The enhanced resistance to Na+-poisoning of MnCoCrOx SCR catalyst by acidity regulation: The mechanism of sulfuric acid pretreatment

Abstract

Low-temperature NH3-selective catalytic reduction (NH3-SCR) catalysts with enhanced resistance to alkali-metal compounds are urgently needed for glass furnace, biomass boilers, etc. flue gases denitrification. A sulfuric acid pretreatment approach, which would be more widely applicable relative to the metal oxides addition method at present, was carefully explored for the excellent MnCoCrOx (MCC) catalyst in this work. The catalytic performance tests show that the decrease in de-NOx efficiency and N2 selectivity caused by Na+ poisoning could be well alleviated via H2SO4 pretreatment. 0.1 M sulfuric acid-treated 1 wt.% Na+ poisoned MnCoCrOx (0.1S-1Na-MCC) catalyst still exhibits a broad T90 (the temperature when de-NOx efficiency reaches 90%) window between 199 and 400 °C. The characterization results demonstrate that H2SO4 pretreatment well restrains the blockage of pore channels and loss of specific surface area caused by Na2O species deposition. A majority of acidity and redox ability of 0.1S-1Na-MCC catalyst were also retained compared with fresh MCC catalyst, which was essential to the SCR process. Sulfuric acid could introduce excessive Brønsted acid sites and cut the loss of Lewis acid sites effectively by the presence of Na2O. Besides, the as-formed HSO4− species would serve as acid sites for NH3 adsorption and activation. The above findings provide new insights with respect to improving the tolerance of metal oxides SCR catalyst to alkali metals by tuning the surface physicochemical properties by acid pretreatment.