Unlocking the significance of high H2O resistance for nickel vanadate phases to improve the kinetic parameters or consequences of catalytic NOX reduction and poison pyrolysis

Abstract

Anthropogenic flue gases consist of NO<INF>X</INF>/SO<INF>2</INF>/H<INF>2</INF>O, among which H<INF>2</INF>O resistance is often underrated in activating the acidic/redox cycles of NH<INF>3</INF>-assisted catalytic NO<INF>X</INF> reduction (SCR), SO<INF>2</INF>/H<INF>2</INF>O-induced evolution of ammonium (bi)sulfate (AS/ABS) poisons, or AS/ABS pyrolysis. Herein, TiO<INF>2</INF>-supported nickel vanadates (Ni<INF>X</INF>V<INF>2</INF>O<INF>X+5</INF>; X = 1-3) were functionalized with SO<INF>Z</INF><SUP>2-</SUP> (Z = 3-4) to simulate the resulting Ni<INF>X</INF>-S surfaces under a SO<INF>2</INF>-containing wet flue gas, at which mono/bidentate SO<INF>Z</INF><SUP>2-</SUP> modifiers transform into Bronsted acidic bonds (B<SUP>-</SUP>-H<SUP>+</SUP>) via protonation. Ni<INF>1</INF>-S exhibited the highest efficiency in the recurring acidic cycle, as proved by its highest NO<INF>X</INF> consumption rate (-r<INF>NO<INF>X</INF></INF>) among Ni<INF>X</INF>-S catalysts. This was enabled by the smallest H<INF>2</INF>O binding affinity to the B<SUP>-</SUP>-NH<INF>4</INF><SUP>+</SUP>MIDLINE HORIZONTAL ELLIPSISO<INF>L</INF><SUP>-</SUP>-M<SUP>(n-1)+</SUP> intermediates involved in the rate-determining step of the SCR, thus revealing the smallest energy barrier needed for SCR on Ni<INF>1</INF>-S. Moreover, Ni<INF>1</INF>-S provided the largest quantity of labile oxygens and the highest oxygen mobility among Ni<INF>X</INF>-S catalysts, leading to the highest efficiency in the recurring redox cycle. Notably, the Ni<INF>1</INF>-S surface repelled H<INF>2</INF>O markedly upon the inclusion of promotive Sb<INF>2</INF>O<INF>5</INF> alongwith the improvement of redox cycling efficiency for the resulting Ni<INF>1</INF>-Sb-S. Hence, aside from exhibiting greater -r<INF>NO<INF>X</INF></INF> values or SCR consequences than Ni<INF>X</INF>-S and a commercial catalyst (V<INF>2</INF>O<INF>5</INF>-WO<INF>3</INF>-S) at low temperatures, Ni<INF>1</INF>-Sb-S also reduced the number of AS/ABS accumulated by evading H<INF>2</INF>O adsorption. H<INF>2</INF>O resistance was also crucial to accelerate desorptive B<SUP>-</SUP>-H<INF>2</INF>OMIDLINE HORIZONTAL ELLIPSISSO<INF>2</INF>MIDLINE HORIZONTAL ELLIPSISH<INF>2</INF>O dissociation on the Ni<INF>1</INF>-Sb-S surface. Ni<INF>1</INF>-Sb-S thus unveiled a higher AS/ABS degradation rate and a smaller energy barrier required for AS/ABS pyrolysis than V<INF>2</INF>O<INF>5</INF>-WO<INF>3</INF>-S. Importantly, Ni<INF>1</INF>-Sb-S significantly enhanced the resistance toward AS/ABS or hydrothermal aging over V<INF>2</INF>O<INF>5</INF>-WO<INF>3</INF>-S and SO<INF>Z</INF><SUP>2-</SUP>-modified Mn<INF>1</INF>V<INF>2</INF>O<INF>6</INF> (or Cu<INF>3</INF>V<INF>2</INF>O<INF>8</INF>) on Sb-promoted TiO<INF>2</INF> reported previously by our group.