Kinetic Study of the HDS of 4,6-DMDBT over NiMo/Al2O3-SiO2(x) Catalysts

Two NiMo/Al2O3-SiO2(X) catalysts with different SiO2 content in the support (0 and 10 wt %) were evaluated at four temperatures (560, 573, 585, and 598 K) in the HDS of 4,6-DMDBT. The reaction products (DMDP, MCHT, and DMDCH) were analyzed to establish a reaction scheme. Then, a kinetic study using Langmuir-Hinshelwood (LH) type equations was carried out to estimate the changes in the rate constants for the direct desulfurization and hydrogenation reaction routes involved in the HDS of 4,6-DMDBT. The results show that incorporation Of SiO2 to the catalyst support increases the HDS of 4,6-DMDBT and that this increase is mainly due to a greater contribution of the hydrogenation reaction. The apparent activation energy and pre-exponential factor estimated for both reaction routes indicated an increase in the number of active sites related to the hydrogenation route when SiO2 is present in the catalyst. This result was corroborated by means of NO adsorption.