Influence of Support Morphology on CO Preferential Oxidation Properties over Cu/α-MnO2 AITranslate
Abstract AITranslate
Given the escalating global energy crisis，there is now a pressing need for a transition towards cleaner and more sustainable energy sources. In this regard，hydrogen energy has emerged as a frontrunner due to its environmentally friendly characteristics，high calorific value，and versatile applications. Proton exchange membrane fuel cells （PEMFCs）have garnered significant attention for their potential to drive this transition，particularly in both mobile and stationary hydrogen energy sectors. Their operational advantages，such as low temperature specifications，high power densities，and zero carbon dioxide emissions，position them as a key player in the future of clean energy technology. However，one of the challenges faced by PEMFCs is that the process of producing the fuel H2 usually involves a water-gas shift reaction，resulting in some residual CO，which can be harmful to the platinum electrodes and cause irreversible damage. In response to this issue，the development of techniques such as preferential oxidation of CO （CO-PROX）has become increasingly crucial in effectively eliminating trace CO from hydrogen-rich gases，thus enhancing the performance and durability of PEMFCs in the long term. Pt-based catalysts are the most commonly used for CO-PROX，but considering the scarcity and high cost of the noble metals，the development of non-precious metal catalysts has become a research hotspot. Cu-based catalysts have been widely investigated because of their excellent catalytic performance in CO oxidation，while MnO2 with its high oxygen mobility and oxygen storage capacity，has been widely used in oxidation reactions. Hence，Cu-Mn system catalysts will be the alternative choice for noble catalysts. In loaded catalysts，the role of the support is critical. The morphological diversity of the supports results in different exposed crystalline surfaces，which not only affects the redox properties of the supports themselves，but can also cause changes in the degree of interaction between the supports and the active components. Such changes in interaction will further alter the electronic structure and coordination environment of the active component，change its chemical state and distribution，and thus have a significant impact on the catalyst's reaction performance and reaction mechanism. In this study，α-MnO2 nanowires （w），nanotubes （t）and nanorods （r）were successfully synthesized by a hydrothermal method and loaded with 1.5 wt% Cu by excess impregnation，the effect of support morphology and exposed crystal planes on the CO-PROX reaction properties on Cu/MnO2 was also investigated. Powder X-ray diffraction （XRD），nitrogen adsorption-desorption，inductively coupled plasma atomic emission spectrometer （ICP-AES）and transmission electron microscope （TEM）were used to characterize the basic information of the catalyst structure. H2-temperature programmed reduction （H2-TPR）and O2-temperature programming desorption （O2-TPD）were used to compare the redox capacities of the catalysts. X-ray photoelectron （XPS）was used to analyze the chemical states of the elements，and in situ diffuse reflectance infrared Fourier transform spectroscopy （in situ DRIFTS）was used to investigate the reaction mechanism of Cu/α-MnO2 with different morphologies. It was found that the reaction properties were strongly influenced by the morphology of the support and the exposed crystal planes. Cu/α-MnO2-w was able to achieve complete CO conversion within a wide operating window of 100-250 ℃，while Cu/α-MnO2-t only reached the highest conversion of 98% at 200 ℃. Cu/α-MnO2-w further investigated the effects of H2O and CO2 on the performance of CO-PROX，and the results presented that the inhibition of CO oxidation by H2O was more significant than CO2，and the temperature for complete CO conversion was shifted to higher temperature of even up to 150 ℃. Characterization results showed that different morphologies of α-MnO2 exposed different crystalline planes： nanowire （w），tube （t）and rod （r）shaped α-MnO2，exposing （110），（200）and （300）crystalline planes，respectively. Differences in support morphology and exposed crystalline planes affected the state of Cu presence. No peaks associated with Cu species were observed in XRD，while TEM showed that Cu existed in different states on different morphologies of α-MnO2： CuO particles were observed only on Cu/α-MnO2-w，whereas lattice fringes of Cu species were not observed on Cu/α-MnO2-t and Cu/α-MnO2-r. Cu exerted a consistent effect on the α-MnO2 with different morphologies： Cu provided additional CO adsorption sites （Cu+）and promoted the creation of Mn3+ and oxygen vacancies，favoring the activation of gas-phase oxygen. In addition，valence cycling between Cu2+/Cu+ and Mn3+/Mn4+ further aggravated the cycling of reactive oxygen species. However，the enhanced redox capacity of different forms of Cu/MnO2 varied： Cu/α-MnO2-w had the most enhanced oxygen supply capacity and the lowest reduction peak temperature （224 ℃）in H2-TPR profiles； XPS showed that Cu/α-MnO2-w had the highest Mn3+/Mn4+ content and the most oxygen adsorbed on the surface，and the smallest temperature difference between the surface lattice oxygen and the main body lattice oxygen was only 179 ℃ in the O2-TPD. The reaction mechanism was explored by in situ DRIFTS，and the strongest CO adsorption was observed on Cu/α-MnO2-w，which showed a significant red-shift of the CO adsorption peak （2108 cm−1）on Cu/α-MnO2-w compared with that on Cu/α-MnO2-t （2132 cm−1）. On Cu/α-MnO2-w，the presence of H2 promoted the generation of unstable bicarbonates and carbonate，whereas in Cu/α-MnO2-t，H2 only promoted the generation of carbonate intermediates that were not easily decomposed.
