Development of supported iron oxide catalyst for destruction of PCDD/F.

Studies on the development of supported iron oxide catalysts for PCDD/F decomposition using 2-monochlorophenol as a surrogate test compound are presented. Iron oxide catalysts supported on titania were prepared by two methods: impregnation and the sol-gel method. The latter preparation method resulted in better dispersion of iron oxide on the surface and the formation of gamma-Fe2O3. This is in contrast to the impregnated samples where alpha-Fe2O3 crystallites were formed. Formation of gamma-Fe2O3 resulted in improved reducibility of the active phase that favorably affected the catalytic oxidation properties of the catalyst, i.e., the light-off curves for the sol-gel samples were shifted toward lower temperature. Addition of calcium oxide to iron oxide catalyst further improved the performance of the system through stabilization and increase in the concentration of gamma-Fe2O3 in the sol-gel prepared samples. Addition of calcium oxide has a dual effect on the performance of the catalyst. First, it creates oxygen vacancies in the reduction-resistant Fe2O3 octahedral structures, thereby improving the reducibility of the active phase. Second, iron oxide can transform during decomposition of chlorinated hydrocarbons into iron chloride. Calcium oxide improved the chlorine transfer from the surface iron oxide species, thereby providing a relatively fresh surface for further catalytic oxidation. Comparison of TPR profiles with the position of light-off curves in 2-monochlorophenol decomposition led to the conclusion that Fe3O4 species are the active phase under conditions that facilitate redox cycling between Fe3+ and Fe2+ ions.