Tunable Highly Dispersed Ni_a-xMn_xAlO_y Catalysts Derived from Layered Double Oxide for Low Temperature NO_x Removal

A series of highly dispersed Ni_a-xMn_xAlO_y catalysts derived from layered double hydroxides (LDHs) were prepared for selective catalytic reduction of NO_x with ammonia (NH₃-SCR) at low temperature. The physicochemical and catalytic performance of the prepared catalysts with different M²⁺/M³⁺molar ratios were systematically investigated by XRD, BET, XPS, TP_X (i.e. TPD and TPR) and in situ DRIFTs. Fortunately, Ni_4-xMn_xAlO_y as the optimal catalyst exhibited prominent NH₃-SCR performance with NO_x conversion greater than 90% at low temperature range of 120~210 °C. Especially, the influence of H₂O and SO₂ revealed that the catalyst activity could be miraculously promoted by H₂O, while deactivated by SO_2. The proper M²⁺/M³⁺molar ratios not only provided the surface acidic sites, the high Mn⁴⁺ content ratio and the adsorbed oxygen of Ni_a-xMn_xAlO_y catalysts, but also promoted the transformation of NO_x intermediate species to more stable bidentate nitrates. Results of the in situ DRIFTs illustrated that the SCR reaction path of Ni_a-xMn_xAlO_y catalysts followed both E-R and L-H mechanisms, and the former played the dominant role.