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