I20-EDE-Energy Dispersive EXAFS (EDE)
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Donato
Decarolis
,
Monik
Panchal
,
Matthew
Quesne
,
Khaled
Mohammed
,
Shaojun
Xu
,
Mark
Isaacs
,
Adam H.
Clark
,
Luke L.
Keenan
,
Takuo
Wakisaka
,
Kohei
Kusada
,
Hiroshi
Kitagawa
,
C. Richard A.
Catlow
,
Emma K.
Gibson
,
Alexandre
Goguet
,
Peter
Wells
Diamond Proposal Number(s):
[21593]
Open Access
Abstract: Unravelling kinetic oscillations, which arise spontaneously during catalysis, has been a challenge for decades but is important not only to understand these complex phenomena but also to achieve increased activity. Here we show, through temporally and spatially resolved operando analysis, that CO oxidation over Rh/Al2O3 involves a series of thermal levering events—CO oxidation, Boudouard reaction and carbon combustion—that drive oscillatory CO2 formation. This catalytic sequence relies on harnessing localized temperature episodes at the nanoparticle level as an efficient means to drive reactions in situations in which the macroscopic conditions are unfavourable for catalysis. This insight provides a new basis for coupling thermal events at the nanoscale for efficient harvesting of energy and enhanced catalyst technologies.
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Jul 2024
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B18-Core EXAFS
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Diego
Gianolio
,
Michael D.
Higham
,
Matthew G.
Quesne
,
Matteo
Aramini
,
Ruoyu
Xu
,
Alex I.
Large
,
Georg
Held
,
Juan-Jesús
Velasco-Vélez
,
Michael
Haevecker
,
Axel
Knop-Gericke
,
Chiara
Genovese
,
Claudio
Ampelli
,
Manfred Erwin
Schuster
,
Siglinda
Perathoner
,
Gabriele
Centi
,
C. Richard A.
Catlow
,
Rosa
Arrigo
Diamond Proposal Number(s):
[24919]
Open Access
Abstract: Operando soft and hard X-ray spectroscopic techniques were used in combination with plane-wave density functional theory (DFT) simulations to rationalize the enhanced activities of Zn-containing Cu nanostructured electrocatalysts in the electrocatalytic CO2 hydrogenation reaction. We show that at a potential for CO2 hydrogenation, Zn is alloyed with Cu in the bulk of the nanoparticles with no metallic Zn segregated; at the interface, low reducible Cu(I)–O species are consumed. Additional spectroscopic features are observed, which are identified as various surface Cu(I) ligated species; these respond to the potential, revealing characteristic interfacial dynamics. Similar behavior was observed for the Fe–Cu system in its active state, confirming the general validity of this mechanism; however, the performance of this system deteriorates after successive applied cathodic potentials, as the hydrogen evolution reaction then becomes the main reaction pathway. In contrast to an active system, Cu(I)–O is now consumed at cathodic potentials and not reversibly reformed when the voltage is allowed to equilibrate at the open-circuit voltage; rather, only the oxidation to Cu(II) is observed. We show that the Cu–Zn system represents the optimal active ensembles with stabilized Cu(I)–O; DFT simulations rationalize this observation by indicating that Cu–Zn–O neighboring atoms are able to activate CO2, whereas Cu–Cu sites provide the supply of H atoms for the hydrogenation reaction. Our results demonstrate an electronic effect exerted by the heterometal, which depends on its intimate distribution within the Cu phase and confirms the general validity of these mechanistic insights for future electrocatalyst design strategies.
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Apr 2023
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B22-Multimode InfraRed imaging And Microspectroscopy
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Mar 2023
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[31082]
Open Access
Abstract: Despite extensive efforts to develop high-performance H2 evolution catalysts, this remains a major challenge. Here, we demonstrate the use of Cd/Pt precursor solutions for significant photocatalytic H2 production (154.7 mmol g-1 h-1), removing the need for a pre-synthesized photocatalyst. In addition, we also report simultaneous in-situ synthesis of Pt single-atoms anchored CdS nanoparticles (PtSA-CdSIS) during photoirradiation. The highly dispersed in-situ incorporation of extensive Pt single atoms on CdSIS enables the enhancement of active sites and suppresses charge recombination, which results in exceptionally high solar-to-hydrogen conversion efficiency of ~1% and an apparent quantum yield of over 91% (365 nm) for H2 production. Our work not only provides a promising strategy for maximising H2 production efficiency but also provides a green process for H2 production and the synthesis of highly photoactive PtSA-CdSIS nanoparticles.
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Feb 2023
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B18-Core EXAFS
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Man
Zhang
,
Shaojun
Xu
,
Mebrouka
Boubeche
,
Donato
Decarolis
,
Yizhe
Huang
,
Biying
Liu
,
Emma K.
