Abstract <p>The effect of the diesel fuel feed rate on silicon adsorption on a NiMo/Al₂O₃-protective layer catalyst in the hydrotreating process is studied. The raw material used is a straight-run diesel fraction containing the additive decamethylcyclopentasiloxane in the amount of 200 million^–1 as an additional source of silicon. Three series of experiments are conducted, each lasting 60 h, at specific feed rates of 0.75, 1.5, and 3.0 h^–1. It is found that with an increase in the specific feed rate, the silicon content in the protective layer catalyst increases. To evaluate the efficiency of the adsorption process, the silicon extraction coefficient is used, which is equal to the ratio of the amount of adsorbed (extracted from the raw material) silicon to that supplied during the experiment. In the speed range of 0.75–3.0 h^–1 the silicon extraction coefficient decreased from 0.93 to 0.61 due to more intensive filling of active centers on the catalyst surface. The influence of external mass transfer on the silicon adsorption process is assessed.</p>