Anthropogenic flue gases consist of NOX/SO2/H2O, among which H2O resistance is often underrated in activating the acidic/redox cycles of NH3-assisted catalytic NOX reduction (SCR), SO2/H2O-induced evolution of ammonium (bi)sulfate (AS/ABS) poisons, or AS/ABS pyrolysis. Herein, TiO2-supported nickel vanadates (NiXV2OX+5; X = 1-3) were functionalized with SOZ2− (Z = 3-4) to simulate the resulting NiX-S surfaces under a SO2-containing wet flue gas, at which mono/bidentate SOZ2− modifiers transform into Brønsted acidic bonds (B−-H+) via protonation. Ni1-S exhibited the highest efficiency in the recurring acidic cycle, as proved by its highest NOX consumption rate (−rNOX) among NiX-S catalysts. This was enabled by the smallest H2O binding affinity to the B−-NH4+⋯OL−-M(n−1)+ intermediates involved in the rate-determining step of the SCR, thus revealing the smallest energy barrier needed for SCR on Ni1-S. Moreover, Ni1-S provided the largest quantity of labile oxygens and the highest oxygen mobility among NiX-S catalysts, leading to the highest efficiency in the recurring redox cycle. Notably, the Ni1-S surface repelled H2O markedly upon the inclusion of promotive Sb2O5 alongwith the improvement of redox cycling efficiency for the resulting Ni1-Sb-S. Hence, aside from exhibiting greater −rNOX values or SCR consequences than NiX-S and a commercial catalyst (V2O5-WO3-S) at low temperatures, Ni1-Sb-S also reduced the number of AS/ABS accumulated by evading H2O adsorption. H2O resistance was also crucial to accelerate desorptive B−-H2O⋯SO2⋯H2O dissociation on the Ni1-Sb-S surface. Ni1-Sb-S thus unveiled a higher AS/ABS degradation rate and a smaller energy barrier required for AS/ABS pyrolysis than V2O5-WO3-S. Importantly, Ni1-Sb-S significantly enhanced the resistance toward AS/ABS or hydrothermal aging over V2O5-WO3-S and SOZ2−-modified Mn1V2O6 (or Cu3V2O8) on Sb-promoted TiO2 reported previously by our group.
Bibliographical noteFunding Information:
We thank Ministry of Science and ICT and National Research Foundation of South Korea for providing a grant for this project (#2020R1A2C2004395 and #2017M3D1A104069021). We are grateful to Korea Institute of Science and Technology for supporting this project through Future R & D. We are thankful to the Basic Science Research Capacity Enhancement Project through Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Education (#2019R1A6C101052).
© 2023 The Royal Society of Chemistry.
ASJC Scopus subject areas
- General Chemistry
- Renewable Energy, Sustainability and the Environment
- General Materials Science