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Influence of Si/Al ratio of MFI zeolites on the microstructure and catalytic performance of Co-based catalyst for N2O decomposition
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Jiajun MA1, 2, Liangliang ZHANG2, *, Ruifang WU2, Xiangqian LIN3, Minxia YANG1, 2, Guangyun ZHU1, 2, Ke ZHENG2, Yongzhao WANG1, 2, *
Journal of Fuel Chemistry and Technology | 2026, 54(8) : 20250331-1730 - 20250331-1741
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Journal of Fuel Chemistry and Technology | 2026, 54(8): 20250331-1730-20250331-1741
• RESEARCH PAPER •
Influence of Si/Al ratio of MFI zeolites on the microstructure and catalytic performance of Co-based catalyst for N2O decomposition
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Jiajun MA1, 2, Liangliang ZHANG2, *, Ruifang WU2, Xiangqian LIN3, Minxia YANG1, 2, Guangyun ZHU1, 2, Ke ZHENG2, Yongzhao WANG1, 2, *
Affiliations
  • 1College of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China
  • 2Research Center for Fine Chemicals Engineering, Ministry of Education, Shanxi University, Taiyuan 030006, China
  • 3Shanxi Dongjin Fertilizer Industry Co., LTD., Lüliang 030500, China
Published: 2026-08-10 doi: 10.1016/S1872-5813(26)60668-8
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A series of Co-based molecular sieve catalysts with different Si/Al ratios was prepared by the impregnation method. The microstructure properties of Co active sites were finely characterized by means of XRD, TEM, Raman, H2-TPR, Py-FTIR and XPS technology. The results show that the surface Co species mainly exist in the form of CoOx nanoclusters and isolated Co2+, and the latter exhibits better N2O decomposition activity. Decreasing the Si/Al ratio of the MFI zeolite promotes the generation of isolated Co2+ active sites, thereby enhancing the catalytic activity. Compared with the Co/S-1 catalyst with pure silicon S-1 carrier, the Co/HZ60 with a low Si/Al ratio of ZSM-5 carrier reduces the temperature required for complete N2O decomposition by 80 °C, and it shows excellent resistance to O2 and NO.

zeolite  /  Si/Al ratio  /  Isolated Co2+  /  N2O decomposition
马佳军, 张亮亮, 武瑞芳, 蔺向前, 杨旻霞, 祝广昀, 郑珂, 王永钊. 分子筛硅铝比对活性Co物种微结构及催化N2O分解性能的影响. 燃料化学学报（中英文）, 2026 , 54 (8) : 20250331-1730 -20250331-1741 . DOI: 10.1016/S1872-5813(26)60668-8
Jiajun MA, Liangliang ZHANG, Ruifang WU, Xiangqian LIN, Minxia YANG, Guangyun ZHU, Ke ZHENG, Yongzhao WANG. Influence of Si/Al ratio of MFI zeolites on the microstructure and catalytic performance of Co-based catalyst for N2O decomposition[J]. Journal of Fuel Chemistry and Technology, 2026 , 54 (8) : 20250331-1730 -20250331-1741 . DOI: 10.1016/S1872-5813(26)60668-8
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N2O is one of the atmospheric pollutant gases, which can induce meteorological disasters, such as photochemical smog, acid rain and haze, and damage the ozone protective layer, causing great harm to the environment[1]. In addition, N2O is also a strong greenhouse gas, its latent heat of heating per molecule is about 265 times that of CO2[2]. Agricultural fertilization, fossil fuel combustion, and chemical production processes such as nitric acid and adipic acid are the main anthropogenic sources of N2O emissions[3−4]. Under the impetus of the national “dual carbon” policy, it is imperative to promote pollution control and carbon emission in the nitric acid and adipic acid production process. Direct catalytic decomposition technology, with its advantages of simplicity, low cost, high efficiency and no secondary pollution, is regarded as the most ideal method for reducing N2O emissions at present. Noble metal catalysts, metal oxide catalysts and molecular sieve catalysts are the three mainstream types of N2O direct decomposition catalysts[5−7]. However, although precious metal and metal oxide catalysts show high catalytic performance at relatively low temperatures, their activity is severely affected by impurity gases such as NOx, O2 and H2O. Additionally, the high cost of precious metals hinders their large-scale industrial application[8−10]. In contrast, molecular sieve catalysts loaded with transition metals have regular channels and stable active sites, which can effectively suppress the influence of impurity gases and showing great application potential in N2O catalytic decomposition reactions[11−12].
