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Study on catalytic combustion performance of CO over Sn-modified CuCeOx catalysts under high humidity conditions
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Juntao XUE, Kehan BI, Hao WU, Chao HUANG*, Jinghui LÜ, Yangyang ZHANG, Yujing WENG, Yulong ZHANG*
Journal of Fuel Chemistry and Technology | 2026, 54(9) : 20250391-1861 - 20250391-1872
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Journal of Fuel Chemistry and Technology | 2026, 54(9): 20250391-1861-20250391-1872
• RESEARCH PAPER •
Study on catalytic combustion performance of CO over Sn-modified CuCeOx catalysts under high humidity conditions
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Juntao XUE, Kehan BI, Hao WU, Chao HUANG*, Jinghui LÜ, Yangyang ZHANG, Yujing WENG, Yulong ZHANG*
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  • Henan Key Laboratory of Coal Green Conversion, and International Joint Laboratory of Coal Clean Utilization, College of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo 454003, China
Published: 2026-09-10 doi: 10.1016/S1872-5813(26)60689-5
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Low-temperature CO oxidation technology has been widely applied in the field of environmental pollution control, yet challenges remain in CO purification under high-moisture environments. In this study, a series of CuCeOx-Sn catalysts supported on CeO2 were prepared via the excess impregnation method, and their catalytic performance in the low-temperature catalytic combustion of CO was systematically evaluated. The results indicate that CuCeOx-Sn0.1 (with a Sn loading of 0.1%) exhibits the optimal low-temperature catalytic activity, with the lowest t50 and t90 values. The temperature for 90% CO conversion (t50 and t90) decreases progressively with increasing Sn loading up to 0.1%. Beyond this threshold, further Sn loading does not lead to a significant reduction in t90; in fact, t90 slightly increases compared to that observed at 0.1% Sn. Furthermore, this catalyst maintains stability during water-on/water-off switching tests, demonstrating excellent water resistance. Through characterization techniques including XPS, O2-TPD, CO-TPD and CO-TPSR, it is revealed that the introduction of Sn effectively increases the concentration of surface oxygen vacancies and promotes the activation and migration of surface adsorbed oxygen and lattice oxygen.

Cu-Ce  /  Sn modification  /  excess impregnation method  /  H2O resistance  /  CO catalytic oxidation
薛俊涛, 毕可涵, 伍浩, 黄潮, 吕璟慧, 张洋洋, 翁育靖, 张玉龙. Sn修饰CuCeOx催化剂的高湿CO催化燃烧性能研究. 燃料化学学报（中英文）, 2026 , 54 (9) : 20250391-1861 -20250391-1872 . DOI: 10.1016/S1872-5813(26)60689-5
Juntao XUE, Kehan BI, Hao WU, Chao HUANG, Jinghui LÜ, Yangyang ZHANG, Yujing WENG, Yulong ZHANG. Study on catalytic combustion performance of CO over Sn-modified CuCeOx catalysts under high humidity conditions[J]. Journal of Fuel Chemistry and Technology, 2026 , 54 (9) : 20250391-1861 -20250391-1872 . DOI: 10.1016/S1872-5813(26)60689-5
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Carbon monoxide (CO) is a common and highly hazardous pollutant that poses significant threats to human health due to its flammability and explosive properties[1−2]. Excessive emissions of CO can also indirectly exacerbate global warming and deplete the ozone layer[3]. Although CO is colorless, odorless, and non-irritating, it can bind with human hemoglobin, reducing the oxygen-carrying capacity and leading to hypoxia or even fatal shock[3]. Data from the Global Burden of Disease Study (GBD 2021) showed that the global number of deaths from accidental CO poisoning was approximately 28900[4]. CO poisoning is a common incident in confined spaces such as ships, coal mines, submarines, and underwater channel work areas. However, the removal of CO still faces challenges due to factors such as complex atmospheric composition and high humidity in these environments. Therefore, there is an urgent need to research and develop CO purification technologies suitable for high-humidity conditions. CO purification technologies mainly include physical adsorption[5], catalytic oxidation, photocatalysis and others. Among these, catalytic oxidation is widely used in the environmental removal of CO due to its high cost-effectiveness. Therefore, it is crucial to design CO removal catalysts with high activity and high cost-performance ratio. Many scholars have found that supported noble metal catalysts (such as Au[6−7], Pd[8−10], Pt[11], Ru) exhibit high catalytic activity, but they generally suffer from the problems of easy deactivation and low economic efficiency. Transition metal catalysts, especially cerium-based metal oxides, have become important catalysts in CO purification technologies due to their high cost-effectiveness and good stability[12−14].
