The design of catalysts and catalytic processes for high efficiency and selectivity of important singlet oxygen ( 1 O 2 ) active species generation in oxidation reactions is still challenging, especially utilizing abundant and environmental O 2 without photoelectric field or extra thermal condition. Herein, a curved Fe 1 −N 4 single-atom site is developed by incorporating isolated Fe single atom into nanodiamond with high-curvature surface. It leads to an unprecedented relay catalysis route, in which the activation of O 2 is coupled with peroxymonosulfate (PMS) activation, to efficiently generate 1 O 2 species. In detail, PMS is first activated on the curved Fe 1 −N 4 site with electron donation to Fe single atom, accompanied by 1/2 equiv of 1 O 2 production. More importantly, due to the compressive strain of the curved Fe 1 −N 4 site with a higher energy level of Fe 3d z 2 orbital, the curved Fe 1 −N 4 site with electron charge acquisition can directly transfer electron to O 2 molecule and consequently trigger the generation of additional 1 equiv of 1 O 2 . Taking advantage of this tandem process, remarkable efficiency and near 100% selectivity of 1 O 2 generation are achieved, which leads to an ultrahigh metal catalytic efficiency of 0.77 min −1 for tetracycline oxidative degradation and an outstanding catalytic performance for benzene alcohol selective oxidation. This work, on the one hand, opens up an efficient way to generate 1 O 2 by O 2 activation in peroxide-based catalytic oxidations, and on the other hand, develops a bifunctional Fe 1 −N 4 single-atom site with rapid electron gain and loss ability, which sheds light on further improving catalytic performance in single-atom catalysts via relay catalysis mechanism.

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Hydroxyl radical (•OH)-induced oxidations are of great importance in chemical transformations. Carbon-supported late transition-metal single-atom catalysts (SACs) with bioinspired M1–N4 single-atom sites can effectively activate the peroxide group to produce •OH. Nevertheless, little is known about how electronic structures of M1–N4 sites affect •OH generation. Herein, dependent on the theoretical design and experimental realization of uniform M1–N4/C (M: Fe, Co, Ni, and Cu) SACs, a positive correlation relationship between •OH-induced oxidation activity and d-band center over the M1–N4 site has been revealed. In detail, by changing the M atoms with different numbers of d electrons, the d-band center of the M1–N4 could be turned. Moreover, the enhancement of d-band center heightens the interaction strength between the •OH intermediate and the M1–N4 site, which results in a higher oxidation activity. In this case, the efficient M1–N4 catalyst for the oxidation reaction can be screened by tuning the doped M atom. Moreover, notably, Fe1–N4 with the highest d-band center value has the lowest free energy change of the rate-determining step (0.06 eV) for •OH generation. Taking advantage of this, in both Fenton-like reaction and •OH-induced C–H bond activation reaction, the Fe1–N4 site displays at least 1 order of magnitude higher activity than the most of the supported late transition-metal catalysts and comparable activity to reported noble metal catalysts. This work is expected to provide guidance for designing high-efficiency heterogeneous catalysts in •OH-induced oxidations and bridge heterogeneous and enzymatic catalysis by using M1/C SAC as a platform.

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Taking the background of the ambiguous role of oxophilic metal oxide in metal-acid bifunctional catalysts for the important field of tetrahydrofurfuryl alcohol (THFA) hydrogenolysis, a linear relationship between the W�O/W−OH content in sub-nano-Rh-supported WO x and 1,5-pentanediol (1,5-PeD) yields from THFA hydrogenolysis has been established. It reveals that the higher reduction temperature promotes the surface Rh/W ratio. Thus, hydrogen spillover is facilitated, leading to more surface W�O structures and thereby more in-situ-reduced W−OH generation. W−OH structures work as the active sites to provide in situ Brønsted acid, resulting in enhanced selective activation for secondary C−O bonds of THFA. This discovery reveals the unique role of the surface structure on oxophilic metal oxide in chemoselective hydrogenolysis of the secondary C−O bond in polyols.