Preparation And Application Of Selective Catalytic Reduction Denitration Catalyst

Nitrogen oxides?NO_x?are the main source of environmental pollution,which will cause greenhouse effect,acid rain,acid mist and photochemical smog,which will cause harm to human health and the environment.Selective catalytic reduction of nitrogen oxides through reducing agents?NH3,CO?is currently the most mature and promising flue gas treatment technology,but dust,water and sulfur dioxide in the flue gas will cover the active sites on the catalyst surface,thus affects catalytic activity.Solving the problem of catalyst stability is urgent.In order to obtain a more efficient and stable SCR denitration catalyst,the preparation of the catalyst is studied from three aspects of catalyst formulation,preparation method and selection of reducing agent.Frist,a two-dimensional MnFeCo layered double oxide has been synthetized,fully characterized and employed as NH₃ selective catalytic reduction catalyst,showing excellent low temperature de-NOx performance.The as-obtained MnFeCo layered double oxide exhibited a specific surface area of 92.3 m²/g with average pore size of 2.1 nm and pore volume of 1.47 cm³/g.At 100°C,the MnFeCo layered double oxide performed an efficient NO conversion of 100%.Even at 25 and 50°C,the NO conversions still reached values as high as49.1 and 86.1%,respectively.Furthermore,the NO conversion reached an efficiency of 89.5%in the presence of H₂O vapor?5%?and SO₂?100 ppm?.Based on these results,it can be said that this NH₃ selective catalytic reduction catalyst shows great potential in NO_x denitration of stationary industrial installations at a low temperature range.Second,two-dimensional?2D?MnAl mixed-metal oxide nanosheets were successfully prepared via a high-shear-mixer-facilitated coprecipitation?HSM-CP?method.The as-obtained2D MnAl-MMO achieved high specific surface area of 180.6 m²/g,average pore size of 9.8 nm and pore volume of 0.45 cm³/g.The as-obtianed MnAl-MMO?HSM-CP?catalysts performed superior NO conversion of 96.3%and N₂ selectivity of 91%at 200°C with a gas hourly space velocity?GHSV?of 30,600 h^-1,all of which are much better than those of MnAl-MMO?CP?.Even at 25 ^oC,the MnAl-MMO?CP?catalysts nearly had catalytic activity whereas MnAl-MMO?HSM-CP?achieved a better NO conversion of 40%.Moreover,MnAl-MMO?HSM-CP?catalysts performed excellent H2O and SO2 resistance,and NO conversion is still remained 75%at 200 ^oC with 5%H₂O and 100 ppm SO₂.HSM-CP provides a new strategy for the development of MMO as efficient denitration catalysts.Three,Cu-benzene-1,3,5-tricarboxylate?BTC?,Cu-BTC?FNP?,and Cu-BTC?SD?precursors were prepared by direct mixing?DM?,flash nanoprecipitation?FNP?and spray drying?SD?,respectively.The precursors were pyrolyzed under nitrogen to obtain the corresponding Cu/C-DM,Cu/C-FNP,and Cu/C-SD catalysts.The physicochemical and catalytic properties of these samples were characterized by scanning electron microscopy?SEM?,N2 adsorption-desorption,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Raman spectroscopy,electronic paramagnetic resonance?EPR?,temperature-programmed reduction with hydrogen?H₂-TPR?,temperature-programmed desorption of oxygen?O₂-TPD?,and CO+NO model reactions.Regarding the CO+NO model reactions,the Cu/C-SD catalyst exhibited the best denitrification performance,reaching complete NO conversion and N2 selectivity of 98.8%at 300°C.The Cu/C-SD catalyst removed 88.1%of the initial NO at temperatures as low as 200°C,being this value was significantly higher than those obtained by Cu/C-DM?2.6%?and Cu/C-FNP?10.2%?catalysts.The Cu/C-SD catalyst also showed excellent stability in the independent presence of O₂?5 vol%?,H₂O?5 vol%?or SO₂?100 ppm?.The Cu⁺/Cu⁰ ratio played a key role in the selective NO catalytic reduction process.The larger specific surface area of the Cu/C-SD catalyst and its ability for the reduction and desorption of oxygen chemically adsorbed has a positive impact on the catalytic performance of this material.These results were theoretically supported by a DFT analysis.