In the past few decades, ceria has been widely used in catalysts for CO oxidation due to its unique high oxygen storage capacity (OSC) and high oxygen mobility. The catalytic combustion performance of copper-doped ceria catalysts is particularly remarkable. Lee et al.[15] found that the bimetallic oxide catalyst constructed by introducing copper into ceria enhanced the interaction between copper and ceria, enriched the surface defects of ceria, and improved its oxidation capacity. Furthermore, methods such as oxide loading and non-metallic atom doping can alter the local chemical environment of the catalyst surface or interface, thereby improving its catalytic oxidation performance and stability for CO[16–17]. For example, the addition of promoters such as cobalt, tin and iron to CuCeOx catalysts can affect the specific surface area, particle size, and active site distribution of the catalyst, thereby effectively improving the low-temperature activity of CO oxidation catalysts. Li et al.[18] found that due to the n-type semiconductor characteristics of SnO2, doping Sn into Cu-based catalysts can enhance the electron transfer capacity of the catalysts. In addition, SnO2 can effectively inhibit the adsorption of water molecules on the catalyst surface, thereby improving the catalytic stability of the catalyst[19]. Owing to the complex properties of polymetallic oxides, although it has been proven that Sn doping can alter the properties of catalysts, its specific role in the CO oxidation reaction process remains unclear. However, the development of characterization techniques, specifically high-resolution imaging of transmission electron microscopy (TEM) and high spatial resolution of X-ray photoelectron spectroscopy (XPS), has made this possible, which is of great significance for deeply understanding the structure-performance relationships, intrinsic nature of active sites and catalytic reaction mechanisms of catalysts, as well as exploring strategies for further enhancing catalytic efficiency.
To improve the water resistance of CuCeOx catalysts for CO catalytic oxidation reaction and investigate the regulatory mechanism of Sn doping on their redox ability and electron transfer capacity, a series of Sn-doped CuCeOx catalysts with different Sn contents were prepared by the excess impregnation method in this study, aiming to improve their catalytic oxidation performance and moisture resistance. A series of systematic characterization techniques including XRD, BET, TEM, H2-TPR, XPS, O2-TPD, CO-TPD and CO-TPSR were employed to clarify the mechanism by which Sn doping regulates the structure, electronic properties, and surface reaction behaviors of CuCeOx catalysts, thereby providing a theoretical basis for understanding its influence mechanism on the catalytic oxidation activity, selectivity, and long-term stability of CO over CuCeOx catalysts under humid conditions. This study also offers technical support for the design of high-performance Cu-based catalysts with water and poisoning resistance, and further lays a foundation for optimizing theprocess of low-temperature catalytic oxidation for CO removal.
1　Experimental
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1.1　Preparation of catalysts
A certain amount of Ce(NO3)2·6H2O was placed in a crucible and spread evenly, and then the crucible was put into a muffle furnace. The temperature was raised from room temperature to 350 °C at a heating rate of 2 °C/min and maintained at this temperature for 2 h. The obtained pale yellow solid powder was denoted as CeO2.
Based on 2 g of CeO2, the corresponding mass of copper nitrate (Cu(NO3)2·3H2O) was calculated and weighed according to the mass fractions of Cu relative to CeO2 (1%, 4%, 6%, 8%, 10% respectively). The weighed copper nitrate was dissolved in deionized water to prepare a 2 mL solution, followed by ultrasonic treatment for 5 min to achieve uniform dispersion. Subsequently, 2 g of CeO2 was placed in a mortar, and the above solution was added dropwise with a dropper at 5 min intervals. Meanwhile, thorough grinding was performed to ensure uniform mixing, and this operation was repeated until the entire solution was added dropwise. The resulting mixture was placed in a drying oven at 100 °C for overnight drying, and finally transferred to a muffle furnace. The temperature was increased to 400 °C at a heating rate of 5 °C/min and calcined at this temperature for 6 h, thus preparing the CuCeOx catalysts.
