Alumina-CoMo hydrodesulfurization

Such a selective hydrodesulfurization must clarify the active sites of CoMo and NiMo sulfides supported on alumina for hydrodesulfurization and hydrogenation. CoMo is certainly more selective for hydrodesulfurization with limited hydrogenation activity than NiMo. Hence, cobalt is applied for the present purpose. Coordinatively unsaturated Co sulfide on M0S2 is often postulated as the active site for both reactions (see Fig.7). The metal with unsaturated valence is proposed as the hydrogenative site in cooperation with a Mo-S-H group while the metal with the unsaturated valences must be the hydrodesulfiiiization site. H2S concentration in HDS can be reduced to enhance the hydrodesulfiiiization selectivity. 

A series of CoMo/Alumina-Aluminum Phosphate catalysts with various pore diameters was prepared. These catalysts have a narrow pore size distribution and, therefore, are suitable for studying the effect of pore structure on the deactivation of reaction. Hydrodesulfurization of res id oils over these catalysts was carried out in a trickle bed reactor- The results show that the deactivation of reaction can be masked by pore diffusion in catalyst particle leading to erro neous measurements of deactivation rate constants from experimental data. A theoretical model is developed to calculate the intrinsic rate constant of major reaction. A method developed by Nojcik (1986) was then used to determine the intrinsic deactivation rate constant and deactivation effectiveness factor- The results indicate that the deactivation effectiveness factor is decreased with decreasing pore diameter of the catalyst, indicating that the pore diffusion plays a dominant role in deactivation of catalyst. 

Farag, H., Mochida, I., and Sakanishi, K. Fundamental comparison studies on hydrodesulfurization of dibenzothiophenes over CoMo-based carbon and alumina catalysts. Applied. Catalysis. A, General, 2000, 194, 147. 

Several patents are issued for selective HDS of FCC gasoline by poisoning the hydrogenation site more than the hydrodesulfurization one over CoMoS/alumina. Amines, alkali metal ions, and carbon deposition have been proposed in the patents to increase the selectivity for hydrogenation. 

Catalyst system chosen based on activity, selectivity, and cycle life and is generally composed of CoMo/NiMo alumina supported catalysts designed for specific objectives such as hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), hydrodeasphaltenization (HDAs), HCR, and Conradson Carbon removal (CCR)... 

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