Preparation of Mn/TiO catalysts using recovered manganese from spent alkaline batteries for low-temperature NH-SCR.

Black mass (BM) from spent alkaline Zn-MnO batteries was used for the first time as a Mn source in the preparation of Mn/TiO catalysts for low-temperature NH-selective catalytic reduction (SCR) of NO. To recover Mn species and eliminate alkali and Zn species, BM powder underwent DI-water washing, followed by carbothermal reduction. The resulting slags were further dissolved in HNO, loaded onto TiO particles with ball milling, and then subjected to calcination. Nearly 100% of Zn species were removed from the BM via carbothermal reduction at 950 °C for 4 h with 5.0 wt% activated carbon. The resulting catalyst, derived from the treated BM, achieved similar NO conversion (97%) as the catalyst prepared using a reagent-grade Mn chemical at 160 °C but a higher NO-to-N conversion rate at 78%. The promoted N selectivity was attributed to a high Mn/Ti ratio and the presence of impurities from BM, such as Fe ions, which enhanced oxidation ability of the catalyst. Conversely, insufficient removal of Zn or carbon additives in the slags led to a decreased Mn concentration, an increased proportion of Mn/Mn species, increased surface OH groups, and reduced oxidation ability on the surface, thus reducing NO conversion and N selectivity.