B18-Core EXAFS
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Diamond Proposal Number(s):
[15151]
Abstract: Lignin is one of the most promising feedstocks for renewable aromatics production. Conversion of such feedstock into aromatics can be attained through catalytic hydrogenolysis. In this work, NixFey/TiN bimetallic catalysts were evaluated in the hydrogenolysis of both: (i) benzyl phenyl ether (BPE) as a model compound for lignin and (ii) real organosolv lignin feedstock under low temperature (150 °C) and low H2 pressure (12 bar). All bimetallic catalysts exhibited superior performance over single-component materials and were shown to compose of uniformly/highly dispersed and intimately mixed Ni and Fe nanoparticles. Among bimetallic materials, Ni5Fe2/TiN possesses the highest activity in BPE hydrogenolysis, which is comparable to that of a 5% Pd/C commercial catalyst while showing significantly higher aromatic selectivity. Ni5Fe2/TiN catalyst also outperformed Pd/C in hydrogenolysis of organosolv lignin, shown by its higher oil yield, greater content of phenolic monomers, and lower content of dimers. This material exhibited good stability in BPE conversion with no noticeable deactivation over 5 recycling cycles. XANES analysis suggests the electron transfer from Ni to Fe, which explains the superior activity observed with Ni5Fe2/TiN.
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Jul 2023
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B18-Core EXAFS
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Diamond Proposal Number(s):
[19850, 17198]
Open Access
Abstract: In this work, we demonstrate that the synergistic effect of PdAu nanoparticles (NPs) in hydrogenation reactions is not only related to high activity but also to their stability when compared to Pd mono-metallic NPs. To demonstrate this, a series of mono- and bi-metallic NPs; Pd, Pd0.75Au0.25, Pd0.5Au0.5, Pd0.25Au0.75 and Au in ionic liquid [C4C1Im][NTf2] have been fabricated via magnetron sputtering process. Bi-metallic NPs possess external shells enriched with Pd atoms that interact with [NTf2]- of the ionic liquid resulting in enhanced catalytic performance in hydrogenation of cinnamanaldehyde compared to their mono-metallic counterparts. This is ascribed to their higher stability over 24 h reaction, whilst the catalytic activity and selectivity are comparable for both catalysts. Using a bespoke kinetic model for in situ catalyst deactivation investigations and electron microscopy imaging at nanoscale, we have shown that PdAu has a deactivation rate constant of 0.13 h-1, compared to 0.33 h-1 for Pd NPs, leaving 60 % and 40 % of available sites after the reaction, respectively. Beyond that, the kinetic model demonstrates that the reaction product has a strong stabilizing factor for bimetallic NPs against coarsening and deactivation, which is not the case for Pd NPs. In summary, our kinetic model enables the evaluation of the catalyst performance over the entire chemical reaction space, probing the contribution of each individual components of the reaction mixture and allowing the design of high-performance catalysts.
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Jun 2023
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B18-Core EXAFS
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Open Access
Abstract: The CO2-assisted oxidative dehydrogenation reaction can possibly become a more sustainable alternative for the production of light olefins. Due to the endothermic nature of this reaction, elevated reaction temperatures are required to achieve conversion levels of interest, with competing side reactions as result. In this study, the effect of reaction temperature on the performance of silica supported molybdenum carbide nanoparticles is investigated. At all applied reaction temperatures, the maximum possible ethylene selectivity of 67 C-% is achieved. An increase in reaction temperature decreases the oxidation of the catalyst under reaction conditions. However, a clear phase change effect on the various carbide allotropes suggests that an oxidation/re-carburization mechanism occurs from β-Mo2C to MoOxCy/MoO2 to α-MoC1-x/β-Mo2C, rather than a prevention of the oxidation in the first place. Nevertheless, catalyst deactivation was still observed and can be assigned to carbon formation on the surface of the catalyst, blocking active sites.