It was reported that the metal ions anchored on the surface of the molecular sieve carrier are the main active centers for N2O catalytic decomposition, and the reaction process involves redox cycles of metal ions. Taking ion-exchanged Co/ZSM-5 as an example, the reaction proceeds as follows: N2O molecules adsorb on Co2+ sites, oxidizing them to Co3+ while cleaving the N−O bond to release N2 and form Co3-O species (Eq.(1)). After that, two Co3+O− species migrate and recombine on the surface of the catalyst desorbing O2 and reducing back to Co2+, (Langmuir-Hinshelwood mechanism, Eq.(2)). In addition, Co3+O− species can also react with another gas-phase N2O molecules facilitating N−O bond cleavage to yield N2 and O2 while reducing Co3+ to Co2+ (Eley-Rideal mechanism, Eq.(3))[13−14]. Among them, the O2 desorption process (Eq.(2) and Eq.(3)) is regarded as the rate-controlling step of the reaction[15].
$ {\text{N}}_{\text{2}}{{\mathrm{O + Co^{2+}}}\to}{\text{N}}_{\text{2}}{+ {\mathrm{Co^{3+}O^-}}} $
$\begin{split} &{\mathrm{Co^{3+}O^-+ Co^{3+}O^- \to {O}_2+ 2 Co^{2+}}}\\&\qquad ({\mathrm{Langmuir\text{-}Hinshelwood\;mechanism}}) \end{split}$
$ \begin{split} & {\mathrm{Co^{3+}O^- + N_{{2}}O \to {{O}}_{{2}}+{N}_{{2}}+ Co^{2+}}}\\&\qquad ({\mathrm{Eley\text{-}Rideal\;mechanism}})\end{split} $
The microscopic electronic structure of Co active species and their distribution in molecular sieve carriers are important factors affecting their catalytic activity, which is closely related to the structural properties of the molecular sieve carrier itself and the method of Co species incorporation[16−18]. Shortening the pore length of zeolite and increasing their specific surface area are conducive to the dispersion of active Co species, thereby enhancing their contact with N2O molecules and improving catalytic activity[19]. Ghahri et al.[20] found that the acid treatment of zeolite could significantly increase their specific surface area and inhibit the agglomeration of cobalt species, which significantly enhanced the N2O decomposition performance. Kang et al.[17] found that the three-dimensional pore structure of the ZSM-5 is more conducive to the dispersion of Co species than that of ZSM-23 with a one-dimensional ten-membered ring pore structure. The experimental result showed that the catalytic activity of Co/ZSM-5 for N2O decomposition is almost twice that of the Co/ZSM-23 catalyst under the reaction conditions of 450 °C, 30% N2O and GHSV = 30000 h−1. Zhang et al.[21] regulated the distribution of Al atoms in the ZSM-5 skeleton by modulating the silicon and aluminum sources in the synthesis system, and found that Co2+ located in sinusoidal channels was more active than that located in straight or intersection channels and formation of smaller, highly dispersed Co active sites. Dong et al.[22] reported that the type of cobalt source significantly affects the physicochemical properties of Co species and their catalytic performance for N2O decomposition. Compared with cobalt nitrate and cobalt acetate, using cobalt chloride as the cobalt source is more conducive to the generation of Co2+ and the decomposition of N2O. Because of the skeleton Al atom is the main anchoring site for alien Co species, the Si/Al ratio of zeolite significantly affects the microstructure of Co species and their catalytic performance for N2O decomposition[23−25]. Zhai et al.[16] found that a higher Si/Al ratio of ZSM-5 was conducive to the generation of highly dispersed Co2+ species. Grzybek et al.[26] found that Co species on ZSM-5 with a high Si/Al ratio exhibit higher reducibility, while those on ZSM-5 with a low Si/Al ratio tend to migrate and form larger oxide particles, which are difficult to reduce completely.
Although there are numerous reports on the catalytic N2O decomposition reaction of Co-based molecular sieve catalysts at present, most of the research focuses on the influence of the structural properties of the zeolite themselves (such as pore structure, aluminum content and distribution) on the catalytic activity. There is still a lack of understanding of influence of Co structure on the catalytic performance of the molecular sieve carrier. In fact, Co species can exist on molecular sieve carriers in various forms, such as isolated Co2+, CoOx clusters and Co3O4 nanoparticles[27]. These Co species exhibit distinct electronic structure characteristics and adsorption properties for N2O molecules. Revealing the structure-activity relationship between these Co species and their performance for N2O decomposition is of great significance for a deeper understanding of the microscopic mechanism of Co-based molecular sieve catalysts on N2O catalytic decomposition.
