Understanding the inner world of catalysts
We’ve talked in previous blogs about how catalyst materials are characterized for their elemental compositions and how the measurement of particle size and shape, are important for packing, flow, and surface area of catalysts. Here we are going to dive a bit deeper to consider the internal crystal structure of catalysts and what is going on between the atoms and ions on the reactive surfaces of catalyst materials.
Being one of the most powerful analytical methods for understanding the crystal structures of materials, X-ray diffraction (XRD) has a big part to play in verifying the constituents of catalysts and in discovering what is happening to their crystal structure whilst they are working.
Simple, single-element catalysts such as platinum nanoparticles, on their own, don’t lend themselves to much in the way of exciting XRD, except if you have access to Empyrean with small- and wide- angle scattering (SAXS and WAXS) you can measure particle size and check the phase and unit cell parameters in one go.
Most catalysts are formed from multiphase inorganic materials with well-defined microstructures. They must be mechanically robust and chemically stable compounds that hold their form and chemistry during their own production and then subsequent use. All the way from early research projects to discover new catalyst candidates right through to quality checking catalyst materials during and after use, XRD has a part to play. So, at Malvern Panalytical, we provide a range of XRD instruments that measure in different environments and with different workflows ranging from detailed research to rapid and automated throughput for quality control.
The crystallography of catalysts
Investigating the crystal structures of these strongly crystalline materials can be carried out on our Aeris and Empyrean instruments. The most common measurements are checking crystalline structure variations, amorphous to crystalline ratios and identifying phases and compositions in multiphase mixtures. The Empyrean can also be used to investigate subtle changes in strain in crystalline unit cells. Even amorphous or highly defective structures can be studied using an advanced measurement method called ‘total scattering’ with pair distribution function (PDF) analysis. Thanks to very sensitive detectors, total scattering profiles, which used to be in the remit only of synchrotron X-ray sources, can now be collected and analyzed in the lab.
Sometimes, catalysts are a combination of a porous inorganic substrate which is ‘loaded’ with a catalytical element, such as a precious metal. X-ray diffraction is very sensitive to any changes in crystal lattice as a result of the presence of new atoms and can be a good way to measure the impact of the loading on the integrity of the crystalline substrate.
Some catalyst materials are designed to be porous within their lattices, with interconnected channels that provide increased surface area to enable catalytic reactions. New materials such as designed mesoporous substrates and metal-organic framework (MOF) materials are always coming out with novel and exciting potential. The micro-, meso- and nano-pores often needed in catalyst materials can be highly ordered and present at multiple length scales, providing a complex system of surfaces and hence a much greater catalytic activity than a non-porous material. In addition to XRD structure refinement, X-ray scattering methods such as SAXS grazing incidence SAXS (GI-SAXS) and reflectometry are available on our Empyrean XRD systems. Together these can probe porosity scaling from lattice voids to nano-pores.
Looking at catalysts operando
Initial research into catalyst systems often involves a mechanistic understanding at the atomic and molecular level. However, when applied in real-world scenarios, the catalytic environment may be considerably more complex. For example, a catalyst may be required to operate under gradually changing physical and thermal conditions to reduce reactor downtime. With Empyrean you can perform operando phase- or structural analysis measurements under a range of simulated reactor conditions. Understanding and charting out safe temperature-pressure-chemical regimes through this kind of lab research can save time and money at a later stage.
Crystallographers are a happy bunch
All in all, with catalysts, there is a lot to keep crystallographers happy. New inorganic materials are a crystallographer’s dream already but add porosity and operando studies and there is no end to the fun to be had with an X-ray diffractometer.
To learn more about all our solutions for catalyst production, download the full brochure here.
Are you interested in MOFs? Find our MOF solutions brochure here!
Or contact our experts to talk about optimizing your production processes today!
Further reading