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Jun 2023
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B18-Core EXAFS
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Diamond Proposal Number(s):
[26801]
Open Access
Abstract: Foaming during vitrification of radioactive waste in Joule-Heated Ceramic Melters (JHCM) is exacerbated by trapping of evolving gases, such as CO2, NOx and O2, beneath a viscous reaction layer. Foaming restricts heat transfer during melting. Sucrose is employed as the baseline additive at the Hanford site in Washington State, USA to reduce foaming. Alternative carbon-based reductant additives were explored in simulated, inactive Hanford high-iron HLW-NG-Fe2 feeds, for both their effect on foaming and to give insight to the behaviour of multivalent species in glass melts under different redox conditions. Graphite, coke (93% C), formic acid and HEDTA additives were compared with sucrose, and a feed with no additive. Graphite and coke additions proved most effective in reducing the maximum foam volume by 51 ± 3% and 54 ± 2%, respectively, compared with 24 ± 5% for sucrose. Lower foaming could result in more efficient vitrification in JHCMs. Reductants also affected redox ratios in the multivalent species present in the feed. The order of reduction, Mn3+/Mn2+ > Cr6+/Cr3+ > Ce3+/Ce4+ > Fe3+/Fe2+ was as predicted on the basis of their redox potentials. There is less reduction overall, particularly in the Fe3+ → Fe2+, than predicted by the calculations, attributed to the oxygenated atmosphere of the experiments.
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May 2023
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B18-Core EXAFS
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Open Access
Abstract: New and exotic ground states of magnetic materials are highly sought after and are extensively studied for the insights they provide into the thermodynamics of disorder and fundamental magnetic interactions. By controlling the crystal structure of an appropriate magnetic lattice, it is possible to cause the strong magnetic exchange interactions to sum to zero and so be frustrated. Due to the presence of this frustration, the lowest energy configuration that results may be crucially dependent on the tiniest of energy differences between a multitude of states that have (almost) the same energy. The keen interest in these materials arises from the fact that these finely balanced systems offer a way of probing classical or quantum mechanical interactions that are of fundamental importance but are too weak to be observed in non-frustrated systems. Here, we combine local and crystallographic probes of the cation-ordered double perovskite Ba2MnMoO6 that contains a face-centered cubic lattice of S = 5/2 Mn2+ cations. Neutron diffraction measurements below 9.27(7) K indicate that a fourfold degenerate non-collinear antiferromagnetic state exists with almost complete ordering of the Mn2+ spins. Muon spin relaxation measurements provide a local probe of the magnetic fields inside this material over the t1/2 = 2.2 µs lifetime of a muon, indicating a slightly lower Néel transition temperature of 7.9(1) K. The dc susceptibility data do not show the loss of magnetization that should accompany the onset of the antiferromagnetic order; they indicate that a strongly antiferromagnetically coupled paramagnetic state [θ = −73(3) K] persists down to 4 K, at which temperature a weak transition occurs. The behavior of this material differs considerably from the closely related compositions Ba2MnMO6 (M = W, Te), which show collinear ordering arrangements and well defined antiferromagnetic transitions in the bulk susceptibility. This suggests that the Mo6+ cation leads to a fine balance between the nearest and next-nearest neighbor superexchange in these frustrated double perovskite structures.
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May 2023
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B18-Core EXAFS
E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[21795, 15151]
Open Access
Abstract: Catalytic allylic alcohol oxidation to aldehydes is an industrial process that necessitates chemoselectivity. Surface PdO (on Pd) enables this transformation but does not represent optimal metal utilisation. Here we report a facile synthesis route to produce isolated surface PdO catalytic sites on an earth-abundant metal (NiO) for cinnamyl alcohol oxidation.
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May 2023
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B18-Core EXAFS
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Diamond Proposal Number(s):
[19850]
Open Access
Abstract: The Fischer–Tropsch (FT) synthesis is traditionally associated with fossil fuel consumption, but recently this technology has emerged as a keystone that enables the conversion of captured CO2 with sustainable hydrogen to energy-dense fuels and chemicals for sectors which are challenging to be electrified. Iron-based FT catalysts are promoted with alkali and transition metals to improve reducibility, activity, and selectivity. Due to their low concentration and the metastable state under reaction conditions, the exact speciation and location of these promoters remain poorly understood. We now show that the selectivity promoters such as potassium and manganese, locked into an oxidic matrix doubling as a catalyst support, surpass conventional promoting effects. La1–xKxAl1–yMnyO3−δ (x = 0 or 0.1; y = 0, 0.2, 0.6, or 1) perovskite supports yield a 60% increase in CO conversion comparable to conventional promotion but show reduced CO2 and overall C1 selectivity. The presented approach to promotion seems to decouple the enhancement of the FT and the water–gas shift reaction. We introduce a general catalyst design principle that can be extended to other key catalytic processes relying on alkali and transition metal promotion.
