Selective catalytic reduction of nitric oxide with ethylene on copper ion-exchanged Al-MCM-41 catalyst

Selective catalytic reduction (SCR) of NO_x by ethylene was investigated on copper and/or cerium ion-exchanged Al-MCM-41 in the presence of excess oxygen. Ce-Al-MCM-41 showed little activity, but Cu-Al-MCM-41 and cerium-promoted Cu-Al-MCM-41 (i.e., Ce-Cu-Al-MCM-41) were found to be active in this reaction. Higher NO_x conversions to N₂ were obtained on Ce-Cu-Al-MCM-41 as compared with Cu-Al-MCM-41. The maximum activity of Ce-Cu-Al-MCM-41 was close to that of Cu-ZSM-5, but the former had a wider temperature window. TPR results indicated that only isolated Cu²⁺ and Cu⁺ ions were detected in the Cu²⁺-exchanged Al-MCM-41 samples, which may play an important role in the selective catalytic reduction of NO_x to N₂. After some cerium ions were introduced into Cu-Al-MCM-41, Cu²⁺ in the molecular sieve became more easily reducible by H₂. This may be related to the increase of catalytic activity of NO_x reduction by ethylene.