The reaction in question, oxidative coupling of methane, or OCM, directly converts methane and oxygen into higher-value C2 hydrocarbons, namely ethane and ethylene. These molecules are foundational feedstocks for the chemical industry, serving as precursors to plastics, solvents, and countless other materials. In principle, OCM could allow producers to bypass the energy-intensive indirect route, in which natural gas is first converted to synthesis gas and then rebuilt into longer hydrocarbons. In practice, however, the reaction has proven notoriously difficult to control, and no industrial process based on direct oxidative coupling has achieved widespread commercial adoption.

The difficulty stems from two intertwined problems. First, the carbon–hydrogen bonds in methane are exceptionally stable, making the molecule reluctant to react at moderate temperatures; substantial energy input is needed to activate it. Second, and more troubling, the desired products are more reactive than methane itself. Once ethane and ethylene form, they are readily attacked further by oxygen, over-oxidizing to carbon oxides and destroying the selectivity that any viable process requires. Conventional OCM catalysts therefore operate near 800 degrees Celsius to achieve acceptable conversion, and even then they tend to deactivate substantially during prolonged operation, as their active surface sites degrade or their crystal structures transform under the harsh reaction conditions.

The Science Tokyo team, led by Professor Keigo Kamata of the Materials and Structures Laboratory in the Institute of Integrated Research, together with Assistant Professor Keiju Wachi of the Department of Applied Chemistry at the Graduate School of Engineering, The University of Tokyo, approached the problem through the emerging field of high-entropy oxides. These are materials in which five or more metallic elements are incorporated into a single common crystal structure, producing a chemically disordered but structurally stable lattice. The entropic stabilization inherent to such compositions can lock in crystal phases that would otherwise collapse, and the mixing of elements creates a dense landscape of tunable surface sites whose properties can be adjusted by changing the elemental recipe.

To find the right recipe, the researchers undertook a broad compositional screen, testing 55 high-entropy oxide compositions that spanned five different crystal structures and 24 elements. According to Kamata, the screening showed that lanthanoid-containing systems emerged as promising candidates, with C-type rare-earth high-entropy oxides combining relatively high C2 yields with structural stability. The lanthanoids, a family of chemically similar rare-earth elements, are attractive for this purpose because they share crystal chemistry that allows them to substitute for one another freely, while their ionic radii vary systematically across the series, providing a built-in dial for tuning surface properties.

Seven of the screened compositions were synthesized as nanoparticle catalysts using a sol–gel method developed in-house. Amorphous precursors prepared from metal acetates and aspartic acid were calcined at 750 to 800 degrees Celsius, yielding oxides in which five elements were homogeneously integrated into a single phase. Further screening singled out one composition, designated HEO-2, as a representative catalyst for detailed study. HEO-2 combines lanthanum, samarium, europium, gadolinium, and dysprosium in the formula (LaSmEuGdDy)0.4O3, adopting the C-type rare-earth oxide structure that had proven most resilient in the initial tests.

The catalytic results were striking. HEO-2 initiated the formation of C2 hydrocarbons at just 525 degrees Celsius, a significantly lower onset temperature than previously investigated OCM catalysts, and at 600 degrees Celsius it reached a C2 yield of 12.3 percent. The team traced this low-temperature activity to the catalyst’s surface basicity. Their analysis revealed a subtle but crucial point: moderately basic sites, rather than the strongest basic sites, are the most favorable for oxidative coupling. Excessively strong basicity promotes over-oxidation of the desired C2 products or binds carbon dioxide too tightly, both of which erode performance. The sweet spot lies in the middle of the basicity range.

What makes the finding especially valuable is that the researchers discovered surface basicity can be systematically tuned through the average ionic radius of the constituent lanthanoid elements, giving chemists a rational design parameter rather than a trial-and-error search. HEO-2, with an average ionic radius of 0.957 angstroms, exhibited carbon dioxide desorption predominantly in the 300 to 400 degrees Celsius range, a signature of the moderately basic sites that proved most effective for C2 production. The high-entropy configuration itself also appears to stabilize these active surface functionalities, anchoring them against the degradation that plagues simpler materials.