Using the optimized CuCeOx catalyst as the precursor, the Sn component was introduced via the excess impregnation-grinding method. 2 g of CeO2 was subjected to dropwise grinding impregnation with a mixed solution of Cu(NO3)2 and Sn(NO3)4 at a specific concentration. The impregnation method was consistent with the above-mentioned method: the above solution was added dropwise with a dropper at 5 min intervals, and thorough grinding was performed simultaneously to ensure uniform mixing, and this operation was repeated until the entire solution was added dropwise. The resulting mixture was placed in a drying oven at 100 °C for overnight drying, and finally transferred to a muffle furnace. The temperature was raised to 400 °C at a heating rate of 5 °C/min and calcined at this temperature for 6 h, thus preparing the CuCeOx-Sn catalysts. By adjusting the loading amount of Sn, a series of samples were prepared and named CuCeOx, CuCeOx-Sn0.05, CuCeOx-Sn0.1, CuCeOx-Sn0.2 and CuCeOx-Sn0.5 according to the mass fractions of Sn relative to CuCeOx (0, 5%, 10%, 20%, 50%), respectively.
1.2　Characterization methods
X-ray diffraction (XRD) was employed to characterize the crystal phases of the catalysts, with Cu Kα radiation (λ = 1.5418 Å) used, operating at a voltage of 40 kV and a current of 40 mA. The 2θ scanning range was set from 10° to 90° with a scanning rate of 10(°)/min. N2 physisorption was performed on a Micromeritics ASAP-2020 M instrument at −196 °C. The samples were degassed under vacuum at 150 °C for 2 h prior to the test. The specific surface area (SBET) and pore size distribution were calculated by the Brunauer-Emmett-Teller (BET) method and the Barrett-Joyner-Halenda (BJH) desorption method, respectively. The surface elements and chemical states of the catalysts were characterized by X-ray photoelectron spectroscopy (XPS) on a Thermo Scientific K-Alpha electron spectrometer, which was equipped with an Al Kα radiation source (hν = 1486.6 eV) operating at a working voltage of 12 kV. All binding energies were calibrated with the standard C 1s peak (284 eV) as the reference.
The reduction performance of the catalysts was characterized by hydrogen temperature-programmed reduction (H2-TPR) using a Micromeritics AutoChem II chemisorption analyzer. Approximately 0.5 g of the catalyst sample was accurately weighed and placed in a quartz U-shaped reaction tube, and its position was fixed with quartz wool. Prior to the start of the test, the catalyst was first pretreated at 150 °C for 30 min under an Ar atmosphere (flow rate: 40 mL/min) to completely remove physically adsorbed impurities on the surface. Subsequently, in an atmosphere of 5% H2/95% Ar mixed gas (flow rate: 40 mL/min), the sample was heated programmatically from 50 to 800 °C at a heating rate of 10 °C/min. A thermal conductivity detector (TCD) was used to monitor the hydrogen consumption signal in real time during the experiment, and pure CuO was employed as a reference sample to calibrate the detection signal.
CO temperature-programmed desorption (CO-TPD) experiments were conducted using an AutoChem II 2920 chemisorption analyzer to investigate the effect of Sn loading amount on the CO adsorption capacity of the catalysts. The specific procedures are as follows: 0.5 g of the sample was placed in a quartz reactor, pretreated in a He atmosphere at 300 °C for 2 h first, and then exposed to a 10% CO/90% He mixed gas with a flow rate of 30 mL/min for adsorption at room temperature for 1 h. Subsequently, the system temperature was raised to 50 °C, and physically adsorbed CO molecules were removed by purging with a pure He gas flow of 30 mL/min for 30 min. Finally, the CO-TPD test was carried out by heating the system programmatically from 50 to 700 °C at a heating rate of 10 °C/min under a pure He atmosphere with a flow rate of 30 mL/min. Oxygen temperature-programmed desorption (O2-TPD) measurements were performed to investigate the effect of Sn loading amount on the oxygen properties of the catalysts. The experimental procedure was basically the same as that for CO-TPD, except that the catalyst treated under an inert atmosphere was saturated by adsorption in 3% O2/97% He with a flow rate of 30 mL/min prior to the O2-TPD experiment.
Temperature-programmed surface reaction (CO-TPSR) experiments were conducted to investigate the surface reaction activity of the CuCeOx-Sn catalysts. During the experiment, 0.5 g of the sample was first held at 350 °C in an inert He atmosphere for approximately 1 h to remove impurities adsorbed on the catalyst surface. Subsequently, the system was cooled to room temperature, and a 10% CO/90% He mixed gas was introduced for 30 min of adsorption at this temperature. After that, the gas was switched to He for purging to remove physically adsorbed CO molecules on the catalyst surface. Finally, the temperature was raised programmatically to 800 °C at a rate of 10 °C/min in a 3% O2/97% He atmosphere, and a mass spectrometer was used to monitor the changes in product signals in the tail gas in real time (O2: m/z = 32, CO2: m/z = 44).
