Vliv modifikování oxidu titaničitého cerem na fotokatalytický rozklad hydroxidu amonného

Abstract

This thesis examines the influence of modifying titanium dioxide with cerium on the photocatalytic decomposition of ammonia. The main purpose of the photocatalytic decomposition of ammonia is its conversion to nitrogen and hydrogen. For the photocatalytic decomposition of ammonia was used an aqueous solution of ammonium hydroxide as the model reaction mixture. The decomposition was carried out in an aqueous solution in a batch stirred annular reactor with suspended catalyst (TiO2, 0,4 wt. % Ce/TiO2, 0,8 wt. % Ce/TiO2, 1 wt. % Ce/TiO2 and commercial TiO2 - Evonik P25). Furthermore, photolysis was performed, when decomposition of ammonium hydroxide was carried without the photocatalyst. The solutions were irradiated by 8 W Hg lamp placed in the center of the reactor. The products of the photocatalytic decomposition in the gas phase were nitrogen and hydrogen. The influence of modifying on the photocatalytic decomposition of ammonia was observed in the interval of 0-12 hours. Based on the experimental data we can say, that all doped catalysts in the photocatalytic decomposition of ammonia showed higher activity than the commercial catalyst TiO2 (Evonik P25). The activity of doped catalysts decreased in the order of 0,8 wt. % Ce/TiO2 < 1 wt. % Ce/TiO2 < 0,4 wt. % Ce/TiO2 < TiO2. Experimental data of the photocatalytic decomposition of ammonia were evaluated by an integral method, the kinetic constants were determined and it was confirmed that the decomposition can be described by the equation of 1st order. Based on correlation of the photocatalytic activity and the physico-chemical characteristics it was found out, that the basic parameters influencing the photocatalytic decomposition of ammonia are specific surface area of the catalyst and its absorption edge size. With the increasing specific surface area and decreasing the absorption edge increased the activity of catalysts.