Highly active and stable Co3O4 catalyst for the Low-temperature oxidative dehydrogenation of propane

https://doi.org/10.1016/j.inoche.2019.107725Get rights and content

Highlights

  • Co3O4 catalyst prepared by using ZIF-8 support possesses tunable morphology, crystallite size and surface area.

  • Co3O4 catalyst exhibited excellent catalytic performance for Low-temperature (175 °C) Oxidative Dehydrogenation of Propane.

  • Loose flake-like morphology could significantly lower reaction temperatures.

  • Surface Co3+ and lattice Cosingle bond Co-O bond are responsible for high activity.

Abstract

Oxidative dehydrogenation of propane (ODP) is an intriguingly alternative approach for presently industrial propene manufacture. However, the high temperature (>500  °C) would aggravate the deep oxidation of propene and catalyst deactivation. Co3O4 catalyst prepared by using ZIF-8 support possesses tunable morphology, crystallite size and surface area, affording low-temperature (175  °C) propane conversion catalyst. Loose flake-like morphology with the smaller crystallite sizes and the larger surface area could significantly lower reaction temperature. At given propene yield, more propane conversion (21.1%) indicated that propene combustion occurred, and lower reaction temperatures contribute to boosting propene yield. The higher catalytic activity could be ascribed to easier reducibility of Co3+, the higher concentration of surface Co3+ and more surface content of lattice Cosingle bondO bond. Moreover, the Co3O4-500 catalyst displays excellent thermostability after a 20 h time on stream at 250  °C.

Introduction

Propene is a vitally basic raw feedstock in the organic petrochemical industry for manufacturing valuable and versatile chemicals and compounds [1], [2], [3]. The presently industrial propene was obtained as a by-product through the direct dehydrogenation of propane and ethane along with high energy-intensive and rapid catalyst deactivation [4], [5], [6]. One intriguingly alternative approach is to couple propane dehydrogenation with oxygen over various heterogeneous catalysts. The use of oxidant such as oxygen not only sharply lower the thermodynamic barrier (an exothermic reaction), but suppress catalyst coke formation and increase the lifetimes of the catalysts [7], [8], [9]. Because propene is more reactive than propane, the higher temperatures would aggravate the deep oxidation of propene, leading to the occurrence of side reactions. Therefore, it is imperative to afford a high active and stable low-temperature oxidative dehydrogenation of propane (ODP) catalyst at lower temperatures [10], [11], [12].

Although many transition-based metal catalysts, such as vanadium-based [5], molybdenum-based [13] and chromium-based [14], have been extensively studied and proved to be active for ODP, these type of reactions usually took place at high temperatures (above 500  °C), certainly resulting in a loss of propene selectivity [15]. Among other oxide systems, nickel-based catalysts have been reported to be active at low temperatures for ODP [16]. For Ce/Nb-modified [12] and Ti-modified [17] NiO catalysts, the lowest active temperature of propane conversion and propene formation could be as low as 250  °C, which is even lower than that of pure NiO. However, compared to these aforementioned various catalysts, metal-organic frameworks (MOFs), an emerging, enormous family of porous materials with charming crystallinity and modularity, have drawn great interest in heterogeneous catalysis, such as selective alkene dimerization/oligomerization reactions and high-temperature gas-phase catalysis reactions [18], [19]. Due to their extraordinary stability and high porosity [20], MOFs have been selected as ideal precursors for transition metal oxides to prepare heterogeneous catalysts [21], [22]. Recently, Li et al. [10] reported that the resulting materials, Co-SIM+NU-1000 and Co-AIM+NU-1000, exhibited catalytic activity for ODP at reaction temperature as low as ~200  °C. The results of subsequent NU-1000-supported bimetallic-oxide clusters suggested that catalytic activity at low temperatures (<230  °C) increases in the following order: Mo(VI) < Ti(IV) < Al(III) < Zn(II) < Ni(II), as Lewis acidity of the promoter ion decreases [23].