In this work, a series of Co/HZSM-5 catalysts were prepared by the impregnation method to catalyze N2O decomposition. The microstructure of the Co species was modulated by varying the Si/Al ratio of the HZSM-5 support while maintaining a constant Co loading. The physicochemical information of the catalyst was precisely characterized by TEM, XRD, Raman, H2-TPR, Py-FTIR and XPS to investigate the influence of the HZSM-5 Si/Al ratio on the microstructure of surface Co species. Combining with the results of performance evaluation and in situ infrared characterization, the influence of the kinds of Co species on N2O catalyzing decomposition were analyzed. This work can provide a reference for the design and development of high-performance N2O decomposition catalysts and a deeper understanding of their reaction mechanisms.
1　Experimental
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1.1　Preparation of catalysts
HZSM-5 molecular sieve carriers with different Si/Al ratios were prepared by the seed-induced hydrothermal crystallization method. Specifically, amount of sodium hydroxide (NaOH), tetrapropyl ammonium hydroxide (TPAOH) and deionized water were mixed in a beaker and stirred thoroughly. Then ethyl orthosilicate (TEOS) was added into above mixture drop by drop. After stirring for 24 h, it was transported to a crystallization reactor and crystallized at 170 °C for 24 h to obtain the crystal seeds. Then, a certain amount of obtained seed crystals was added to the ZSM-5 molecular sieve growth feed solution. The molar composition of the feed solution was 4.4 TPAOH∶0.1 Na2O∶25 SiO2∶0.04 Al2O3∶1048 H2O∶100 ETOH. Further continuous stirring for 3 h, it was crystallized in the crystallization reactor at 210 °C for 3 h. The obtained crystallization product was centrifuged and washed repeatedly with deionized water until the supernatant reached pH value 7.0, dried at 100 °C, and calcined at 550 °C for 6 h. Subsequently, the sample was subjected to ion exchange with a 0.80 mol/L NH4Cl aqueous solution. After drying and calcination, the H-type ZSM-5 molecular sieve was obtained and named HZ-X (X is the Si/Al ratio of the HZSM-5 carrier). Finally, 0.335 g of cobalt nitrate hexahydrate was dissolved in 4 g of deionized water, and the resulting solution was dropwise added to 5 g of the HZ-X support. The mixture was ultrasonicated for 30 min, allowed to stand at room temperature for 4 h, dried at 100 °C for 6 h, and finally calcined at 500 °C for 4 h, yielding the Co/HZSM-5 catalysts with different Si/Al ratios, which were denoted as Co/HZ-X.
1.2　Characterization
The X-Ray powder diffraction (XRD) tests were conducted on the SmartLab9 X-ray diffractometer equipped with Cu Kα rays as the radiation source. The scanning range and scanning speed for the XRD test were 5°−70° and 2(°)/min, respectively. The X-ray fluorescence (XRF) was carried out on a ZSX Primus II spectrometer equipped with a 4 kW Rh target X-ray tube to analyze the elemental composition of the samples. The texture properties of samples were tested by N2-physical adsorption technology on an ASAP 2020 physical adsorption instrument. The test samples were degassed under vacuum conditions at 250 °C for 4 h, and the isotherms were measured at −196 °C. The morphology of samples was tested using the HT7800 transmission electron microscope, and the pressurized voltage selected for the test is 200 kV. The Raman spectra were measured on the Horiba LabRAM HR Evolution Raman spectrometer. A 532 nm laser light source with a laser power of 10 mW was selected during the test, and the spectral resolution was 1 cm−1. The PHI Genesis X-ray photoelectron spectrometer equipped with an Al Kα ray source was adopted for XPS testing. The binding energy (BE) value was calibrated with a C 1s signal of 284.8 eV. The analysis of H2-TPR and NH3-TPD was carried out on the Micromeritics AutoChemII 2920 analyzer. During the H2-TPR test, the sample was pretreated at a temperature of 300 °C for 1 h, and then a mixture of 10% H2/Ar was purged when the temperature cooled to 50 °C. The H2-TPD curve was recorded as the temperature was raised to 700 °C at a rate of 10 °C/min. As for NH3-TPD, the sample was pretreated at 550 °C for 1 h to clean the surface, then 5% NH3/He mixed gas was introduced when the temperature decreased to 100 °C. The physically adsorbed ammonia was removed by a He flow. The NH3-TPD spectrum was recorded by a TCD detector as the temperature increased from 100 to 550 °C at a rate of 10 °C/min in a He atmosphere. The Py-FTIR testing was conducted on the Bruker Tensor 27 infrared spectrometer. Before the test, the impurity gas on sample was removed at 400 °C under a vacuum atmosphere. Then, pyridine is introduced and adsorbed for 10 min, followed by vacuuming at 200 °C to remove the weakly adsorbed pyridine molecule. When the temperature cooled to room temperature, the Py-FTIR spectra were recorded. The in situ infrared experiment was conducted on the Nicolet iS50 Fourier Transform infrared spectrometer. The catalyst was pre-treated in N2 at 500 °C for 1 h. After reducing the temperature to 150 °C, 0.1% N2O/He is introduced at a flow rate of 30 mL/min. After stabilizing for 10 min, the temperature is increased to 400 °C at a rate of 2 °C/min. The spectrum was recorded at the wavenumber acquisition range of 400−4000 cm−1, and the spectral resolution was set at 4 cm−1. The spectrum at the same temperature without the introduction of raw gas as the background.
