Influence of alumina crystal size on the hydrotreating activity of supported NiMo catalysts using real feedstock

Three different alumina substrates having different crystal sizes were used as supports for NiMoS_x catalysts. The supports were analyzed by XRD, pyridine FTIR-TPD, and nitrogen physisorption in order to determine their crystal size, surface acidity, and textural properties, respectively. After the NiMo was loaded on the γAl₂O₃ supports, the metallic particles were characterized during the preparation steps (annealing and sulfidation) using transmission electron microscopy (TEM). Hydrogen TPR studies of the NiMo catalysts were carried out to correlate their hydrogenating properties and their catalytic functionality, such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and aromatic hydrogenation (HDA) using Mexican gas oil (LGO). Experiments were carried out in a pilot plant at temperatures of 613°, 633°, and 653°K at pressure of 54 Kg cm ^-2. XRD measurements were performed on the alumina supports A, B, and C to determine their crystal size (3, 5, and 10 nm, respectively), using Scherer's equation. Transmission electron microscopy was used to analyze the metallic NiMo species dispersion; the dimensions and distribution of non-sulfided and sulfided metallic crystallites were confirmed by TEM. The catalytic evaluation results showed that the rate constants of hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodearomatizing (HDA) at 613-653°K decreased in the following order, A > B > C, corresponding to the increase of NiMoS crystal size associated with these catalysts.