Ammonia selective catalytic reduction (NH₃-SCR) is widely used to control NOₓ emissions, which contribute to acid rain, photochemical smog, and risks to environmental and public health. Industrial systems commonly employ vanadium–titanium catalysts, but these materials generally operate most effectively between 300 and 400 °C and may pose toxicity, sulfur exposure, and particulate-blockage concerns. Mn-modified carbon materials offer large pore networks and strong low-temperature redox activity, yet conventional aqueous impregnation can produce unevenly distributed or aggregated MnOₓ. High-temperature treatment can also convert active Mn⁴⁺ into lower-valence species, limiting catalytic efficiency. These problems have created a need for a simpler method that improves both MnOₓ dispersion and Mn⁴⁺ formation.
A study (DOI: 10.48130/scm-0026-0009) published in Sustainable Carbon Materials on 05 March 2026 by Kai Li's team, North China Electric Power University, reports that combining ethanol-assisted manganese impregnation with low-temperature air calcination substantially improves NO removal by MnOₓ/AC catalysts.
The researchers first crushed coconut-shell-derived activated carbon into particles measuring 0.42–0.85 mm and dried them at 105 °C for eight hours. Four grams of the prepared carbon were immersed in either an aqueous or ethanolic manganese nitrate solution and treated ultrasonically at room temperature for two hours. The resulting precursors were calcined for two hours under air or nitrogen. To determine the best preparation conditions, the team varied manganese loading from 4 to 12 wt%, calcination temperature from 180 to 260 °C for ethanol-derived samples, and solvent and calcination atmosphere. Catalyst performance was tested in a quartz-tube reactor containing two grams of material. Simulated flue gas contained 0.03 vol% NO, 0.035 vol% ammonia, and 3 vol% oxygen, with nitrogen as the balance gas. Tests were conducted at 150 °C and a gas hourly space velocity of 20,000 h⁻¹, with every sample evaluated at least three times. Nitrogen adsorption, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were used to examine pore structure, MnOₓ distribution, surface oxygen, and manganese valence states. The analyses showed that ethanol's lower polarity and surface tension, together with its better wettability, strengthened contact between manganese nitrate and activated carbon. Consequently, MnOₓ penetrated and spread more uniformly across the carbon support instead of forming aggregates that could block pores. Under identical calcination conditions, the ethanol-derived catalyst contained 43.63% Mn⁴⁺—42.96% more than the water-derived counterpart. Low-temperature air calcination also generated oxygen-containing surface groups that supported NH₃ adsorption and catalytic reactions. Process optimization identified 200 °C and 8 wt% manganese as the best combination. Under the test conditions, this catalyst converted 96.3% of NO, compared with 82.9% for the water-impregnated catalyst and only 30.4% for a water-derived catalyst calcined at 500 °C under nitrogen. Conversion declined when manganese loading was either too low to provide sufficient active sites or high enough to cause aggregation and pore blockage.
Overall, the study demonstrates that changing the impregnation solvent can significantly influence catalyst structure and performance without requiring complicated equipment or energy-intensive processing. Ethanol promoted more uniform MnOₓ loading, while calcination at 200 °C in air preserved a high concentration of catalytically active Mn⁴⁺. Although further testing under realistic industrial conditions—including long-term operation and exposure to water vapor, sulfur compounds, and particulates—would help establish practical durability, the method offers a low-cost and equipment-compatible route toward more efficient low-temperature NOₓ control.
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References
DOI
10.48130/scm-0026-0009
Original Source URL
https://doi.org/10.48130/scm-0026-0009
Funding information
The authors thank the National Key R&D Program of China (2024YFE0111000), the Science and Technology Project of China Huaneng Group (HNKJ22-H150), the Fundamental Research Funds for the Central Universities (2024MS039), and the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation (CPSF) (GZC20230788) for financial support.
About Sustainable Carbon Materials
Sustainable Carbon Materials (e-ISSN 3070-3557) is a multidisciplinary platform for communicating advances in fundamental and applied research on carbon-based materials. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon materials around the world to deliver findings from this rapidly expanding field of science. It is a peer-reviewed, open-access journal that publishes review, original research, invited review, rapid report, perspective, commentary and correspondence papers.