Sara Blomberg is a postdoc at Department of Chemical Engineering, Lund University. Her research project “In situ activation study of NiMo catalyst tailored for biofuel production” focuses on characterisation of catalysts used in the hydrogenation processes of depolymerisation of lignin. What this translates to in layperson language is “trying to understanding how a catalyst cuts lignin into smaller pieces”.
Lignin is the second most common organic substance on earth (cellulose is the most common) and serves as the glue between cellulose fibers in plants and trees. Illustration by @em.draws.and.animates
When manufacturing good quality paper from pulp you separate the cellulose and the lignin and the latter becomes the so-called black liquor. Until today this has been treated as waste and burned directly on the paper mills site but recently, in a pilot plant, it has been proven that the lignin can be converted into biofuel. In the process the largel ignin polymer (a polymer is a very large molecule) is cut into smaller molecules and the black liquor is also purified by removal of impurities that originate from the paper making process such as sulphur, oxygen, nitrogen and metals. you would be able to make a biofuel based on a renewable source.
Sara’s research project is part of the Lignin research project carried out at Lund University. Her part is to understand the fundamentals of the nickel-molybdenum catalysts doing the actual cutting of lignin. And for this she needs X-rays and therefore travels around the globe to get beamtime at synchrotrons offering the XPS (X-ray photoelectron spectroscopy) technique. One beamline that offers XPS is SPECIES at MAX IV where she is now doing measurements using a so called lab-source, a magnesium source to generate the X-rays.
With her research project Sara wants to gain knowledge on how, on the atomic scale, the nanoparticles work as catalysts. The nickel-molybdenum alloy nanoparticle is a somewhat “hilly” surface (again, on an atomic scale) and the actual catalysis can take place anywhere on it, however, some sites are more favourable than others. Depending on where it actually happens different chemical reactions occur.
Using XPS gives Sara data in the form of different spectrums that tells her what chemicals on the surface, in this case nickel or molybdenum or the nickel-molybdenum alloy, is most active and therefore most useful as catalytic material.
When using the technique XPS the X-rays knock out the electrons from the probed material, in the exemplifying image above it is Palladium. Because of the very short mean free path of electrons the technique is extremely surface sensitive and in the observed signal (picture to the left) it is possible to distinguish if the detected electrons originate from the very first atomic layer or the atoms in the bulk. This is useful when the surface structure and the surface interaction with gas molecules are investigated.