**Author details**

spectral energy resolution [62]. Moreover, HEROS spectra are not perturbed by the selfabsorption process [63]. This makes HEROS a commanding tool to identify and quantify the

**Figure 17.** (a) Temporal evolution of the HEROS spectra during CO/O2 switches at 300 °C on 1.3 wt% Pt/Al2O3. (b) Temporal evolution of the HEROS signals at 9426 and 9427 eV (whiteline region) during CO/O2 switches. (Reproduced

We performed an in situ time-resolved HEROS study with subsecond resolution providing insight into the oxidation and reduction steps of a Pt catalyst during CO oxidation with 500 ms resolution [64]. Figure 17 displays a gentle oxidation step, comprised of two distinguishing stages, namely dissociative adsorption of oxygen followed by partial oxidation of Pt subsur‐ face. By comparing the experimental spectra with theoretical calculations, we found that the intermediate chemisorbed O on Pt is adsorbed on atop position, insinuating CO surface poisoning or surface reconstruction. This indicates HEROS ability to perform chemical speciation with subsecond time resolution, which opens exciting opportunities to follow catalysis in real time. Since the HEROS spectra are collected in a single shot, the time resolution can be further improved since it depends only on the number of incoming photons and element concentration, which makes it particularly suited for experiments at the XFELs. Recently, it was shown that experiments with 100 ms resolution could be achieved at the synchrotron [65].

Further developments in the field of X-ray spectroscopy applied to catalysis science are nowadays focused in multiple aspects. Most importantly, improvements in the experimental time resolution are necessary for deep insight knowledge of many chemical processes. For this, a range of complementary X-ray sources is necessary due to timescale changes in the chemical

catalyst electronic changes during reaction and as it happens.

26 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

from elsewhere [64] with permission)

**4. Outlook and future trends in the field**

Jakub Szlachetko1\* and Jacinto Sá2

\*Address all correspondence to: jakub.szlachetko@psi.ch

1 Paul Scherrer Institute, Switzerland & Institute of Physics, Jan Kochanowski University of Kielce, Poland

2 Department of Chemistry, Uppsala University, Sweden & Institute of Physical Chemistry, Polish Academy of Sciences, Poland
