Diamond Annual Review 2023/24

48 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 Synchrotron studies show balance is the key to catalysingmethanol production In 2022, global energy-related carbon dioxide (CO2) emissions reached a new high of more than 36.8 billion tonnes and remain on an unsustainable growth trajectory. Tackling this challenge requires a multifaceted approach: increasing energy efficiency, exploiting renewable energy sources and developing ways to capture, use and store CO2. One vibrant area of research explores transforming captured CO2 into fuels and other useful chemicals. The hydrogenation of CO2 to methanol offers one potential pathway to producing more sustainable plastics, fuels and chemicals. Pd/In 2O3 (Palladium on Indium Oxide) catalysts have been well investigated on account of their high methanol selectivity and CO2 conversion. However, these platinum group metals are expensive, and the reason for their activity in this reaction is not fully understood. an international team of researchers demonstrated that a cheaper alternative - Pd/In2O3 species dispersed on Al2O3 - can match the performance of pure Pd/In2O3 catalysts. The team used Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy on the B18 beamline to probe the palladium and indium environments in the catalyst during the reaction. By collecting EXAFS measurements for both metals, they could correlate changes and explore any bimetallic interactions. Complementary high-pressure operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments, carried out at the UK Catalysis Hub, helped them understand the catalytic mechanism and synergistic enhancement in the Pd/In 2 O 3/ Al 2 O 3 system. The results confirm that Pd/In 2 O 3/ Al 2 O 3 canmatch the catalytic performance of pure Pd/In 2 O 3 systems. The team also determined the nature of the active sites and their influence on the catalytic mechanism. While In 2 O 3 readily activates CO2, it struggles to split hydrogen. Introducing other metals - in this case, palladium - improves hydrogen splitting. The results of this work suggest that careful balancing of these separate activation processes, and the precise location and interactions of Pd and In 2 O 3 , are key to future catalyst optimisation. These insights are likely to extend to other bimetallic CO2 hydrogenation systems. Potter, M.E. et al . DOI:10.1002/anie.202312645 Serpentinisation offers clues to the early history of Mars Olivines are silicate minerals containing varying proportions of magnesium and iron. Magnesium-rich olivines are common on Earth, being the primary component of the upper mantle. Ferromagnesian minerals such as olivines react with water, releasing hydrogen, in a process known as serpentinization. Serpentinites are rocks composed predominantly of one or more serpentine group minerals, and serpentinization has played a significant role in the development of Earth’s surface environments over time. Our current understanding of Mars, pieced together from our examination of meteorites, satellite images and data collected by NASA’s rovers, is that the planet was once warm and wet. In work recently published in Science Advances , researchers from the University of Calgary and the University of Cambridge undertook a detailed study of iron-rich olivines fromMinnesota. Researchers used X-ray Absorption Near Edge Structure (XANES) to analyse the rock samples. Microfocus Spectroscopy beamline I18 allowed not only measuring redox state of iron which was important for this study, but also made it possible to measure it in individual mineral grains which could be as small as several micron in size. This is a unique capability of I18, and recent advances in data collection and processing made it possible to quickly survey the areas of interest in seconds and select rock grains of interest for more detailed analysis. This research could inform the future geological explorations of Mars, which could help us understand early Earth. Over time, the dynamic movements of tectonic plates have churned up Earth’s surface, constantly dragging down older rocks and replacing them with newer ones. As a result, there are few places on Earth where geologists can study ancient rocks. And although iron-rich olivine rocks aren’t abundant on Earth, it’s possible that they could be used to produce hydrogen as a sustainable fuel source, meaning that the serpentinization processes that once kept Mars warm could help Earth keep its cool. Tutolo, B.M. & Tosca, N.J. DOI: 10.1126/sciadv.add8472 Spectroscopy Science Highlights Figure: (A) Kernel density plot of 52 x-ray absorption near-edge spectroscopy (XANES) measurements of Fe oxidation states in Duluth Complex samples. Labeled lines indicate the percentage of Fe(III) (B) Kernel density plot of 93 electron microprobe (EMP) analyses of Duluth Complex serpentines compared to end member serpentine values. Graphical Abstract of the article.