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Improving the efficiency of CO catalytic oxidation at low temperatures is, in essence, a systematic engineering problem that spans from precise regulation of catalyst active sites to overall system optimization. The low‑temperature catalytic oxidation of CO is constrained by two core obstacles: first, the insufficient activation of surface oxygen species on the catalyst at low temperatures, where the reaction rate is limited by the dissociative adsorption step of O₂ molecules; second, the strong adsorption of CO on active sites, which leads to “self‑poisoning”—once CO occupies the sites, it is difficult to desorb, preventing subsequent CO and O₂ from approaching the catalytic centers. The technical approaches to overcoming these two obstacles have evolved from single‑material optimization to multi‑dimensional synergistic strategies—through elemental doping and oxygen‑vacancy engineering to enhance low‑temperature reducibility and oxygen activation capability, 13% Mn‑doped Co₃O₄ achieves 100% CO conversion at 84°C; through atomically dispersed dual‑active‑site design to break through the competitive adsorption bottleneck of single‑atom catalysts, a Pt‑Ru dual‑atom catalyst reaches a CO oxidation turnover frequency (TOF) of 17.6×10⁻² s⁻¹ at 30°C; and through high‑entropy strategies and support synergy effects to achieve poisoning resistance and long‑term stability under complex operating conditions, ultra‑low‑loading high‑entropy catalysts maintain high stability in flue gas containing H₂O and SO₂. However, to translate laboratory achievements into reliable industrial operation, a systematic engineering methodology must also be established in catalyst selection, system design, and operation and maintenance management. The following discussion addresses four aspects: low‑temperature deactivation mechanisms, oxygen‑vacancy engineering strategies, dual‑active‑site design, and engineering applications.
The reaction formula for CO catalytic oxidation is 2CO + O₂ → 2CO₂. Without a catalyst, this reaction requires temperatures above 200°C to proceed significantly. The role of the catalyst is to lower the activation energy, enabling the reaction to occur at lower temperatures. However, under low‑temperature conditions, improving catalytic efficiency faces multiple barriers.
The rate‑determining step of the CO oxidation reaction is typically the adsorption and activation of O₂ molecules, rather than the adsorption of CO. At low temperatures, the concentration of oxygen vacancies and the oxygen mobility on the catalyst surface are both suppressed, making it difficult for O₂ to be activated into reactive oxygen species. Studies have shown that metal doping weakens the metal–oxygen bond, enhances low‑temperature reducibility and oxygen mobility, and thereby generates abundant surface oxygen defects that promote molecular oxygen activation. This mechanism reveals a key to improving low‑temperature activity—the catalyst must have enhanced “oxygen supply capability” at low temperatures.
CO molecules generally have high adsorption energy on transition‑metal active sites, and at low temperatures they are especially prone to form strong chemisorption bonds that are difficult to desorb. Spectroscopic and theoretical analyses indicate that Mn doping redistributes CO adsorption from strongly bound irreversible sites to moderately bound sites, facilitating rapid catalytic turnover. In undoped catalysts, CO occupies strong adsorption sites and is hard to release, preventing subsequent CO and O₂ from accessing the active centers, causing a sharp decline in catalyst activity.
In actual industrial flue gas, the presence of water vapor and SO₂ further aggravates catalyst deactivation. The CO concentration in sintering flue gas can reach 0.4%–1%, accounting for more than half of the total emissions from the steel industry. Although conventional precious‑metal catalysts have high intrinsic activity, they are prone to poisoning at active sites in high‑concentration H₂O/SO₂ sintering flue gas environments, leading to performance degradation. Non‑precious‑metal catalysts, while lower in cost, generally suffer from insufficient low‑temperature activity and poor dispersion of active sites. Understanding the nature of these barriers is a prerequisite for formulating efficiency‑improvement strategies.
Oxygen‑vacancy engineering intentionally introduces lattice defects such as oxygen vacancies into the catalyst, providing more active sites for O₂ adsorption and activation, and is one of the core means to improve low‑temperature catalyst activity.
Researchers prepared Mn‑doped Co₃O₄ catalysts with different Mn concentrations (3–15%) by a simple co‑precipitation method. Among all compositions, 13% Mn was identified as the optimal doping threshold. This catalyst achieved 100% CO conversion at 84°C and operated stably for over 60 hours at both 72°C and 85°C, while also exhibiting high moisture resistance. Further doping (15% Mn) led to performance degradation, confirming 13% as the optimal threshold.
Spectroscopic and theoretical analyses confirmed that Mn doping shifts the CO oxidation mechanism from a lattice‑oxygen pathway to a surface‑adsorbed‑oxygen‑species pathway, consistent with the Mars‑van Krevelen (MvK) mechanism. The Mn³⁺⇌Mn⁴⁺ and Co³⁺⇌Co²⁺ redox pairs synergistically lower the oxygen‑vacancy formation energy. The Co²⁺/Co³⁺ ratio increased from 0.30 to 0.90, the Oads/Olat ratio increased from 0.15 to 0.86, and the lattice constant expanded from 8.024 Å to 8.096 Å. The innovation of this work lies in determining the precise optimal doping threshold and achieving 100% CO conversion at only 84°C without using precious metals.
