Abstract: This article studies the mechanism of the adsorption of metallo-porphyrin on the surface of HDS catalysts. The model compound used, metallo-porphyrin, is VO-TPP and the HDS catalysis used are Co-Mo-Al₂O₃ systems.
When VO-TPP is adsorbed on the surface of the catalysts, the central ion VO²⁺ has two different orientations to the surface, and will lead to two kinds of adsorptions:center 1 and center 2.
In most cases only center 1 can occur because of the adsorption of eletron donor (H₂O, OH^-, etc.) on the cational spots of the surface. When the catalysts are calcined the adsorbed electron donor will be desorbed, and when the calcined catalysts are used to adsorb VO-TPP center 2 will occur.
The interaction in center 2 between VO-TPP and the catalysts' surface is much stronger than in center 1. But center 2 is less stable than center 1 when the adsorbed sample is exposed to air. It turns into center 1 in air.

Key words: Hydrodesulfurization (HDS) catalysts, Metallo-porphyrin, ESR, Mechanism of adsorption