That stabilization was most evident in long-term testing. At 600 degrees Celsius, HEO-2 maintained its C2 yield after 240 hours of continuous operation, essentially unchanged from its initial performance. Its calculated deactivation rate of 1.0 millimole of carbon per gram of catalyst per hour squared was more than 25 times lower than those of the corresponding single oxides. Surface analysis showed that the moderately basic sites were substantially preserved after the reaction, and the catalyst retained its C-type polycrystalline framework throughout. In contrast, the single oxides either underwent structural transformation or progressively lost their active basic sites, illustrating precisely the failure modes that high-entropy mixing appears to suppress.

Beyond the immediate performance gains, the study establishes a design principle that could extend well beyond methane conversion. By identifying the average ionic radius as a descriptor for surface basicity, the researchers provide a framework for engineering selective oxidation catalysts that operate at lower temperatures with sustained activity, a goal relevant to many industrial processes that currently demand extreme conditions. As Kamata concluded, the work offers a rational foundation for designing such catalysts. If the approach can be scaled from laboratory nanoparticles to industrial reactors, the direct conversion of abundant natural gas into ethylene and ethane could move closer to commercial reality, with significant implications for energy efficiency and the carbon footprint of the chemical industry.

Subject of Research: High-entropy lanthanoid oxide catalysts for low-temperature oxidative coupling of methane

Article Title: High-entropy lanthanoid oxide catalyst enables low-temperature oxidative coupling of methane

Article References: High-entropy lanthanoid oxide catalyst enables low-temperature oxidative coupling of methane. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: oxidative coupling of methane, high-entropy oxide, lanthanoid, catalysis, C2 hydrocarbons, ethylene, ethane, surface basicity, sol-gel method, methane conversion, heterogeneous catalysis, selective oxidation

The challenge the team set out to solve is one of the deepest in catalysis. Ethane, the second-largest component of natural gas, is held together by carbon–hydrogen bonds that are among the least reactive in chemistry. Breaking one of these bonds selectively, and then persuading the resulting fragment to bond with a carbon monoxide molecule rather than simply burning to carbon dioxide or over-oxidizing into a soup of byproducts, has defeated generations of catalyst designers. Conventional approaches rely on high temperatures that push reactions toward complete combustion, destroying precisely the selectivity that makes a process commercially attractive.

The new work, led by Qi Lu of Tsinghua University together with Bingjun Xu of Peking University and Mu-jeng Cheng of National Cheng Kung University, sidesteps this problem by splitting the catalytic labor between two distinct chemical roles of the same metal. Adsorbed oxygen species on an oxidized copper surface are responsible for activating ethane, abstracting a hydrogen atom to create a surface ethyl species. Meanwhile, copper ions released from the surface oxide into the acidic solution form carbonyl species with dissolved carbon monoxide, and it is at the interface between these two worlds that the crucial carbon–carbon bond forms.

Carbon monoxide plays a double role in this scheme, and that dual function is central to the reaction’s unusual selectivity. It serves as the C1 building block that is inserted into the ethane-derived fragment, ultimately delivering the carboxylic acid functionality of propionic acid. But it also acts as a selectivity-directing agent, intercepting the reactive ethyl intermediates before they can drift into unproductive oxidation pathways. By capturing the C–H activation intermediate quickly, CO essentially funnels the chemistry toward a single desired product rather than the mixture of alcohols, aldehydes and acids that typically plagues partial oxidation of light alkanes.

The experimental evidence for this mechanism is unusually thorough. The team used isotopic labelling to confirm that both the two-carbon skeleton of the product derives from ethane and the single added carbon from carbon monoxide, ruling out alternative carbon sources. In situ surface-enhanced infrared and Raman spectroscopies, techniques the group has refined in earlier studies of carbon monoxide electroreduction on copper, allowed the researchers to watch copper carbonyl species and surface ethyl intermediates directly on the working catalyst. Density functional theory calculations performed by the Cheng group in Tainan provided the energetic underpinning, showing that interfacial coupling between the copper carbonyl and the ethyl species is feasible under the mild conditions of the experiment.

