Boron modification of the hydrotreating catalysts has unraveled that the application of boron provokes changes in structural characteristics, the acidic properties of the supports and catalysts, the morphology of the active components, and the catalytic activity in HDS reactions [
11–
17]. Peil et al. [
1] confirmed that with the incorporation of boron to the catalyst, the acidity of the carrier was adjusted, resulting in higher activities of CoMo/Al
2O
3 and NiMo/Al
2O
3 catalysts for HDS reactions. Similarly, boron introduction can regulate Brønsted acidity of the supports and modify the electronic properties of the sulfide sites [
10,
19]. Changing acidity may associate with different interactions of boron with alumina. Houalla and Delmon [
20] proposed that the alumina acidity increased due to the boron addition through the formation of Al-O-B-O-Al bonds. However, most researches highlighted that the addition of boron decreased the chemical interaction between the supported metal and alumina. Usman et al. [
16] concluded that boron modification improved the catalyst’s performance by weakening the interactions between molybdenum oxides and Al
2O
3 surface, thus leading to a shift of the types from a less active Co-Mo-S I to a more active Co-Mo-S II phases. The weakened interactions between Mo species and Al
2O
3 surface concomitantly resulted in a decrease in the dispersion of Mo species in CoMo/Al
2O
3 catalysts, in agreement with the results of Morishige and Akai [
21]. Furthermore, Lewandowski and Sarbak [
22,
23] found that boron did not change the pore volumes significantly, while increased the pore diameters to 20, 25, 30 and 40 Å in comparison with the unmodified catalyst, resulting in better sulfidation of the supported metals. Moreover, the combination usage of boron with other additives, such as phosphorus [
24,
25] or fluorine [
15], will intensify a positive boron influence.