The deactivation of a catalyst located at the first bed of a bench-scale hydrotreating reactor operated at co-current downflow mode was studied. The deactivation, caused by metal and coke depositions, is analyzed by the characterization of catalyst recovered along the reactor bed. Metals trapped in catalysts remain as metal sulfides in the spent catalysts and their amount decreases from top to bottom of the bed length whereas coke increases toward bed outlet. Deposited foulants are classified according to removability by regeneration at 550 degrees C. Below this temperature the removable coke by oxidation is labeled as soft coke and hard coke corresponds to carbonaceous compounds that can only be oxidized above this temperature. By C-13 CP-MAS NMR it was found that the aromaticity of the deposited coke is constant throughout the catalytic bed. By regeneration of spent catalysts near half of the hydrodesulfurization activity is recovered. However, the hydrocracking activity is the same or higher compared with the fresh catalyst. The extra hydrocracking activity is the result of the creation of Bronsted acid sites after regeneration. (C) 2014 Elsevier Ltd. All rights reserved.