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May 2023
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Shunsuke
Sasaki
,
Souvik
Giri
,
Simon J.
Cassidy
,
Sunita
Dey
,
Maria
Batuk
,
Daphne
Vandemeulebroucke
,
Giannantonio
Cibin
,
Ronald I.
Smith
,
Philip
Holdship
,
Clare P.
Grey
,
Joke
Hadermann
,
Simon J.
Clarke
Diamond Proposal Number(s):
[25166, 14239]
Open Access
Abstract: Topochemistry enables step-by-step conversions of solid-state materials often leading to metastable structures that retain initial structural motifs. Recent advances in this field revealed many examples where relatively bulky anionic constituents were actively involved in redox reactions during (de)intercalation processes. Such reactions are often accompanied by anion-anion bond formation, which heralds possibilities to design novel structure types disparate from known precursors, in a controlled manner. Here we present the multistep conversion of layered oxychalcogenides Sr2MnO2Cu1.5Ch2 (Ch = S, Se) into Cu-deintercalated phases where antifluorite type [Cu1.5Ch2]2.5- slabs collapsed into two-dimensional arrays of chalcogen dimers. The collapse of the chalcogenide layers on deintercalation led to various stacking types of Sr2MnO2Ch2 slabs, which formed polychalcogenide structures unattainable by conventional high-temperature syntheses. Anion-redox topochemistry is demonstrated to be of interest not only for electrochemical applications but also as a means to design complex layered architectures.
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May 2023
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B18-Core EXAFS
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Open Access
Abstract: Co-precipitation was used to prepare a copper, zinc, and aluminium hydrotalcite-like precursor to make a methanol synthesis catalyst. Treatment of the wet precursor with an aqueous miscible organic solvent led to the delamination of the sheet-like structure of the precursor phase, dramatically increasing the surface area to 340 m2 g−1 in comparison to 22 m2 g−1 for the untreated material. We show that the copper is initially sequestered within the hydrotalcite phase, and during calcination a CuO phase evolves out from the lamellar structures. Reduction proceeds to Cu0, and neither the calcination nor reduction of the material cause the loss of the lamellar morphology. This leads to high Cu0 surface areas in the final catalyst (66 m2 g−1) and high activity in the methanol synthesis reaction.
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May 2023
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B18-Core EXAFS
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Nicola
Schiaroli
,
Leila
Negahdar
,
Mads
Lützen
,
Phuoc
Hoang Ho
,
Lisa J.
Allen
,
Alejandro
Natoli
,
Francesca
Ospitali
,
Francesco
Maluta
,
Enrique
Rodríguez-Castellón
,
Christian D.
Damsgaard
,
Giuseppe
Fornasari
,
Andrew M.
Beale
,
Patricia
Benito
Abstract: Pd-In2O3 catalysts are among the most promising alternatives to Cu-ZnO-Al2O3 for synthesis of CH3OH from CO2. However, the intrinsic activity and stability of In2O3 per unit mass should be increased to reduce the content of this scarcely available element and to enhance the catalyst lifetime. Herein, we propose and demonstrate a strategy for obtaining highly dispersed Pd and In2O3 nanoparticles onto an Al2O3 matrix by a one-step coprecipitation followed by calcination and activation. The activity of this catalyst is comparable with that of a Pd-In2O3 catalyst (0.52 vs. 0.55 gMeOH h-1 gcat-1 at 300°C, 30 bar, 40,800 ml h-1 gcat-1) but the In2O3 loading decreases from 98 to 12 wt.% while improving the long-term stability by three-fold at 30 bar. In the new Pd-In2O3-Al2O3 system, the intrinsic activity of In2O3 is highly increased both in terms of STY normalized to In specific surface area and In2O3 mass (4.32 vs 0.56 g gMeOH h-1 gIn2O3-1 of a Pd- In2O3 catalyst operating at 300°C, 30 bar, 40,800 ml h-1 gcat-1).The combination of ex situ and in situ catalyst characterizations during reduction provides insights into the interaction between Pd and In and with the support. The enhanced activity is likely related to the close proximity of Pd and In2O3, wherein the H2 splitting activity of Pd promotes, in combination with CO2 activation over highly dispersed In2O3 particles, facile formation of CH3OH.
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May 2023
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