Operando High-Energy X-Ray Scattering Studies of Pt/Al2O3 Catalysts during LOHC Dehydrogenation

Liquid organic hydrogen carriers offer a promising route for hydrogen storage and transport. The durability of catalysts remains a major challenge in their commercial deployment. In this study, we investigate the dehydrogenation of the benzyltoluene/perhydrobenzyltoluene system under realistic conditions using model catalysts—2 nm thick Pt nanoparticles supported on an Al2O3 single crystal—embedded in a packed bed of commercial catalyst. Using operando grazing incidence X-ray diffraction, complemented by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and gas chromatography, we correlate structural changes in the platinum lattice with catalytic activity and operating parameters such as temperature, pressure, or position along the catalytic bed. We find that while the Pt lattice remains mainly stable parallel to the support, contraction occurs along the surface normal under certain dehydrogenation conditions. This perpendicular contraction correlates with the accumulation of coke and catalyst degradation, which can be rationalized by considering the influence of the chemisorbed reaction intermediates and the physisorbed carbonaceous deposits on the Pt strain. The lattice contraction and catalyst degradation are more pronounced downstream in the reactor and at elevated temperatures, where H2 gas is more prevalent, whereas higher pressures moderate it by favoring liquid-phase conditions. Selective sulfur poisoning leads to a pronounced restructuring of the Pt lattice, which is observed under thermal and operando reaction conditions.