Selective Catalytic Reduction Of NO With Methane Over The Superacid Catalysts

The selective catalytic reduction (SCR) of NO with methane has attracted a lot ofattention in recent years. Many kinds of catalysts have been found to be active forthis reaction. However, water vapor and sulfur dioxide are typically present in theexhausts and will cause seriously deactivation to the SCR catalysts. Therefore,improving of the tolerance of catalysts to the poisoning of water and SO₂ is veryimportant. In this work, a series of metal-loaded sulfated zirconia (SZ) and sulfatedalumina (SA) catalysts were firstly used in the SCR of NO with methane.For the first time, a series of non-noble metals were found to exhibit promotingeffect on the catalytic activity of SZ for the SCR of NO with methane. Among theinvestigated metals, Co and Mn have the best effect. The most attractive feature ofCo/SZ and Mn/SZ catalyst is that they are less sensitive to the poisoning of water andSO₂ than ZSM-5 based catalysts and exhibit higher reversibility after the removal ofSO₂. BET, NH₃-TPD, H₂-TPR, DRS and XPS results show that the sulfation ofsupport can increase the BET surface areas of catalysts and generate strong acid sites.Both effects inhibit the formation of bulk metal oxide which is only active for thecombustion reaction and improve the selectivity of methane to NO reduction.NO-TPD results indicate that the loading of Co (or Mn) facilitates the NO reductionby activating methane and increasing the NO adsorption of SZ catalysts.Pd/?-Al₂O₃, as one of the most used three way catalysts, exhibited lower activityfor the SCR of NO with methane. In this work, we found that Pd/?-Al₂O₃ can beturned into a high effective and SO2-tolerant catalyst for the SCR of NO withmethane by simply pretreating the support with H2SO4. The results of NH3-TPDshow that the sulfation increases the acidity of support which is very important forthe SCR of NO with methane over Pd catalysts. NO-TPD results indicate that theloading of Pd facilitates the NO reduction by activating methane and increasing theNO adsorption of sulfated alumina catalysts.