Operando X-ray Absorption Fine Structure (XAFS) Spectroscopy has played a pivotal role in shedding light on one of the major challenges in all forms of catalysis (homogeneous, heterogeneous, bio, electro) - the identification of the working active sites and how these are affected by reaction conditions, reaction time and also how these are distributed within the reactor. Amongst the beamlines at Diamond Light Source, several sample environments have been developed over the years to perform XAFS under operando conditions. The most effective approach has been using capillary-based reactors, where the catalyst, typically in powder form, is loaded into the capillary between glass wool plugs. The capillary is then loaded onto the reactor and the sample is treated under the desired conditions (gases, temperature, pressure, etc.). The main drawback of mounting one capillary at a time is that a significant amount of beamtime is lost during sample changes and especially in experiments where the samples require a long pre-treatment before measurements with x-rays are performed on the beamline.

To improve the efficiency of operando catalysis experiments at Diamond, we are working towards the design of a multi-capillary reactor, which would allow the possibility to run operando experiments on multiple capillaries at the same time. The reactor will allow the treatment of multiple samples simultaneously with one of two gas mixtures, making it possible to alternate between them for XAFS measurements. This implies that the reaction on one sample can continue while another one is being measured. Additionally, each capillary will have independent temperature control, making it possible to perform independent temperature treatment on each catalyst, and individual mounts, making it easier to mount the capillaries. The reactor is expected to cut down significantly the time required for operando catalysis experiments.

Additional capabilities of the reactor, owing to its geometry, would be the possibility to perform combined measurements (XRD, Raman, Infra-red) with XAFS, offering the potential to understand better the structure-activity relationships in working catalysts.

The reactor’s design will be compatible with mounting across all the spectroscopy beamlines (B18, I20, I18, and in the future SWIFT) at Diamond.