A series of Cu/Mn co‑doped Co₃O₄ catalysts were synthesized by co‑precipitation. When the Cu/Mn ratio was 0.35/0.65, the catalyst significantly improved low‑temperature CO conversion while maintaining stability. Multiple characterization techniques (XRD, XPS, H₂‑TPR, O₂‑TPD) revealed that Cu/Mn co‑doping weakens the Co–O bond, enhances low‑temperature reducibility and oxygen mobility, thereby generating abundant surface oxygen defects that promote molecular oxygen activation.
Studies have shown that Fe–Co composite oxide catalysts exhibit excellent performance in low‑temperature CO oxidation. This catalyst achieved 100% CO conversion at 72°C and demonstrated outstanding long‑term stability at 60°C. The improved performance is mainly attributed to the higher specific surface area, oxygen‑vacancy content, and enhanced lattice‑oxygen mobility.
Single‑atom catalysts (SACs) offer an ideal pathway to reduce the cost of precious‑metal catalysts by maximizing atom utilization. However, SACs suffer from competitive adsorption between CO and O₂ because of their single‑type active sites. In recent years, atomically dispersed dual‑active‑site designs have opened new routes to overcome this bottleneck.
Researchers successfully constructed atomically dispersed Pt‑Ru dual‑atom catalysts on a nanodiamond@graphene support. Electronic structure analysis indicated that the bonding between Pt and Ru atoms enhances the metallic character of both, synergistically promoting the adsorption and activation of CO and O₂.
At 30°C, this catalyst achieved a CO oxidation turnover frequency (TOF) as high as 17.6×10⁻² s⁻¹, which is more than 10 times that of the corresponding single‑atom Pt catalyst. Mechanistic studies revealed that CO molecules preferentially adsorb on the Pt atoms with enhanced metallic character, while O₂ molecules preferentially adsorb on the bridge sites formed by the Pt‑Ru dual atoms. This synergistic effect significantly enhances O₂ adsorption and activation.
In a study on a low‑Pt‑loading (0.15 wt%) Pt/TiO₂ catalyst, researchers achieved low‑temperature CO oxidation by simultaneously activating molecular oxygen and surface lattice oxygen. The catalyst performed efficient CO oxidation below 100°C. Mechanistic studies showed that Pt species on the catalyst surface not only promote O₂ adsorption and dissociation but also activate the lattice oxygen of the TiO₂ support through metal‑support interactions, allowing both oxygen species to participate in the CO oxidation reaction, thereby breaking the limitation of a single oxygen source.
High‑performance catalysts developed in the laboratory often face activity decay under industrial complex conditions. The high concentrations of H₂O and SO₂ in sintering flue gas are two major “killers” that must be dealt with in practical applications.
One research team designed an ultra‑low‑loading (0.1 wt%) high‑entropy catalyst that anchors multiple transition metals (Mn, Fe, Co, Ni) together with Pt onto an anatase TiO₂ surface, forming strong metal‑support interactions. The high‑entropy feature enables strong synergistic effects among multiple metals and TiO₂, optimizes the electronic structure of the elements, and increases the electron density on the TiO₂ surface.
Notably, the introduction of the high‑entropy component lowered the temperature for complete CO conversion (T₁₀₀) from 270°C to 230°C. This catalyst maintained high stability in flue gas containing H₂O and SO₂. In‑situ diffuse reflectance infrared spectroscopy and DFT calculations confirmed that the high‑entropy active components increase the local electron density on the TiO₂ surface, promoting the conversion of CO and O₂ molecules into reactive species. By filling metal interstitial electrons into the sub‑gap states of TiO₂, the activation of TiO₂ lattice oxygen is promoted. This strategy provides a viable path for CO catalytic oxidation under complex industrial conditions.
Hopcalite (CuMnOx) is a classic low‑temperature CO oxidation catalyst known for its low cost and high activity. Researchers adjusted the lattice structure of Hopcalite by Ce doping. The modified catalyst with 7.5 wt% Ce doping exhibited the best intrinsic activity. Characterization results indicated that the enhanced low‑temperature activity mainly originates from lattice distortion that weakens the bonding strength of oxygen atoms. On the Ce‑modified sample, the reactivity of both adsorbed oxygen and lattice oxygen was enhanced at low temperatures.
Loading catalysts onto structured supports such as honeycomb ceramics or metal meshes can effectively improve mass transfer and reduce bed pressure drop. Researchers synthesized MOF‑74‑derived Co₃O₄/Mn₃O₄ monolithic catalysts in‑situ on nickel foam via a solvothermal method. This catalyst achieved a T₉₀ temperature of 20°C, enabling efficient CO oxidation at room temperature. The enhanced activity is associated with increased oxygen‑vacancy concentration, abundant Co³⁺, Mn²⁺+Mn³⁺, and surface adsorbed oxygen species.