1.3　Performance evaluation
The N2O catalytic decomposition performance for the prepared catalysts was evaluated in a micro-fixed-bed reactor. Before the test, the catalyst was first pressed into tablets, then crushed and sieved into particles of 40−60 mesh. 0.3 g of catalyst was packed into the reactor. After increasing the temperature to 280 °C, 0.1% N2O/He was introduced with the space velocity of 10000 h−1. For every 20 °C increase, the concentration of N2O in the reaction tail gas was detected by gas chromatography (GC) equipped with a TCD detector. The calculation formula for N2O conversion is shown below:
$ {x =}\frac{{{c}}_{\text{in}}-{{c}}_{\text{out}}}{{{c}}_{\text{in}}}{\times 100\%} $
Herein, x represents the conversion rate of N2O, $ {{c}}_{\text{in}} $ refer to the N2O concentration at the inlet of the reactor, and $ {{c}}_{\text{out}} $ are the N2O concentration at the outlet of the reactor.
2　Results and discussion
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2.1　Characterization of physical properties
The actual Si/Al ratio of the prepared molecular sieve carrier was tested by X-ray fluorescence spectrometry (XRF), and the results are listed in Table 1. Apparently, the actual Si/Al ratios of HZ60 and HZ390 molecular sieve carriers are 35 and 164, lower than the corresponding feed Si/Al of 60 and 390, respectively.
This is because the alkali-mediated desilication occurred during the strongly alkaline and relatively high-temperature synthetic environment, which reduced the actual Si/Al ratio of the molecular sieve. As for the S-1 molecular sieve carrier, although no aluminum source was added during its synthesis process, the actual Si/Al ratio detected was 700. This might be caused by the trace aluminum impurities inherent in the template agent and the silicon source, combined with the trace aluminum species remaining in the inner lining of the reaction vessel. After treating the HZ60 molecular sieve with 2 mol/L nitric acid, the Si/Al ratio significantly increased from 35 to 85, indicating that some of the framework aluminum had been etched by the acid.
Figure 1 shows the XRD patterns of the Co/HZ60, Co/HZ390 and Co/S-1 catalysts. It can be seen that diffraction peaks belonging to MFI zeolite appeared in all samples at 2θ angles of 7°−9° and 23°−25°, indicating that the impregnation process of Co precursors did not damage the framework structure of the zeolite[16]. Meanwhile, no diffraction peaks belonging to CoO or Co3O4 were observed in the XRD patterns, suggesting that the Co species were highly dispersed on the surface of MFI molecular sieve carriers with different Si/Al ratios, and their grain sizes were below the XRD detection limit[28].
Figure 2(a)−(c) shows the TEM images of S-1, HZ390 and HZ60 zeolite. All the samples presented a cubic structural morphology. Unlike HZ390 and S-1 samples, a unique structure accumulated by tiny grains can be observed around the cubic grains of HZ60, which indicates that excessively increasing the aluminum species in the synthesis liquid system is harmful to the epitaxial growth of the molecular sieve skeleton structure.