Gibson
,
Xin
Li
,
Yuchen
Wang
,
Huixia
Luo
,
C. Richard A.
Catlow
,
Kai
Yan
Diamond Proposal Number(s):
[19850]
Abstract: Green and highly selective synthesis of organonitrogen chemicals (ONCs) using the renewable energy source biomass over noble-metal free solid catalysts under common room temperature and pressure conditions is still a major challenge. Here, we report a sustainable electrochemical method for selective synthesis of several valuable ONCs with high yields using biomass-derived furanic aldehydes over greenly fabricated TiS2 nanosheets through a facile synthesis. Based on a range of characterization techniques including high-resolution transmission electron microscopy and X-ray absorption fine structure, a well-defined structure of the TiS2 nanosheets (3.86 nm with 1T phase) was constructed. These as-prepared catalysts were applied to the electrochemical reductive amination (ERA) of three biomass-derived aldehydes, i.e. furfural (FF), 5-methylfurfural (MF) and 5-hydroxymethylfurfural (HMF), and exhibited superior performance whereby over 95% conversion of each furanic aldehyde and nearly perfect selectivity of ONCs were achieved. TiS2 nanosheets, in particular, exhibited a marked ∼2-fold increase in conversion (∼49%) compared with the monometallic Ti electrode. Besides, the reaction kinetics and rational pathway were also studied. In addition, these exfoliated TiS2 nanosheets maintained high durability over 6 h, providing a promising and versatile route for the sustainable upgrading of biomass-derived sources.
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Nov 2022
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E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[29599]
Open Access
Abstract: Solar H2O2 produced by O2 reduction provides a green, efficient, and ecological alternative to the industrial anthraquinone process and H2/O2 direct-synthesis. We report efficient photocatalytic H2O2 production at a rate of 73.4 mM h–1 in the presence of a sacrificial donor on a structurally engineered catalyst, alkali metal-halide modulated poly(heptazine imide) (MX → PHI). The reported H2O2 production is nearly 150 and >4250 times higher than triazine structured pristine carbon nitride under UV–visible and visible light (≥400 nm) irradiation, respectively. Furthermore, the solar H2O2 production rate on MX → PHI is higher than most of the previously reported carbon nitride (triazine, tri-s-triazine), metal oxides, metal sulfides, and other metal–organic photocatalysts. A record high AQY of 96% at 365 nm and 21% at 450 nm was observed. We find that structural modulation by alkali metal-halides results in a highly photoactive MX → PHI catalyst which has a broader light absorption range, enhanced light absorption ability, tailored bandgap, and a tunable band edge position. Moreover, this material has a different polymeric structure, high O2 trapping ability, interlayer intercalation, as well as surface decoration of alkali metals. The specific C≡N groups and surface defects, generated by intercalated MX, were also considered as potential contributors to the separation of photoinduced electron–hole pairs, leading to enhanced photocatalytic activity. A synergy of all these factors contributes to a higher H2O2 production rate. Spectroscopic data help us to rationalize the exceptional photochemical performance and structural characteristics of MX → PHI.
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Jun 2022
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E01-JEM ARM 200CF
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Naomi
Lawes
,
Isla
Gow
,
Louise R.
Smith
,
Kieran
Aggett
,
James
Hayward
,
Lara
Kabalan
,
Andrew J.
Logsdail
,
Thomas J. A.
Slater
,
Malcolm
Dearg
,
David J.
Morgan
,
Nicholas F.
Dummer
,
Stuart H.
Taylor
,
C. Richard A.
Catlow
,
Michael
Bowker
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[27530]
Open Access
Abstract: A number of Pd based materials have been synthesised and evaluated as catalysts for the conversion of carbon dioxide and hydrogen to methanol, a useful platform chemical and hydrogen storage molecule. Monometallic Pd catalysts shows poor methanol selectivity, but this is improved through the formation of Pd alloys, with both PdZn and PdGa alloys showing greatly enhanced methanol productivity compared with monometallic Pd/Al2O3 and Pd/TiO2 catalysts. Catalyst characterisation shows that the 1:1 β-PdZn alloy is present in all Zn containing post-reaction samples, including PdZn/Ga2O3, while the Pd2Ga alloy formed for the Pd/Ga2O3 sample. The heats of mixing were calculated for a variety of alloy compositions with high heats of mixing calculated for both PdZn and Pd2Ga alloys, with values of ca. -0.6 eV/atom and ca. -0.8 eV/atom, respectively. However, ZnO is more readily reduced than Ga2O3, providing a possible explanation for the preferential formation of the PdZn alloy, rather than PdGa. when in the presence of Ga2O3.
