Writing in Nature Nanotechnology, a research group led by Xun Hong of the University of Science and Technology of China and Yadong Li of Tsinghua University describes a catalyst in which isolated copper atoms are anchored to two-dimensional boron nanosheets. The material, designated Cu-SAs/B, features copper atoms coordinated by four boron atoms, forming what the authors call Cu–B4 sites. When used to catalyse the direct oxidation of methane with hydrogen peroxide as the oxidant, this apparently simple single-atom catalyst converted methane to acetic acid with a selectivity of 97 percent, a figure that places it among the most selective systems yet reported for this transformation. Equally striking was the activity: 221.3 millimoles of product per gram of copper per hour, achieved without any addition of carbon monoxide, which many earlier approaches to acetic acid synthesis had required as a co-reactant.

The significance of the selectivity number is difficult to overstate. In direct methane oxidation, the desired partial oxidation products are typically more reactive than methane itself, so catalysts tend to over-oxidize them to carbon dioxide or to produce a mixed soup of methanol, formaldehyde, formic acid and other species. Producing a single C2 oxygenate in near-quantitative selectivity means the catalyst is not merely activating methane but orchestrating a precise sequence of bond-breaking and bond-forming steps. The carbon–carbon coupling step in particular is the chemical bottleneck: it requires two different carbon-containing intermediates to meet on the surface in the right form, at the right time, and to join together before they are lost to side reactions.

The key discovery of the new study is how this catalyst manages that feat, and the answer challenges the conventional wisdom that single-atom catalysts and cluster catalysts represent separate, static design strategies. Using in situ X-ray absorption fine structure spectroscopy, the researchers watched the catalyst while it was actually working under methane oxidation conditions. What they saw was that the isolated copper atoms do not stay isolated. Under the reaction environment, and specifically in the presence of hydrogen peroxide, the copper atoms dynamically aggregate into Cu4 clusters, and when the reactive conditions are removed, they disperse back into single atoms. This reversible switching between two distinct nuclearity states happens repeatedly, meaning the catalyst is not a fixed structure at all but a dynamic ensemble that reshapes itself on demand.

Each of those two states turns out to carry a distinct job in the reaction mechanism. Through a combination of in situ spectroscopic techniques, including diffuse reflectance infrared Fourier transform spectroscopy, the researchers established that the CH3* intermediate, the methyl fragment that results from the initial activation of methane’s carbon–hydrogen bond, is formed on the copper single atoms, while the CHO* intermediate, the formyl species, forms on the Cu4 clusters. The carbon–carbon bond of the acetic acid product is then created by the coupling of these two complementary intermediates: a methyl unit contributed by the single-atom state and a formyl unit contributed by the cluster state. In effect, the catalyst divides the labour across its own two switchable configurations, so that a reaction requiring two incompatible surface chemistries can proceed on a single material.

This division of labour resolves a long-standing dilemma in catalyst design. Single-atom catalysts, in which every metal atom is individually anchored to a support, maximize atom efficiency and often excel at breaking strong bonds, but they lack the adjacent metal atoms needed to hold and combine larger carbon fragments. Metal clusters and nanoparticles, by contrast, provide ensembles of atoms capable of multi-site chemistry, but they waste material in their bulk and frequently promote unwanted deep oxidation. Conventional approaches force designers to choose one or the other. The switchable copper-on-boron system sidesteps the trade-off entirely, because the same pool of copper atoms reorganizes into whichever geometry each step of the reaction requires, and then restores itself to the dispersed state for the next catalytic cycle.

The choice of support was essential to making this dynamic behaviour possible. Boron nanosheets, a two-dimensional form of the light element boron first realized experimentally in 2016, provide a lattice in which copper atoms can be trapped in well-defined Cu–B4 coordination sites, yet from which they can still migrate and reassemble when the chemical environment changes. The researchers verified the atomic structure of the catalyst with aberration-corrected electron microscopy and X-ray absorption measurements, confirming the isolated dispersion of copper in the resting state, and then used operando X-ray absorption spectroscopy, including simulations of the X-ray absorption near-edge structure, to track the emergence of the Cu4 clusters during the reaction. Density functional theory calculations performed by the team supported the mechanistic picture, showing how the switching is triggered by peroxide and how the methyl and formyl intermediates form on their respective sites and couple to yield acetic acid.

The practical implications reach well beyond a single reaction. Methane is both a vast energy resource and a potent greenhouse gas, and flaring, venting and leakage of associated gas from remote oil fields waste enormous quantities of it every year. A technology that could convert stranded natural gas directly into liquid acetic acid, one of the world’s most widely produced commodity chemicals and itself a precursor to vinyl acetate monomer and acetic anhydride, would change the economics of gas utilization. Because the reported catalyst operates without carbon monoxide co-feed, it removes one of the major complications of earlier routes, and the use of hydrogen peroxide as oxidant suggests compatibility with relatively mild reaction conditions. The authors note that independent replication of the methane oxidation experiments by collaborators confirmed the catalytic results, an unusually rigorous check for a field where reproducibility has often been a source of controversy.

More broadly, the work establishes what the researchers call a proof of concept for switchable nanocatalysts as a design principle. Instead of freezing a catalyst into a single, optimized static structure, chemists may increasingly build materials whose active sites reconfigure themselves in response to the reaction environment, accessing transient geometries that cannot exist under ordinary conditions. The reversible single-atom to cluster transition observed here echoes related dynamic behaviour seen in other atomically dispersed metal systems, but the new study is among the first to show a switchable catalyst in which each configuration performs a specific mechanistic role in a multi-step industrial reaction. If the concept can be generalized to other metals, supports and transformations, the shape-shifting copper atoms on boron may mark the beginning of a new chapter in catalysis, one in which the most useful catalyst is not the most stable structure but the most adaptable one.

Subject of Research: Switchable single-atom copper catalysts on boron nanosheets for direct methane oxidation to acetic acid

Article Title: Switchable single-atom catalysts for highly selective C–C coupling in direct methane oxidation

Article References: Han, X., Cui, P., Wu, G., Cai, J., Wang, C., Sun, F., Qiao, P., Liu, X., Zhuang, J., Liu, H., Su, F., Wang, G., Yan, W., Qi, Z., Lin, Y., Hong, X., & Li, Y. (2026). Switchable single-atom catalysts for highly selective C–C coupling in direct methane oxidation. Nature Nanotechnology. https://doi.org/10.1038/s41565-026-02271-5

Image Credits: AI Generated

DOI: 10.1038/s41565-026-02271-5

Keywords: methane oxidation, single-atom catalyst, copper, boron nanosheets, acetic acid, C–C coupling, Cu4 clusters, hydrogen peroxide, reversible switching, in situ XAFS, heterogeneous catalysis, Nature Nanotechnology