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Selective catalytic reduction of nitric oxide with propane and oxygen was investigated on Cu-exchanged ZSM-5, mordenite, X-type and Y-type zeolites at temperatures in the range of 200 to 600°C. Catalytic activities of Cu-X and Cu-Y are negligible, activity of Cu-mordenite moderate, and that of Cu-ZSM-5 very high, converting > 90% of nitric oxide to nitrogen at 400°C and at a space velocity of 102 000 h⁻¹. Effects of space velocity, nitric oxide concentration, C₃H₈/NO ratio, oxygen concentration, and water vapor on the activities of Cu-ZSM-5 and Cu-mordenite were investigated. Nitric oxide conversion decreases with increasing space velocity, decreasing propane and nitric oxide concentrations, and decreasing propane/NO ratio. Water vapor decreases the activity significantly at all temperatures. At temperatures above 400°C, propane oxidation by oxygen is a significant competing reaction in decreasing the …