Next Article in Journal
Exploring Growth of Mycobacterium smegmatis Treated with Anticarcinogenic Vanadium Compounds
Previous Article in Journal
An Experimental and Theoretical Study of the Optical Properties of (C2H7N4O)2BiCl5 for an Optoelectronic Application
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Flower-like Co3O4 Hierarchical Microspheres for Methane Catalytic Oxidation

1
Anhui Provincial Engineering Laboratory of Silicon-Based Materials, School of Materials and Chemical Engineering, Bengbu University, Bengbu 233030, China
2
Yankuang Technology Co., Ltd., Shandong Energy Group Co., Ltd., Jinan 250101, China
3
College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
*
Authors to whom correspondence should be addressed.
Submission received: 26 January 2022 / Revised: 23 March 2022 / Accepted: 29 March 2022 / Published: 2 April 2022
(This article belongs to the Section Inorganic Materials)

Abstract

:
The development of non-noble Co3O4 catalysts exposing highly active crystal planes to low-temperature methane oxidation is still a challenge. Hence, a facile solvothermal method was adapted to construe flower-like Co3O4 hierarchical microspheres (Co3O4-FL), which are composed of nanosheets with dominantly exposed {112} crystal planes. The flower-like hierarchical structure not only promotes the desorption of high levels of active surface oxygen and enhances reducibility, but also facilitates an increase in lattice oxygen as the active species. As a result, Co3O4-FL catalysts offer improved methane oxidation, with a half methane conversion temperature (T50) of 380 °C (21,000 mL g−1 h−1), which is much lower than that of commercial Co3O4 catalysts (Co3O4-C). This study will provide guidance for non-noble metal catalyst design and preparation for methane oxidation and other oxidative reactions.

1. Introduction

The emission of volatile organic compounds (VOCs) is a global environmental issue related to atmospheric pollution and is harmful to human health and the environment due to toxic and/or carcinogenic smog and greenhouse gasses. Thus, it is necessary to develop various methods to eliminate VOCs, including incineration, catalytic removal, adsorption, absorption, condensation, and biofiltration, among which catalytic oxidation is regarded as the most efficient process, and it is especially effective in addressing low concentrations of VOCs [1,2].
Methane, with ultralow concentrations in air, is a highly chemically stable compound, with the highest C–H bond energy of ~435 kJ mol−1 in its hydrocarbons, and it has 28~36 times the greenhouse effect of carbon dioxide [3]. Therefore, designed catalysts should be capable of the catalytic oxidation of methane, with a high activity, low catalytic temperature and excellent selectivity for carbon dioxide. Before now, the catalysts for methane have been divisible into noble metal and transition metal oxides. The former achieves high catalytic performance at low temperatures; however, they are expensive, and prone to deactivation. The latter have high potential activity, low costs and thermal stability [4,5].
Among the transition metal oxide catalysts, Co3O4 has attracted wide attention for the catalytic oxidation of VOCs (methane, toluene, n-hexanal), given its different potential morphologies, its spinel structure with strong Co3+/Co2+ redox properties, and its unique exposed crystal planes [6,7,8,9,10,11].
Studies have shown that Co3O4 nanosheets exhibit high catalytic activity, despite their lower special surface area compared with Co3O4 nanobelts and nanocubes [12]. The main reason for the different capacity for catalytic oxidation shown by methane is that the {112} exposed planes of nanosheets are more reactive than the exposed planes in the other morphologies, due to the low energy required for breaking the C–H bond [13]. Meanwhile, Co3O4 nanotubes also present better catalytic activity than Co3O4 nanorods and nanoparticles during methane oxidation, which is not only related to the presence of {112} exposed planes, but also its open structure [14]. Nevertheless, using lattice oxygen as the active species and the presence of defects should induce the improvement of catalytic activity [15].
The objective of this work is to study the preparation of flower-like Co3O4 (FL) hierarchical microspheres stacked with mass nanosheets via a simple solvothermal method and to examine its catalytic activity for methane oxidation. The as-synthesized Co3O4-FL was characterized by N2 physisorption, X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and O2 temperature-programmed desorption (O2-TPD) in order to investigate the physical-chemical properties. The enhanced catalytic performance can be attributed to the highly exposed {112} planes of the nanosheets, together with the active lattice oxygen and derivative oxygen vacancies on their surfaces.