1.3　Performance evaluation
1.3.1　Evaluation of CO oxidation activity in a fixed-bed reactor
The catalytic reaction setup used in this experiment is shown in Figure 1. The CO oxidation activity of the catalysts was evaluated in a fixed-bed reactor in this experiment. 0.2 g of the 40–60 mesh catalyst was loaded into the middle of the reaction tube, and both ends were fixed with quartz wool. Under atmospheric pressure, 80 mL/min of air and 20 mL/min of a 20% CO/80% N2 mixed gas were introduced into the reaction system, maintaining the volume fraction of CO in the reaction atmosphere in the range of 1%–4%, with a weight hourly space velocity (WHSV) of 30000 mL/(g·h). The regulation of different water contents was achieved by the following method: the reaction mixed gas was passed through a bubble column to introduce water vapor, and the temperature of the bubble column was precisely controlled by a water bath, thereby adjusting the water content in the atmosphere. The reaction temperature was raised programmatically from room temperature at a rate of 2 °C/min, and held isothermally for 30 min for every 10 °C increase to ensure the reaction reached a steady state. The CO2 concentration in the outlet gas was monitored in real time using a CO2 sensor, and the CO conversion rate (xCO) was calculated according to the following formula (1)[20−21]:
$ {{x}}_{\text{CO}}=\frac{\left({{n}}_{\mathrm{CO},\text{in}}-{{n}}_{\mathrm{CO},\text{out}}\right)}{{{n}}_{\mathrm{CO},\text{in}}}{\times }100{\% } $
In the above formula, $ {n}_{{\mathrm{CO,in}}} $ represents the CO content in the inlet mixed gas, and $ {n}_{{\mathrm{CO,out}}} $ denotes the CO content in the outlet mixed gas.
$ {r}_{{\mathrm{CO}}}=\frac{{{x}}_{\text{CO}}\times {F}_{{\mathrm{in}}}\times {C}_{{\mathrm{CO}}}\times 60}{22400} $
The formula for calculating the CO reaction rate in this experiment is given by Equation (2), where $ {r}_{{\mathrm{CO}}} $ (mol/h) represents the CO reaction rate, $ {{x}}_{\text{CO}} $ denotes the CO conversion, and $ {F}_{{\mathrm{in}}} $ (mL/min) stands for the inlet gas flow rate and $ {C}_{{\mathrm{CO}}} $ is the CO concentration in the gas.
1.3.2　Long-term stability and water tolerance test
A stability test was performed using 0.2 g of catalyst under a total flow rate of 100 mL/min (reaction conditions: 0.1 MPa, 2% CO in the reaction atmosphere, 30000 mL/(g·h)). Initially, CO catalytic oxidation was carried out under dry conditions by heating the catalyst at a ramp rate of 2 °C/min and holding for 30 min at each 10 °C increment until CO conversion no longer increased with temperature, indicating that the reaction had essentially reached completion. The temperature was then maintained constant for 5 h to assess initial steady-state performance. Subsequently, water vapor was introduced into the feed gas, adjusting the moisture content to 3.8% H2O. The same stepwise temperature-ramping procedure was repeated until CO conversion reached a plateau and the outlet CO concentration stabilized. The system was then kept at this temperature for an additional 5 h to evaluate catalyst stability under humid conditions. Finally, the water vapor supply was stopped, and the reaction temperature was gradually decreased until the CO conversion stabilized again. The catalyst was maintained at this temperature for a further 5 h to examine its activity recovery after water removal. Throughout the test, CO conversion was monitored continuously to comprehensively assess the long-term stability and water tolerance of the catalyst.
2　Results and discussion
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2.1　Catalyst performance testing
In this study, the reaction temperatures corresponding to 50% and 90% CO conversion rates (t50 and t90) in the CO catalytic combustion reaction were used as the main evaluation indicators for catalytic oxidation activity.
To investigate the influence of copper loading on catalytic performance, a series of CuCeOx catalysts with varying Cu contents were systematically evaluated under identical reaction atmosphere and space velocity conditions. As shown in Figure S1, both the t50 and t90 for CO catalytic oxidation decreased with increasing Cu loading, indicating that higher Cu content effectively enhances the low-temperature activity of the catalyst. However, when the Cu loading exceeded 6%, the downward trend in t50 and t90 leveled off, and the values slightly increased compared to those of the sample with 6% Cu. Therefore, an optimal Cu loading of 6% was identified for the CO oxidation reaction, under which the catalyst exhibited the best low-temperature catalytic performance.
