Rational Design of Zr-Mofs Pyrolyzed to Pinpoint Rate-Directing Stage and Catalytic Functions of Surface Acidic Species in Homolytic H2o2 Scission

Homolytic/heterolytic H2O2 scissions are central in producing •OH used to fragment aqueous contaminants. However, homolytic H2O2 cleavage is under-explored in kinetic/mechanistic/energetic aspects. This study designed/synthesized/pyrolyzed UiO-66 and its analogues functionalized with -NH2/-SO3H(UiO-66-NH2/UiO-66-SO3H) to generate ZrO2 poly-crystallites on N/S-doped carbon catalysts via pyrolysis(CUiO-66/CUiO-66-NH2/CUiO-66-SO3H). The catalyst surfaces provided distinct concentrations of Lewis basic N and/or S dopants, which donated electrons to adjacent Brönsted acidic(-OH; BA) and Lewis acidic Zr4+(LA) species dissimilarly, leading to vary Brönsted/Lewis acidic strengths(EBA/ELA) and areas(SBA/SLA) for the catalysts. CUiO-66 revealed the largest ELA and smallest EBA, which are proper to distort H2O2 geometry endothermically, whereas CUiO-66-SO3H exhibited the smallest ELA and largest EBA, wherein EBA only is amicable to desorb •OH endothermically, while leaving the other elementary stages exothermic. Kinetic assessments/DFT calculations of the catalysts unveiled that energy barrier(EBARRIER) was the smallest in CUiO-66-SO3H. This substantiated •OH desorption was the rate-directing stage along with the vitality of strong EBA in lowering EBARRIER. Meanwhile, pre-factor was the largest in CUiO-66 with the greatest SLA, which corroborated the significance of large SLA in escalating collision frequency among Zr4+ and H2O2/•OH. This study poses the necessity of tuning EBA and SLA for elevating •OH productivity via homolytic H2O2 dissection.