Site blocking effects on P-modified Pd/Al2O3 catalysts for LOHC hydrogenation: an in situ DRIFTS study

In this paper, we investigate structural changes of a P-modified Pd/Al2O3 catalyst for the hydrogenation of liquid organic hydrogen carriers (LOHCs) e.g., benzyl-toluene (H0-BT). We elucidate the effect of P modification on the Pd nanoparticles and the support material via a systematic combination of reactor studies, in situ diffuse reflectance FT-IR spectroscopy using CO as a probe molecule (CO-DRIFTS), and density functional theory (DFT). We find that P modification induces structural changes as well as site-blocking effects on the Pd NPs. In particular, phosphates on the Al2O3 support induce the formation of smaller Pd NPs. Phosphate species further reside on the terrace sites of Pd NPs, which leads to competitive adsorption between phosphates and CO/H2 especially at the Pd(111) facet. This demonstrates rearrangement of surface and adsorbate species on the P-modified Pd/Al2O3 catalysts under reactive gas atmosphere.