In situ/ operando characterization of heterogeneous catalysts

Catalysts are ubiquitous in industry for improving the efficiency and sustainability of chemical reactions. Since catalyst structure and function are inseparable, it is essential to develop a level of understanding and control over the so-called ‘structure-activity’ relationships of a given catalyst system. With this in mind, the most accurate and realistic catalyst characterisation results rely on ‘in situ’ and ‘operando’ analysis.

• In situ means the application of analytical methods such as spectroscopy, diffraction or microscopy, under conditions relevant for catalytic function (e.g. reactive gases, temperature, pressure; these can be model or real conditions).
• Operando means the simultaneous collection of catalytic activity data, together with in situ measurements (making operando a special class of in situ).

Heterogeneous catalysts are complex materials which come in many shapes and sizes, often exhibiting structural elements and features of interest on multiple length scales. These can range from metal active sites (atomic to nm scale), to porosity (micro-/meso-/macropores on nm to µm scale), to global catalyst form or morphology (mm to cm scale). Multimodal and multiscale characterisation is therefore essential to develop full understanding of catalyst form and function. This includes surface methods such as XPS and DRIFTS (IR) to bulk analytical methods such as XRD and Raman. Synchrotron radiation plays a key role in this, with techniques ranging from X-ray absorption spectroscopy (XAS), to photon-in photon out spectroscopies (XES), to high resolution synchrotron X-ray diffraction (XRD), and imaging studies using X-ray microscopy.

In our group, in situ and operando characterisation is generally divided into three strongly interacting areas:

(i) design and construction of in situ / operando reactors and cells
(ii) application of in situ and operando spectroscopy, diffraction and microscopy
(iii) correlative characterization by multiple complementary techniques (e.g. combination of XAS, XRD, and Raman, or XAS and DRIFTS).

A deep understanding of catalytic performance can only be obtained through deriving structure-activity relationships. This in turn leads to the rational design of more efficient catalysts tuned for specific reactions and chemical processes. These activities strongly interact with industry, where real catalysts are applied.

Measurements can be performed at the CAT-ACT beamline, a new beamline dedicated to CATalysis and ACTinide research at the KIT synchrotron!