The performance numbers tell a story of deliberate trade-offs. At propionic acid formation rates of up to 120 micromoles per gram of copper per hour, the selectivity settles at around 50 percent. When the team tuned conditions to slow the rate, selectivity climbed to its optimum of 83 percent, indicating that the competing pathways can be suppressed at the cost of throughput. This rate–selectivity relationship is a familiar feature of partial oxidation chemistry, but the fact that both ends of the trade-off are respectable at ambient temperature is what distinguishes the result. The researchers suggest that the strategy establishes CO-mediated alkane carbonylation under mild conditions as a genuine synthetic platform for organic acid production.

The intellectual lineage of the work stretches back decades. Carbonylation, the insertion of carbon monoxide into metal–carbon bonds, is the backbone of some of the largest industrial processes on Earth, most famously the methanol-to-acetic acid route that feeds global demand for one of the most important commodity chemicals. Applying carbonylation to saturated hydrocarbons, however, has required either superacidic media, precious metal catalysts or harsh temperatures. Early hints came from work in the 1970s showing that copper(I) carbonyl cations could carbonylate saturated hydrocarbons in strong acids, and more recent studies have explored carbonylation of alkanes over zeolites and via photocatalytic hydrogen atom transfer. The new study brings these threads together in a heterogeneous, aqueous system that operates at room temperature.

Copper’s starring role is itself notable. The metal has enjoyed a renaissance in catalysis over the past decade, particularly in electrochemistry, where oxide-derived copper electrodes proved capable of converting carbon dioxide and carbon monoxide into multicarbon products such as ethanol and acetate. That literature established that copper carbonyl species on oxidized copper surfaces can engage in carbon–carbon bond formation, and the present work transplants that insight from electrochemistry into a purely chemical, oxygen-driven setting. The researchers’ earlier investigations into how carbon monoxide coverage governs coupling on copper surfaces clearly informed the design of the new reaction, illustrating how mechanistic understanding in one field can seed breakthroughs in another.

The sustainability implications are considerable. Ethane is abundant, cheap and often flared or simply burned as fuel in regions far from petrochemical infrastructure. Converting it directly into propionic acid, a preservative, feed additive and chemical intermediate currently produced largely through petrochemical routes, would add value to a stranded resource while avoiding the energy intensity of steam cracking or high-temperature oxidation. Running the reaction in dilute acid with molecular oxygen as the terminal oxidant, rather than stoichiometric oxidants or precious metals, keeps the reagent palette inexpensive and environmentally benign. The authors acknowledge that the current rates, while scientifically impressive, remain far from industrial scale, and that catalyst durability and reactor engineering will need attention before any commercial translation.

What makes the result resonate beyond its immediate application is the demonstration that the most inert bonds in organic chemistry can be tamed at ambient conditions when activation and functionalization are assigned to different, cooperating chemical environments on a single catalyst. The interfacial coupling concept, in which a surface-bound alkyl fragment meets a solution-phase carbonyl species precisely at the boundary between oxide and liquid, offers a design principle that could extend to methane, propane and other light alkanes. If the strategy generalizes, the humble copper surface, working quietly at room temperature, may become the stage on which natural gas is rewritten into the building blocks of the chemical industry.

Subject of Research: Room-temperature catalytic coupling of ethane and carbon monoxide to synthesize propionic acid over copper

Article Title: Propionic acid synthesis via room-temperature coupling of ethane and CO

Article References: Hou, J., Liu, W., Wang, K.-H., Li, M., Wen, S.-C., Cheng, M.-J., Xu, B., & Lu, Q. (2026). Propionic acid synthesis via room-temperature coupling of ethane and CO. Nature Synthesis. https://doi.org/10.1038/s44160-026-01168-4

Image Credits: AI Generated

DOI: 10.1038/s44160-026-01168-4

Keywords: catalysis, copper catalyst, ethane, carbon monoxide, propionic acid, carbonylation, C–H activation, selectivity, mild conditions, organic acids, sustainability, heterogeneous catalysis