2. Experimental

2.1. Co3O4-FL Preparation

All reagents were purchased from Aladdin Co., Ltd. (Shanghai, China) and used without further purification. In a typical procedure, 2 mmol CoCl2 and 0.01 g polyvinyl alcohol (PVA) was dissolved with stirring for 30 min in a 30 mL mixture of deionized water and ethylene glycol, with a volume ratio of 2:1, to form a homogeneous solution, and then the solution was transferred into a 50 mL Teflon-lined stainless-steel autoclave and maintained at 180 °C for 24 h. After cooling to room temperature, the precipitate was then collected by centrifugation and washed with deionized water and ethanol several times, then dried in an oven at 60 °C overnight to obtain the Co(OH)2 precursor. Co3O4-FL was obtained by calcining the as-prepared precursor at 450 °C for 2 h in air. The commercial Co3O4 (Co3O4-C) was made from agglomerate nanoparticles with grain sizes of 30 nm on a micro scale, which were provided for comparison by Aladdin Co., Ltd. (Shanghai, China). In a typical procedure, the precipitate of the Co(OH)2 precursor collected after the solvothermal process is approximately 0.15 g. The mass of the final Co3O4-FL after calcining is about 0.13 g. Both the Co3O4-FL and Co3O4-C were utilized directly as catalysts for methane oxidation without further treatment.

2.2. Characterizations

The X-ray diffraction (XRD) pattern of the catalyst was determined on a Bruker D8 diffractometer (Billerica, MA, USA) with Cu Kα radiation (λ = 0.154184 nm). Scanning electron microscopy (SEM) was performed on an FEI Inspect F50 microscope (Hillsboro, OR, USA), while transmission electron microscopy (TEM) was performed on an FEI Tecnai F30 microscope (Hillsboro, OR, USA). The specific surface areas were measured at liquid nitrogen temperature using a ASAP2020 Micromeritics instrument (Norcross, GA, USA). Specific surface areas of the samples were calculated using the BET equation. The hydrogen temperature-programmed reduction (H2-TPR) was performed on a Quantachrome Chembet Pulsar (Boynton Beach, FL, USA) using 10 vol.% H2/Ar (50 mL∙min−1) as the reducing gas. The reduction temperature increased from 50 to 600 °C at a rate of 10 °C∙min−1. The oxygen temperature-programmed desorption (O2-TPD) experiment was performed on a Quantachrome Chembet Pulsar (Boynton Beach, FL, USA). Firstly, 100 mg of catalyst was pretreated in a 3 vol.% O2/He flow at 450 °C for 30 min. After cooling to 50 °C under the same oxidative atmosphere, the catalyst was purged by a stream of purified He (30 mL∙min−1). Then, the reactor was heated up to 600 °C at an increasing rate of 10 °C∙min−1. X-ray photoelectron spectroscopy (XPS) analysis was carried out on a Thermo Fisher ESCALAB 250Xi spectrometer (Waltham, MA, USA) using an Al Kα (1486.6 eV) radiation source. The binding energy of the C 1s electron (284.6 eV) was used to calibrate the spectra.

2.3. Catalytic Tests

The methane oxidation reaction was performed on a fixed bed reactor operated with 0.1 g of catalysts at atmospheric pressure. The reactant gas consisted of 2 vol.% of CH4, 20 vol.% of O2 and 78 vol.% of Ar passed through the catalysts with a gas flow rate of 35 mL min−1, which corresponds to a weight hourly space velocity (WHSV) of 21,000 mL∙g−1∙h−1. The reaction temperature was raised from 50 to 550 °C at a rate of 2 °C∙min−1. The reactant and products were analyzed online with a gas chromatograph (Shimadzu, GC-2014, Kyoto, Japan) equipped with a flame ionization detector (FID) and a chromatographic column (GDX 502, 2 m × 3 mm). The conversion of methane was determined every 30 °C with the following equation:
CH4 conversion (%) = (1 − [CH4]out/[CH4]in) × 100

