The efficient use of natural gas will require catalysts that can activate the first C-H bond of methane while suppressing complete dehydrogenation and avoiding overoxidation. We report that single iron sites embedded in a silica matrix enable direct, nonoxidative conversion of methane, exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C-C coupling, further oligomerization, and hence, coke deposition. At 1363 kelvin, methane conversion reached a maximum at 48.1% and ethylene selectivity peaked at 48.4%, whereas the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The lattice-confined single iron sites delivered stable performance, with no deactivation observed during a 60-hour test.

Reactions occurring in nanosized space often present new and extraordinary behaviors due to the nanoconfinement effect. [1][2][3] Understanding of the reaction mechanism relies heavily on the real-time imaging of the reactions with spatial information at the microscopic level. Although studies of surface reactions at the single-molecular-layer or even singlemolecule level are feasible at open surfaces, [4][5][6] imaging reactions within a confined environment remains challenging. Herein, we show that interfacial reactions under graphene can be directly observed using in situ surface imaging techniques. Our results demonstrate that the graphene sheet can function as an imaging agent for reactions under its cover and, furthermore, tune the interfacial reactions.Although two-dimensional (2D) graphene has attracted tremendous interest in the fields of physics and materials science, [7][8][9] the chemistry of graphene is much less explored, especially when compared to its allotrope of 1D carbon nanotubes (CNTs). [2,10] The hollow structure of the CNTs provides a confined environment for catalysts and reactants and serves as a nanoreactor. [2,11,12] Due to the tubular structure, it is difficult to probe the reactions occurring inside CNTs. Graphene as a planar material can open up a new avenue for studying surface chemistry in a confined space. The distance between graphene and substrate typically falls within 1 nm, [13] and, thus, adsorbates trapped in the small space may present novel physical and chemical properties. Moreover, dynamic processes occurring at the interface are reflected through changes in the graphene surface, thereby allowing both spectroscopic and microscopic studies of interfacial reactions. [14][15][16] Herein, reactions of CO confined between Pt and graphene are studied by real-time low-energy electron microscopy (LEEM)/photoemission electron microscopy (PEEM) and in situ X-ray photoelectron spectroscopy (XPS). The effect of the graphene cover on the surface chemistry of CO on Pt is also discussed.Single-layer graphene islands were grown on a Pt(111) surface by the surface segregation process, to form singlecrystalline graphene domains of micrometer size (Figure 1 and Figure S1 in the Supporting Information). [13] Inside the graphene islands, large-scale wrinkles were identified by LEEM (as marked in Figure 1 a and Figure S1). The formation of these hollow nanostructures is attributed to the different thermal expansion of Pt substrate and graphene. Upon cooling, the compressive stress built up within the graphene layer is relieved through the formation of curved carbon structures, for example, 0D nanobubbles [17] and 1D wrinkles. [13,18,19] Exposure of CO to the graphene/Pt(111) surface was carried out at room temperature. We observed a contrast change in the LEEM images of the graphene islands when the partial pressure of CO (pCO) was raised to 1 10 À6 mbar, which suggests the onset of CO intercalation. Figure 1 a-f displays a series of snapshots from a LEEM video recording the CO intercalation...

The growth mechanism of monolayer (ML) graphene on Ru(0001) via pyrolysis of C 2 H 4 was studied by scanning tunneling microscopy (STM), high-resolution electron energy loss spectroscopy (HREELS), and ultraviolet photoelectron spectroscopy (UPS). On the basis of the mechanistic understanding, graphene overlayers ranging from nanographene clusters to graphene film with 1 ML coverage were prepared in a well-controlled way. O 2 adsorption on the graphene/Ru(0001) surface was investigated by STM, UPS, and X-ray photoelectron spectroscopy (XPS). It is revealed that the Ru(0001) surface fully covered by graphene becomes passivated to O 2 adsorption at room temperature and only activated again at elevated temperatures (>500 K). The adsorbed oxygen intercalates between the topmost graphene overlayer and the Ru(0001) substrate surface. These intercalated oxygen atoms decouple the graphene layer from the Ru(0001) substrate, forming quasi-freestanding monolayer graphene atomic crystals floating on the O-Ru(0001) surface.