KeyWords AITranslate
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Basic Information:
DOI：10.13373/j.cnki.cjrm.XY24050006
Chinese Library Classification Number:O643
Citation Information:
Given the escalating global energy crisis，there is now a pressing need for a transition towards cleaner and more sustainable energy sources. In this regard，hydrogen energy has emerged as a frontrunner due to its environmentally friendly characteristics，high calorific value，and versatile applications. Proton exchange membrane fuel cells （PEMFCs）have garnered significant attention for their potential to drive this transition，particularly in both mobile and stationary hydrogen energy sectors. Their operational advantages，such as low temperature specifications，high power densities，and zero carbon dioxide emissions，position them as a key player in the future of clean energy technology. However，one of the challenges faced by PEMFCs is that the process of producing the fuel H2 usually involves a water-gas shift reaction，resulting in some residual CO，which can be harmful to the platinum electrodes and cause irreversible damage. In response to this issue，the development of techniques such as preferential oxidation of CO （CO-PROX）has become increasingly crucial in effectively eliminating trace CO from hydrogen-rich gases，thus enhancing the performance and durability of PEMFCs in the long term. Pt-based catalysts are the most commonly used for CO-PROX，but considering the scarcity and high cost of the noble metals，the development of non-precious metal catalysts has become a research hotspot. Cu-based catalysts have been widely investigated because of their excellent catalytic performance in CO oxidation，while MnO2 with its high oxygen mobility and oxygen storage capacity，has been widely used in oxidation reactions. Hence，Cu-Mn system catalysts will be the alternative choice for noble catalysts. In loaded catalysts，the role of the support is critical. The morphological diversity of the supports results in different exposed crystalline surfaces，which not only affects the redox properties of the supports themselves，but can also cause changes in the degree of interaction between the supports and the active components. Such changes in interaction will further alter the electronic structure and coordination environment of the active component，change its chemical state and distribution，and thus have a significant impact on the catalyst's reaction performance and reaction mechanism. In this study，α-MnO2 nanowires （w），nanotubes （t）and nanorods （r）were successfully synthesized by a hydrothermal method and loaded with 1.5 wt% Cu by excess impregnation，the effect of support morphology and exposed crystal planes on the CO-PROX reaction properties on Cu/MnO2 was also investigated. Powder X-ray diffraction （XRD），nitrogen adsorption-desorption，inductively coupled plasma atomic emission spectrometer （ICP-AES）and transmission electron microscope （TEM）were used to characterize the basic information of the catalyst structure. H2-temperature programmed reduction （H2-TPR）and O2-temperature programming desorption （O2-TPD）were used to compare the redox capacities of the catalysts. X-ray photoelectron （XPS）was used to analyze the chemical states of the elements，and in situ diffuse reflectance infrared Fourier transform spectroscopy （in situ DRIFTS）was used to investigate the reaction mechanism of Cu/α-MnO2 with different morphologies. It was found that the reaction properties were strongly influenced by the morphology