The influence of activation atmosphere on the active phase and hydrotreating activity of LDH-based NiW pre-sulfurized catalysts

Abstract

A tetrathiotungstate intercalated NiAl layered double hydroxide (LDH) was synthesized and activated to prepare NiW pre-sulfurized hydrotreating catalysts. The influence of activation atmosphere (N₂ and H₂) on the active phase, hydrodesulfurization (HDS) and hydrodearomatization (HDA) activities was investigated. At 300 °C, the catalyst activated under H₂ had more S₂²⁻ and NiWS phase than that under N₂. The deeper decomposition of the LDH under H₂ formed more WS₃ while the partial removal of sulfur at the edge of WS₂ by H₂ generated more sulfur-deficient sites to facilitate the decoration of Ni. At 600 °C, metallic Ni and NiWO₄ were formed under H₂ and N₂, respectively. Moreover, the H₂ atmosphere generated more –SH groups on the catalysts. The catalysts activated under H₂ exhibited higher HDS activity for dibenzothiophene (DBT) and HDA activity for tetralin (THN) than those activated under N₂, because of the fewer S₂²⁻, NiWS and –SH groups in the latter. The catalyst activated under H₂ at 600 °C showed the highest HDS activity, principally because metallic nickel could adsorb DBT to form highly flowable complexes migrating to active sites. Activating under H₂ at 300 °C offered the catalyst the highest HDA activity, due to more S₂²⁻ and –SH groups present. The use of different activation temperatures under H₂ may be a convenient way to tune the HDS and hydrogenation activity of LDH-based pre-sulfurized catalysts.