3. Results and Discussion

3.1. Catalytic Characterization

The XRD patterns of the as-prepared precursors Co(OH)2, Co3O4-FL, and Co3O4-C are presented in Figure 1. The diffraction peaks of Co3O4-FL observed at 19.0, 31.3, 36.9, 38.5, 44.8, 55.7, 59.3 and 65.2° can be assigned to the (111), (220), (311), (222), (400), (422), (511) and (440) lattice planes of the Co3O4 phase (JCPDS NO.43-1003), respectively. The Co3O4-FL was prepared from the as-prepared Co(OH)2 precursor, which was formed through the hydrothermal method from CoCl2 and PVA. All the diffraction peaks can be assigned to Co(OH)2, in agreement with the standard diffraction file (JCPDS No. 30-0443). After calcination, no other peaks suggesting impurities were found in the XRD pattern of the Co3O4-FL, which indicates that the Co(OH)2 precursor was completely transitioned into Co3O4 without any impurities. Co3O4-C was also identified without any impurities by XRD analysis. Nevertheless, there are obvious differences in the specific surface areas of Co3O4-FL and Co3O4-C catalysts, which were 22 and 12 m2·g−1, respectively.
Figure 2 shows the SEM and high-resolution (HR)TEM images of the Co3O4-FL and Co3O4-C. Figure 2a shows that most Co3O4-FLs are monodispersed microspheres with a diameter size of 10–15 μm. Closer observations show that these hierarchical microspheres are composed of large numbers of nanosheets with smooth surfaces (Figure 2b,c). The HRTEM image of the Co3O4-FL is presented in Figure 2d. The dominant exposed planes are {112}, which are the only planes displayed in both the set of (220) planes with a lattice space of 0.288 nm and the set of (311) planes with a crossing lattice space of 0.245 nm [16]. Co3O4-C, on the other hand, has no definite shape, and just agglomerates nanoparticles (Figure 2e,f).
The H2-TPR profiles show two reduction peaks on both the Co3O4-FL and the Co3O4-C catalysts (Figure 3). This figure shows overlapping peaks at 385 and 435 °C, observed on Co3O4-C, which are assigned to the reduction of Co3+ into Co0. However, there are two peaks in the Co3O4-FL catalyst at 342 and 406 °C, indicating the successive reduction behavior of Co3+ to Co2+ and Co2+ to Co0, in two reduction steps. Additionally, the temperature of the reduction peaks over Co3O4-FL is lower than that over Co3O4-C, which could imply that the Co3O4-FL composed of nanosheets presents the better reducibility, whereby the more susceptible to reduction an oxide is, the more easily it can generate oxygen vacancies [17].
The O2-TPD of catalysts was carried out to evaluate the mobility of oxygen species, as shown in Figure 4. Generally, there are four oxygen species on the surfaces of metal oxides, with the release order: O2 (molecular oxygen) → O2− (superoxide anion) → O (oxygen anion) → O2− (lattice oxygen). The physically adsorbed O2 species can be desorbed below 200 °C. The O2− and O species are chemically adsorbed oxygen, which can be liberated in the range of 200–400 °C. The rest of the O2− species are attributed to surface and/or lattice oxygen released above 400 °C [18]. It seems that the Co3O4-FL catalysts present desorption peaks at 206 and 345 °C, which can be attributed to the desorption of O2 and O species, respectively, whereas another peak is located at 415 °C, which can be assigned to the desorption of O2− species. The desorption temperature of the Co3O4-C catalysts shifts from 206 to 257 °C, and from 415 to 482 °C, respectively, indicating that the desorption of O2, O, and O2− species was facilitated, implying an enhancement in the catalytic activity of Co3O4-FL through a suprafacial mechanism.
The spectra of Co 2p and O 1s are displayed in Figure 5a,b, illustrating the chemical surface compositions and valence states. The BE value of Co 2p3/2 is 779–780 eV, and a 2p1/2 splitting of 15 eV is characteristic of the octahedral Co3+ component of Co3O4 [19]. The satellite peaks at 785 eV evidence the existence of Co2+ species in the octahedral sites [20,21]. Here, the Co 2p spectra were resolved using a fitting procedure partially based on that suggested by Biesinger et al. [22]. The contributions of the Co3+ and Co2+ cations can be identified at 779.5 and 781.1 eV, respectively [23]. Additionally, two satellite peaks, S1 and S2, at 785.3 and 789.4 eV, appeared due to electron correlations and the final state effects in the Co2+ and Co3+ cations, respectively [24]. Meanwhile, the satellite peak S3 indicates the spin orbit contributions of Co 2p1/2, as do the satellites S1 and S2 [25,26]. The O 1s spectra in Figure 5b are also decomposed into two peaks. The peaks located at 529.7 and 531.2 eV can be ascribed to lattice oxygen (Olatt, i.e., O2-) and oxygen adsorbed onto the surface oxygen vacancies (Osur, i.e., O, O22−, and OH), respectively [27].
Based on the quantitative analysis, the Co2+/Co3+ molar ratio of the two catalysts was Co3O4-FL (1.46) > Co3O4-C (1.31). The higher molar ratio of Co2+/Co3+ than Co3O4-FL indicates that a higher abundance of Co2+ cations was presented on the surface of Co3O4-FL, which could manifest an increased redox activity for methane oxidation [28]. This trend is in good agreement with that of low-temperature reducibility. According to the quantitative analysis of the O 1s spectra, the Osur/Olatt malor ratio of Co3O4-FL (0.50) is similar to that of Co3O4-C (0.51), whereas Co3O4-FL can provide other active sites for the surface oxygen species and boost the catalytic activity.

