620 / 2019-01-20 13:02:27

Sulfated red mud as catalyst for selective catalytic reduction (SCR) of NOx with ammonia

Red mud, sulfated, solid super acid, NH3-SCR, acid properties

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Red mud is one kind of high alkaline waste of Bayer process for refining aluminum with high contents of Fe2O3, Al2O3 and TiO2 which can generate SO42+/MxOy solid super acid. The increasing acid properties can improve the catalytic activity of selective catalytic reduction of NOx with NH3. In this paper, the sulfated red mud catalyst was prepared by two-step method. The raw red mud was removed alkaline substance by hydrochloric acid leaching with controlled parameters and keep active component Fe2O3 retained in the leaching residue at the same time, then the leaching residue was impregnated with different concentrations of sulfuric acid to get the catalyst. The dealkalization efficient of red mud was above 95% and the residual rate of Fe2O3 was more than 90% calculated by ICP-AES and XRF. The samples were then systematically characterized by XRD, N2 physisorption, SEM, and XPS to assess structure, texture, morphology and surface composition, as well as H2-TPR and NH3-TPD to evaluate reducibility and surface acidity. The new material Fe2(SO4)3 was generated after sulfated which could provide more activate sites. The Fe3+/Fe2+ ratio of red mud and modified red mud remained same while the surface oxygen Oαincreased about 20% which could benefit to the performance of NOx conversion. The BET surface area decreased after impregnated with H2SO4 but the pore size distribution (PSD) of the catalyst was optimized by some mesoporous structure which could enhance the adsorption and reaction. The acid properties of samples was improved about three times than raw red mud which could promote the adsorption of NH3 during the reaction, this was the primary cause of the excellent catalytic activity. The catalytic performance of samples was studied in the NH3-SCR reaction and the sulfated red mud catalysts showed excellent catalytic activity with 100% NOx conversion in a broadened temperature from 300 to 450 ℃ and high SO2 and H2O resistances.