After impregnating Co species, the Co/HZ60, Co/HZ390 and Co/S-1 catalysts exhibited a cubic morphology which was similar to that of the carriers, but the edges of grains became rougher and some irregular attachments were formed on the surfaces (Figure 2(d)−(f)). Compared with Co/S-1 and Co/HZ390 catalysts, the surface of Co/HZ60 grains possessed more tiny attachments. Despite this, no obvious Co3O4 nanoparticles were observed on the surface of all Co-based molecular sieve catalysts, which suggested that the introduced Co species were highly dispersed on the catalyst surface. These results were consistent with the XRD results.
The texture properties of the prepared samples were characterized by N2 physical adsorption-desorption technology. As shown in Figure 3(a), the HZ60, HZ390 and S-1 carriers exhibit type I isothermal curves, suggesting the microporous structures for molecular sieve carriers. Among them, the HZ60 carrier shows an H4 type hysteresis loop at 0.8 < p/p0 < 1.0, indicating the existence of a mesoporous structure. These mesoporous pores might be formed by the accumulation of tiny attachments on the surface of HZ60 grains. The Co/HZ60, Co/HZ390 and Co/S-1 catalysts exhibited type I isothermal curves similar to the corresponding carriers. However, unlike the HZ60 carrier, no hysteresis loop structure was observed in the isotherms of the Co/HZ60 catalyst, indicating that the introduced Co species blocked the surface mesoporous structure. The texture properties of the catalyst are listed in Table 1. Compared with HZ60, HZ390 and S-1 carriers, the total specific surface area of Co/HZ60, Co/HZ390 and Co/S-1 catalysts decreased from 486, 569 and 509 m2/g to 389, 384 and 435 m2/g, respectively. And the total pore volumes of Co/HZ60, Co/HZ390 and Co/S-1 catalyst decreased from 0.272, 0.284 and 0.261 cm3/g of HZ60, HZ390 and S-1 to 0.261, 0.188 and 0.219 cm3/g, respectively. These results indicated that the introduction of Co species blocked the pore structure of the molecular sieve carrier to some extent.
2.2　Characterization of Co species
The Raman spectroscopy was used to characterize the properties of Co species on the surface of molecular sieve carriers with different Si/Al ratios. As shown in Figure 4(a), no obvious Raman peak was observed in the spectrum of the Co/HZ60 catalyst, while the Co/HZ390 catalyst exhibited a symmetrical vibrational peak belonging to the octahedral CoO6 species at 683 cm−1 [29]. The Co/S-1 catalyst exhibited other symmetrical vibrational peaks at 477 and 517 cm−1, which belonged to the tetrahedral CoO4 species[30]. This result indicates that the Co species existed in the form of oxides on the zeolite with high Si/Al ratios (such as Co/HZ390 and Co/S-1). The reduction properties of Co species on the catalyst were further characterized by H2-TPR. As the H2-TPR curves shown in Figure 4(b), the Co/HZ60, Co/HZ390 and Co/S-1 catalysts present two H2 reduction peaks at 350−500 °C. The peaks located near 415.5 and 460 °C are attributed to the reduction processes of Co3+ → Co2+ and Co2+ → Co0, respectively[31−32]. These results revealed the presence of cobalt oxide on all catalysts. The similar H2 reduction temperatures of cobalt oxides in the three catalysts suggested that the Si/Al ratio of the molecular sieve has a relatively low influence on the reduction performance of surface cobalt oxides. However, the peak area of H2 reduction decreases significantly with the reduction of the Si/Al ratio of molecular sieve carriers. The H2 consumption calculated based on the reduction peak area is shown in Table 2. The hydrogen consumption of Co/HZ390 catalyst decreased from 570 μmol/g of Co/S-1 to 390 μmol/g, and Co/HZ60 sharply reduced to 100 μmol/g. These results indicate that the cobalt oxide content for different catalysts decreases with the reduction of the Si/Al ratio. Considering the same load amount of Co species, it can be found that there are other forms of Co species present on these catalysts with different Si/Al ratios.
