Metal-organic framework-derived ZrO2 on N/S-doped porous carbons for mechanistic and kinetic inspection of catalytic H2O2 homolysis

Minsung Kim, Jinseon Park, Sang Hoon Kim, Jung Hyun Lee, Keunhong Jeong, Jongsik Kim

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

Homolytic and heterolytic H2O2 scissions are central to produce OH for aqueous contaminant fragmentation. However, the kinetic, mechanistic, and energetic aspects of homolytic H2O2 cleavage remain under-explored, providing impetus for research with the use of difficult-to-degrade phenol as a model pollutant. Herein, UiO-66 and its analogues functionalized with –NH2/-SO3H (UiO-66-NH2/UiO-66-SO3H) were synthesized to generate ZrO2 poly-crystallites on N/S-doped carbon catalysts via pyrolysis (CUiO-66/CUiO-66-NH2/CUiO-66-SO3H). The catalyst surfaces contained distinct concentrations of Lewis basic N/S dopants, which donated electrons to adjacent Brönsted acidic –OH (BA) and Lewis acidic Zr4+ (LA) species dissimilarly, resulting in the catalysts with diverse BA/LA strengths (EBA/ELA) and areas (SBA/SLA). CUiO-66 exhibited the highest ELA and lowest EBA, which are favorable for endothermic H2O2 distortion, whereas CUiO-66-SO3H exhibited the lowest ELA and highest EBA, with only EBA being favorable for endothermic OH desorption, while leaving the other elementary steps exothermic. Kinetic analysis and DFT calculations revealed that CUiO-66-SO3H possessed the lowest energy barrier (EBARRIER), demonstrating OH desorption was the rate-determining step alongside with the significance of high EBA for reducing EBARRIER. Meanwhile, the highest pre-factor was observed for CUiO-66 with the largest SLA, corroborating the significance of large SLA for escalating the collision frequency between Zr4+ and H2O2/OH. These results boost to adjust EBA/SLA for promoting OH productivity via catalytic H2O2 homolysis.

Original languageEnglish
Pages (from-to)630-649
Number of pages20
JournalCarbon
Volume203
DOIs
Publication statusPublished - 2023 Jan 25

Bibliographical note

Funding Information:
Hence, the moderate reusability of the catalysts could be ascribed to the generation of oligomeric phenols and their continuous deposition on the BA or LA sites of the ZrO2 clusters. Oligomeric phenols might act as poisons to significantly reduce the •OH productivities of the catalysts during the recycle runs. This was partially evidenced by the SN2 and VMICRO values of the used catalysts, which plummeted up to <20 m2 gCAT−1 and 0 cm3 gCAT−1, respectively, post the 3rd recycle runs (Table S11). This was con-current to the XRD patterns of the used catalysts, which showed that the intensities of the prime diffractions for tetragonal ZrO2 (crystallinities) with 2θ values centered at 30–35° were continuously declined post each of the recycle runs ((101), (110), (002) in Fig. S19). Moreover, the EDX spectra of the used catalysts also revealed a gradual increase in the atomic ratios of C/Zr post each of the recycle runs (e.g., C/Zr of 4.9 → 7.9 for CUiO-66 in Fig. 15B–D). This substantiated that the surface poison incurred by oligomeric phenols became increasingly severe post each of the recycle runs. In addition to disclosing intermediates that were potentially mineralized to form CO2 and H2O (Fig. S25) [ 89–93], the LC-MS spectra of the reaction solutions collected post the recycle runs proved the generation of phenol dimers and trimers potentially via H• abstraction/coupling and •OH addition/dehydration/coupling, respectively (Fig. 15A) [ 89–93]. The production of oligomeric poisons initiated by H• abstraction/•OH addition appeared to be imperative in the •OH-mediated degradation of refractory aromatics. However, this could be avoided by altering the function of •OH from aromatic decomposer to radicalizer of supported SO42−/NO3− located near the BA or LA sites of ZrO2. •OH could generate supported SO4•-/NO3• species via radical transfer [ 4–7], which could degrade aromatics primarily via electron transfer, while minimizing the formation of oligomeric poisons.We thank Ministry of Science and ICT and National Research Foundation of South Korea for providing a grant for this project (#NRF-2020R1A2C2004395). We are grateful to Korea Institute of Science and Technology for supporting this project through Future R & D.

Funding Information:
We thank Ministry of Science and ICT and National Research Foundation of South Korea for providing a grant for this project ( #NRF-2020R1A2C2004395 ). We are grateful to Korea Institute of Science and Technology for supporting this project through Future R & D.

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

  • Brӧnsted/Lewis acidity
  • Dopant
  • Homolytic HO scission
  • Metal-organic framework
  • Non-reducible metal
  • Pyrolysis

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science

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