Given that an appropriate amount of promoter can improve the water resistance of Cu-based catalysts, different contents of Sn were introduced into the CuCeOx catalyst in the experiment, and its catalytic performance was evaluated in a mixed reaction atmosphere containing water vapor. As shown in Figure 2(a) and 2(b), the CO conversion rate showed no significant change when the reaction temperature was below 50 °C, indicating that catalysts with different Sn loadings exhibited no significant catalytic activity for CO combustion in this temperature range. When the temperature exceeded 50 °C, the CO conversion rate increased rapidly with the rise in temperature. Notably, as the Sn loading increased from 0 to 0.5%, t50 and t90 exhibited a typical “inverted volcano-shaped” variation trend (Figure 2(a)), reaching the minimum values at a Sn loading of 0.1%, which indicates that the catalyst achieved the optimal CO catalytic combustion activity under this condition. From the perspective of reaction rate, the catalytic combustion reaction rate was significantly increased after the introduction of Sn compared with the catalyst without Sn doping; Furthermore, at the same reaction rate, the catalyst with 0.1% Sn loading required the lowest reaction temperature, which further confirms that it exhibits excellent CO catalytic combustion performance under low-temperature conditions. Within a certain loading range, the catalyst performance was significantly improved with the increase in Sn content; however, when the Sn loading exceeded 0.1%, the performance improvement tended to level off, and t50 and t90 even increased slightly. In practical industrial applications and motor vehicle exhaust treatment, the CO catalytic combustion reaction is often carried out in a water-containing atmosphere, and the presence of water vapor can significantly inhibit the CO oxidation performance of Cu-based catalysts. Specifically, H2O molecules can undergo competitive adsorption at active sites, hindering the adsorption and activation of CO. To investigate the effect of water vapor on catalytic performance, the CuCeOx-Sn0.1 catalyst with the optimal activity was selected in this study, and experiments were conducted by introducing different contents of water vapor into the feed gas, with the results shown in Figure 3(a) and 3(b). With the increase in water vapor content, the CO catalytic combustion activity was significantly inhibited, and t50 and t90 showed an overall upward trend, which confirms the negative effect of water vapor. Notably, the catalyst maintained a low t90 (below 140 °C) at different water vapor contents, indicating that it possesses good water resistance. From the perspective of the change in reaction rate (Figure 2(d)), the increase in water vapor content led to a gradual decrease in the catalytic reaction rate, which further verifies its inhibitory effect on the activity. In addition, the optimal catalyst in this study was compared in terms of performance with typical catalysts reported in the literature[22] (Table S1). The data show that the temperatures for 50% conversion (t50) and 90% conversion (t90) of the catalyst in this study are lower than the values reported in the literature under both water vapor-containing and dry reaction conditions, demonstrating more excellent low-temperature catalytic activity.
The catalytic performance at different space velocities to identify the general trend was evaluated. As shown in the Figure S2, the catalytic performance varied with space velocity: the t90 value first decreased and then increased with increasing space velocity. Therefore, 30000 mL/(g·h) was chosen as it corresponds to a relatively low t90.
To evaluate the stability of the CuCeOx-Sn0.1 catalyst under water-containing conditions, a stability test was conducted in a water vapor atmosphere (Figure 4). The results show that: under water-free conditions, the CO conversion rate reached 90% when the temperature rose to 80 °C and remained stable for 8 h; subsequently, 3.8% H2O was introduced, and t90 increased slightly, but the catalyst still maintained stable performance for the subsequent 8 h at the same reaction temperature; Finally, after the water vapor was removed, t90 recovered to the initial level and remained stable for the subsequent 8 h, which indicates that the catalyst can maintain stability under the switching of water-containing and water-free environments.
2.2　Study on the structure-activity relationship between catalyst performance and structure
2.2.1　Analysis of pore channel characteristics
As can be observed from Figure S3, the adsorption isotherms of all samples exhibit a typical Type IV isotherm with a Type H3 hysteresis loop. This can be attributed to capillary condensation occurring inside the slit-shaped porous structure formed by the aggregation of oxide particles. The different gaps in the hysteresis loop are due to the changes in the pore structure of the catalyst[9]. As shown in Table S2, the doping of Sn increases the specific surface area and pore volume of the CuCeOx catalyst. With the increase in Sn content, the specific surface area of the catalyst increases from 61.6 to 80.0 m2/g, and the pore volume increases from 0.0295 to 0.0399 cm3/g. Among these catalysts, the CuCeOx-Sn0.1 catalyst exhibits a uniform pore size distribution and the largest pore volume, indicating that the CuCeOx-Sn0.1 catalyst has a similar particle size and excellent pore structure. As can be seen from Table S1, the pore size of the CuCeOx catalyst is mainly concentrated in the range of 2−15 nm, which further confirms the existence of a mesoporous structure (2−50 nm), and this is mostly attributed to the agglomerated pores of secondary particles.