Herein, the research results show that cobalt oxide deposited on a support is the most active for propane oxidation [24], and the activity toward propane conversion and propene formation has been found to be highly dependent on the properties of the support [25]. Therefore, the most propitious precursors interacting with cobalt oxide would increase low-temperature propane conversion activity and promote propene formation. With regard to ZIF-8 (Zn(MeIM)2, MeIM = 2-methylimidazole), as a typical MOF, it has an intersection three-dimensional structure with large Brunauer-Emmett-Teller (BET) surface area (1413 m2g−1), pore size of 11.6 Å and good thermostability [26], [27], and has been selected as a template for preparing Co3O4 nanoparticles by using impregnation to introduce the cobalt ions.

Section snippets

Catalyst synthesis

ZIF-8 nanocrystals were prepared according to a previous literature report with minor modifications [27]. Typically, 1.68 g Zn(NO3)2·6H2O was dissolved in 80 mL methanol under vigorous magnetic stirring. Then a mixture of 3.70 g 2-methylimidazole and 80 mL methanol was added to the above solution and stirred vigorously for 24 h at room temperature. The precipitate was separated by centrifugation, then washed with methanol three times, and soaked in fresh methanol for 24 h. Finally, the ZIF-8

Results and discussion

Fig. S1 confirms the phase purity and crystallographic structure of the ZIF-8 template, matching perfectly with the results of the published PXRD patterns [27]. It could be found that ZIF-8 nanocrystals exhibited polyhedral morphology displayed in Fig. S3a, after Co ions were introduced to the ZIF-8 precursor via impregnating with Co(NO3)2 (tend to transform into flake morphology in Fig. S3b,c), then suffered to heating at 200  °C to decompose the nitrate (flake morphology in Fig. S3d).

Conclusions

In summary, Zeolite imidazolate frameworks (ZIFs), as an ideal template and precursor, have been extensively used to synthesize porous carbon materials. As pyrolysis temperatures increased, the morphology of Co3O4 catalysts varied from loose flakes to pyknotic granules. Due to much smaller crystallite sizes and larger BET surface area of loose flake-like morphology, Co3O4-400 exhibited the highest catalytic activity for ODP process at reaction temperature as low as 175  °C. Higher propane

CRediT authorship contribution statement

Lei Wang: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - Original Draft, Writing - Review & Editing, Visualization. Chengcheng Ao: Software, Data curation. Yitong Zhai: Resources. Beibei Feng: Data curation. Junrui Duan: Writing - Review & Editing. Siyu Qian: Software, Resources. Wei Zhao: Resources. Lidong Zhang: Conceptualization, Methodology, Supervision, Project administration, Funding acquisition. Fuyi Liu: Conceptualization, Methodology, Supervision,

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 51676176, No. 51976207, No. 91544105, No. 412751127) and the Fundamental Research Funds for the Central Universities (No.WK2320000038).

References (36)

  • B. Jibril et al.

    Catal. Commun.

    (2006)
  • M.A. Atanga et al.

    Appl. Catal., B

    (2018)
  • S. Sim et al.

    Mol. Catal.

    (2017)
  • G. Mitran et al.

    Catal. Today

    (2018)
  • N. Kuznetsova et al.

    Appl. Catal., A

    (2014)
  • E.V. Kondratenko et al.

    J. Catal.

    (2005)
  • F. Solymosi et al.

    J. Catal.

    (2005)
  • R. You et al.

    J. Catal.

    (2017)
  • F. Ma et al.

    Appl. Surf. Sci.

    (2014)
  • T. Blasco et al.

    Appl. Catal., A

    (1997)
  • Y. Wu et al.

    Appl. Surf. Sci.

    (2006)
  • K. Chen et al.

    J. Catal.

    (2001)
  • W. Wang et al.

    Catal. Commun.

    (2011)
  • B. de Rivas et al.

    J. Catal.

    (2011)
  • W. Tang et al.

    Appl. Catal., B

    (2018)
  • M. Herrero et al.

    Catal. Today

    (2007)
  • M. Salavati-Niasari et al.

    J. Phys. Chem. Solids

    (2009)
  • Y. Fu et al.

    J. Alloys Compd.

    (2018)
  • Cited by (0)

    View full text