Introduction

Hydrogen is expected to play a key role in a future sustainable energy system. Essential for the use of hydrogen as an energy carrier is the development of the technologies used for its storage and transportation. In this respect, liquid organic hydrogen carriers (LOHC) represent a very promising alternative [1,2]. LOHC technology enables high H₂ storage densities in a liquid at ambient conditions [3].  In order to make this process truly cyclic and sustainable, a high selectivity of the catalytic dehydro­genation reaction and a high catalyst stability is necessary. This requires further research, to understand in more detail the processes taking place in the interphase between the solid catalyst and the liquid LOHC.

Materials and Methods

Here we are studying the dehydrogenation reaction of perhydro benzyl-toluene with model Pt catalysts. For understanding the processes contributing to the catalyst degradation at the atomic level, we use high energy X-Ray diffraction (HEXRD) and X-Ray absorption spectroscopy (XAS) in operando mode under realistic conditions (300 °C, 1-5 bar).

We use Pt catalysts synthetized by PVD over single crystal Al₂O₃ support, that allows us to follow the evolution of the Pt nanoparticles with grazing incidence wide angle X-Ray scattering (WAXS) and small angle X-Ray scattering (SAXS). While we use model catalysts as a simplified system for X-Ray measurements, we replicate the real chemical environment in a large reactor filled with commercial Pt/Al₂O₃ egg-shell catalyst (Fig.1). The measurements are performed at the ID31 beamline of the ESRF.

Results and Discussion

In this presentation we will report on the design of a semi-industrial reactor adapted for both model and commercial catalysts suitable for operando HEXRD studies at large scale X-ray facilities. We will also discuss the representativeness of model catalysts for these studies, and the importance of the chemical potential and the overall physical conditions in the reactor.

Furthermore, we will present the results from our operando HEXRD measurements, where we can follow the changes of the nanoparticles morphology and, through the lattice parameter change, also the chemical state of the catalyst. In these results, we are able to compare the influence of different sample treatments, such as the selective poisoning of Pt with S, as well as the different results obtained at various positions in the catalytic bed.

We will also report the design of a model cell adapted to study the reaction at small scale using XAS, and show the first results acquired with this technique.

The X-Ray studies have been also complemented with ex-situ characterization (XPS, AFM) to understand the full picture of the processes both structurally and chemically.

Significance

Further research of the dehydrogenation reaction in LOHC technology is a prerequisite for the development of better and fully recyclable catalysts, making this technology more competitive.