Heterogeneous catalysts based on gamma aluminum oxide with immobilized xylanase for hydrolytic decomposition of xylane

In this work, heterogeneous catalysts based on powdered γ-alumina with an immobilized xylanase enzyme were obtained and a study of their catalytic activity and the possibility of their repeated use was carried out. The aim of this research work was to create an effective heterogeneous catalytic system based on γ-alumina with an immobilized enzyme for the decomposition of the natural polysaccharide xylan with the maximum yield of the target product. In the course of the work, xylanase was immobilized on γ-Al2O3 by two methods, namely, physical adsorption and covalent binding using glutaraldehyde as a cross-linking agent. The reactions of enzymatic hydrolysis of xylan, the study of the catalytic activity and operational stability of the immobilized enzyme in 4 cycles were carried out on the obtained systems. An alumina sample was synthesized by the sol-gel method with a temperature of calcination of 550 °C for 4 hours, which corresponds to the γ-phase of alumina. The surface charge of the obtained sample was characterized by EPR of pH-sensitive nitroxide radicals. According to the shifts of the EPR titration curves, the surface of γ-Al2O3 was found to have a positive charge which implies the presence of Lewis centers on its surface. The catalytic activity of xylanase immobilized on the γ-Al2O3 surface by the method of covalent attachment through glutaraldehyde is 1.83 times higher than in case of immobilization by physical adsorption and is equal to 12.23 U/mg. The enzymatic activity of covalently immobilized xylanase in the first two cycles was found to be quite high, in the third cycle it decreases to 37.5 % and reaches a plateau. When the enzyme is immobilized by physical adsorption, the activity continues to decrease to 23 % in the 4th cycle. The decomposition of xylan by heterogeneous catalytic systems based on γ-Al2O3 and the xylanase enzyme immobilized on it by various methods, and a comparative analysis of the data obtained, allows us to conclude that further use of the obtained systems is promising, for example, in poultry farming due to the effectiveness of the use of immobilized xylanase in the release of reducing sugars.