Sulfur resistance enhancement by grafted TiO2 in SiO2-supported Pd catalysts: Role of grafted TiO2 and genesis of Pd clusters

Pd clusters on TiO2-grafted SiO2 (TiO2–SiO2), SiO2, and TiO2 particles were prepared via impregnation with palladium (II) acetate followed by air calcination and hydrogen reduction. The prepared catalysts were tested by tetralin hydrogenation with sulfur-poisoning reaction. The results show that Pd/TiO2–SiO2 presents the highest activity maintenance. To investigate the role of the grafted TiO2 in improving the activity maintenance, the catalyst samples were characterized by FT-IR, EXAFS, and XRD. The results indicated that layer-like TiO2 clusters formed on SiO2 help anchoring palladium oxides during air calcination. This anchoring leads to the formation of relatively small Pd clusters having less electronic density as opposed to the other two catalysts. Combining structural characterization with kinetic study results, we concluded that the superior catalytic performance for Pd/TiO2–SiO2 could arise from the decrease of the affinity of Pd for H2S and the increase of hydrogen reducibility for PdS2.