The team, led by Xiaoxue Liu, Yazhong Chen, Haifeng Wu, Xiaolin Sun, Bing Li, Xueping Wu, and Xianlong Zhang, prepared a family of catalysts labeled Mnx/SFCCC, where x denotes the weight percent of manganese loaded onto the support. The support, SFCCC, is spent fluid catalytic cracking catalyst, the used zeolite-based material that petroleum refineries discard by the ton once it loses activity in cracking units. Rather than letting this spent material go to landfill, the researchers repurposed it as a scaffold for manganese oxide, dramatically cutting the cost of the final catalyst while giving the waste a second life.

Because the way a catalyst is made can matter as much as what it is made of, the group synthesized their materials by three distinct routes: in situ deposition, precipitation-deposition, and incipient wetness impregnation. In situ deposition forms manganese oxide directly on the support surface under reaction conditions, precipitation-deposition builds the oxide through controlled precipitation onto the support, and incipient wetness impregnation soaks the support pores with a precursor solution before drying and calcination. Each technique distributes the manganese differently, and those differences in dispersion, particle size, and surface chemistry translate directly into differences in catalytic behavior.

To understand why one preparation outperformed the others, the researchers characterized their samples with an extensive toolkit. Low-temperature nitrogen adsorption measured surface area and pore structure, X-ray diffraction and scanning electron microscopy probed crystalline phase and morphology, hydrogen temperature-programmed reduction and oxygen temperature-programmed desorption assessed redox behavior and oxygen mobility, and X-ray photoelectron spectroscopy and electron paramagnetic resonance revealed surface oxidation states and defect sites. Inductively coupled plasma optical emission spectrometry confirmed the actual manganese loading in each batch. Together these measurements connected synthetic route, physical structure, and chemical functionality in a single coherent picture.

The performance results were striking. The catalyst prepared by in situ deposition with 14 weight percent manganese, Mn14/SFCCC-SP, delivered the best outcomes of the entire series. In static testing with an initial formaldehyde concentration of 4.5 parts per million, it removed 90.0 percent of the gas within 120 minutes at room temperature. Under dynamic conditions in a fixed-bed reactor, more representative of a real air purification device, it achieved greater than 95 percent removal at a gas hourly space velocity of 34,000 milliliters per gram per hour with an initial formaldehyde concentration of 7.0 parts per million. The catalyst also showed good stability and consistent performance across repeated use cycles, a critical requirement for any practical air-cleaning product.

The characterization data explain this superiority. Mn14/SFCCC-SP possesses a high specific surface area of 158 square meters per gram together with substantial pore volume, providing abundant sites where formaldehyde molecules can adsorb and react. The spent FCC support itself contributes porosity and a chemically heterogeneous surface, while the in situ deposition method deposits manganese oxide in a highly dispersed, well-contacted form rather than in bulky crystalline aggregates that bury active sites. High dispersion means more manganese atoms sit at the interface where gas molecules can reach them.

Even more important is the catalyst’s oxygen chemistry. X-ray photoelectron spectroscopy and electron paramagnetic resonance showed that the best sample carries a high concentration of surface-adsorbed oxygen species and oxygen vacancies, defects in the oxide lattice where an oxygen atom is missing. These vacancies are generated through the Mn4+/Mn3+ redox couple: when manganese cycles between its +4 and +3 oxidation states, lattice oxygen is consumed and replenished, continuously creating and refilling vacancy sites. The redox couple also gives the material good low-temperature reducibility, meaning it can activate oxygen molecules from air and transfer them to adsorbed formaldehyde even without external heating.

This mechanism sits at the heart of why the result matters. In the Mars-van Krevelen-type process that governs manganese oxide catalysts, formaldehyde first adsorbs on the surface, reacts with reactive oxygen to form intermediates such as formate and dioxymethylene species, and is finally oxidized to carbon dioxide and water, while gas-phase oxygen refills the vacancies the reaction consumed. A catalyst rich in vacancies and easily exchanged oxygen keeps this cycle running briskly at ambient temperature. The Hefei team’s evidence that the Mn4+/Mn3+ redox couple generates the vacancies that drive the reaction provides a clear design rule: maximize the interfacial contact between well-dispersed manganese oxide and a porous, defect-friendly support.

The choice of support is what makes the work economically compelling. Spent FCC catalysts are generated worldwide in enormous quantities, and disposal is an ongoing cost and environmental burden for refiners. Previous studies have explored supports ranging from activated carbon and diatomite to palygorskite, halloysite, and montmorillonite, often with excellent catalytic results but at a price that hinders scale-up. Using a pre-existing industrial waste stream as the support flips the cost equation: the raw material is essentially free, widely available, and already engineered to have favorable particle properties from its first life in the refinery. The authors specifically highlight that SFCCC was chosen to significantly reduce the cost of the catalyst, and the strong performance of the in situ deposition route shows that low cost need not come at the expense of activity.

For consumers, the implications are tangible. A room-temperature formaldehyde oxidation catalyst that maintains over 95 percent removal under demanding flow conditions could be integrated into air purifiers, ventilation systems, and building materials, continuously eliminating a carcinogenic pollutant rather than temporarily trapping it. Because the active component is abundant manganese rather than precious platinum, silver, or gold, the materials cost of deployment falls by orders of magnitude. And because the support is recycled refinery waste, the catalyst’s own footprint shrinks, turning one industrial waste problem into a solution for another environmental one. The study, published in Catalysis Letters, demonstrates that careful attention to preparation method, manganese loading, and support chemistry can transform a discarded powder into a high-performing environmental catalyst. As indoor air quality gains attention as a public health issue, such cheap, stable, and efficient room-temperature catalysts may soon move from the laboratory bench into the devices quietly cleaning the air in homes, offices, and schools.

Subject of Research: Room-temperature catalytic oxidation of formaldehyde using manganese oxides supported on spent FCC catalyst

Article Title: Room-Temperature Catalytic Oxidation of Formaldehyde Over Manganese Oxides Supported on SFCCC Prepared via Different Methods

Article References: Liu, X., Chen, Y., Wu, H., Sun, X., Li, B., Wu, X., & Zhang, X. (2026). Room-Temperature Catalytic Oxidation of Formaldehyde Over Manganese Oxides Supported on SFCCC Prepared via Different Methods. Catalysis Letters, 156(10), Article 279. https://doi.org/10.1007/s10562-026-05513-2

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05513-2

Keywords: formaldehyde, manganese oxides, spent FCC catalyst, room temperature catalysis, oxygen vacancies, indoor air purification, catalyst preparation, redox couple, waste recycling, Catalysis Letters, Room-Temperature, Catalytic