Study Of Deactivation And Regeneration Of Pillared Clays Based Catalysts During Selective Catalytic Reduction Of Nitric Oxde By Ammonia

The selective catalytic reduction （SCR） of NO_xwith NH₃as reductant hasproven to be a promising technology to reduce the NO_xemission in the flue gas.Catalysts are critical to selective catalytic reduction of NO_x. Much attention ispresently focused on developing catalysts with high activity and good resistant topoison. Since most of the flue gases contain some amounts of ultra-fine particles,sulfur and water after desulfurization and dedust equipment, deactivation of catalystsis inevitable in the using process. Recently, low-temperature SCR has attracted moreand more interests for its low energy consumption. However, the poisoning effects ofsulfur and ash in flue gas has not invested systemly in the low-temperature SCR. Inthis dissertation, pillared clays were prepared and used as catalyst support. Thelab-scale investigations of activity performance and potential deactivation of MnO_xbased catalysts were investigated for low-temperature NO_x-SCR.The catalysts of Zr-pillared calys （ZrO2-PILC） supported MnO_xshowed highDeNO_xperformance in the low-temperature （80-240℃） SCR. It was found that theintroduction of Ce could improve the dispersion of MnO_x, enhance the oxygenstorage capacity and the adsoroption of NH₃, which is beneficial to NO_x-SCR. Theresults showed that NO_xconversion would be more than90%in the range of180-240℃. The operating parameters, such as NH₃concentration and O2concentration on theDeNO_xwere also investigated.The comprehensive study of the effects of alkali metals oxides （K2O/Na2O） anddifferent species of potassium （K₂SO₄, KCl） were conducted over theMn-Ce/ZrO2-PILC catalyst. Activity assessments of poisoned samples indicated thatcatalyst deactivation involves decrease of BET surface area, restraint of adsorptioncapacity of NH₃and reduction features of the catalysts. It also showed that Kexhibited greater poisoning effect than Na. Potassium in the form of chloride andsulfate is also a strong poison for the catalyst, and the resultes indicated that thepoisoning mechanism of potassium salt is similar to that of alkali metal oxides. Regeneration of deactivated catalysts were conducted by washing with water anddiluted sulphuric acid. Water washing was a promising method to the catalystsdeactivated with lower molar ratio of poison to Mn, except for the heavily deactivatedcatalyst. Washing with0.1mol/L H₂SO₄solution could increase the adsorption ofNH₃and the catalyst activity was even higher than the fresh one.Alkaline-earth metals could also induce serious deactivation to the NO_x-SCRcatalysts. The deposition of poison resulted in pore plugging and decrease of surfaceacidity and low-temperature reducibility. Washing with diluted acid solution, such assulphuric acid and nitric acid, presented to be more effective than water washing.Washing with sulphuric acid could create new acid sites and enhance the adsorptionof NH₃, which is beneficial to the NO_x-SCR.The effects of H₂O and SO2were also investigated in the research. H₂O wouldinhibit the catalytic activity, and the effect relateed with vapor content and thereaction temperature. However, the activity restored quickly to its original level aftercutting off of H₂O. While the catalyst was sensitive to the SO2in the gas, andpoisoning effect was irreversible. The deposition of ammonium salts on catalystsurface and sulfation of catalyst active phase were found to be the main reasons forthe deactivation of catalysts. Furthermore, thermal treatment and water-washing wereapplied for the regeneration of the SO2-deacivited catalysts. It was found that washingwith water could recover the most catalyst activity, thermal treatment, in contrast, dolittle to the regeneration.