Identifying and Mitigating Adverse X‑ray Induced Effects in Operando Spectroscopic Studies of Copper Exchanged Zeolites.

Abstract

The increase in brilliance and global proliferation of synchrotron facilities has established synchrotron radiation as an indispensable tool in modern science. However, as synchrotron sources become more powerful, the risk of X-ray induced alterations becomes increasingly pronounced. These beam-induced effects will compromise results, leading to unusable data at best and incorrect conclusions at worst. Techniques that guarantee that the means of observation do not cause the observed phenomena are therefore an absolute necessity. This work presents a methodology to mitigate beam-induced effects, consisting of performing a mesh scan  in which the beam is rastered across the sample bed  to avoid local overexposure. The validity of this approach is demonstrated using copper-exchanged zeolites  materials frequently investigated at synchrotron facilities  by monitoring the change in oxidation state of copper during exposure to oxidizing, reducing and inert atmospheres via time-resolved X-ray absorption spectroscopy (XAS) as a function of X-ray dose. This method reveals that beam-induced effects can manifest at significantly lower X-ray doses than previously reported for this class of material. More importantly, it provides a blueprint for conducting operando measurements that ensure uncompromised results as well as the full exploitation of the capabilities offered by state-of-the-art fourth generation synchrotron facilities.