B18-Core EXAFS
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Hongman
Sun
,
Yu
Zhang
,
Chunfen
Wang
,
Mark A.
Isaacs
,
Ahmed I.
Osman
,
Yehong
Wang
,
David
Rooney
,
Youhe
Wang
,
Zifeng
Yan
,
Christopher M. A.
Parlett
,
Feng
Wang
,
Chunfei
Wu
Diamond Proposal Number(s):
[19850]
Abstract: Integrated carbon capture and utilization (ICCU) presents an ideal solution to address anthropogenic carbon dioxide (CO2) emissions from industry and energy sectors, facilitating CO2 capture and subsequent utilization through conversion into high-value chemicals, as opposed to current release into the atmosphere. Herein, we report the synergistic coupling of porous CaO, as a sorbent for CO2 capture, and Ni doped CeO2 nanorods, as catalytic sites for CO2 reduction. It is found that ceria is shown to possess the capacity for CO2 utilization, however, critically it only results in the generation of CO due to the weak CO-ceria bonding. The addition of Ni active sites gives rise to CH4 being the predominant product, via the strong interaction between Ni species and CO, which facilitates further reduction. Through tuning Ni loadings, we have evaluated the role of catalytic active site size, with a Ni loading of only 0.5 wt% providing optimal performance through the formation of sub-nanometer sized clusters. This near-atomic active site dispersion gives rise to CH4 productivity and selectivity of 1540 mmol g−1 Ni and 85.8%, respectively, with this optimal combination of catalyst and sorbent demonstrating high stability over 10 cycles of ICCU process. These observations in parallel with the synergistic coupling of earth-abundant, low-cost materials (CaO and Ni) will have broad implications on the design and implementation of high efficiency, cost-effective ICCU materials and processes.
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Jun 2022
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E01-JEM ARM 200CF
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Shanshan
Xu
,
Thomas J. A.
Slater
,
Hong
Huang
,
Yangtao
Zhou
,
Yilai
Jiao
,
Christopher M. A.
Parlett
,
Shaoliang
Guan
,
Sarayute
Chansai
,
Shaojun
Xu
,
Xinrui
Wang
,
Christopher
Hardacre
,
Xiaolei
Fan
Diamond Proposal Number(s):
[29468]
Open Access
Abstract: The stability of catalysts in dry reforming of methane (DRM) is a known issue. In this paper an encapsulation strategy has been employed to improve the stability compared with conventional impregnation methods. Herein, nickel nanoparticles encapsulated in silicalite-1 were prepared using a range of methods including post treatment, direct hydrothermal and seed-directed methods to investigate the effect of synthesis protocol on the properties of catalysts, such as degree of encapsulation and Ni dispersion, and anti-coking/-sintering performance in DRM. The Ni@SiO2-S1 catalysts obtained by the seed-directed synthesis presented the full encapsulation of Ni NPs by the zeolite framework with small particle sizes (∼2.9 nm) and strong metal-support interaction, which could sterically hinder the migration/aggregation of Ni NPs and carbon deposition. Therefore, Ni@SiO2-S1 showed stable CO2/CH4 conversions of 80% and 73%, respectively, with negligible metal sintering and coking deposition (∼0.5 wt.%) over 28 h, which outperformed the other catalysts prepared. In contrast, the catalysts developed by the post-treatment and ethylenediamine-protected hydrothermal methods showed the co-existence of Ni phase on the internal and external surfaces, i.e. incomplete encapsulation, with large Ni particles, contributing to Ni sintering and coking. The correlation of the synthesis-structure-performance in this study sheds light on the design of coking-/sintering-resistant encapsulated catalysts for DRM.
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Jun 2022
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Abstract: Ordered mesoporous silicas are widely used in separation science and catalysis, however, their slow batch synthesis is a barrier to scale-up and new applications. SBA-15 is one of the most extensively studied and commercially available mesoporous silicas, whose textural properties can be readily tuned through judicious choice of synthesis conditions. Here we demonstrate the continuous flow synthesis of SBA-15 in high yield at 80 °C using a simple tube reactor without any mixing device. The resulting SBA-15 exhibits excellent textural properties, with a BET surface area of 566 m2 g−1 and ordered 5.1 nm mesopore channels in a p6mm arrangement, akin to those from conventional batch synthesis, but with far higher productivity than previously reported in batch or flow (5.3 g L−1 h−1 versus 0.4 and 0.6 g L−1 h−1 respectively).
