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

Lee, SeokhyunHa, Heon PhilLee, Jung-HyunKim, Jongsik
Issue Date
Royal Society of Chemistry
Journal of Materials Chemistry A, v.11, no.23, pp.12062 - 12079
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.
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