The effect of Co species loading on the surface acidity of the zeolite was investigated by NH3-TPD. As shown in Figure 5(a), three NH3 desorption peaks can be observed in the NH3-TPD curves of HZ60 and HZ390 samples. The NH3 desorption peaks observed in the ranges of 100−170, 200−260 and 400−500 °C are attributed to weak acid, moderate-strength acid, and strong acid sites, respectively. Different from that of HZ60 and HZ390, the S-1 carrier only showed a weak NH3 desorption peak at about 130 °C, suggesting that the acid sites on its surface were mainly weak acids. After the introduction of the Co species, the NH3 desorption peaks at 400−500 °C disappeared for Co/HZ60 and Co/HZ390 catalysts, while the peak at 135 °C was significantly enhanced. This indicated that the introduced Co species primarily interacted with the strong acid sites on the zeolite support surface and generated new weak acid sites. As for the Co/S-1 catalyst, it showed a similar NH3 desorption peak to that of the S-1 carrier at about 125 °C. Based on the integration of the area of the NH3 desorption peak, the acid content of catalysts with different Si/Al ratios was calculated (Table 2). Because the high aluminum content of the HZ60 carrier, its total acid content can reach 800 μmol/g, while the HZ390 carrier with low aluminum content has a total acid content of 500 μmol/g. The total acid content of the S-1 carrier is the least, only 120 μmol/g. Due to the shielding effect of Co species on acid sites, the total acid contents of Co/HZ60, Co/HZ390 and Co/S-1 catalysts slightly decreased compared with the corresponding carriers, which were 740, 480 and 104 μmol/g, respectively.
The acid structure of the molecular sieve carrier and the corresponding catalyst were further analyzed by Py-FTIR, and the test results were shown in Figure 6. The peaks located at 1450 and 1550 cm−1 in the spectrum belong to the infrared absorption peaks of pyridine molecules on Lewis acid (L-acid) and Brønsted acid (B-acid) sites, respectively[33]. Because of the high amount of acid sites, the infrared absorption peaks of the HZ60 carrier at 1450 and 1550 cm−1 are significantly greater than those of the HZ390 carrier. No distinct infrared peaks were observed in the range of 1400−1600 cm−1 for the purely siliceous S-1, indicating the absence of acidic sites on its surface. This is because the Brønsted and Lewis acidities in HZSM-5 zeolite originate from tetrahedrally coordinated framework aluminum and extra-framework aluminum species, respectively[33]. Compared with the HZ60 and HZ390 carriers, the infrared peaks of the Co/HZ60 and Co/HZ390 catalysts at 1550 cm−1 were significantly weakened, while the infrared peaks at 1450 cm−1 were apparently enhanced (Figure 6(b)). This was because the introduced Co species can react with B acid sites and convert them into L acid sites (isolated Co2+)[27]. No obvious infrared peak was observed in the range of 1400−1600 cm−1 for the S-1 carrier and Co/S-1 catalyst due to the lack of acidic sites. The acid content of B acid sites and L acid sites was listed in Table 2. HZ60 has the highest amounts of B acid and L acid, which reached up to 71.7 and 37.7 μmol/g respectively.
The amounts of B acid and L acid in the HZ390 catalyst were reduced to 24.5 and 6.7 μmol/g, respectively. After impregnating the Co species, the amounts of B acid in Co/HZ60 and Co/HZ390 decreased significantly to 45.1 and 2.1 μmol/g, respectively, while the amounts of L acid increased to 44.3 and 12.6 μmol/g, respectively. These results indicated that isolated Co2+ species exist in both Co/HZ60 and Co/HZ390 catalysts.
The oxygen species in Co/HZ60, Co/HZ390 and Co/S-1 catalysts were characterized by XPS. The results are shown in Figure 7(a). A large peak could be observed between 529−537 eV for Co/HZ60, Co/HZ390 and Co/S-1 catalysts. Among them, the signal peak at 532.9 eV (Oα) was attributed to the skeleton oxygen species of the molecular sieve carrier, while the peaks at about 531.0 eV (Oβ) and 534.5 eV (Oγ) are attributed to the lattice oxygen species of the CoOx species and surface hydroxyl oxygen species, respectively[22]. Based on the integration of peak areas, the relative contents of each oxygen species on the catalyst surface were calculated, and the results are listed in Table 3. Because the zeolite is mainly composed of tetrahedral silicon-oxygen species, the oxygen species in their framework are the main oxygen species of Co-based molecular sieve catalysts, which account for 92.2%, 86.9% and 88.3% for Co/HZ60, Co/HZ390 and Co/S-1 catalysts, respectively. Correspondingly, the relative content of lattice oxygen species associated with CoOx species increased with the increasing Si/Al ratio of the zeolite. Compared with the Co/HZ60 catalyst, the lattice oxygen content (Oβ) in the Co/HZ390 and Co/S-1 catalysts increased from 3.6% to 5.5% and 5.9%, respectively, and the Oβ/Oα ratio also increased from 0.04 to 0.06 and 0.07, respectively. This indicated that increasing the Si/Al ratio of the molecular sieve carrier can promote the generation of more CoOx species, which is consistent with the characterization results of H2-TPR.
