to the strong mediating properties of Ce(IV)/Ce(III) with one electron complementary redox coupling reactions, the ceria promotion to Au catalysts gives enhanced activity and stability. Total pre-reduction of Au species to inactive Au nanoparticles of Au/CeO2&AC when placed in a C2H2/HCl stream can also rapidly rejuvenate. This is dramatically achieved by re-dispersing the Au particles to Au(0) atoms and oxidising to Au(I) entities, whereas Au/AC does not recover from the deactivation.
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Feb 2019
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Tugce
Ayvali
,
Lin
Ye
,
Simson
Wu
,
Benedict T. W.
Lo
,
Chen
Huang
,
Bin
Yu
,
Giannantonio
Cibin
,
Angus I.
Kirkland
,
Chiu
Tang
,
Abdulaziz A.
Bagabas
,
S. C. Edman
Tsang
Diamond Proposal Number(s):
[16358, 14647]
Abstract: Deposition of gold on supports can produce catalytically active forms of gold as well as spectators, but previous understanding of the nature of active immobilized precursors is poor. By using synchrotron X-ray powder diffraction (SXRD) and X-ray absorption spectroscopy (XAS) techniques, we report a novel synthesis and structural elucidation of atomically dispersed gold species anchored to the internal surface of TS-1 as K+Au(OH)2Na+(Of)3 (“f” signifies the framework atoms of TS-1 in the formula.). It is found that the choice of alkali ions plays a crucial role in nucleation and stabilization of the atomic precursor. These anchored single Au upon controlled reduction in H2 can form uniform gold clusters in direct contact with the TS-1 surface containing isolated Ti sites: their interface exhibits excellent specificity and stability towards epoxidation of propylene in H2/O2 due to synergetic effect.
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Nov 2018
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B18-Core EXAFS
I22-Small angle scattering & Diffraction
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Elizabeth
Raine
,
Adam
Clark
,
Glen
Smales
,
Andrew
Smith
,
Diego
Gianolio
,
Tong
Li
,
Jianwei
Zheng
,
Benjamin
Griffith
,
Timothy I.
Hyde
,
Mark
Feaviour
,
Paul
Collier
,
John V.
Hanna
,
Gopinathan
Sankar
,
Shik Chi Edman
Tsang
Diamond Proposal Number(s):
[16316, 16583]
Abstract: The strong directing effects and difficulties in the removal of organic based surfactants makes the templated synthesis of nanoparticles in solid porous structures of defined molecular sizes such as SBA-15, without the use of surfactants, considerably attractive. However, the effects of their internal surface structures, adsorption affinities and lattice mis-match on the particle morphology grown therein have not been fully appreciated. Here, we report the internal surface of the silica preferentially hosts isolated tetrahedrally coordinated oxidic Zn species on the molecular walls of the SBA-15 channels from wet impregnated Zn2+ and Pt2+ species. This leads to less thermodynamic stable but kinetic controlled configuration of atomic zinc deposition on core platinum nanoparticles with unique confined lattice changes and surface properties to both host and guest structures at the interface upon reduction of the composite. This method for the formation templated nanoparticles may generate interests to form new tunable materials as dehydrogenation catalysts.
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Nov 2018
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18250]
Abstract: A series of surfactant-free nickel-core and silver-shell (Ni@Ag) nanoparticles encapsulated within the mesopores of SBA-15 were synthesized and tested as catalysts for direct propylene oxidation by molecular oxygen. The influences of temperature, Gas Hour Space Velocity (GHSV) and Ni/Ag ratio on catalytic activity were systematically investigated. Among the prepared samples, Ni1Ag0.4/SBA-15 exhibited the best catalytic performance with selectivity of 70.7% and PO production rate of 4.4 nmol/g/s under 1 bar at 220 °C with GHSV of 192 h-1. High selectivity was attributed to longer Ag-Ag interatomic distance obtained by careful engineering the thickness of Ag shell over preformed Ni nanoparticles. In addition, all prepared new Ni@Ag core-shell catalysts presented excellent stability, which could maintain the conversion and selectivity for at least 10 hours. These results suggest that new designs based on Ag surface atoms tailoring might pave the way to highly efficient and robust Ag catalysts for direct propylene oxidation using molecular oxygen as sole oxidant.
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Oct 2018
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B18-Core EXAFS
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Abstract: Transition metal-doped nickel phosphide nanoparticles with metallic properties are prepared by a simple and facile wet-chemical method. It is shown for the first time that these transition metals: iron, cobalt, manganese, and molybdenum, can atomically substitute nickel in the parent hcp phosphide lattice as a single phase without significant change in its metallic structure and morphology. They are employed as electro- and photocatalysts for hydrogen evolution reaction, which show highly tunable activities dependent on electron filling of their metallic bands and H coverage according to our experimental and theoretical rationalizations. Molybdenum-doped nickel phosphide nanoparticle with lower H coverage exhibits the best hydrogen evolution performance in electrocatalytic hydrogen evolution reaction, which also shows excellent photocatalytic hydrogen production with organic photosensitizer. In addition, cobalt-doped nickel phosphide nanoparticle with higher H coverage with aqueous photosensitizer gives more superior hydrogen evolution rate.
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Oct 2018
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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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