Читать книгу Handbook of Biomass Valorization for Industrial Applications - Группа авторов - Страница 21

The selection of suitable photocatalyst depends on the compatibility between band position of oxidation and reduction potentials of the reactants in a reaction. There are two types of band positions: conduction band position and valence band position. To carry out reduction reactions with electrons from the conduction band of photocatalyst, the position of conduction band should have more negative value than the reduction potential of reagents. In opposite of this, for the occurrence of oxidation reactions in photocatalysis with holes, the position of valence band should have more positive value than the oxidation potential of the reagents. The search of optimal photocatalysts for the photocatalytic reactions is based on band gap which initiate redox reactions with over potentials. TiO₂ is the more chosen photocatalyst by researchers because it is non-toxic, stable, biological and chemically inert [5, 14, 15]. TiO₂ is a very active photocatalyst under ultraviolet and visible light radiation especially for the conversion of biomass substrates. UV-photocatalysts can be divided into oxide (Ti⁴⁺, Sn⁴⁺, Ge⁴⁺, Zr⁴⁺, etc.) and non oxide groups. Many UV active photocatalysts can be improved by increasing the range of visible light so that more absorption of light can be done. Nowadays, the development of new catalysts for maximum absorption of visible light is in great attention with mixed metal oxides, sulfides, and nitrides for biomass utilization. Table 1.3 provides a list of important homogeneous and heterogeneous catalysts as follows in which mostly heterogeneous catalysts are associated with TiO₂.