TY - JOUR
T1 - Contrasting Catalytic Functions of Metal Vanadates and Their Oxide Composite Analogues for NH3-Assisted, Selective NOXTransformation
AU - Lee, Seokhyun
AU - Lee, Jung Hyun
AU - Ha, Heon Phil
AU - Kim, Jongsik
N1 - Funding Information:
We thank the Ministry of Science and ICT and National Research Foundation of South Korea for providing a grant for this project (#NRF-2017M3D1A104069021). We are grateful to the Korea Institute of Science and Technology (KIST) for supporting this project through the Atmospheric Environment Research Program, Future R&D Program, and K-Lab Program.
Publisher Copyright:
© 2022 American Chemical Society.
PY - 2022/2/8
Y1 - 2022/2/8
N2 - V2O5 fuses with transition metals to create dozens of different metal vanadates, whose acidic/redox traits can be diverse yet optimized for selective catalytic NOX reduction (SCR) by changing the metals used or their metal:vanadium stoichiometry. However, no metal vanadate has been compared with its metal oxide composite analogue as an active phase for SCR, albeit a vanadate occasionally outperforms an oxide composite simulating a commercial catalyst (V2O5-WO3). Herein, Cu3V2O8 and CuO-VO2/V2O5 were rationally selected as model phases of metal vanadates and oxide composites and isolated using pH regulation of their synthetic mixture to ≤∼5 (pH1/pH5) and ∼11 (pH11), respectively. The pH1/pH5/pH11 samples were comparable with regard to morphological, textural, and compositional traits but not for crystallographic features. This thus provided the impetus to simulate the pH1/pH5/pH11 surfaces under a SO2-containing feed-gas stream, by which SOA2-/HSOA- functionalities (A = 3-4) were anchored on their (defective) Lewis acidic metals and/or labile oxygens (Oα). This could result in the formation of pH1-S/pH5-S/pH11-S, whose major surface species were Brönsted acidic bonds (SOA2-/HSOA-) and redox sites (Oα; mobile oxygen (OM); oxygen vacancy (OV)). pH1-S/pH5-S/pH11-S were similar in terms of NH3 binding energies and energy barriers in SCR yet escalated collision frequencies among the surface species involved in the sequence of pH11-S < pH5-S < pH1-S (via kinetic assessments), as was the case with the numbers of SOA2-/HSOA- functionalities of the catalysts (via temperature-resolved Raman spectroscopy). These were coupled to elevate the efficiency of acidic cycling on the order of pH11-S < pH5-S < pH1-S. Meanwhile, the amounts of Oα and OV (or OM) innate to pH1-S/pH5-S were smaller than and comparable to those of pH11-S, respectively. Nonetheless, pH1-S/pH5-S provided greater OM mobility than pH11-S, thereby proceeding better with redox cycling than pH11-S (via 18O-labeling O2-on/off runs). Furthermore, pH1-S/pH5-S outperformed pH11-S in SCR under diffusion-limited domains, while enhancing the resistance to H2O, ammonium (bi)sulfate poisons, or hydro-thermal aging over pH11-S by diversifying the selective N2 production pathway other than SCR.
AB - V2O5 fuses with transition metals to create dozens of different metal vanadates, whose acidic/redox traits can be diverse yet optimized for selective catalytic NOX reduction (SCR) by changing the metals used or their metal:vanadium stoichiometry. However, no metal vanadate has been compared with its metal oxide composite analogue as an active phase for SCR, albeit a vanadate occasionally outperforms an oxide composite simulating a commercial catalyst (V2O5-WO3). Herein, Cu3V2O8 and CuO-VO2/V2O5 were rationally selected as model phases of metal vanadates and oxide composites and isolated using pH regulation of their synthetic mixture to ≤∼5 (pH1/pH5) and ∼11 (pH11), respectively. The pH1/pH5/pH11 samples were comparable with regard to morphological, textural, and compositional traits but not for crystallographic features. This thus provided the impetus to simulate the pH1/pH5/pH11 surfaces under a SO2-containing feed-gas stream, by which SOA2-/HSOA- functionalities (A = 3-4) were anchored on their (defective) Lewis acidic metals and/or labile oxygens (Oα). This could result in the formation of pH1-S/pH5-S/pH11-S, whose major surface species were Brönsted acidic bonds (SOA2-/HSOA-) and redox sites (Oα; mobile oxygen (OM); oxygen vacancy (OV)). pH1-S/pH5-S/pH11-S were similar in terms of NH3 binding energies and energy barriers in SCR yet escalated collision frequencies among the surface species involved in the sequence of pH11-S < pH5-S < pH1-S (via kinetic assessments), as was the case with the numbers of SOA2-/HSOA- functionalities of the catalysts (via temperature-resolved Raman spectroscopy). These were coupled to elevate the efficiency of acidic cycling on the order of pH11-S < pH5-S < pH1-S. Meanwhile, the amounts of Oα and OV (or OM) innate to pH1-S/pH5-S were smaller than and comparable to those of pH11-S, respectively. Nonetheless, pH1-S/pH5-S provided greater OM mobility than pH11-S, thereby proceeding better with redox cycling than pH11-S (via 18O-labeling O2-on/off runs). Furthermore, pH1-S/pH5-S outperformed pH11-S in SCR under diffusion-limited domains, while enhancing the resistance to H2O, ammonium (bi)sulfate poisons, or hydro-thermal aging over pH11-S by diversifying the selective N2 production pathway other than SCR.
UR - http://www.scopus.com/inward/record.url?scp=85123523613&partnerID=8YFLogxK
U2 - 10.1021/acs.chemmater.1c03416
DO - 10.1021/acs.chemmater.1c03416
M3 - Article
AN - SCOPUS:85123523613
SN - 0897-4756
VL - 34
SP - 1078
EP - 1097
JO - Chemistry of Materials
JF - Chemistry of Materials
IS - 3
ER -