The Study On The Morphology Control And The Relationship With SCR Denitration Performance Of Mn-based Catalysts At Low Temperature

Nitrogen oxides?NO_x?emitted from stationary sources pose serious environmental problems and have a serious impact on human health.Selective catalytic reduction?SCR?of NO with NH₃ is considered the most effective and economic technology for the removal of NO_x.The catalysts widely employed in the SCR process for nitrogen oxides abatement request relatively high reaction temperature,so the SCR unit has to be located upstream of the desulfurizer and electrostatic precipitator.As a result,the catalysts was severely damaged by dust and suffered from sulfur poisoning.Therefore,it is important to develop highly active SCR catalysts that show good low temperature catalytic activity,have good sulfur-poisoning resistance,and are less expensive.In recent years,manganese oxide-based catalysts have attracted considerable interest due to their excellent catalytic performance at low temperatures.In this paper,the effect of different?-MnO₂ exposed active crystal facets on the catalytic activity was studied.The different exposed active?-MnO₂ crystal facets were regulated and prepared by the use of four different capping agents?PVP,P123,HAc,CTAB?.Meanwhile,the effects of exposed crystal plane on the physicochemical properties and catalytic SCR denitration activity of catalysts were studied.The result showed that all?-MnO₂ catalyst samples prepared could present nanowires cristal morphology.The sample modified by PVP as capping agent with abundantly exposed MnO₂?200?facet was observed to have the highest amount of surface acidic sites and the strongest NH₃adsorption capacity,and thus showed the highest catalytic SCR catalytic.The effects of doping different transitional metal promoters on the physicochemical properties and denitration activity of Mn-based composed oxide catalysts were also studied systematically.The results showed that the Mn-based composed oxide catalysts modified with different transitional metal promoters chouls still maintain the original crystal form of?-MnO₂,but the crystal morphology has changed.The Co-doped Mn-based composed oxide catalyst exhibited the best low temperature catalytic SCR deNO_x activity and ideal resistance to sulfur.The conversion of NO reached 99%at 180°C,and the activity of catalyst was almost unaffected by the addition of 5%H₂O,200 ppm SO₂ and 5%H₂O+100 ppm SO₂ in the reaction atmosphere.Even adding water up to 10%into the reaction atmosphere,the NO conversion decreased only about 10%,and the adverse effect could be quickly eliminated when the water environment was removed.In addition,the MnO₂-Co composed catalysts with different Co contents were prepared by the hydrothermal method.It was found that MnO₂-Co-0.8?Mn/?Mn+Co?mole ratio of 0.8?catalyst sample showed the highest catalytic activity,giving 100%NO_x conversion at the temperature of 135°C.The sulfur resistance of MnO₂-Co-0.8 sample was also excellent,remaining the NO conversion of 99%after adding 100ppm SO₂ into the reaction atmosphere.Finally,the exposed crystal facets of MnO₂-Co-0.8 sample was regulated and controlled by the capping agent PVP.The results showed that the MnO₂-Co-0.8-PVP catalyst sample prepared by PVP as capping agent maintained original nanowires form crystal morphology but exposed the MnO₂?310?crystal facets.And this sample showed good low temperature catalytic SCR denitration activity.