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Nov 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[15151]
Open Access
Abstract: Hierarchical zeolites have the potential to provide a breakthrough in transport limitation, which hinders pristine microporous zeolites and thus may broaden their range of applications. We have explored the use of Pd-doped hierarchical ZSM-5 zeolites for aerobic selective oxidation (selox) of cinnamyl alcohol and benzyl alcohol to their corresponding aldehydes. Hierarchical ZSM-5 with differing acidity (H-form and Na-form) were employed and compared with two microporous ZSM-5 equivalents. Characterization of the four catalysts by X-ray diffraction, nitrogen porosimetry, NH3 temperature-programmed desorption, CO chemisorption, high-resolution scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy allowed investigation of their porosity, acidity, as well as Pd active sites. The incorporation of complementary mesoporosity, within the hierarchical zeolites, enhances both active site dispersion and PdO active site generation. Likewise, alcohol conversion was also improved with the presence of secondary mesoporosity, while strong Brønsted acidity, present solely within the H-form systems, negatively impacted overall selectivity through undesirable self-etherification. Therefore, tuning support porosity and acidity alongside active site dispersion is paramount for optimal aldehyde production.
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Oct 2021
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I18-Microfocus Spectroscopy
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Abstract: Platinum nanoparticles exhibit unique catalytic properties and have a number of important applications: as an industrial catalyst for fuel cells, in the synthesis of nitric acid, as well as in the reduction of exhaust gases from vehicles. While there have been many studies demonstrating size and morphology control of platinum nanoparticles, a molecular level understanding of the nucleation and growth mechanisms underlying nanoparticle formation, which is crucial for efficient optimization of size controlled synthesis, is lacking in the literature. Structurally incisive experimental in situ probes with enough spatial and temporal resolution are needed to monitor nucleation and growth processes.
Here we use operando X-ray Absorption Spectroscopy (XAS) coupled with continuous flow microfluidics to study the mechanisms of platinum nanoparticle formation by reduction of H2PtCl6 using ethylene glycol as a reducing agent. In contrast to a batch synthesis, a continuous flow device allows for rapid and efficient mixing of precursors and fine control over the synthesis parameters such as concentration, flow rate and temperature. The XAS results capture the intermediate stages of nanoparticle formation through to complete reduction to Pt nanoparticles. The setup described here can, in principle, be used to study nanoparticle nucleation and growth mechanisms of a wide range of nanoparticles that occur at fast (microsecond) timescales.
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Jul 2021
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Abstract: Catalytic hydrodeoxygenation (HDO) provides a promising route for upgrading biomass-derived fatty acids to alkanes, which are potential biofuels (e.g. jet fuel (C8–C16) and diesel (C12–C22)) that could reduce our reliance on unsustainable fossil fuels. Currently, catalytic HDO, conducted over catalysts such as molybdenum disulfide, necessitates harsh operating conditions (>300 °C) which is both environmentally and economically unsustainable and promotes unwanted side reactions, e.g. cracking, which compromises product selectivity. Accordingly, the development of novel catalysts, which enable efficient and sustainable HDO, under milder operating conditions, and their translation from lab bench to large-scale production are highly desired. This review discusses the recent development of heterogeneous catalysts for HDO (including reaction pathways, mechanisms, and side reactions) and explores design strategies for the development of new multifunctional catalysts with potential to enable future development of HDO processes under mild conditions. In particular, we consider the sequential cascade transformation of fatty acids into fatty alcohols (via hydrodeoxygenation) and then hydrocarbons (via dehydration and hydrogenation), which requires the coupling of different but complementary catalytic sites, as an attractive alternative mild HDO strategy.
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Mar 2021
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I11-High Resolution Powder Diffraction
I20-EDE-Energy Dispersive EXAFS (EDE)
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Longfei
Lin
,
Mengtian
Fan
,
Alena M.
Sheveleva
,
Xue
Han
,
Zhimou
Tang
,
Joseph H.
Carter
,
Ivan
Da Silva
,
Christopher
Parlett
,
Floriana
Tuna
,
Eric J. L.
Mcinnes
,
German
Sastre
,
Svemir
Rudic
,
Hamish
Cavaye
,
Stewart F.
Parker
,
Yongqiang
Cheng
,
Luke L.