It can be seen from the Co 2p3/2 XPS spectrum that three distinct signal peaks were observed at 792.50−776.40 eV for the Co/HZ60, Co/HZ390 and Co/S-1 catalysts (Figure 7(b)). Specifically, the signal peaks located at approximately 782.00 and 784.65 eV (for Co/HZ60 and Co/HZ390) are attributed to Co3+ and Co2+, respectively, while the peak at about 787.50 eV corresponds to the satellite peak of Co2+[34−35]. However, the binding energies of Co2+ and Co3+ in the Co/S-1 catalyst were noticeably lower than those of the other samples, shifting down to 784.12 and 781.31 eV, respectively. This suggested that the Co species of the Co/S-1 catalyst presented a relatively higher electron cloud density than that of Co/HZ60 and Co/HZ390 catalysts. The relative contents of Co2+ and Co3+ of each catalyst are listed in Table 4. Among them, the Co/HZ60 catalyst possessed the highest Co2+/Co3+ ratio, which attained 0.79. When the Si/Al ratio of the molecular sieve increased to 390, the Co2+/Co3+ ratio of Co/HZ390 catalyst significantly decreased to 0.66. For the Co/S-1 catalyst supported on pure silicon molecular sieve carrier, the ratio of Co2+ to Co3+ was apparently reduced to 0.54. This was because the abundant ion-exchange sites present in low Si/Al ratio zeolite, where the strongly interacting Co2+ ions anchored at these sites are less susceptible to oxidation to Co3+.
2.3　Evaluation of catalyst activity
Figure 8 shows the N2O catalytic decomposition performance of Co-based molecular sieve catalysts with different Si/Al ratios. It could be seen from Figure 8(a) that the order of catalytic activity of the prepared catalyst is Co/HZ60 > Co/HZ180 > Co/HZ390 > Co/HZ600 > Co/S-1. Among them, Co/HZ60 exhibited the best catalytic activity, achieving an N2O decomposition conversion of 55% at 420 °C. When the reaction temperature was raised to 460 °C, complete decomposition of N2O could be attained. As the Si/Al ratio of the molecular sieve increased from 60 to 180 and 390, the activity of the catalyst declined to a certain extent. At 420 °C, the N2O decomposition conversion of Co/HZ180 and Co/HZ390 catalysts decreased to 44% and 32%, respectively, while the complete decomposition temperature of N2O (t100) significantly increased to 500 °C and 520 °C, respectively (Figure 8(b)). When the Si/Al ratio was further increased to 600, the Co/HZ600 catalyst exhibited similar N2O catalytic decomposition activity to that of Co/S-1. The t100 of Co/HZ600 and Co/S-1 was as high as 540 °C, and the N2O conversion was only about 20% at 420 °C. These results revealed that reducing the Si/Al ratio of zeolite is conducive to enhancing the catalytic decomposition activity of N2O. In actual industrial exhaust gases (such as those from the nitric acid industry), apart from N2O, there are also impurity gases like O2 and NO[1]. The performance of resisting impurity gases is an important indicator for evaluating N2O decomposition catalysts. Figure 8(c) and 8(d) showed the O2 resistance and NO resistance of the Co/HZ60 catalyst, respectively. It can be seen that when 3.0% O2 and 0.1% NO were respectively introduced into the reaction gas, the t50 and t100 of the Co/HZ60 did not show a significant decrease, indicating a good impurity resistance for Co/HZ60 catalyst.
2.4　 In situ infrared experiment
The in situ infrared spectrogram of Co/HZ60 and Co/HZ390 catalysts is shown in Figure 9. The infrared peaks located at 1557 and 1682 cm−1 in the spectrum can be attributed to the stretching vibration of the nitro species (*NO2) and the bending vibration of the nitrosyl group (*NO), respectively. The infrared peak located at 2050−2270 cm−1 can be attributed to the antisymmetric stretching vibration of gaseous N2O[36−37]. It is generally believed that there are two adsorption activation methods for N2O molecules. One type is adsorbed on the metal active site through the oxygen terminal, which tends to break the N−O bond and generate N2 and surface-adsorbed oxygen *O species. Another type tends to generate NO and *N species through nitrogen terminal adsorption, which breaks the N−N bond. The generated NO can combine with surface-adsorbed *O species to form nitro species[37−38]. Therefore, whether N2O molecules have decomposed can be analyzed by the species of nitro or nitrosyl groups on the surface of the catalyst. As shown in Figure 9(a) and (b), the Co/HZ60 catalyst exhibited distinct nitro or nitrosyl species at 250 °C, indicating the onset of N2O decomposition at this temperature. However, the obvious peaks attributed to nitro or nitrosyl species appeared at 350 °C for the Co/HZ390 catalyst (Figure 9(c) and (d)). This phenomenon indicated that the Co species on zeolite carrier with a low Si/Al ratio presented higher catalytic activity for N2O decomposition.