of the support and the exposed crystal planes. Cu/α-MnO2-w was able to achieve complete CO conversion within a wide operating window of 100-250 ℃，while Cu/α-MnO2-t only reached the highest conversion of 98% at 200 ℃. Cu/α-MnO2-w further investigated the effects of H2O and CO2 on the performance of CO-PROX，and the results presented that the inhibition of CO oxidation by H2O was more significant than CO2，and the temperature for complete CO conversion was shifted to higher temperature of even up to 150 ℃. Characterization results showed that different morphologies of α-MnO2 exposed different crystalline planes： nanowire （w），tube （t）and rod （r）shaped α-MnO2，exposing （110），（200）and （300）crystalline planes，respectively. Differences in support morphology and exposed crystalline planes affected the state of Cu presence. No peaks associated with Cu species were observed in XRD，while TEM showed that Cu existed in different states on different morphologies of α-MnO2： CuO particles were observed only on Cu/α-MnO2-w，whereas lattice fringes of Cu species were not observed on Cu/α-MnO2-t and Cu/α-MnO2-r. Cu exerted a consistent effect on the α-MnO2 with different morphologies： Cu provided additional CO adsorption sites （Cu+）and promoted the creation of Mn3+ and oxygen vacancies，favoring the activation of gas-phase oxygen. In addition，valence cycling between Cu2+/Cu+ and Mn3+/Mn4+ further aggravated the cycling of reactive oxygen species. However，the enhanced redox capacity of different forms of Cu/MnO2 varied： Cu/α-MnO2-w had the most enhanced oxygen supply capacity and the lowest reduction peak temperature （224 ℃）in H2-TPR profiles； XPS showed that Cu/α-MnO2-w had the highest Mn3+/Mn4+ content and the most oxygen adsorbed on the surface，and the smallest temperature difference between the surface lattice oxygen and the main body lattice oxygen was only 179 ℃ in the O2-TPD. The reaction mechanism was explored by in situ DRIFTS，and the strongest CO adsorption was observed on Cu/α-MnO2-w，which showed a significant red-shift of the CO adsorption peak （2108 cm−1）on Cu/α-MnO2-w compared with that on Cu/α-MnO2-t （2132 cm−1）. On Cu/α-MnO2-w，the presence of H2 promoted the generation of unstable bicarbonates and carbonate，whereas in Cu/α-MnO2-t，H2 only promoted the generation of carbonate intermediates that were not easily decomposed.
quote
| GB/T 7714-2015 | [1] Xiaoyu Mao, Lichuan Song, Li Zhang, et al. Influence of Support Morphology on CO Preferential Oxidation Properties over Cu/α-MnO2[J]. Chinese Journal of Rare Metals, 2025, 49(9): 1331-1341. DOI:10.13373/j.cnki.cjrm.XY24050006. |
| MLA | [1] Xiaoyu Mao, et al., "Influence of Support Morphology on CO Preferential Oxidation Properties over Cu/α-MnO2." Chinese Journal of Rare Metals, vol. 49, no. 9, 2025, pp. 1331-1341, https://doi.org/10.13373/j.cnki.cjrm.XY24050006. |
| APA | [1] Xiaoyu Mao, Lichuan Song, Li Zhang, Jia Shen, Chunliang Ge, Tongtong Feng, Yun Guo, & Li Wang. (2025). Influence of Support Morphology on CO Preferential Oxidation Properties over Cu/α-MnO2. Chinese Journal of Rare Metals, 49(9), 1331-1341. https://doi.org/10.13373/j.cnki.cjrm.XY24050006 |
| IEEE | [1] Xiaoyu Mao, Lichuan Song, Li Zhang, Jia Shen, Chunliang Ge, Tongtong Feng, Yun Guo, and Li Wang, "Influence of Support Morphology on CO Preferential Oxidation Properties over Cu/α-MnO2," Chinese Journal of Rare Metals, vol. 49, no. 9, pp. 1331-1341, 2025, doi: 10.13373/j.cnki.cjrm.XY24050006. keywords: {CO-PROX;Cu/MnO;support morphology;reaction mechanism} |