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Jun 2022
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E01-JEM ARM 200CF
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Michael
Bowker
,
Naomi
Lawes
,
Isla
Gow
,
James
Hayward
,
Jonathan
Ruiz Esquius
,
Nia
Richards
,
Louise R.
Smith
,
Thomas J. A.
Slater
,
Thomas E.
Davies
,
Nicholas F.
Dummer
,
Lara
Kabalan
,
Andrew
Logsdail
,
Richard C.
Catlow
,
Stuart
Taylor
,
Graham J
Hutchings
Diamond Proposal Number(s):
[27530]
Open Access
Abstract: The rise in atmospheric CO2 concentration and the concomitant rise in global surface temperature have prompted massive research effort in designing catalytic routes to utilize CO2 as a feedstock. Prime among these is the hydrogenation of CO2 to make methanol, which is a key commodity chemical intermediate, a hydrogen storage molecule, and a possible future fuel for transport sectors that cannot be electrified. Pd/ZnO has been identified as an effective candidate as a catalyst for this reaction, yet there has been no attempt to gain a fundamental understanding of how this catalyst works and more importantly to establish specific design criteria for CO2 hydrogenation catalysts. Here, we show that Pd/ZnO catalysts have the same metal particle composition, irrespective of the different synthesis procedures and types of ZnO used here. We demonstrate that all of these Pd/ZnO catalysts exhibit the same activity trend. In all cases, the β-PdZn 1:1 alloy is produced and dictates the catalysis. This conclusion is further supported by the relationship between conversion and selectivity and their small variation with ZnO surface area in the range 6–80 m2g–1. Without alloying with Zn, Pd is a reverse water-gas shift catalyst and when supported on alumina and silica is much less active for CO2 conversion to methanol than on ZnO. Our approach is applicable to the discovery and design of improved catalysts for CO2 hydrogenation and will aid future catalyst discovery.
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Apr 2022
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B22-Multimode InfraRed imaging And Microspectroscopy
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Diamond Proposal Number(s):
[18680, 20906, 22347, 23081]
Open Access
Abstract: Synchrotron FTIR microspectroscopy coupled with mass spectrometric analysis of desorbed products has been used to investigate the initial stages of the methanol to olefins (MTO) reaction in single crystals of SAPO-34. Surface methoxy groups (SMS) are key to initial dimethylether (DME) and subsequent carbon–carbon bond formation. Deprotonation of SMS is the critical first step in direct olefin formation at low temperatures and DME is not involved in the carbon–carbon forming step. Experiments with CD3OH confirm the deprotonation step and show an inverse kinetic isotope effect consistent with irreversible deprotonation. The subsequent formation of alkoxide species, which are the precursors of the olefinic hydrocarbon pool present in working MTO catalysts, is initiated via insertion of surface carbene-like species into adjacent SMS. The observed induction period for this process is determined by the limited mobility of SMS and/or carbene species. Olefins formed from cracking of the alkoxide species then transmit carbon–carbon bond formation through the SAPO-34 by rapid diffusion and reaction with further SMS. Acetyl species seen with methanol at higher temperatures support the insertion of CO into SMS suggested in the literature, but these species do not play a role in direct olefin formation.
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Feb 2022
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B22-Multimode InfraRed imaging And Microspectroscopy
I14-Hard X-ray Nanoprobe
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Diamond Proposal Number(s):
[22298]
Open Access
Abstract: Unwanted N2O formation is a problem that has been noted in selective catalytic reduction (SCR) where copper zeolite catalysts are utilized. With its immense global warming potential and long-term stability, elevated atmospheric N2O has already been identified as a future challenge in the war on climate change. This paper explores the phenomenon of N2O formation during NH3-SCR over Cu-SSZ-13 catalysts, which are currently commercialized in automotive emissions control systems, and proposes a link between N2O production and the local copper environment found within the zeolite. To achieve this, a comparison is made between two Cu-SSZ-13 samples with different copper co-ordinations produced via different synthesis methods. A combination of synchrotron X-ray absorption near-edge spectroscopy, UV–vis, Raman, and density functional theory (DFT) is used to characterize the nature of copper species present within each sample. Synchrotron IR microspectroscopy is then used to compare their behavior during SCR under operando conditions and monitor the evolution of nitrate intermediates, which, along with further DFT, informs a mechanistic model for nitrate decomposition pathways. Increased N2O production is seen in the Cu-SSZ-13 sample postulated to contain a linear Cu species, providing an important correlation between the catalytic behavior of Cu-zeolites and the nature of their metal ion loading and speciation.
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Oct 2021
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