The pore size in metal oxide catalysts mainly depends on the size of secondary particles and the interaction force between oxides. A large specific surface area and excellent pore structure can significantly increase the number of active sites and promote the mass transfer of reactants[23]. Therefore, the CuCeOx-Sn0.1 catalyst with a large specific surface area and uniform pore size distribution after Sn doping exhibits more excellent CO catalytic combustion performance. The reasons why the CuCeOx-Sn0.1 catalyst achieves the lowest t50 and t90 in the performance evaluation test shown in Figure 2(a) are elaborated from the perspective of pore channel characteristics.
2.2.2　Analysis of crystal structure and reducibility
To investigate the effect of Sn doping on the crystal structure of CeCuOx, XRD characterization was performed on the catalysts, and the results are shown in Figure 5(a). The XRD patterns show that all samples exhibit the characteristic diffraction structure of cubic CeO2. The diffraction peaks appearing at 2θ = 14.3°, 29.5°, 34.7°, 47.7° and 57.4° correspond to the (111), (222), (400), (511) and (531) crystal planes of CeO2, respectively. In addition, characterization analyses were performed on the catalyst samples before and after the reaction under different water content treatment conditions (Figure S4). The results show that the positions and relative intensities of the diffraction peaks of all samples remain basically unchanged, indicating that the crystal structure of the catalyst does not change during the reaction, which confirms its excellent stability. Notably, the introduction of Sn significantly enhances the diffraction peak intensity of the CuCeOx catalyst, indicating that Sn doping promotes the formation of metal oxide crystal phases and the improvement of crystallinity. The doping of Sn also enhances the activity of oxygen species on the catalyst surface, which can be further verified by the results of the H2-TPR test (Figure 5(b)). Reported literature indicates that the initial reduction temperature of pure CeO2 is approximately 350 °C, and thus the reduction peaks below 350 °C are mainly associated with the reduction of CuO species[24]. Depending on the differences in coordination environment and valence state, the Cu species in the catalyst exhibit diverse reduction behaviors. Two distinct reduction peaks can be observed in the CuCeOx sample: among them, the strong reduction peak at approximately 239 °C corresponds to the reduction of bulk CuO particles. After the introduction of Sn, the reduction behavior of the catalyst changes significantly. Based on the comparison of the peak areas of each reduction peak, the reducibility of the catalysts can be ranked as follows: CuCeOx-Sn0.1 > CuCeOx-Sn0.2 > CuCeOx-Sn0.5 > CuCeOx-Sn0.05 > CuCeOx. When the Sn content is 0.1%, the CuCeOx-Sn0.1 catalyst not only exhibits a lower initial reduction temperature (approximately 129 °C) but also has a larger reduction peak area, indicating that the reactivity of oxygen species on its surface is enhanced. In addition, compared with Sn-undeficient CuCeOx, its reduction temperature is shifted forward by approximately 30 °C, which confirms that Sn doping effectively improves the reducibility of the catalyst and promotes the migration of electrons inside the catalyst. The optimal reducibility exhibited by CuCeOx-Sn0.1 is closely related to its enhanced electron transfer capacity, which provides an important foundation for its high activity in the CO catalytic combustion reaction.
