Selective Oxidation of NH_3 to N_2 over Cu Catalysts Supported on MFI-type Metallosilicate

摘要

Copper catalysts supported on MFI-type metallosilicate were prepared and their activities for selective oxidation of NH_3 were examined. Among the catalysts tested in this study, copper catalysts supported on MFI-type metallosilicate showed the highest activity. This catalyst selectively converted NH_3 to N_2 at 250-400 deg C in the presence of excess oxygen. The characterization of acidity and the effect of copper content revealed that active site of the catalyst in selective oxidation of NH_3 was the copper supported on the strong acidic site of metallosilicate. From NH_3-TPD, NH_3-O_2 pulse reaction and FT-IR measurements, amino groups formed on the catalyst surface were found to be intermediates of the NH_3 selective oxidation. The following mechanism for the selective oxidation of NH_3 was suggested; NH_3 is first adsorbed on the Bronsted acid site of metallosilicate and then converted to NH_4~+. Secondly, dinitrogen group intermediate is formed by the oxidative dehydration of NH_4~+. Finally, dinitrogen group intermediate is dehydrated oxidatively to N_2.