B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[34682]
Abstract: Excessively strong adsorption of CO onto a Pt-based catalyst results in the poisoning effect during numerous CO-containing catalysis reactions, including the dehydrogenation process of alcohols. Traditional strategies via modifying the electronic state of Pt atoms are beneficial for weakening CO adsorption; however, they are normally detrimental to C–H cracking, thereby degrading catalytic efficiency toward alcohol dehydrogenation reaction. In this work, we present a synergistic function of Pt1 single atoms and heterostructured MoOx/Mo2N for efficiently dehydrogenating alcohols, allowing high CO resistance along with excellent capacity for C–H and O–H activation. This conjunction renders electron transfer via a strong Pt-MoOx/Mo2N interaction and thus induces the low 5d occupancy of Pt sites, enabling the facile CO desorption, which thereby boosts the efficiency of entire reaction cycles. Based on in situ structural characterizations and isotopic labeling analysis, we found that the spontaneously formed thin MoOx-Ov layer enables the barrierless breakage of O–H bonds even at as low as room temperature, which further energetically facilitates C–H cracking on interfacial Pt1 sites. Therefore, this strategy can be applied to fabricate CO-tolerant Pt-based catalysts toward numerous CO-containing reactions without compromising reactivity by coupling the advantages of single-atom and defective support materials.
|
Apr 2025
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
I06-Nanoscience (XPEEM)
|
Abstract: The Sabatier reaction (CO2 methanation) represents a facile catalytic process to produce CH4 at relatively low temperatures and with high yields. Ni supported on ceria (Ni/CeO2) is widely recognised as an active catalyst due to the enriched Ni–CeOx interfacial sites. Here, the physicochemical properties of Ni/CeO2 are investigated by a variety of characterisation methods, including but not limited to X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and kerr-gated Raman to establish structure-activity relationships for CO2 methanation. In Chapter 3, the critical role of Ni availability, affected by both Ni particle size and potential encapsulation by reduced CeOx due to a strong metal-support interaction (SMSI), in forming interfacial sites, is highlighted. Chapter 4 examines the positive role of the surface oxygen vacancies (Ov) which was found to enhance Ni availability and MSI in Ni/CeO2 catalysts by creating a disordered and defective ceria film at the interface. This defect-dense Ni–CeOx interface altered the bonding mode between bidentate carbonates during the reaction. Results in chapter 5 evidenced the presence of Ni encapsulation, and confirmed the catalyst stability under at different activation temperatures and operating conditions. In Chapter 6, a two-dimensional (2D) Ni/CeO2 with single Ni NPs on CeO2 (100) crystal was explored using quasi in situ X-ray photoemission electron microscope (X-PEEM) and soft XAS. Detailed spatial analysis of Ni NPs and the surrounding Ce environment proposed the positive role of MSI for Ni reducibility and potential tuning methods. Also, the potential reconfigurations of Ni/CeO2 (e.g. oxidation/reduction and sintering/redispersion), were revealed under CO2 hydrogenation. In summary, the comprehensive research allowed us to better understand the role of Ov, Ni size and MSI in the formation of interfacial sites, and the correlation among these properties, essential for future designs of promising supported Ni catalysts for CO2 hydrogenation.
|
Apr 2025
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
E02-JEM ARM 300CF
I20-EDE-Energy Dispersive EXAFS (EDE)
|
Lu
Chen
,
Xuze
Guan
,
Zhaofu
Fei
,
Hiroyuki
Asakura
,
Lun
Zhang
,
Zhipeng
Wang
,
Xinlian
Su
,
Zhangyi
Yao
,
Luke L.
Keenan
,
Shusaku
Hayama
,
Matthijs A.
Van Spronsen
,
Burcu
Karagoz
,
Georg
Held
,
Christopher S.
Allen
,
David G.
Hopkinson
,
Donato
Decarolis
,
June
Callison
,
Paul J.
Dyson
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[30622, 33257, 31922]
Open Access
Abstract: Selective catalytic oxidation (SCO) of NH3 to N2 is one of the most effective methods used to eliminate NH3 emissions. However, achieving high conversion over a wide operating temperature range while avoiding over-oxidation to NOx remains a significant challenge. Here, we report a bi-metallic surficial catalyst (PtSCuO/Al2O3) with improved Pt atom efficiency that overcomes the limitations of current catalysts. It achieves full NH3 conversion at 250 °C with a weight hourly space velocity of 600 ml NH3·h−1·g−1, which is 50 °C lower than commercial Pt/Al2O3, and maintains high N2 selectivity through a wide temperature window. Operando XAFS studies reveal that the surface Pt atoms in PtSCuO/Al2O3 enhance the redox properties of the Cu species, thus accelerating the Cu2+ reduction rate and improving the rate of the NH3-SCO reaction. Moreover, a synergistic effect between Pt and Cu sites in PtSCuO/Al2O3 contributes to the high selectivity by facilitating internal selective catalytic reduction.
