Research Progress of Supported Hydrodesulfurization Catalyst Additives

The commonly used additives of hydrodesulfurization catalysts are P, F, B, etc., with the purpose of regulating the properties of the carrier, weakening the strong interaction between the metal and the carrier, improving the surface structure of the catalyst, improving the reducibility of the metal, and promoting the reduction of the active component to a low valence state, to improve the catalytic performance of the catalyst.

Phosphorus is one of the most commonly used additives. Phosphorus is usually used as the third component of HDS catalyst.P can promote the HDS, HDN and HDA activities of the catalyst. The main reason is that P interacts with Al2O3, forming AIPO4 on the surface of Al2O3 and improving the acidity of Al2O3. Usman  pointed out that the addition of phosphorus can promote the transformation of type I Co-Mo-S phase to type II Co-Mo-S phase, and phosphorus also reacts with the hydroxyl groups on the surface of Al2O3, thus weakening the interaction between MoS2--Al2O3. Van Veen  also believed that the addition of phosphorus can promote the transformation of type I Co-Mo-S phase to type II Co-Mo-S phase. Kwak  studied the effect of adding phosphorus on Co-Mo/Al2O3 catalyst HDS, the results showed that adding phosphorus increased B acid, improved metal dispersion, increased active centers, and improved activity. However, there are also some literature reports that phosphorus does not promote hydrodesulfurization.

Boron reacts with Al2O3 to form Al-O-B bonds, and the acid strength of B-OH is higher than that of Al-OH, so the impregnation of B increases the surface acidity of the carrier. In addition, the electronegativity of B is larger than that of Al, so the interaction between Mo7O246- and B3+ is stronger than that of Al3+, which increases the octahedral Ni2+ or Co2+. There are more CoMoO or NiMoO on the surface of the carrier, resulting in more active centers for hydrodesulfurization and hydrogenation, thereby improving the activity of the catalyst.

Adding fluorine can increase the acidity of the carrier, enhance the cracking and isomerization ability of the catalyst, increasing the hydrogenolysis reaction activity of C-N, C-S, and C-O, reducing the isoelectric point of Al2O3, improving the metal distribution, and increase the hydrogenation activity of the catalyst. When the sulfur content of F is low, F can replace the hydroxyl groups on the surface of Al2O3 and inhibit the formation of tetrahedral Mo, which is beneficial to the production of octahedral Mo. Kwak believed that F could promote the hydrogenation of the benzene ring, the cleavage of the CS bond and the transfer of the methyl group on the benzene ring. In addition, adding F lowers the isoelectric point of Al2O3, increases the dispersion of Mo, and improves the hydrogenation performance.