Abstract: Cr-modified In/WO₃/ZrO₂ (In/WZr) catalysts were prepared by impregnation and mechanical mixing methods. Their activity for selective catalytic reduction of NO with CH₄ was investigated. The results showed that the catalyst activity was enhanced by mixing Cr₂O₃ with In/WZr. The enhancement of the activity was due to the oxidation ability of Cr₂O₃, which improved the conversion of NO to NO₂. However, for the catalysts prepared by impregnation, some of the trivalent chromium (Cr³⁺) was converted to Cr⁶⁺, which resulted in the lower activity than the initial In/WZr catalyst by the complete oxidation of CH₄ to CO₂ and H₂O.

Key words: nitrogen oxide, selective catalytic reduction, methane, indium, tungstated zirconia, chromium