|
Jan 2025
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
|
Diamond Proposal Number(s):
[36863]
Open Access
Abstract: A series of CeO2 supports were treated in an N2 plasma before being impregnated with Ni precursors to evaluate the impact this has on the metal-support interface and catalytic performance. This impact was determined using a suite of characterization methods including X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), ex situ and in situ X-ray absorption spectroscopy (XAS) and in situ Kerr-gated Raman. The combined and self-consistent results indicated that plasma treatment of CeO2 can lead to the generation of an increasing number of oxygen vacancies, and a loss of long-range order in samples treated for 1 h, realizing a highly defective CeOx film at the interface between the Ni metal nanoparticles and the bulk CeO2. However, this highly defective CeOx surface significantly enhances the Ni-CeOx interaction, resulting in a number of smaller Ni NPs in intimate contact with the support, leading to improved catalytic performance for CO2 methanation. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed that the more defect-dense Ni−CeOx interface leads to the formation of more bidentate bridged carbonates (vs. bidentate chelate) and which are more readily consumed during reaction, suggesting the identification of an important parameter to effect low-temperature (< 300 °C) CH4 production.
|
Jan 2025
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[26045]
Open Access
Abstract: Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was employed to investigate the effect of applied potential on the interface of TiO2(110) with 0.1 M HCl. The study, which involved operando electrochemical characterization, enabled real-time monitoring and analysis of electrochemical processes. There is a significant influence on the interface composition; in particular, the surface Cl– surface coverage varies with electrochemical potential. Moreover, there appears to be a reaction of evolved Cl with adventitious carbon to form C–Cl and C–Cl2 species.
|
Nov 2024
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[29265]
Abstract: Harnessing the power of water to produce clean, renewable hydrogen energy is a critical mission for humanity. Given the abundance of oceans on earth, and with freshwater supplies already depleted, the photocatalytic splitting of seawater offers vast potential for a sustainable hydrogen economy as the world transitions away from fossil fuels.
The photocatalytic process of water-splitting uses sunlight to break down water molecules into hydrogen and oxygen gases with a light-absorbing catalyst. But in the past, using seawater has been limited by poor energy conversion efficiencies, instability, and the negative effects of electrolytes in seawater at room temperature. In addition, high electricity consumption and desalination capital costs have impaired technological advancements.
However, in January 2024, breakthrough results published in Nature Catalysis revealed for the first time that the natural ionic composition of seawater can improve photocatalytic efficiency at elevated temperatures (around 270°C) without additional sacrificial reagents, addressing negative electrolyte effects and instability in seawater.
|
Oct 2024
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Abstract: Hydrocarbons such as gasoline and short olefins are among the most important chemical raw materials in industry. They are used as energy sources and to power most means of transport and machines worldwide. For a long time, these chemicals were produced almost exclusively in the petrochemical industry. However, the over-exploitation of these resources has led to various environmental problems and has been shown to play a crucial role in greenhouse gas emissions into the atmosphere. As a possible environmentally friendly alternative, hydrocarbons can also be synthesized through the catalytic reduction of CO2 with green H2. This process has the great advantage that the CO2 can be used as a raw material. It is particularly attractive if the CO2 is extracted directly from the atmosphere in order to generate a neutral CO2 cycle.
This work deals with the characterization of iron-based catalysts for the hydrogenation of CO2 to hydrocarbons. In particular, a combination of real catalysts (powder catalysts) and flat model catalysts (planar catalysts) is used. The advantage of such an approach is that surface science tools and methods can be used in addition to the conventional methods commonly used to characterize catalysts. The reason for this work is the numerous contradictions regarding the parameters controlling the catalytic performance of CO2 hydrogenation with Fe-based catalysts. My goal is to gain a better understanding of the fundamental behavior of the active catalytic Fe phase for the CO2 hydrogenation reaction. For this purpose, a combination of operando, in situ and ex situ characterizations are carried out and correlated with the catalytic performance of the various catalysts produced. Particular attention was paid to in situ surface characterization using X-ray photoelectron spectroscopy (NAP-XPS) and operando characterization using X-ray absorption spectroscopy (XAS).
