The conventional way of making manganese-cerium mixed oxides starts with soluble metal salts, typically nitrates, which are combined through coprecipitation or impregnation. Those routes carry real drawbacks: the procedures are multi-step and difficult to control, the salt solutions generate their own pollutant streams, and the active metal loading on the final support tends to be low. The research team, led by Min Kang and Jian Yu with collaborators at several Chinese institutions, sidestepped the problem by starting from manganese carbonate and cerium carbonate, cheap and stable crystalline solids that are already produced at industrial scale. The trick was finding a way to persuade two stubbornly insoluble carbonates to mix intimately at the molecular level, and the answer turned out to be a humble kitchen-adjacent chemical: oxalic acid.

When the powdered carbonate precursors are treated with oxalic acid, a remarkable transformation occurs. The crystalline carbonates dissolve and reprecipitate as viscous, amorphous oxalate species in which manganese and cerium are chemically intermingled rather than merely sitting side by side as separate grains. This chemical mixing, which the authors distinguish from simple physical blending, is the heart of the method. Structural characterization by X-ray diffraction showed that the oxalate intermediates lose their long-range order, while thermogravimetric analysis revealed a second crucial benefit: the homogeneous oxalate precursors decompose at a lower temperature, between 250 and 300 degrees Celsius, compared with physically mixed carbonates. During that decomposition they also release more carbon dioxide gas, and it is this escaping gas that does the sculpting.

As the oxalate precursor breaks down and CO2 streams out of the shrinking solid, it leaves behind a porous manganese-cerium oxide framework riddled with voids. Measurements of surface area and pore volume using the Brunauer-Emmett-Teller method confirmed that the chemically mixed catalyst possesses a significantly larger specific surface area and pore volume than material made by physically mixing the same carbonates. The morphology that emerges is strip-shaped, a form the authors highlight as suitable for industrial catalyst bodies, which are often shaped into pellets, plates, or honeycombs that must withstand gas flow without excessive pressure drop. Large pores matter in real flue gas service because they allow molecules to diffuse quickly to active sites and are less prone to clogging by dust and aerosols.

Why does intimate mixing of manganese and cerium matter so much for the catalysis itself? The answer lies in the electronic handshake between the two oxides. When manganese oxide domains and cerium oxide domains are finely interspersed, the interface generates abundant defect sites, including oxygen vacancies where an oxygen atom is missing from the crystal lattice. These vacancies, together with highly mobile surface active oxygen species, form the reactive heart of the catalyst. X-ray photoelectron spectroscopy indicated a higher proportion of surface active oxygen in the chemically mixed sample, and the manganese and cerium atoms engage in a facile redox cycle, shuttling electrons back and forth as the reaction proceeds. Ammonia temperature-programmed desorption experiments showed an increased density of acid sites, which anchor the ammonia reductant molecules needed for the selective catalytic reduction reaction.

In the selective catalytic reduction process, ammonia is injected into the flue gas and reacts with nitric oxide over the catalyst surface to produce harmless nitrogen and water. The performance figures reported for the carbonate-derived MnCeOx catalyst are striking. At 150 degrees Celsius, a temperature at which many commercial vanadia-based catalysts are essentially dormant, the material achieved close to 100 percent denitrification efficiency. More important for any real installation, the catalyst held its activity over a 168-hour continuous test, maintaining conversion above 94 percent even under demanding conditions: 30 volume percent water vapor, a level typical of wet flue gases, and a sulfur dioxide concentration of 50 milligrams per normal cubic meter. Sulfur and water resistance has historically been the Achilles heel of manganese-based low-temperature catalysts, because sulfur dioxide reacts with surface sites to form stable sulfates and water competes with ammonia for adsorption.

The authors attribute the exceptional sulfur tolerance to the same structural features that drive the high activity. The large pore volume gives sulfur species less opportunity to block the network of channels, and the sheer abundance of exposed active sites means that even if some are deactivated by sulfate formation, plenty remain available to keep the reaction going. The strong Mn-Ce interaction also appears to moderate the severity of sulfation on the manganese sites themselves, a phenomenon that previous studies of Mn-Ce systems have linked to cerium’s oxygen storage and release capacity. Cerium oxide is famous as an oxygen buffer, absorbing and releasing oxygen as conditions fluctuate, and that buffering stabilizes the redox state of neighboring manganese atoms under the reducing and oxidizing swings of a working flue gas stream.

The comparative experiments in the study sharpen the message about preparation chemistry. Samples made by physically mixing the two carbonates and calcining them at either 300 or 400 degrees Celsius performed markedly worse than the chemically mixed counterparts calcined at the same temperatures. The difference traces back to the precursor stage: physical mixing leaves manganese and cerium in separate crystalline carbonate grains, so even after decomposition the two oxides remain poorly interleaved, with fewer interface sites, fewer defects, and less active oxygen. The oxalic acid route effectively performs the mixing at the molecular scale before any heat is applied, which is why the resulting oxide inherits such a favorable architecture. Calcination temperature mattered as well, with the 300-degree samples retaining the fine dispersion that higher temperatures begin to erode through sintering.

There is also a green-chemistry dimension to the work that extends beyond the catalyst’s performance. By replacing soluble metal salts with carbonates, the synthesis avoids nitrate-containing waste streams and the corrosive, fuming solutions that industrial plants must handle and treat. Oxalic acid is inexpensive, widely available, and acts here as a chemical molding additive that shapes the precursor into workable strips. The lower decomposition temperature of the oxalate route, 250 to 300 degrees Celsius rather than the higher temperatures often needed to fully break down carbonates, translates directly into lower energy consumption during the calcination step, which for a catalyst produced in tonnage quantities is a meaningful cost and emissions saving. The released carbon dioxide is the only major gaseous byproduct of the precursor transformation.

The broader context makes the advance timely. Low-temperature denitrification is increasingly demanded by industries such as coking, cement, glass, and steel, where exhaust gases leave stacks at temperatures far below the window in which conventional catalysts operate, and where reheating the gas is economically prohibitive. Manganese-based catalysts have long been recognized as the most promising family for sub-200-degree operation, but translating laboratory powders into durable industrial bodies has remained the bottleneck. By demonstrating a route that starts from cheap carbonates, uses a simple acid treatment, yields a strip-shaped body suited to industrial forming, and delivers near-complete NOx conversion with robust resistance to water and sulfur, the researchers have addressed several of those bottlenecks at once. If the approach scales as its chemistry suggests it should, the humble carbonate, long treated as a dull industrial commodity, may find a new starring role in cleaning the air above the world’s heaviest industries.

Subject of Research: Carbonate-derived MnCeOx catalysts for low-temperature selective catalytic reduction of NOx in flue gas

Article Title: The Fabrication of Strip-Shaped Industrial MnCeOx Catalyst Derived from Carbonates for Flue Gas Denitrification

Article References: Kang, M., Xu, M., Xiao, P., Xiao, Y., Li, C., Fu, W., Xu, Y., Yu, Z., & Yu, J. (2026). The Fabrication of Strip-Shaped Industrial MnCeOx Catalyst Derived from Carbonates for Flue Gas Denitrification. Catalysis Letters, 156(9), Article 268. https://doi.org/10.1007/s10562-026-05520-3

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05520-3

Keywords: MnCeOx catalyst, flue gas denitrification, NH3-SCR, carbonate precursors, oxalic acid, low-temperature catalysis, nitrogen oxides, sulfur resistance, oxygen vacancies, industrial catalysts, manganese oxide, cerium oxide