Retrofitting Zr-Oxo Nodes of UiO-66 by Ru Single Atoms to Boost Methane Hydroxylation with Nearly Total Selectivity

Abstract

Direct selective oxidation of methane (DSOM) to high value-added oxygenates under mild conditions is attracting considerable interest. Although state-of-the-art supported metal catalysts can improve methane conversion, it is still challenging to avoid the deep oxidation of oxygenates. Here, we develop a highly efficient metal−organic frameworks (MOFs)-supported single-atom Ru catalyst (Ru 1 /UiO-66) for the DSOM reaction using H 2 O 2 as an oxidant. It endows nearly 100% selectivity and an excellent turnover frequency of 185.4 h −1 for the production of oxygenates. The yield of oxygenates is an order of magnitude higher than that on UiO-66 alone and several times higher than that on supported Ru nanoparticles or other conventional Ru 1 catalysts, which show severe CO 2 formation. Detailed characterizations and density functional theory calculations reveal a synergistic effect between the electrondeficient Ru 1 site and the electron-rich Zr-oxo nodes of UiO-66 on Ru 1 /UiO-66. The Ru 1 site is responsible for the activation of CH 4 via the resulting Ru 1 �O* species, while the Zr-oxo nodes undertake the formation of oxygenic radical species to produce oxygenates. In particular, the Zr-oxo nodes retrofitted by Ru 1 can prune the excess H 2 O 2 to inactive O 2 more than • OH species, helping to suppress the over-oxidation of oxygenates.

Deciphering structural evolution of adsorbed ˙OH species on Zr-oxo nodes of UiO-66 to modulate methane hydroxylation

“…), where the p-band centers of O atoms in these oxygenic species constitute the underlying critical factors to determine the catalytic activity for the DSOM reaction. This trend can provide important guidance to improve the DSOM performance via rational design of a UiO-66-H based catalyst to avoid the competitive reaction of active cOH species, either by fabricating more functional sites over pristine MOFs, 36 and by creating a synergistic effect with additional single-atom metals, 37,38,87 or via the substitution/doping of metal-oxo nodes of MOFs. 88,89 Fig.…”

“…29,30 Besides, the strategies combining supported metal catalysts and the use or in situ production of highly efficient oxidants such as H 2 O 2 have been proposed to accelerate the methane activation at low temperatures (<100 °C) in the gas-liquid-solid phase mode. 19,[31][32][33][34][35][36][37][38] Nevertheless, the structured metal-oxo species are rarely considered as the host active component in this mode DSOM reaction under mild conditions, although they can play a key role in the oxidation processes of photocatalysis and thermal catalysis with adsorbed oxygenic radical species. 36,[39][40][41][42][43][44][45][46] Moreover, the detailed mechanism of reactive oxygenic species on the structured metal-oxo sites for the DSOM reaction has not been demonstrated.…”

“…Recently, we found that Zr-based metal organic frameworks (MOFs), UiO-66-H, and its supported single atom Ru could promote the formation of adsorbed cOH species and electron decient Ru 1 ]O* sites on Zr-oxo nodes to facilitate methane hydroxylation with a lower energy barrier and ∼100% selectivity of oxygenates. 36,37 In contrast to thorough research on methane activation over the metal-oxygen (M-O) sites of supported metal catalysts, 47 the relationship between the adsorbed oxygenic species on Zr-oxo nodes and the DSOM performance needs further clarication. In this work, we systematically studied the geometric and electronic structures of the formed sites on Zroxo nodes of UiO-66-H under different cOH concentrations.…”

Atomic Single-Layer Ir Clusters Enabling 100% Selective Chlorine Evolution Reaction

“…Under industrial conditions, pH values are usually ≥2 due to the limited stability of the membrane, which limits the CER selectivity of DSAs . Single-atom catalysts (SACs) have exhibited impressive selectivity in many competing reactions. − SACs can adsorb target reactants on the metal sites, thereby breaking the limitation of the scaling relationship. In recent years, SACs have also been explored for CER catalysis, such as carbon nanotube supported platinum single atoms (Pt 1 /CNT), ,, titanium foam supported ruthenium single atoms (Ru 1 –TiO x /Ti), oxygen-coordinated ruthenium-based single atom catalyst (Ru–O 4 SAM), and so on.…”

Investigation of in situ sulfide/nitride/phosphide treatments of hematite photoanodes for improved solar water oxidation

“…Surface modification of α-Fe 2 O 3 photoanodes, such as the introduction of passivation/catalyst layers 9–11 and the construction of heterogeneous/homogeneous junctions, 12–14 can effectively reduce the external bias voltage and on-set potential of light-driven water splitting and extend the lifetime of photogenerated carriers, thereby improving their PEC-WS performance. 15–17 How to achieve surface engineering, with controllable heterogeneous junctions and effective action scope and without introducing additional defects, has become the research focus and a difficult challenge. 18,19 It may be addressed by in situ surface functional sulfide/nitride/phosphide treatments along with the formation of metal chalcogenides and coordination complexes, which effectively promote surface photogenerated carrier transport without introducing additional defects.…”