Oxo dicopper anchored on carbon nitride for selective oxidation of methane

Abstract

Selective conversion of methane (CH4) into value-added chemicals represents a grand challenge for the efficient utilization of rising hydrocarbon sources. We report here dimeric copper centers supported on graphitic carbon nitride (denoted as Cu2@C3N4) as advanced catalysts for CH4 partial oxidation. The copper-dimer catalysts demonstrate high selectivity for partial oxidation of methane under both thermo- and photocatalytic reaction conditions, with hydrogen peroxide (H2O2) and oxygen (O2) being used as the oxidizer, respectively. In particular, the photocatalytic oxidation of CH4 with O2 achieves >10% conversion, and >98% selectivity toward methyl oxygenates and a mass-specific activity of 1399.3 mmol g Cu−1h−1. Mechanistic studies reveal that the high reactivity of Cu2@C3N4 can be ascribed to symphonic mechanisms among the bridging oxygen, the two copper sites and the semiconducting C3N4 substrate, which do not only facilitate the heterolytic scission of C-H bond, but also promotes H2O2 and O2 activation in thermo- and photocatalysis, respectively.

Single Atom Catalysts for Selective Methane Oxidation to Oxygenates

“…These concepts are exploited in CH 4 OR too, where homonuclear DSACs composed of either Cu and Fe sites displayed better performance. For example, pMMO-like oxo-dicopper moiety containing CN catalysts can sustain the methane oxidation rate higher than the benchmark Cu/ZSM-5 catalyst (Figure d) . In another work, Fe 2 N 6 dimer with two iron supported on graphene network could activate the O 2 atom due to per-oxo-like O 2 adsorption configuration (Figure e). − Despite the advancement, the use of heteronuclear DSACs that can produce interesting chemistry are not explored for CH 4 OR leaving plenty of room for future investigation.…”

“…(d) Oxo dicopper anchored carbon nitride (Cu 2 @C 3 N 4 ) mimicking the structure of pMMO and used for photocatalytic methane oxidation. Reprinted with permission under a Creative Commons CC-BY License from ref . Copyright 2022 Springer Nature.…”

“…In contrast to spaced dual Cu atom sites, Xie et al reported the synthesis of oxo dicopper sites (Cu–O–Cu) in a C 3 N 4 scaffold mimicking natural pMMO structure (Figure ). For the synthesis of Cu 2 @C 3 N 4 catalysts a “precursor-preselected” approach was used where [Cu 2 (bpy) 2 (μ-ox)]­Cl 2 was immobilized on C 3 N 4 followed by the removal of ligands at 250 °C in the air (Figure a). HAADF-STEM displayed dimeric copper moieties with 2.8 (±0.2 Å) spacing which was less than [Cu 2 (bpy) 2 (μ-ox)]­Cl 2 precursor suggesting the reorganization of Cu centers on C 3 N 4 after the removal of ligands (Figure b).…”

“…(h) EPR spectra recorded for various control experiments using DMPO (i) In situ irradiation XPS spectra collected in the O 1s region. Reprinted with permission under a Creative Commons CC-BY License from ref . Copyright 2022 Springer Nature.…”

W Single‐Atom Catalyst for CH4 Photooxidation in Water Vapor

“…[ 44 ] In this field, using high concentration H 2 O 2 or O 2 as the oxidants is the dominant way for CH 4 activation. [ 45 ] It is highly desirable to rational design and synthesis of photocatalysts for in situ H 2 O 2 formation from low‐cost H 2 O to achieve highly efficient CH 4 activation with suppressing complete dehydrogenation and avoiding overoxidation. Remarkably, biogenic CH 4 has been regarded as the final product of anoxic decomposition of organic matter in the presence of H 2 O, [ 46 ] which represents a core technology for biomass waste treatment in landfills.…”