2.5　Discussion
For transition metal-molecular sieve catalysts, the introduced metal species can exist in the form of cations, metal-oxygen clusters, and oxide particles. The Raman results show that CoOx species exist in the Co/HZ390 and Co/S-1 catalysts. The H2-TPR results indicate that Co/HZ60, Co/HZ390 and Co/S-1 all exhibited H2 reduction peaks belonging to the CoOx species within the range of 350−500 °C. However, no diffraction peaks belonging to CoO or Co3O4 are observed in the corresponding XRD patterns, and no obvious cobalt oxide particles are observed in the TEM images either. These results indicate that the cobalt oxides on the catalyst surface are predominantly present as nanoclusters. It can be known from the hydrogen consumption of catalysts that the content of cobalt oxide on the catalyst surface decreases with the reduction of the Si/Al ratio of the molecular sieve carrier. The Py-FTIR characterization shows that the amount of L-acid on the surfaces of Co/HZ60 and Co/HZ390 is significantly higher than that of HZ60 and HZ390 carriers, indicating that more Co species exist in the form of isolated Co2+ in the catalyst with a low Si/Al ratio. The Co 2p3/2 XPS characterization results reveal that the ratio of Co2+/Co3+ of the catalyst increased from 0.54 of Co/S-1 to 0.66 of Co/HZ390 and further increased to 0.79 of Co/HZ60. It can be seen that the Co species on the surface of the prepared catalyst exist in the form of cobalt oxide clusters and isolated Co2+.
With a decreasing Si/Al ratio of the zeolite carrier, the proportion of cobalt oxide clusters gradually declines, while the proportion of isolated Co2+ gradually increases. The microstructural variation of Co species significantly influences their catalytic activity for N2O decomposition. The activity evaluation results show that the catalytic activity sequence is Co/HZ60 > Co/HZ390 > Co/S-1, indicating that the catalytic activity of isolated Co2+ is higher than that of cobalt oxide clusters. When nitric acid is used to pre-destroy the skeletal Al sites anchored to isolated Co2+, the catalytic activity of Co/HZ60 decrease significantly. As shown in Figure 10, the t50 of the acid-treated sample (Co/HZ60-Acid) increased by 12 °C compared to before the treatment (Co/HZ60), while the t100 increased by 40 °C. This experimental result once again proves that the catalytic activity of isolated Co2+ on the surface of zeolite is significantly higher than that of cobalt oxide nanoclusters.
3　Conclusion
Less
In this work, a series of Co-based molecular sieve catalysts with different Si/Al ratios was prepared by the impregnation method. The experimental results show that during the impregnation process, the Co precursors do not damage the molecular sieve structure, and the Co species are mainly highly dispersed on the molecular sieve surface in the form of cobalt oxide nanoclusters and isolated Co2+. Under the same Co loading amount, reducing the Si/Al ratio of the molecular sieve is conducive to generating highly active isolated Co2+ species. The strong interaction between the molecular sieve carrier and Co2+ species effectively inhibits the oxidation of Co2+ to Co3+, thereby improving the adsorption and activation capacity of N2O molecules. Compared to the Co/S-1 catalyst supported on pure silica, the low Si/Al ratio Co/HZ60 catalyst, which possesses a greater number of isolated Co2+ active sites, reduces the temperature required for complete N2O decomposition by 80 °C and demonstrates excellent resistance to both O2 and NO.
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Year 2026 volume 54 Issue 8
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doi: 10.1016/S1872-5813(26)60668-8
  • Receive Date：2025-10-31
  • Online Date：2026-09-23
  • Published：2026-08-10
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  • Received：2025-10-31
  • Revised：2025-12-10
  • Accepted：2026-01-02
Affiliations
    1College of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China
    2Research Center for Fine Chemicals Engineering, Ministry of Education, Shanxi University, Taiyuan 030006, China
    3Shanxi Dongjin Fertilizer Industry Co., LTD., Lüliang 030500, 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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