Low Temperature SCR Of NO Over Palygorskite-Supported Manganese Oxide Catalyst

With the increasing of the air pollution, exploration and application of noval flue gas DeNOx technology that suit power plant situation that lower temperatures after downstream of dust removal and desulfurization is of great significance to pollution control of our country. Ammonia selective catalytic reduction (SCR) of nitrogen oxide is the only industrialized flue gas DeNO_x technology. Currently the widely used commercial SCR catalyst is V₂O₅/TiO₂ and V₂O₅-WO₃/TiO₂, of which the temperature window is 350⁴00 oC. It is not suitable for most of our national power plant's flue gas emission conditions. Efficient low temperature (100²50 oC) catalyst that can not only reduce the energy consumption of SCR, but also can resist the deactivation of SO₂, therefore shows perfect attraction.This dissertation studied the activity of manganese oxides catalyst supported by palygorskite catalyst in lower temperatures for selective catalytic reduction of NO and its physic-chemical properties.A MnO_x/palygorskite catalyst for low temperature selective catalytic reduction (SCR) of NO by NH₃ was prepared by heterogeneous co-precipitation followed by drying and calcination. Physic-chemical properties of the catalyst were characterized by X-ray diffraction, transmission electron microscope, temperature programmed reduction in H2, Brunauer–Emmett–Teller. The results showed that manganese oxides are highly dispersed on the surface of the palygorskite support. The surface manganese species exist as Mn2O₃ and Mn₃O₄ at calcination temperature lower than 550 oC as Mn₃O₄ at 550 oC.The SCR performance of MnO_x/PG catalyst was evaluated in the fixed bed reactor.The effect of catalyst preparation conditions (calcination temperature, manganese oxide loading) and reaction conditions (reaction temperature, space velocity, H2O, SO₂) on the SCR activities as well as N₂ selectivities were investigated. The results show that, in the space velocity of 9220 h-1, the SCR performance of Mn10/PG catalyst calcined at 300 oC is the best, the NO conversion is 91% at 175 oC and even up to 97% at 200³00 oC, while the N₂ selectivity is 100% at 175³00 oC. Palygorskite and MnO_x/PG catalyst were investigated by experiments of NH₃, NO and SO₂ adsorption and temperature-programmed desorption (TPD). The results showed that the catalysts have adsorption capacity of NH₃ and SO₂, while almost no adsorption capacity of NO, NH₃ which enter into the inner-tunnel of palygorskite was adsorbed through formation of H bond with crystal water. Adsorption of ammonia on the catalyst occurs mainly on the palygorskite support. The manganese oxide loading does not promote the NH₃ adsorption on the catalyst but increases the activation of the adsorbed NH₃. MnO_x is the activity center of catalyst, selective catalytic reduction of NO mechanism of catalyst is in line with Eley-Rideal mechanism: NH₃ adsorption on the catalyst surface was activated of dehydrogenation reacted with NO, produced N₂ and H2O. Gas O₂ oxided the reduced Mn³⁺ ion to complete the catalytic circle.