3.2. Methane Catalytic Oxidation

The effect of methane oxidation on Co3O4-FL and Co3O4-C catalysts is depicted in Figure 6. It seems that the activity is influenced by the different morphologies. The temperatures for the 50% conversion of methane (T50) and 90% conversion of methane (T90) in Co3O4-FL are 380 and 430 °C, respectively, which are much lower than these temperature values for Co3O4-C at the same conversion rate. This can be explained by the relatively high specific surface area, the greater number of active surface oxygen species, and the higher reducibility of highly exposed Co3O4-FL. Interestingly, Co3O4-FL showed nearly identical T50 and T90 values in the first three recycles, indicating the robust catalytic stability of Co3O4-FL. Meanwhile, other thermal stability tests were carried out at T50, T80 and T100 under the same catalytic conditions (Figure 7). The values of T50, T80 and T100 within the 20 h tests were 380, 415, and 520 °C, respectively, without variation. This result confirms that Co3O4-FL has excellent thermal stability, suggesting its great potential practical applicability.
Based on the previous characterizations and test results, the catalytic methane oxidation of Co3O4-FL can be enacted via a suprafacial mechanism, whereby the dissociatively adsorbed surface oxygen and the surface lattice oxygen act as the reaction active species. Besides this, the role of the reactive {112} plane in the Co3O4 nanosheets, and the oxygen vacancies derived from the mobility of lattice oxygen after the surface oxygen is consumed during methane oxidation, appear to be necessary.

4. Conclusions

In this study, flower-like Co3O4 hierarchical microspheres composed of nanosheets were prepared via a solvothermal method for methane oxidation. The dominantly exposed {112} crystal planes, together with the desorption of higher levels of active surface oxygen and the active species of lattice oxygen, lead to the presence of more active sites for C–H bond-breaking, which boosted the methane oxidation activity to a T90 of 430 °C at 21,000 mL g−1 h−1. These results provide guidance for the design and preparation of non-noble metal catalysts for methane oxidation and other oxidative reactions.

Author Contributions

Conceptualization, C.L.; data curation, J.Z.; formal analysis, D.D. and Y.H.; project administration, C.W. and M.L.; resources, J.G. and Y.Q.; supervision, C.L.; writing—original draft, C.W.; writing—review & editing, C.L. and M.L. funding acquisition, C.L., C.W. and M.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by National Natural Science Foundation of China (NSFC) (21978003), Key Research Project of Natural Science in Universities of Anhui Province (No. KJ2019ZD62, No. KJ2019A0850, No. KJ2020A0749), Excellent Young Talents Foundation in Universities of Anhui Province (gxyq2021223), and Natural Science Foundation of Shandong Province (ZR2020QB139).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data is available within the manuscript.

