Selective Oxidation of NH3 to N2 over Cu Catalysts Supported on MFI-type Metallosilicate

Shigeru NOJIMA*, Kozo IIDA and Norihisa KOBAYASHI

Hiroshima R & D Center, Mitsubishi Heavy Industries LTD; 4-6-22 Kanonshin-machi, Nishi-ku, Hiroshima-shi 733-8553 Japan
Power Systems Headquarters, Mitsubishi Heavy Industries LTD; 3-3-1 Minatomirai, Nishi-ku, Yokohama-shi 220-0012 Japan

Copper catalysts supported on MFI-type metallosilicate were prepared and their activities for selective oxidation of NH3 were examined. Among the catalysts tested in this study, copper catalysts supported on MFI-type metallosilicate showed the highest activity. This catalyst selectively converted NH3 to N2 at 250−400 °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 NH3 was the copper supported on the strong acidic site of metallosilicate. From NH3-TPD, NH3-O2 pulse reaction and FT-IR measurements, amino groups formed on the catalyst surface were found to be intermediates of the NH3 selective oxidation. The following mechanism for the selective oxidation of NH3 was suggested; NH3 is first adsorbed on the Brφnsted acid site of metallosilicate and then converted to NH4+. Secondly, dinitrogen group intermediate is formed by the oxidative dehydration of NH4+. Finally, dinitrogen group intermediate is dehydrated oxidatively to N2.

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