Abstract: To study the competitive adsorption of various species on the surface of alumina carrier in metal impregnation solution, the corresponding equilibrium adsorption experiments were conducted by introducing different types of additives into the solution. The results showed that the addition of ammonium metatungstate into ammonium heptamolybdate solution could reduce molybdenum equilibrium adsorption capacity to a certain extent, and the competitive adsorption on the neutral hydroxyl groups of alumina was beneficial for weakening the strong interaction between tungsten species and alumina. Adding ammonium nitrate, ammonium chloride, ammonium sulfate, glycerol and polyethylene glycol into ammonium heptamolybdate solution had little effect on molybdenum equilibrium adsorption capacity, but adding phosphoric acid or its ammonium salt could significantly reduce molybdenum equilibrium adsorption capacity. The results showed that the molybdenum species could be adsorbed competitively, the interaction between molybdenum species and alumina was weakened, and the sulfidation of molybdenum species was promoted. The introduction of ammonium citrate could also significantly reduce molybdenum equilibrium adsorption capacity. In addition, molybdenum equilibrium adsorption capacity of the alumina carrier in the phosphomolybdic acid solution dominated by the [PMo₁₂O₄₀]^3- structure was significantly higher than that in the phosphomolybdic acid solution dominated by the [P₂Mo₅O₂₃]^6- structure. Furthermore, the molecular structure of molybdenum precursors and the amount of free phosphate and citrate ions could be changed by adjusting the P/Mo mole ratio in metal impregnation solutions containing citric acid. The molybdenum equilibrium adsorption capacity of the alumina carrier gradually decreased with the increase of the P/Mo mole ratio in the solution. The results provide the necessary theoretical and technical support for designing the composition of metal impregnation solution and developing high-efficiency hydrotreating catalyst.

Key words: alumina, molybdenum equilibrium adsorption capacity, metal precursor, phosphorous, citric acid, competitive adsorption