Tunable Synthesis Of CoMnAl Hydroxides And Study Of CoMnAl Mixed Oxides For Low-temperature DeNOx Performance

Regarding to its abundant variable valence states,Co was selected to be dopant to modify Mn-based oxides which could offer the benefits of electron transfer effect and further enhance the NH₃-SCR performance.Meanwhile,Al₂O₃ support can facilitate the thermal stability and acid ability over the catalysts.This paper starts with the synergy effect of Co,Mn,Al to build CoMnAl composite oxides in the most efficient way to improve catalytic performance for NH₃-SCR is of significant importance.The mixed metal oxides?LDO?derived from layer double hydroxides?LDHs?offer a number of advantages such as high specific sueface area,grain high dispersion,good cation dispersion and well thermal stability.Hence,this paper attempts to take the advantages of LDHs to regularly construct CoMnAl mixed metal oxides catalysts which could contribute to excellent DeNO_x efficiency,N₂ selectivity and SO₂ resistance.The main research content and conclusions are as follows:1.?Co??Mn?Al-LDHs were fabricated by using HMT hydrolysis method.The?Co??Mn?Al composite oxides obtained by calcining as-prepared LDHs and tested as NH₃-SCR catalyst.The results indicated that Co₄Al₁-NO₃-LDH,Mn₄Al₁-CO₃-LDH,Co₃Mn₁Al₁-CO₃-LDH were successfully prepared and Co₃Mn₁Al₁-CO₃-LDH possessed relatively completed crystal structure,better defined crystallinity and well hexagonal lamellar morphology as compared to Co₄Al₁-NO₃-LDH and Mn₄Al₁-CO₃-LDH.The Co₃Mn₁Al₁-500 calcined at500?possessed better dispersion of active components.Compared to Co₄Al₁-500 and Mn₄Al₁-500 catalysts,Co₃Mn₁Al₁-500 displayed preferable DeNO_x performance.Meanwhile,Co₃Mn₁Al₁-500 possessed wider operating low temperature window as compared to Co-Mn/?-Al₂O₃-500 synthesized by traditional impregnation.2.Co_x Mn_4-xAl₁-500 composite oxide from Co_xMn_4-xAl₁-LDHs?x was 1,2,3?precursors were prepared to select the optimal proportion.Co₃Mn₁Al₁-T?T was 500?,600?,700??were prepared to select the optimal calcining temperature.When the Co/Mn molar ration is 3:1,a well-crystallized hydrotalcite-like phase with no impurity phase can be obtained.The Co₃Mn₁Al₁-500 calcined at 500?exhibited the highest surface area(85.3 m²g^-1),and more favorable ratios Mn⁴⁺and Co³⁺as well as surface adsorbed oxygen species which consequently provided stronger redox property and multiple acid sites.The results proposed that Co₃Mn₁Al₁-500 catalyst exhibited excellent DeNO_x activity?NO_x yield above 90%?,N₂ selectivity and sulfur tolerance in the temperature range of 120-280?.3.Based on interlayer anion exchangeability and redox reaction between Co???and Mn???,MnO₂-pillared CoAl-LDH was successfully fabricated and investigated the influence of LDHs precursor templates on the catalytic performance of CoMnAl composite metal oxides.The anionic exchanging of Co₃Al₁-NO₃-LDH can ensure the replacement of NO₃^-anions with MnO₄^-ions?denoted as Co₃Al₁-MnO₄-LDH?.Subsequently,MnO₄^-ions can be reduced to MnO₂ particles due to the redox reaction between Co???and Mn????pH=5.7??denoted as Co₃Al₁-MnO₂-LDH?.MnO₂/Co₃Al₁-500 exhibited the highest surface area(156.8 m² g^-1),which could promote dispersion of abundant Mn⁴⁺and Co³⁺species,and resultantly afforded stronger redox ability and more acid sites.Catalytic performances of the as-acquired CoMnAl catalysts were vulnerable to the preparation method of precursor template,in which MnO₂/Co₃Al₁-LDO presented preferable DeNO_x activity?over 90%NO_x conversion?,N₂ selectivity and SO₂ resistance in much broader working temperature window?90-300??than Co₃Mn₁Al₁-500.