The presence of χ-Al₂O₃ resulting from thermal decomposition gibbsite as part of alumina catalysts is unfavorable because of its acid characteristics. One of the available techniques of χ-Al₂O₃ removal is crystallization under hydrothermal conditions into boehmite, which is a main precursor of active γ-Al₂O₃. The influence of products of the hydrothermal treatment of χ-Al₂O₃ obtaining in result of thermal decomposition gibbsite under T = 150–200 °C, P = 0.5–1.5 MPa and pH = 4.0–9.2 were studied. The hydrothermal treatment products in these conditions are gibbsite and boehmite phases which are formed coincidently by parallel ways. In the alkaline medium at pH = 8.0–9.2 three-dimensional parallelepiped boehmite crystals with the edge length > 200 nm are formed, at pH = 4.0 two-dimensional rhombic-shaped plates with thickness 20–100 nm and with the edge length ~ 80–500 nm are formed. Crystallization of coarse boehmite particles promotes the formation of large and closed mesoporous.

Co-Mo/γ-Al₂O₃ catalysts with different pore shapes were synthesized for the ex situ upgrading of extra heavy oils by hydrodesulfurization (HDS), hydrodemetallization (HDM), and hydrodeasphaltization (HDA). The catalysts were synthesized using aluminum oxides that were prepared by various methods. It was found that using the product obtained by the thermochemical activation of gibbsite leads to the formation of slit-shaped pores in aluminum oxide, while the application of the hydroxide deposition method by the precipitation of sodium aluminate and nitric acid gives cylindrical pores in aluminum oxide. Co-Mo catalysts synthesized using these two types of pores exhibit different catalytic activities. The catalyst synthesized on a carrier with cylindrical pores exhibited a higher catalytic activity in sulfur, heavy metals, and asphaltenes removal reactions that are synthesized on a carrier with slit-like pores. This is because the presence of cylindrical pores leads to a decrease in diffusion restrictions when removing large molecules of asphaltenes and sulfur-containing and metal-containing compounds.

Highly porous cellular material (α-Al₂O₃-HPCM) support was synthesized by the template method. Highly porous support was used for the synthesis of the catalyst. A thin secondary layer with 25–30 μ thick γ-Al₂O₃ and zeolite Y was applied on the α-Al₂O₃-HPCM surface ((γ-Al₂O₃ (85%)-zeolite Y (15%))/α-Al₂O₃-HPCM). The catalyst based on the highly porous support was tested in a process of decreasing oil viscosity. The catalyst in the form of cylindrical granules and a thermal process of decreasing oil viscosity without the catalyst were used as the basis for comparison. α-Al₂O₃-HPCM in the catalyst provides low-quantity pores (d < 10 nm) and a quantity of general acid centers compared with the granular catalyst. On the other hand, it shows a more significant oil viscosity decrease (from 2500 to 41 cPs) and a low rate of gas generation (137 mL/h) for the catalyst with highly porous support. A high oil fraction was observed in the presence of the (γ-Al₂O₃-zeolite Y)/α-Al₂O₃-HPCM compared to the granular catalyst. The presence of large transport cells (pores) 1500–2000 μ for the catalyst based on highly porous support allowed a work period four times longer than that of experiment only with temperature without catalysts.

In order to obtain an efficient alumina catalyst for skeleton isomerization of n-butenes with a high catalytic activity, we study the influence of hydrothermal treatment (HTT) of alumina systems at 150–200°C on the parameters of the crystalline and pore structure, and acid-base properties of industrial γ-Al₂O₃. It is shown that the HTT of aluminum hydroxide increases the sizes of microcrystallites and reduces the alumina’s specific surface area and the number of acid-base centers. This reduces the activity in the reaction of skeletal isomerization of n-butenes. HTT of the two-phase alumina-aluminum hydroxide system produces smaller crystallites of γ-Al₂O₃ and raises the acidity of the alumina obtained after calcination at 550°C; as a result, the catalytic activity increases. This method can be used to enhance the activity of industrial samples of alumina in the reaction of skeletal isomerization of n-butenes.

The reasons for deactivation of alumina catalyst during the skeletal isomerization of n-butenes, reducing conversion from 31 to 26%, are investigated. It is shown that contamination with metal Fe and Mg microimpurities lowers n-butene conversion in total by approximately 2.5%. The catalyst’s activity can be restored by washing out metal microimpurities. Water vapor and feedstock pipelines turn out to be the source of metal impurities. The δ-modification of alumina accumulates during catalyst operation, reducing n-butene conversion by ∼3 abs % and creating an irreversible type of deactivation. The drop in the temperature of phase transition in the presence of Fe and Mg microimpurities is one possible reason for the partial phase transition at a temperature lower than 600°C. It is shown that the accumulation of microimpurities and the alumina δ-phase reduces the number of acid sites and thus the efficiency of alumina catalytic conversion. To prolong the catalyst’s operational life, it is recommended that metal impurities be captured from the vapor-feedstock flow by installing a protective layer of a macroporous material with a developed surface inert to the butane fraction upstream of the catalyst.