Daemen
,
Anibal J.
Ramirez-Cuesta
,
Martin P.
Attfield
,
Yueming
Liu
,
Chiu C.
Tang
,
Buxing
Han
,
Sihai
Yang
Diamond Proposal Number(s):
[2359]
Open Access
Abstract: Optimising the balance between propene selectivity, propene/ethene ratio and catalytic stability and unravelling the explicit mechanism on formation of the first carbon–carbon bond are challenging goals of great importance in state-of-the-art methanol-to-olefin (MTO) research. We report a strategy to finely control the nature of active sites within the pores of commercial MFI-zeolites by incorporating tantalum(V) and aluminium(III) centres into the framework. The resultant TaAlS-1 zeolite exhibits simultaneously remarkable propene selectivity (51%), propene/ethene ratio (8.3) and catalytic stability (>50 h) at full methanol conversion. In situ synchrotron X-ray powder diffraction, X-ray absorption spectroscopy and inelastic neutron scattering coupled with DFT calculations reveal that the first carbon–carbon bond is formed between an activated methanol molecule and a trimethyloxonium intermediate. The unprecedented cooperativity between tantalum(V) and Brønsted acid sites creates an optimal microenvironment for efficient conversion of methanol and thus greatly promotes the application of zeolites in the sustainable manufacturing of light olefins.
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Feb 2021
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Abstract: A range of Pt:Cu bimetallic nanoparticles were investigated for the liquid-phase selective hydrogenation of furfural, an important platform biomass feedstock. Alloying of the two metals had a profound effect on the overall catalytic activity, providing superior rates of reaction and achieving the needed high selectivity towards furfuryl alcohol. Furthermore, we investigated the catalytic activity of an Ultra Dilute Alloy (UDA) formed via the galvanic replacement of Cu atoms by Pt atoms on dispersed host Cu nanoparticles (atomic ratio Pt:Cu 1:20). This UDA, after overcoming an induction period, exhibits exceptionally high initial rates of hydrogenation under modest hydrogen pressures of 10 and 20 bar, rivalling the catalytic turnover for the monometallic Pt (containing 12 times more Pt), and outdoing the pure Cu or other compositions of bimetallic nanoparticle alloy catalysts. These atom efficient catalysts are ideal candidates for the valorization of furfural due to their activity and vastly greater economic viability.
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Nov 2020
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Open Access
Abstract: Many industrially important chemical transformations occur at the interface between a solid catalyst and liquid reactants, despite which relatively little attention has been paid to spectroscopic methods for interrogating the working solid–liquid interface. This partly reflects a limited number of analytical techniques that give access to interface-specific information. Direct observation of surface species at catalytic solid–liquid interfaces is a daunting challenge for many in situ techniques due to the low concentration and/or short lifetime of chemical species in dynamic reactions. This review discusses the application of in situ and operando spectroscopies to probe solid–liquid interfaces, with a focus on the resulting mechanistic insight in the context of catalysis for sustainable chemistry.
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Aug 2020
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Abstract: Hydrodeoxygenation (HDO) is a promising technology to upgrade fast pyrolysis bio‐oils but it requires active and selective catalysts. Here we explore the synergy between the metal and acid sites in the HDO of anisole, a model pyrolysis bio‐oil compound, over mono‐ and bi‐functional Pt/(Al)‐SBA‐15 catalysts. Ring hydrogenation of anisole to methoxycyclohexane occurs over metal sites and is structure sensitive; it is favored over small (4 nm) Pt nanoparticles, which confer a turnover frequency (TOF) of approximately 2000 h−1 and a methoxycyclohexane selectivity of approximately 90 % at 200 °C and 20 bar H2; in contrast, the formation of benzene and the desired cyclohexane product appears to be structure insensitive. The introduction of acidity to the SBA‐15 support promotes the demethyoxylation of the methoxycyclohexane intermediate, which increases the selectivity to cyclohexane from 15 to 92 % and the cyclohexane productivity by two orders of magnitude (from 15 to 6500 mmol gPt−1 h−1). Optimization of the metal–acid synergy confers an 865‐fold increase in the cyclohexane production per gram of Pt and a 28‐fold reduction in precious metal loading. These findings demonstrate that tuning the metal–acid synergy provides a strategy to direct complex catalytic reaction networks and minimize precious metal use in the production of bio‐fuels.
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Jun 2020
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