Catalysts based on cordierite modified with transition metal oxides

Catalysts active in ammonia oxidation have been obtained by the substitution of transition metal (Mn, Fe, Co, Ni, and Cu) ions for Mg ions in the cordierite structure 2MgO · 2Al2O3 · 5SiO2 at 1100°C. Their phase composition, texture, and activity depend on the type and amount of introduced transition metal oxide. The Mn- and Cu-containing catalysts, which consist of substituted cordierites 2(Mg1 − xMx)O · 2Al2O3 · 5SiO2 and Mn2O3 or CuO crystallites located on their surface, are most active in ammonia oxidation. The catalysts are characterized by a small specific surface area and have large pores, whose total volume is small. The Fe-containing catalysts consist of the Fe-substituted cordierite phase and particles of an iron oxide phase. These particles are mostly located in internal pores of the catalysts and are, therefore, hardly accessible to ammonia molecules. The introduction of Co or Ni oxide leads to the formation of a low-active spinel phase rather than the cordierite phase.