2.2.3　Effect of chemisorption and desorption behaviors of reactant molecules (CO and O2) on catalytic performance
To clarify the effect of Sn content on the CO and O2 adsorption-desorption behaviors of CuCeOx-Snx catalysts, CO-TPD and O2-TPD were conducted and the relevant results are shown in Figure 5(c). CO molecules are first adsorbed and activated on the catalyst surface, then react with active surface oxygen or lattice oxygen to form CO2, and the consumed oxygen sites are replenished and regenerated by gaseous O2[25]. Therefore, the CO adsorption capacity of the catalyst has an important influence on its overall catalytic performance. A typical CO desorption peak appears at approximately 100 °C for all catalysts, which corresponds to the weak chemisorption process of CO. Compared with the CuCeOx catalyst without Sn addition, the peak temperature of the CO desorption peak shows a “volcano-type” variation trend after the introduction of Sn, and reaches the maximum value when the Sn content is 0.1% (CuCeOx-Sn0.1). This phenomenon indicates that the introduction of an appropriate amount of Sn enhances the desorption strength of CO on the catalyst surface, which helps to promote the sufficient reaction between CO and surface oxygen species, thereby improving its activity in the CO catalytic combustion reaction. As shown in Figure 5(d), the O2-TPD method was used to analyze the activation and migration capacity of oxygen species in the catalyst. According to the differences in desorption temperature, the O2-TPD curves can usually be divided into three regions: the α region (< 200 °C) corresponds to the desorption of surface chemisorbed oxygen, the β region (200–550 °C) is attributed to surface lattice oxygen, and the γ region (> 550 °C) reflects the release behavior of bulk lattice oxygen[26]. The bulk lattice oxygen desorption peak of the unmodified CuCeOx catalyst is at 707 °C, while the introduction of Sn significantly enhances the dissociation tendency of surface and bulk lattice oxygen. This phenomenon can be attributed to the fact that Sn doping weakens the bonding interaction between Ce and Cu atoms, thereby reducing the stability of lattice oxygen and promoting its migration. Compared with other catalysts, CuCeOx-Sn0.1 exhibits the optimal oxygen activation performance: the temperatures of its α and β desorption peaks are the lowest, indicating that surface adsorbed oxygen and surface lattice oxygen are more prone to desorption and participation in the reaction. This characteristic directly contributes to the highest reaction activity of CuCeOx-Sn0.1 in CO catalytic combustion.
2.2.4　Microstructure analysis
To further investigate the microstructure of CuCeOx, TEM characterization was conducted. As shown in Figure 6(a1) and (b1), clear lattice fringes can be observed, corresponding to the characteristic crystal planes of CuO and CeO2, respectively, with the measured lattice spacings of approximately 0.27 nm (CuO) and 0.31 nm (CeO2). Moreover, CuO and CeO2 are in an inter-doped state, which indicates the presence of CuO and its close contact with CeO2, and this result verifies the analysis results of XRD and H2-TPR. After diffraction analysis was performed on the (a1) and (b1) images, the corresponding diffraction patterns (a3) and (b3) were obtained. Among them, the positions of the characteristic diffraction peaks of CuO and CeO2 are completely consistent with the lattice spacing results measured in the aforementioned (a1) and (b1) images. In addition, the results of elemental distribution characterization show that the Cu and Ce elements are uniformly distributed in the catalyst. Combined with the XRD analysis results, this phenomenon indicates that Cu species are highly dispersed on the surface of the CeO2 support.
2.2.5　Analysis of elemental composition and chemical valence states
As shown in Figure 7 below, the surface composition, chemical states and oxygen species of the CuCeOx-Snx catalysts were analyzed by XPS. The surface elemental composition of the catalysts obtained from the fitting calculation of XPS curves is summarized. As shown in Figure 7(c), the Cu 2p XPS spectra of all catalysts exhibit two characteristic peaks, and the peaks at 930.6–937.5 and 949.2–957.9 eV are attributed to Cu2+[27–28]. The oxidation state of Sn was analyzed by fitting the Sn 3d spectra (Figure 7(d)). The Sn 3d spectra of the prepared catalysts can be fitted into two peaks located at the binding energies of 495 and 487 eV[29]. Table 1 lists the surface contents of Sn2+ and Sn4+, among which the CuCeOx-Sn0.1 catalyst has the highest Sn4+/(Sn2+ + Sn4+) ratio. The O 1s XPS spectrum shows three distinct peaks corresponding to surface lattice oxygen OL (529.7 eV), surface chemisorbed oxygen OS (530.9 eV) and hydroxyl oxygen Oγ (532.1 eV). Compared with the CuCeOx catalyst, the CuCeOx-Sn0.1 catalyst exhibits higher contents of OS (44.8%) and Oγ (11%), which is consistent with the result of the lower desorption peak temperature of surface adsorbed oxygen in the O2-TPD curves. In addition, the OS/OL ratio of 1.01 is significantly higher than that of other catalysts, indicating that it has a higher content of surface active oxygen, which indirectly proves the presence of more oxygen vacancies on the catalyst surface. The deconvolution of the Ce 3d XPS spectra of the five catalysts yields eight peaks.