Against the backdrop of ultra‑low emission retrofitting in the steel industry, CO catalytic oxidation technology has entered the industrial application stage. In 2025, a CO oxidation catalyst was successfully applied in a sintering machine flue gas energy‑saving and consumption‑reduction retrofit project at a steel enterprise. The project passed the 168‑hour performance assessment and has been operating stably for more than one month. Third‑party authoritative testing showed that the CO removal efficiency remained stable at around 85%, with the outlet CO concentration below 1200 mg/m³, far lower than local emission limits; the gas consumption of the heating furnace was reduced by more than 60%, yielding significant environmental and economic benefits.
Other engineering practices have demonstrated that sintering machine flue gas CO catalytic purification units can stably control CO emissions below 200 ppm over the long term. By the end of June 2025, 590 million tons of crude steel production capacity nationwide had completed full‑process ultra‑low emission retrofitting, accounting for more than 80% of the country’s total capacity. CO is one of the six basic controlled pollutants specified in the Ambient Air Quality Standard, and many regions in China have set emission limits for it—an industrial city took the lead in 2018 in setting a CO emission concentration red line for sintering machines, and relevant provinces introduced local standards for CO emissions from sintering flue gas in 2025. These policies and engineering practices have jointly driven the continuous progress and large‑scale application of low‑temperature CO catalytic oxidation technology.
The selection of industrial CO catalysts is not simply a matter of comparing activity levels; it requires a comprehensive evaluation of operating conditions, gas composition, humidity level, structural form, pressure‑drop requirements, and service life. Humidity is one of the key external factors affecting catalyst life: water vapor tends to cover the active sites on the catalyst surface, leading to a decline in catalytic efficiency. At 25°C, when relative humidity increases from 30% to 80%, the CO conversion of a typical Hopcalite sample can drop from 96% to 43% within 2 hours. During selection, the applicability of the catalyst should be assessed based on actual flue gas conditions—when flue gas humidity is high, priority should be given to catalyst systems that have undergone hydrophobic modification or moisture‑resistance optimization.
Space velocity directly affects gas‑solid contact time; excessively high space velocity leads to incomplete reaction, while excessively low space velocity increases equipment volume and capital costs. For typical industrial flue gas conditions, the space velocity should be optimized in conjunction with the specific catalyst characteristics. Pressure drop is an important indicator for evaluating fixed‑bed reactors, directly affecting reaction performance and overall energy consumption. The shape and size of catalyst particles are key factors influencing the pressure drop in fixed‑bed reactors. Structured catalysts such as honeycomb types can effectively reduce bed pressure drop while ensuring catalytic efficiency.
The poisoning resistance of high‑quality catalysts determines their actual service life. Through support modification (e.g., using alumina with specific pore structures) and active‑component protection techniques, service lives of 3–5 years or even longer can be achieved. For catalysts that have undergone some degree of deactivation, thermal regeneration may partially restore activity—studies have shown that in‑situ treatment with CO at 200°C can effectively improve catalyst durability by creating surface oxygen vacancies. However, it should be noted that regeneration is only effective for reversible deactivation; for irreversible poisoning caused by sulfate deposition or sulfidation of active metals, the regeneration effect is limited. It is recommended to regularly monitor the outlet CO concentration and bed pressure drop during catalyst operation, and schedule maintenance or replacement promptly when the pressure drop rises significantly or the outlet concentration approaches the emission limit.
The improvement of low‑temperature CO catalytic oxidation efficiency is steadily advancing along the path of “mechanism understanding → materials innovation → engineering translation.” From Mn‑doped Co₃O₄ achieving 100% CO conversion at 84°C, to the Pt‑Ru dual‑atom catalyst delivering a TOF of 17.6×10⁻² s⁻¹ at 30°C; from the high‑entropy catalyst lowering the complete‑conversion temperature by 40°C while maintaining high stability in flue gas containing H₂O/SO₂, to CO catalysts achieving over 85% removal efficiency and outlet concentrations below 1200 mg/m³ in industrial sintering flue gas—these advances demonstrate that improving low‑temperature CO catalytic oxidation efficiency is no longer a single‑dimensional materials‑optimization problem, but a multi‑level technical system involving oxygen‑vacancy engineering, atomic‑scale precision design, high‑entropy strategies, and engineering system integration. For engineers and technicians engaged in the design, selection, and operation of CO catalytic purification systems, understanding the fundamental mechanisms of low‑temperature deactivation, knowing the performance boundaries and applicable conditions of various catalysts, and making rational selection and system design decisions based on actual flue gas conditions are the fundamental pathways to achieving efficient CO catalytic oxidation at low temperatures. Currently, several material suppliers in China, including Minstrong, have achieved mass production of CO catalysts, providing diverse material choices for engineering applications under different operating conditions.
author: Gloria
date:2026/7/14
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