Diamond Annual Review 2023/24

49 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 3 / 2 4 Using nature’s solution to break down biomass Dry plant matter (biomass) is an abundantly available raw material for the production of biofuels. The principal carbohydrate polymer it contains, cellulose, is packed with glucose units that can be fermented into bioethanol - a sustainable liquid fuel. These polymers are difficult to break down chemically, but we get a helping hand from the natural enzymes that have evolved to do the job. Widely found enzymes, lytic polysaccharide monooxygenases (LPMOs), are major contributors to natural carbon recycling and are now used in commercial bioethanol production. However, questions remain around how these enzymes survive the powerful chemistry they wield.​ Researchers from the University of Manchester, Novozymes, Graz University of Technology, the University of York and Diamond Light Source, used a combination of stopped-flow spectroscopy, targeted mutagenesis, TD-DFT calculations, electron paramagnetic resonance spectroscopy and High Energy Resolution Fluorescence Detection X-ray Absorption Spectroscopy (HERFD−XAS) to investigate how these oxidative enzymes protect themselves fromharmful side reactions. Their results show a previously unseen, short-lived intermediate step in the reaction, and its role in defending the enzyme against oxidative damage. As well as demonstrating the protective mechanisms built- in to biological systems, this study has practical implications formaximising the efficiency of oxidative catalysts. Achieving optimal catalyst performance will require careful balancing of oxidant concentration and reducing equivalents. The team will now continue their research at Diamond to study how these enzymes associate with their substrates - the target material - and how they are activated by its arrival. Zhao, J. et al. DOI : 10.1021/jacs.3c06607 Exploring the dynamics of catalysis: single atoms vs. nanoparticles Heterogeneous catalysis - where the catalyst is in a different phase to the reactants - is a stalwart of the chemicals and energy industries. The development of active, selective, and energy-efficient heterogeneous catalysts is, therefore, a crucial pillar of our transition to more sustainable technologies. There has been a recent focus on single-atomheterogeneous catalysts (SAHCs), due to their maximummetal utilisation and unique reactivity. However, while carbon-nitrogen supports are widely used for SAHCs, most studies of their dynamics through a reaction have used oxide supports. It is not yet clear whether single atoms or sub nanometre clusters that form under reaction conditions are active species. In work recently published in the Journal of Catalysis, a team of researchers used aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) to investigate the dynamics of palladium SAHCs on graphitic carbon nitride supports during two reactions - ethylene hydrogenation and H2-D2 exchange. On Diamond’s I20- EDE beamline, the team collected X-ray absorption spectra of catalysts after treatment in the reactions at different temperatures: 50°C, 100°C, 150°C and 200°C. As synchrotron-based XAS has a lower detection limit than laboratory- based XPS, and penetrates further into the sample, the spectra collected at Diamond offered more information about the electronic state of palladium and the chemical environment. Their results show that, at 100°C in a gas containing ethylene and hydrogen, the palladium single atoms form clusters, and suggest that these clusters are the active species. Their work offers new insights into the effect of gas atmosphere on speciation. Vennewald, M. et al. DOI:10.1016/j.jcat.2023.03.011 Caption: Impact of point mutations on intermediate formation and decay. Crystal structure of LsAA9 active site, for each of the mutants, concentration profiles of Int1 (red) and Int2 (blue) derived from global fitting software are shown as a function of time in comparison to the wild-type enzyme. Caption: Tiny palladium crystals, the largest are 1-2 mm in sizeCourtesy of http://images- of-elements.com/palladium.php, CC BY 3.0, https://commons.wikimedia.org/w/index. php?curid=28857838.