Formation and conversions of titanium(iii) complexes in the photocatalytic production of hydrogen from alcohols

EPR and spectrophotometry were used to study the products of the photochemical reduction of titanium(IV) ions in alcohols which act as photocatalysts for the production of molecular hydrogen. Tetrahedral complexes of the type [TiOHL₃] and [TiORL₃] were detected besides the octahedral complexes [TiCl₂(ROH)₄]⁺ and [TiCl₃(ROH)₃]. The EPR spectra of the compounds at 77 and 295°K have been obtained and their parameters determined. The influence of temperature, the addition of water, and alkali on the concentration ratio of the compounds studied has been established. It has been found that the addition of small amounts of water increases the content of the hydroxocomplex, while at the same time the alkoxocomplex decomposes irreversibly. Analogous changes take place when the photolysis time is increased. One of the conditions for effective hydrogen evolution is maintaining the temperature close to room temperature or slightly higher. The efficiency of the process increases somewhat after prolonged operation of the system.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 23, No. 3, pp. 295–302, May–June 1987.