Acknowledgments

This research was supported in part by Engineering Technology Research Center of Silicon-based Materials (Anhui) and Functional Powder Materials Laboratory of Bengbu.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kamal, M.S.; Razzak, S.A.; Hossain, M.M. Catalytic oxidation of volatile organic compounds (VOCs)—A review. Atmos. Environ. 2016, 140, 117–134. [Google Scholar] [CrossRef]
  2. Fletcher, S.E.M.; Schaefer, H. Rising methane: A new climate challenge. Science 2019, 364, 932–933. [Google Scholar] [CrossRef] [PubMed]
  3. Vickers, S.M.; Gholami, R.; Smith, K.J.; MacLachlan, M.J. Mesoporous Mn- and La doped cerium oxide/cobalt oxide mixed metal catalysts for methane oxidation. Appl. Mater. Interfaces 2015, 7, 11460–11466. [Google Scholar] [CrossRef] [PubMed]
  4. Liu, W.; Xiang, W.; Guan, N.; Cui, R.; Cheng, H.; Chen, X.; Song, Z.; Zhang, X.; Zhang, Y. Enhanced catalytic performance for toluene purification over Co3O4/MnO2 catalyst through the construction of different Co3O4-MnO2 interface. Sep. Purif. Technol. 2022, 278, 119590. [Google Scholar] [CrossRef]
  5. Yu, Q.; Wang, C.; Li, X.; Li, Z.; Wang, L.; Zhang, Q.; Wu, G.; Li, Z. Engineering an effective MnO2 catalyst from LaMnO3 for catalytic methane combustion. Fuel 2019, 239, 1240–1245. [Google Scholar] [CrossRef]
  6. Yu, Q.; Liu, C.; Li, X.; Wang, C.; Wang, X.; Cao, H.; Zhao, M.; Wu, G.; Su, W.; Ma, T.; et al. N-doping activated defective Co3O4 as an efficient catalyst for low-temperature methane oxidation. Appl. Catal. B 2020, 269, 118757. [Google Scholar] [CrossRef]
  7. Sanchis, R.; García, A.; Ivars-Barceló, F.; Taylor, S.H.; García, T.; Dejoz, A.; Vázquez, M.I.; Solsona, B. Highly active Co3O4-based catalysts for totaloxidation of light C1–C3 alkanesprepared by a simplesoft chemistry method: Effect of the heat-treatment temperature and mixture of alkanes. Materials 2021, 14, 7120. [Google Scholar] [CrossRef]
  8. Choya, A.; de Rivas, B.; Gutiérrez-Ortiz, J.I.; López-Fonseca, R. Bulk Co3O4 for methane oxidation: Effect of the synthesis route on physico-chemical properties and catalytic performance. Catalysts 2022, 12, 87. [Google Scholar] [CrossRef]
  9. Yu, Q.; Zhuang, R.; Gao, W.; Yi, H.; Xie, X.; Zhang, Y.; Tang, X. Mesoporous Co3O4 with large specific surface area derived from MCM-48 for catalytic oxidation of toluene. J. Solid State Chem. 2022, 307, 122802. [Google Scholar] [CrossRef]
  10. Miao, L.; Tang, X.; Zhao, S.; Xie, X.; Du, C.; Tang, T.; Yi, H. Study on mechanism of low-temperature oxidation of n-hexanal catalysed by 2D ultrathin Co3O4 nanosheets. Nano Res. 2022, 15, 1660–1671. [Google Scholar] [CrossRef]
  11. Wang, X.; Chen, X.; Gao, L.; Zheng, H.; Zhang, Z.; Qian, Y. One-Dimensional Arrays of Co3O4 Nanoparticles:  Synthesis, Characterization, and Optical and Electrochemical Properties. J. Phys. Chem. B 2004, 108, 16401–16404. [Google Scholar] [CrossRef]
  12. Hu, L.; Peng, Q.; Li, Y. Selective synthesis of Co3O4 nanocrystal with different shape and crystal plane effect on catalytic property for methane combustion. J. Am. Chem. Soc. 2008, 130, 16136–16137. [Google Scholar] [CrossRef]
  13. Liotta, L.F.; Wu, H.; Pantaleo, G.; Venezia, A.M. Co3O4 nanocrystals and Co3O4–MOx binary oxides for CO, CH4 and VOC oxidation at low temperatures: A review. Catal. Sci. Technol. 2013, 3, 3085–3102. [Google Scholar] [CrossRef]
