Study on the Durability of Ir Catalyst Supported on MFI-type Metallosilicates for Selective Reduction of NOX with Hydrocarbons

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

Iridium catalysts supported on MFI-type metallosilicates with activation treatment in 10%H2O-N2 at 700 °C showed very high NOX reduction activity at 300--500 °C under oxygen rich condition.
The activated catalyst showed stable NOX reduction activity in lean burn atmosphere with steam gas and rich atmosphere gas treatment and was durable to SO2-poisoning.
This catalyst had stable NOX reduction activity in continuous treatment at 450 °C of lean burn gas atmosphere, but showed catalytic deactivation in continuous treatment over 500 °C of lean burn gas atmosphere. However , the activity of deactivated catalyst is easily regenerated by the lean/stoichiometry alternate gas treatment. Moreover, this catalyst showed stable NOX reduction activity of lean/stoichiometry alternate atmosphere gas treatment for 450 h.
The characterization by XRD and XPS revealed that the reason of catalytic deactivation in continuous treatment of lean burn gas atmosphere was in the form of Ir oxide around the Ir-metal surface. Ir oxide around the Ir-metal surface is easily removed by the hydrocarbon treatment in the stoichiometry gas atmosphere.


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