The first part of this work addresses the role of the oxide support in the catalytic performance of Fe-based nanoparticles. It is shown how the traditionally considered inert substrates (Al2O3 and SiO2) alter the selectivity of small Fe nanoparticles during CO2 hydrogenation. The selectivity changes depending on the substrate are associated with the interaction and influence of the carrier on the Fe nanoparticles and how the carrier defines the chemical state of the active Fe phase. The second section focuses on how the size of Fe nanoparticles affects the catalytic performance in CO2 hydrogenation. In particular, the size of the Fe nanoparticles influences the reducibility of the Fe precursors during the activation of the catalyst and thus directly affects the chemical state of the Fe under the reaction conditions. In this way, it determines the observed catalytic performance. This work ends by linking both effects in Fe-based catalysts (size and support effects) as they are coupled with each other. In summary, my work shows that the catalytic performance of Fe-based materials is highly dependent on parameters such as their support and the size of the nanoparticles. This results in a deeper understanding of the complex behaviors of these Fe-based systems described in the literature.
|
Oct 2024
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
B18-Core EXAFS
|
Diamond Proposal Number(s):
[35991, 33143]
Abstract: Achieving efficient water-splitting under acidic conditions for hydrogen production is severely limited by the anodic oxygen evolution reaction (OER). Overcoming this obstacle is vital to realise effective electrolysers and deliver a hydrogen-driven economy. Iridium oxides remain one of the only viable catalysts under acidic conditions due to their corrosion resistance, however, a fine balance exists between the activity and stability of differing oxide morphologies. We have previously shown that heat-treating high-activity amorphous iridium oxyhydroxide in the presence of residual lithium carbonate leads to the formation of lithium-layered iridium oxide, suppressing the formation of low-activity crystalline rutile IrO2. We now report our recent work on the synthesis of similar compounds, Na-IrOx and K-IrOx, featuring similarly layered crystalline structures. Electrocatalytic tests confirm Li-IrOx has similar electrocatalytic activity as commercial amorphous IrO2·2H2O and with increasing size of the intercalated cation, the activity towards the OER decreases. However, the synthesised electrocatalysts show greater stability than crystalline rutile IrO2 and amorphous IrO2·2H2O, suggesting these compounds could be viable alternatives for industrial PEM electrolysers where durability is a key performance criterion.
|
Aug 2024
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
I09-Surface and Interface Structural Analysis
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
|
Xuze
Guan
,
Rong
Han
,
Hiroyuki
Asakura
,
Bolun
Wang
,
Lu
Chen
,
Jay Hon Cheung
Yan
,
Shaoliang
Guan
,
Luke
Keenan
,
Shusaku
Hayama
,
Matthijs A.
Van Spronsen
,
Georg
Held
,
Jie
Zhang
,
Hao
Gu
,
Yifei
Ren
,
Lun
Zhang
,
Zhangyi
Yao
,
Yujiang
Zhu
,
Anna
Regoutz
,
Tsunehiro
Tanaka
,
Yuzheng
Guo
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[23759, 24450, 29092, 31852]
Open Access
Abstract: Single-atom catalysts have garnered significant attention due to their exceptional atom utilization and unique properties. However, the practical application of these catalysts is often impeded by challenges such as sintering-induced instability and poisoning of isolated atoms due to strong gas adsorption. In this study, we employed the mechanochemical method to insert single Cu atoms into the subsurface of Fe2O3 support. By manipulating the location of single atoms at the surface or subsurface, catalysts with distinct adsorption properties and reaction mechanisms can be achieved. It was observed that the subsurface Cu single atoms in Fe2O3 remained isolated under both oxidation and reduction environments, whereas surface Cu single atoms on Fe2O3 experienced sintering under reduction conditions. The unique properties of these subsurface single-atom catalysts call for innovations and new understandings in catalyst design.
|
Jul 2024
|
|
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
|
Diamond Proposal Number(s):
[31867]
Open Access
Abstract: Oxygen vacancy (Ov) is an anionic defect widely existed in metal oxide lattice, as exemplified by CeO2, TiO2, and ZnO. As Ov can modify the band structure of solid, it improves the physicochemical properties such as the semiconducting performance and catalytic behaviours. We report here a new type of Ov as an intrinsic part of a perfect crystalline surface. Such non-defect Ov stems from the irregular hexagonal sawtooth-shaped structure in the (111) plane of trivalent rare earth oxides (RE2O3). The materials with such intrinsic Ov structure exhibit excellent performance in ammonia decomposition reaction with surface Ru active sites. Extremely high H2 formation rate has been achieved at ~1 wt% of Ru loading over Sm2O3, Y2O3 and Gd2O3 surface, which is 1.5–20 times higher than reported values in the literature. The discovery of intrinsic Ov suggests great potentials of applying RE oxides in heterogeneous catalysis and surface chemistry.
|
Jul 2024
|
|