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

Abstract

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., benzyltoluene (H0-BT). We elucidate the effect of P modification on the Pd nanoparticles (NPs) 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.