Designing direct redox reaction chemically coupling NO and SO2 removal

A novel simultaneous removal strategy for NO and SO2 was proposed to meet the increasingly strict emission requirements, i.e. triggering the direct redox reaction between two pollutants (SO2 + NO + O2− = SO42− + 1/2N2), which chemically couples SOx and NOx removal and prevents the possible competition between DeNOx and DeSOx reactions. In this fundamental study, we tailor-made an efficient Pd-La1.5Co0.5O3 catalyst that accelerated the designed reaction to an industrially applicable level, achieving a prominent SO2 adsorption capacity of 2465.2 μmol g−1 and NO reduction capacity of 1891.3 μmol g−1 over 60 min when SO2 and NO are simultaneously fed at 680 °C. Over this catalyst, SO2 adsorbed on the La site underwent disproportionation via sulfite intermediate into oxysulfate and sulfide, which gave access to NO reduction. Co in the catalyst played a complex role. The active oxygen species binding to Co3+ in perovskite competed with NO in SO2 oxidation. However, this generated Co2+ that was found to take part in sulfite disproportionation through forming Co9S8, which accelerated the disproportionation and NO reduction. The catalyst is promising to be industrially applied as an additive of the FCC catalyst or flue gas aftertreatment catalyst and exhibited 45 % higher DeNOx efficiency and 28 % higher DeSOx efficiency in a simulated catalytic cracking/coke combustion cycle than the commercial additives. The findings open a new avenue for the development of novel environmentally benign and cost-effective simultaneous removal technology.