The u peaks are attributed to the characteristic peaks of Ce3+, while the v peaks are assigned to the characteristic peaks of Ce4+, indicating that Ce3+ and Ce4+ coexist in the catalysts. As shown by the Ce3 +/(Ce3 ++Ce4 +) ratio in Table 1, the CuCeOx-Sn0.1 catalyst contains a higher content of Ce3+ species. This further confirms the presence of more oxygen vacancies in CuCeOx-Sn0.1. In summary, abundant oxygen species, excellent electron transfer capacity, and more CO adsorption sites are the main reasons for the outstanding activity and stability of the CuCeOx-Sn0.1 catalyst in a high-humidity environment.
2.2.6　Study on the dynamic evolution of CO catalytic combustion reaction pathways on catalyst surfaces by CO-TPSR
To investigate the influence of surface active oxygen species on the CO catalytic combustion surface reaction over the CuCeOx-Sn catalysts, CO-TPSR characterization analysis was carried out, and the results are shown in Figure 8. All catalysts start to generate CO2 at around 100 °C (Figure 8(a)), indicating that the CO oxidation reaction has occurred in this temperature range. Among them, the CuCeOx-Sn0.1 catalyst exhibits the lowest CO2 generation peak temperature (approximately 185 °C), which is about 15–20 °C lower than that of other catalysts, directly indicating that it has the optimal low-temperature CO oxidation performance. Combined with the analysis results of XPS and O2-TPD, the CuCeOx-Sn0.1 catalyst has the highest ratio of surface adsorbed oxygen (OS) to lattice oxygen (OL) (0.442), indicating that the introduction of Sn promotes the generation of surface active oxygen species. Meanwhile, the Ce3+/(Ce3++Ce4+) ratio increases to 25.3%, which further confirms the formation of more oxygen vacancies and provides favorable conditions for oxygen activation. The above characterization results are highly consistent with the phenomena observed in the O2-TPD analysis, and the desorption peaks all shift towards lower temperatures, indicating that the migration capacities of both surface chemisorbed oxygen and surface lattice oxygen are significantly enhanced. From the O2 consumption curves (Figure 8(b)), the CuCeOx-Sn0.1 catalyst shows a distinct O2 consumption peak at 135 °C. The lower O2 consumption temperature indicates that the catalyst can achieve the adsorption-activation-conversion cycle of gas-phase oxygen under mild conditions, providing a sufficient source of active oxygen for the continuous CO oxidation reaction. The systematic characterization results of XRD, BET, TEM, H2-TPR, XPS, O2-TPD, CO-TPD and CO-TPSR mentioned above jointly reveal the intrinsic reasons for the excellent performance of the CuCeOx-Sn0.1 catalyst. The introduction of Sn effectively increases the concentration of surface oxygen vacancies, promotes the activation and migration of oxygen species, and the rapid cycling and continuous replenishment of surface active oxygen species enable the catalyst to maintain stable CO oxidation activity even in a water-containing atmosphere.
3　Conclusions
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In this work, CuCeOx-Sn catalysts were prepared via incipient wetness impregnation using CeO2 as the support and evaluated for low-temperature CO catalytic combustion. With Sn loading increasing from 0 to 0.5%, the t50 and t90 followed an inverted volcano trend, reaching minima at 0.1% Sn loading, corresponding to optimal catalytic activity. Elevated water vapor content inhibited CO oxidation, yet all catalysts retained a low t90 (< 140 °C) with stable performance under alternating humid/dry atmospheres, demonstrating good water resistance. XPS, O2-TPD, CO-TPD and CO-TPSR characterizations revealed that appropriate Sn doping increased surface oxygen vacancy concentrations, promoted oxygen species activation and migration, and enhanced CO desorption strength. This facilitated sufficient reaction between CO and surface oxygen species, enabling rapid cycling and replenishment of active oxygen species. Consequently, the optimized CuCeOx-Sn0.1 catalyst exhibited superior performance and water tolerance, providing a novel strategy for CO catalytic oxidation under high-humidity, low-temperature conditions.
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Year 2026 volume 54 Issue 9
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Article Info
doi: 10.1016/S1872-5813(26)60689-5
  • Receive Date：2025-12-05
  • Online Date：2026-09-23
  • Published：2026-09-10
Article Data
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History
  • Received：2025-12-05
  • Revised：2026-01-08
  • Accepted：2026-01-15
Affiliations
    Henan Key Laboratory of Coal Green Conversion, and International Joint Laboratory of Coal Clean Utilization, College of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo 454003, China

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表12种不同金属材料的力学参数
科
Family		 属数
Number of
genus		 种数
Number of
species		 占总种数比例
Percentage of
total species (%)		 属
Genus		 种数
Number of
species		 占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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