  14. Fei, Z.; He, S.; Li, L.; Ji, W.; Au, C.T. Morphology-directed synthesis of Co3O4 nanotubes based on modified Kirkendall effect and its application in CH4 combustion. Chem. Commun. 2012, 48, 853–855. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  15. Setiawan, A.; Kennedy, E.M.; Dlugogorski, B.Z.; Adesina, A.A.; Stockenhuber, M. The stability of Co3O4, Fe2O3, Au/Co3O4 and Au/Fe2O3 catalysts in the catalytic combustion of lean methane mixtures in the presence of water. Catal. Today 2015, 258, 276–283. [Google Scholar] [CrossRef]
  16. Liu, S.; Liu, P.; Niu, R.; Wang, S.; Li, J. Facile synthesis of mesoporous Co3O4 nanoflowers for catalytic combustion of ventilation air methane. Chem. Res. Chin. Univ. 2017, 33, 965–970. [Google Scholar] [CrossRef]
  17. Liu, Y.; Dai, H.; Du, Y.; Deng, J.; Zhang, L.; Zhao, Z.; Au, C.T. Controlled preparation and high catalytic performance of three-dimensionally ordered macroporous LaMnO3 with nanovoid skeletons for the combustion of toluene. J. Catal. 2012, 287, 149–160. [Google Scholar] [CrossRef]
  18. Cai, T.; Huang, H.; Deng, W.; Dai, Q.; Liu, W.; Wang, X. Catalytic combustion of 1,2-dichlorobenzene at low temperature over Mn-modified Co3O4 catalysts. Appl. Catal. B 2015, 166, 393–405. [Google Scholar] [CrossRef]
  19. Konsolakis, M.; Sgourakis, M.; Carabineiro, S.A.C. Surface and redox properties of cobalt-ceria binary oxides: On the effect of Co content and pretreatment conditions. Appl. Surf. Sci. 2015, 341, 48–54. [Google Scholar] [CrossRef] [Green Version]
  20. Barreca, D.; Massignan, C.; Daolio, S.; Fabrizio, M.; Piccirillo, C.; Armelao, L.; Tondello, E. Composition and microstructure of cobalt oxide thin films obtained from a novel cobalt (II) precursor by chemical vapor deposition. Chem. Mater. 2001, 13, 588–593. [Google Scholar] [CrossRef]
  21. Wei, W.; Chen, W.; Ivey, D.G. Rock salt—Spinel structural transformation in anodically electrodeposited Mn−Co−O nanocrystals. Chem. Mater. 2008, 20, 1941–1947. [Google Scholar] [CrossRef]
  22. Biesinger, M.C.; Payne, B.P.; Grosvenor, A.P.; Lau, L.W.M.; Gerson, A.R.; Smart, R.S.C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717–2730. [Google Scholar] [CrossRef]
  23. Díaz-Fernández, D.; Méndez, J.; Bomatí-Miguel, O.; Yubero, F.; Mossanek, R.J.O.; Abbate, M.; Domínguez-Cañizares, G.; Gutiérrez, A.; Tougaard, S.; Soriano, L. The growth of cobalt oxides on HOPG and SiO2 surfaces: A comparative study. Surf. Sci. 2014, 624, 145–153. [Google Scholar] [CrossRef] [Green Version]
  24. Lykhach, Y.; Faisal, F.; Skála, T.; Neitzel, A.; Tsud, N.; Vorokhta, M.; Dvořák, F.; Beranová, K.; Kosto, Y.; Prince, K.C.; et al. Interplay between the metal-support interaction and stability in Pt/Co3O4 (111) model catalysts. J. Mater. Chem. A 2018, 6, 23078–23086. [Google Scholar] [CrossRef]
  25. Chen, J.; Shi, W.; Yang, S.; Arandiyan, H.; Li, J. Distinguished roles with various vanadium loadings of CoCr2–xVxO4 (x = 0–0.20) for Methane Combustion. J. Phys. Chem. C 2011, 115, 17400–17408. [Google Scholar] [CrossRef]
  26. Gautier, J.L.; Rios, E.; Gracia, M.; Marco, J.F.; Gancedo, J.R. Characterisation by X-ray photoelectron spectroscopy of thin MnxCo3−xO4 (1 ≥ x ≥ 0) spinel films prepared by low-temperature spray pyrolysis. Thin Solid Film. 1997, 311, 51–57. [Google Scholar] [CrossRef]
