**1. Introduction**

Catalysis is a fascinating field located at the edge of a multitude of disciplines and fields. Spectroscopy dedicated to understanding catalytic phenomenon is among the most active research areas in field. The ability to visualize a catalytic transformation in real time has lured scientists due to the technical challenges and the potential for unprecedented understanding. The importance in accessing fundamental understanding of catalysis was masterfully high‐ lighted in the 2007 report of the US Department of Energy, Basic Energy Sciences Workshop [1]*:[T]o realize the full potential of catalysis for energy applications, scientists must develop a profound understanding of catalytic transformations so that they can design and build effective catalysts with atom-by-atom precision and convert reactants to products with molecular precision. Moreover, they must build tools to make real-time, spatially resolved measurements of operating catalysts. Ultimately,*

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*scientists must use these tools to achieve a fundamental understanding of catalytic processes occurring in multiscale, multiphase environments.* However, this is applicable for any kind of catalytic system.

At its most fundamental level, catalysis is directly related to the electronic structure of the valence shells because they control chemical bond formation/rupture [2]. Several spectros‐ copies can provide information on valence shells but only X-rays do it directly. Hard X-rays are the epitome of spectroscopic probes because of their great penetration depth, and element specificity, which enables studies of catalytic states under working conditions [3]. X-ray photon-in photon-out core level spectroscopy is a powerful tool to understand catalytic reactions because it enables us to map the entire electronic structure of the catalyst under catalytic relevant conditions.

In this book chapter, we summarize our latest efforts in the use of synchrotron-based highresolution X-ray spectroscopy to study a plethora of academic and industrial relevant catalytic systems. We will start by covering in a succinct manner the developments in the field that allow for the understanding of catalysis in situ/operando and time-resolved, keeping the highenergy resolution and element specificity. This section includes an overview on techniques, spectrometers, and experimental setups. After that we will describe the studies we carried out to understand catalysis and materials. Our work spans over three fundamental aspects of catalysis:


Vast majority of the studies were carried out on a dispersive von Hamos-type spectrometer [4]; however, when a higher peak-to-background signal level was necessary the experiments were carried out with a Johann-type spectrometer [5]. The studies were carried out both in homo‐ geneous and heterogeneous catalytic systems. The latest includes also studies on photocatal‐ ysis.

The future of this spectroscopy concerns its application at the X-ray free electron lasers (XFELs). The advent of XFELs enabled scientist to achieve the goal of producing a movie of a catalytic transformation. XFEL light sources are in its beginning but their effect on the field of timeresolved X-ray science will be deep and comprehensive because reactions can be followed not only in situ but also in real time, this of course if the current limitations in respect to selective triggering and sample stability are overcome. Quoting Sá & Szlachetko*: in a cinematographic analogy, we have the camera (von Hamos Spectrometer), the film (HEROS), the set (catalytic reactor), the script (catalytic reaction) and the actors (catalyst and reagent molecules); what is missing is the director to shout 'action' and direct the scenes (pulse shaping), and that the actors do not fall ill (sample refreshment)* [6]. The insights gathered from the high-resolution X-ray spectroscopy provide deeper understanding of the systems and reactions, which can be used to improve or develop novel catalysts with enhanced properties.
