Low-temperature combustion synthesis of the Mn-CeO_x catalyst and its performance in the selective catalytic reduction of NO_x by NH₃

A series of Mn-CeO_x(LCS) catalysts with different molar ratios of metal nitrates to citric acid were prepared by low-temperature combustion synthesis (LCS) method. Through a comparison with the Mn-CeO_x(CP) catalysts prepared by coprecipitation method (CP) as well as various characterization techniques such as XRD, XPS, FESEM, H₂-TPR and nitrogen physisorption, the catalytic performance of Mn-CeO_x(LCS) in the selective catalytic reduction (SCR) of NO_x by NH₃ was then investigated. The results show that the molar ratio of metal nitrate to citric acid is an important factor affecting the denitrification performance of the Mn-CeO_x(LCS) catalysts. In comparison with the Mn-CeO_x(CP) catalysts, the Mn-CeO_x(LCS) catalysts are provided with a higher manganese content and high O_α/(O_α+O_β) ratio on the surface as well as more hierarchical pores favorable for adsorption and reaction of reactants, which affords the Mn-CeO_x(LCS) catalysts much better denitrification performance. Over the Mn-CeO_x(LCS) catalyst with a molar ratio of metal nitrate to citric acid of 36:22, the denitrification rate at 80-180℃ reaches 75%-100%; even in the presence of SO₂, the denitrification rate over the Mn-CeO_x(LCS) catalyst at 180℃ keeps at the level of 74%.