Elsevier

Applied Clay Science

Volume 200, January 2021, 105909
Applied Clay Science

Research Paper
Novel fabrication of a sepiolite supported cobalt-based catalyst via a coprecipitation-reduction method

https://doi.org/10.1016/j.clay.2020.105909Get rights and content

Highlights

  • A novel clay supported cobalt-based catalyst was successfully prepared via a coprecipitation-reduction method.

  • The introduction of sepiolite can improve the distribution of CoAl2O4 nanoparticles.

  • The route via reduction of CoAl2O4/sepiolite composite could provide more active sites.

  • The CoAl2O4 as a transition layer can provide cobalt source for subsequent reduction process.

Abstract

In this work, a novel supported cobalt-based catalyst Co-CoAl2O4/sepiolite was successfully prepared via a coprecipitation-reduction method. The nanocomposites were examined by various surface characterization techniques to explore the optimal preparation conditions which were found to be: 750 °C for the calcination temperature, 9 for the pH value of the precursor, 7.5:1 for the mass ratio of the metal salt to sepiolite and 650 °C for the reduction temperature. The introduction of sepiolite not only reduced the calcination temperature of forming spinel CoAl2O4, but also improved the distribution of the CoAl2O4 nanoparticles, which provided more active sites to support Co nanoparticles produced via the reduction of the CoAl2O4/sepiolite composite subsequently. Moreover, the existence of CoAl2O4 as a transition layer provided a cobalt source for the subsequent reduction process and increased the service life of the catalyst. This work is believed to provide a new strategy for designing low cost and efficient cobalt-based catalysts.

Introduction

Cobalt-based catalysts are widely used in environmental catalysis and petrochemical industry due to their low cost, stable product selectivity, and good catalytic activity (Khodakov et al. 2007; Piao et al. 2020). Different from iron-based catalysts, cobalt-based catalysts have the characteristics of poisoning resistance and anti-coking in the products (Zhang et al. 2014; Qi et al. 2020). Meanwhile, the price of Co is much lower than that of noble metals. Cobalt-based catalysts are mostly supported, and usually used in Fischer-Tropsch synthesis (Ail and zDasappa 2016). The most common carriers are zeolite, aluminum oxide, titanium dioxide, silica, carbonaceous materials, and so on (Ma et al. 2011; Vosoughi et al. 2017; Jin et al. 2019; Kliewer et al. 2019; Chen et al. 2020; Izhab et al. 2020). Recently, more attention has been paid to prepare highly efficient cobalt-based catalysts and explore the effect of their micromorphologies and structures on the catalytic performance. To date, cobalt-based catalysts have been frequently synthesized by the methods of impregnation, coprecipitation, hydrothermal, solution combustion, and so on (Su et al. 2009; Shi et al. 2012; Ewbank et al. 2014; Budiman et al. 2016; Eschemann et al. 2016; Labuschagne et al. 2016; Albadi et al. 2017; Feng et al. 2018; Rajesh et al. 2019). At present, cobalt-based catalysts still suffer from many drawbacks, such as the lack of suitable carriers, poor active components dispersion and low degree of reduction, which obstruct their industrial application (Khodakov et al. 2007).

In recent years, inorganic minerals have attracted much attention and been widely used in the carrier field (Jiang et al. 2017; Wang et al., 2019b; Zhang et al. 2019; Zhu et al. 2019), which can not only reduce the preparation cost, but also prevent the accumulation of products. Sepiolite is an environment-friendly natural clay mineral with a special pore structure and fibrous shape which make it have excellent properties of adsorption, rheology, catalysis, and high-temperature resistance, thus it becomes one of the key research subjects in non-metallic minerals (García-Romero and Suárez 2013; Demirel and Aksakal 2015; Abbaslou et al. 2016; Sabah and Ouki 2017).

In our previous studies, different methods were adopted to prepare CoAl2O4/sepiolite nanocomposites (Zhang et al. 2018; Wang et al. 2019a), which effectively improved the dispersion of the catalysts. In this study, a novel supported cobalt-based catalyst Co-CoAl2O4/sepiolite was prepared via a coprecipitation-reduction method. Different from the previous cobalt-based catalysts with a single carrier, sepiolite increased the dispersion of CoAl2O4 which existed as a transition layer, and also improved the distribution of the metallic Co reduced on the surface of highly dispersed CoAl2O4. This new transition layer structure not only improved the dispersion of the active component (metallic Co herein), but also served as the source of Co in the subsequent reaction. However, research on this new structure of the sepiolite-supported cobalt-based catalyst has not been reported yet.

Section snippets

Materials

Sepiolite was acquired from Henan province of China. It was composed of SiO2 (53.56%), MgO (36.79%), CaO (5.53%), Fe2O3 (1.17%), igloss (2.95%). Co(NO3)2·6H2O and Al(NO3)3·9H2O were purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China). All the reagents were used without further purification.

Preparation of Co-CoAl2O4/sepiolite composite

The process of preparation is shown in Fig. 1. 5.0 g of Co(NO3)2·6H2O and 12.89 g of Al(NO3)3·9H2O were dissolved in 50 mL of deionized water, and an appropriate amount of sepiolite

Results and discussion

Fig. 3 shows the TG-DTA curves of the CoAl2O4/sepiolite precursor. It is clear that the mass change during the heating process can be divided into four stages. The first and second stages were mainly caused by the evaporation of physical adsorption water on the surface of the precursor, the crystal water of the nitrate, and the zeolitic water of sepiolite. In the third stage, the metal ions in the precursor were transferred to Co3O4 by the redox effect, and the coordinated water of the

Conclusion

In this study, the sepiolite nanofiber-supported Co-CoAl2O4 composites with high crystallization, even dispersion, and small particle size have been successfully prepared via a coprecipitation-reduction method. The optimal preparation conditions have been explored to be: calcination at 750 °C, the pH of the precursor was 9, the mass of the metal salt to sepiolite was 7.5:1 and the reduction temperature was 650 °C. As the calcination temperature and pH value increased, the crystallinity of the

Author statement

J.S.L. and F.W. developed and directed the work. T.T.Z., Y.P.D and H.Z. performed the experiments and measurements. B.Z.F., P.Z.G. and M.H. analyzed the results and helped with writing the paper.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by National Natural Science Foundation of China (No. 51874115), the Postdoctoral Science Foundation funded project of China (No. 2020 T130166), Introduced Overseas Scholars Program of Hebei province, China (No. C201808), Enterprise Science and Technology Commissioner Project of Tianjin City, China (No. 19JCTPJC56100) and Excellent Young Scientist Foundation of Hebei province, China (No. E2018202241).

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