  27. Valeri, S.; Borghi, A.; Gazzadi, G.C.; Di Bona, A. Growth and structure of cobalt oxide on (001) bct cobalt film. Surf. Sci. 1999, 423, 346–356. [Google Scholar] [CrossRef]
  28. Yuan, C.; Liu, S.Y.; Wang, Z.Q.; Wang, G.Y. Catalytic oxidation of low concentrations of vinyl chloride over spinel-type Co3O4 catalysts. React. Kinet. Mech. Catal. 2018, 125, 757–771. [Google Scholar] [CrossRef]
Figure 1. XRD patterns of the as-prepared Co(OH)2 precursor, Co3O4-FL, and Co3O4-C.
Figure 1. XRD patterns of the as-prepared Co(OH)2 precursor, Co3O4-FL, and Co3O4-C.
Inorganics 10 00049 g001
Figure 2. SEM images of the Co3O4-FL catalysts at low (a) and high (b,c) magnifications, TEM image of the Co3O4-FL catalysts (d), and SEM images of the Co3O4-C catalysts at low (e) and high (f) magnifications.
Figure 2. SEM images of the Co3O4-FL catalysts at low (a) and high (b,c) magnifications, TEM image of the Co3O4-FL catalysts (d), and SEM images of the Co3O4-C catalysts at low (e) and high (f) magnifications.
Inorganics 10 00049 g002
Figure 3. H2-TPR profiles of the Co3O4-FL and Co3O4-C catalysts.
Figure 3. H2-TPR profiles of the Co3O4-FL and Co3O4-C catalysts.
Inorganics 10 00049 g003
Figure 4. O2-TPD profiles of the Co3O4-FL and Co3O4-C catalysts.
Figure 4. O2-TPD profiles of the Co3O4-FL and Co3O4-C catalysts.
Inorganics 10 00049 g004
Figure 5. (a) Co 2p and (b) O 1s XPS spectra of the Co3O4-FL and Co3O4-C catalysts.
Figure 5. (a) Co 2p and (b) O 1s XPS spectra of the Co3O4-FL and Co3O4-C catalysts.
Inorganics 10 00049 g005aInorganics 10 00049 g005b
Figure 6. The light-off curves of CH4 oxidation as a function of reaction temperature over the Co3O4-FLcatalysts (a) and the catalytic stability of Co3O4-FLcatalysts (b) (reactant composition of 2% CH4, 20% O2, air balanced, WHSV = 21,000 mL g−1 h−1).
Figure 6. The light-off curves of CH4 oxidation as a function of reaction temperature over the Co3O4-FLcatalysts (a) and the catalytic stability of Co3O4-FLcatalysts (b) (reactant composition of 2% CH4, 20% O2, air balanced, WHSV = 21,000 mL g−1 h−1).
Inorganics 10 00049 g006
Figure 7. The catalytic stability of CH4 oxidation over Co3O4-FLcatalysts at T50, T80 and T100, respectively.
Figure 7. The catalytic stability of CH4 oxidation over Co3O4-FLcatalysts at T50, T80 and T100, respectively.
Inorganics 10 00049 g007
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Lv, C.; Du, D.; Wang, C.; Qin, Y.; Ge, J.; Han, Y.; Zhu, J.; Liu, M. The Flower-like Co3O4 Hierarchical Microspheres for Methane Catalytic Oxidation. Inorganics 2022, 10, 49. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics10040049

AMA Style

Lv C, Du D, Wang C, Qin Y, Ge J, Han Y, Zhu J, Liu M. The Flower-like Co3O4 Hierarchical Microspheres for Methane Catalytic Oxidation. Inorganics. 2022; 10(4):49. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics10040049

Chicago/Turabian Style

Lv, Changpeng, Dan Du, Chao Wang, Yingyue Qin, Jinlong Ge, Yansong Han, Junjie Zhu, and Muxin Liu. 2022. "The Flower-like Co3O4 Hierarchical Microspheres for Methane Catalytic Oxidation" Inorganics 10, no. 4: 49. https://0-doi-org.brum.beds.ac.uk/10.3390/inorganics10040049

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop