60 61 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 Control of zeolitemicroenvironment for biomass conversion Bioenergy – Sustainable Energy Systems – Energy – Climate Change – Physical Chemistry – Catalysis - Chemistry Pentadienes serve as key building blocks for the chemical and polymer industries and are widely used as monomers in the production of adhesives, plastics, and resins. However, state-of-the- art processes to produce pentadienes are based on steam cracking of naphtha (typically at 850ºC) and rely on fossil fuels with the attendant environmental impacts. Therefore, the sustainable production of pentadienes from renewable resources, such as biomass-derived materials, is a vitally important and urgent task. Methyltetrahydrofuran (2-MTHF) can be produced readily from lignocellulose-derived furfural via low-cost, high-yield processes and has been identified as a sustainable resource for making pentadienes via ring-opening, hydrogen transfer and dehydration processes. Leading catalysts for this reaction include amorphous SiO 2 /Al 2 O 3 , and Al or B- zeolites. However, these microporous catalysts often suffer from deactivation due to the formation of cokes. Furthermore, achieving effective selectivity control towards pentadienes in this reaction is still a significant challenge. MCM-41 is amesoporous silica-basedmaterial used as a catalyst or catalyst support for a wide range of reactions; emerging niobium-based catalysts have shown exceptional performance for the hydrodeoxygenation of biomass under mild conditions. An international team of researchers studied whether MCM-41 materials containing weak acid sites and active niobium sites effectively address the challenges of pentadiene production. The reaction mechanism of conversion of 2-MTHF is complex, involving multiple reaction intermediates and products. The ring-opening of 2-MTHF is the rate-limiting step in this conversion. The research team aimed to determine the full molecular details of the catalytic mechanism through the use of operando X-ray Absorption Spectroscopy (XAS), combined with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and in situ high-field solid-state Nuclear Magnetic Resonance spectroscopy. On Diamond’s I20-EDE beamline, they used the spectroscopy group’s recently commissioned high-temperature synchronous gas/vapour phase XAS/DRIFTS set-up coupled to the mass spectrometer and in-house developed gas dosing rig. This combination enabled them to propose a detailed reaction mechanism via temperature programmed spectroscopy. This work reported the synthesis of a series of new (Al,Nb)-bimetallic mesoporous silica materials for the first time. AlNb-MCM-41(35/1/0.9) shows excellent catalytic performance for converting biomass-derived 2-MTHF to pentadienes. The direct transformation of biomass derivatives to C5 dienes under mild conditions described in this study will have a significant impact on the development of future sustainable chemical processes. In addition, these findings have revealed the nature of Nb(V) sites during the conversion of 2-MTHF, and promoted the understanding of the catalytic role of Nb(V) sites in MCM-41, which will be of interest to those working in the fields of solid-state materials, catalysis and sustainable chemical production. Related publication: Fan, M. et al. Bimetallic Aluminum‐and Niobium‐doped MCM‐41 for efficient conversion of biomass‐derived 2‐Methyltetrahydrofuran to pentadienes. Angewandte Chemie International Edition 51 , (2022). DOI: 10.1002/anie.202212164 Funding acknowledgement: EPSRC (EP/S023755/1, EP/R00661X/1, EP/S019367/1, EP/P025021/1 and EP/P025498/1) Corresponding authors: Prof Sihai Yang, University of Manchester,
[email protected] The highly selective conversion of biomass-derived 2-methyltetrahydrofuran (2-MTHF) into pentadienes has been achieved over an aluminium and niobium bimetallic atomically doped on MCM-41. The Nb(V) sites enhance the catalytic performance by binding 2-MTHF. Investigating the damage tolerance of high-temperature superconductors for fusion power plants High Energy & Particle Physics – Superconductors – Quantum Materials – Energy – Physics – Materials Science High-temperature superconductors are an essential component of compact tokamak fusion reactors, which promise to provide a commercial route towards fusion power plants by the mid-2030s. However, there are many technical challenges with achieving this ambitious goal, including a lack of understanding of what will happen to the superconducting magnets bombarded with high-energy neutrons produced by the fusion reaction. Researchers from the University of Oxford and Diamond Light Source sought to discover what kinds of defects are generated by irradiation with energetic particles in the high-temperature superconducting tapes used to make demonstrator fusion magnets by companies such as Tokamak Energy and Commonwealth Fusion Systems. Superconductivity in high-temperature superconductors is strongly suppressed by structural disorder. When neutrons or other energetic particles collide with atoms in the superconductor, some get knocked out of position, creating defects in the crystal that reduce superconductivity. Figuring out what kinds of defects are produced during irradiation will help to determine, in combination with other experimental and modelling studies, how long these materials may survive under realistic operating conditions in a fusion reactor. That will inform engineering decisions, such as how much neutron shielding the magnets will require. Using atomic resolution Electron Microscopy at ePSIC enabled the team to determine that the crystalline arrangement of the heavy metal ions in the structure remains largely intact, even at a dose where superconductivity has been completely lost. However, individual atomic defects are difficult to ‘see’ with an electron microscope, particularly the light oxygen atoms that turn out to be very important. Using high energy resolution X-ray Spectroscopy, the I20-Scanning beamline allowed the team to probe changes in the local chemical bonding environment around the copper atoms that occur when oxygen atoms move to different sites in the structure. By correlating with spectra simulated using first principles computational methods, the researchers identified specific crystal defects that may be responsible for the loss of superconductivity. Their results gave conclusive evidence for the first time that irradiation produces considerable changes to the environment surrounding the copper atoms that reside in the superconducting planes of the crystal. Prior to this, it had been speculated that oxygen atoms in the regions of the crystal between the superconducting planes would be more likely to be displaced. Comparing the nature of the defects created in high-temperature superconductors under irradiation by different kinds of energetic species, and at different temperatures, is a key part of being able to predict how these materials will behave in operation in a real fusion device. Experiments with neutrons are very challenging and costly, so it is essential to identify suitable alternatives that can mimic neutron damage. Diamond has recently opened a new Active Materials Laboratory, which has allowed the team to repeat their spectroscopy experiments on neutron- irradiated superconductors that are radioactive. This is a significant step towards qualifying which energetic particles produce the same type of damage as neutrons. The fundamental understanding gained from these experiments will lead to more robust interpretation of a range of irradiation data. Ultimately, the hope is that it will provide magnet designers with more reliable information. Related publication: Nicholls, RJ. et al. Understanding irradiation damage in high-temperature superconductors for fusion reactors using high resolution X-ray absorption spectroscopy. Communications Materials 3 , 52 (2022). DOI: 10.1038/s43246- 022-00272-0 Funding acknowledgement: EPSRC (EP/W011743/1, EP/L022907/1) Corresponding authors: Rebecca Nicholls, Department of Materials, University of Oxford, Rebecca.
[email protected] Susannah Speller, Department of Materials, University of Oxford, Susannah.
[email protected] Spectroscopy Group Beamline I20 Scanning (and ePSIC from the Imaging andMicroscopy Group) This figure illustrates the use of first principles computational modelling to interpret experimental XANES spectra (a). The spectra from copper atoms occupying different sites in the crystal structure, labelled Cu 1 and Cu 2 in (b), are calculated separately, enabling key features of the experimental spectra to be identified. Atomic resolution images, taken using the high angle annular dark field imaging mode in a scanning transmission electron microscope, show that the crystalline lattice of the heavy cations remains intact after irradiation (c). Data adapted from Commun Mater 5, 52 (2022) under Creative Commons Licence CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) Spectroscopy Group Beamline I20-EDE