Hollow mesoporous silica sphere supported cobalt catalysts for F–T synthesis
Introduction
Cobalt catalysts for CO hydrogenation are the excellent ones to convert coal and natural gas to clean, environmental-sounded fuels and chemicals via syngas [1], because of their high Fischer–Tropsch (F–T) activity, selectivity for linear hydrocarbons and low activity for water-gas shift reaction (WGS). Supported cobalt catalysts [2], [3], [4] have been found to be promising catalysts for F–T synthesis. In order to gain high metal dispersion, cobalt is typically supported on oxides with high surface area, such as silica [5], [6], alumina [2], [7], [8], titania [9], [10] and zeolites [11], [12]. The texture and chemical properties of support have important influence on the activity and product selectivity of Co catalysts [13], [14].
Recently, well-defined mesoporous molecular sieves have been used as the support to prepare cobalt catalysts. There include MCM-48 [5], MCM-41 [15], SBA-15 [16], and HMS [17]. Manuel Arruebo et al. [18] used a wet impregnation technique to deposit Fe2O3 on hollow mesoporous silica spheres (HMSS). Fe2O3 clusters with a uniform size were present at the external surface of HMSS. Small-size clusters could also be seen in the mesoporous channels and the interior void space of HMSS. Because of the hollow structure of HMSS, the interior cavities could offer more location to deposit catalyst and provide better transport channels for reactants to access the active centers and for products to move out. Lopes et al. [19] deposited cobalt nano-particles inside the pores of SBA-15 using the “two-solvent” technique. This method is based on a volume of aqueous solution equal to the pore volume of the silica support (determined by N2 sorption). The interest of this technique lies in loading cobalt species in the pores of support and minimizing the crystallization of Co3O4 particles on the external surface of the silica grains. However, the application of HMSS as the supports for cobalt catalyst prepared by using “two-solvent” technique is not reported so far.
In this work, hollow mesoporous silica spheres (HMSS) were used as a support of cobalt catalyst for Fischer–Tropsch synthesis. High dispersion Co3O4 nano-particles supported on HMSS were prepared by “two-solvent” technique. The catalysts showed good activity and high selectivity C5+ hydrocarbons in F–T synthesis.
Section snippets
Synthesis of catalysts
HMSS were prepared following references [20]. In a typical synthesis, a total of 39.2 g of hexadecyltrimethylammonium bromide (CTAB) followed by 46 g Na2SiO3·9H2O were dissolved in 674 ml of water, resulting in a clear solution. Afterwards 70 ml ethyl acetate was quickly added, the mixture was homogenized and the stirring was stopped. The resulted mixture was allowed to stand at 303 K for 5 h, and finally aged at 90 °C for 48 h. the solid product was collected by filtration, washed several times with
Catalyst texture
Similar shapes of wide-angle XRD patterns for catalysts are shown in Fig. 1. Diffraction peaks at 2θ of 31.3°, 36.9°, 45.1°, 59.4° and 65.4° indicate that after calcination, cobalt was present in the form of Co3O4 crystalline phase [21], [22] on all the catalysts. The mean Co3O4 crystallite sizes (Table 1) were calculated from the widths of XRD peaks using the Scherrer equation (2θ = 36.9°) [1], [22]. Larger Co3O4 crystallites were detected in the catalysts with higher cobalt content. An increase
Conclusion
In summary, Co3O4 nano-particles have been successfully loaded in HMSS by two-solvent technique. The cobalt catalysts supported on HMSS are highly dispersed. The F–T catalytic behavior of cobalt species can be affected by Co loading. Lower F–T activity and higher methane selectivity observed on low cobalt loading catalyst are principally attributed to the small cobalt particles could be easily reoxidized by water and other reaction products. With increasing Co loading, the cobalt crystallite
Acknowledgement
The financial support from the National Basic Research Program of China (No. 2005CB221402) was acknowledged.
References (26)
Appl. Catal. A-Gen.
(1997)- et al.
J. Mol. Catal. A-Chem.
(2006) - et al.
Catal. Today
(2000) - et al.
J. Catal.
(1996) - et al.
Appl. Catal. A-Gen.
(1999) Appl. Catal. A-Gen.
(1995)- et al.
J. Catal.
(2002) - et al.
J. Catal.
(2002) - et al.
Catal. Today
(2004) - et al.
Micropor. Mesopor. Mater.
(2001)
Int. J. Inorg. Mater.
Appl. Catal. A-Gen.
J. Mol. Catal. A: Chem.
Cited by (31)
Phosphate removal and recovery by lanthanum-based adsorbents: A review for current advances
2022, ChemosphereCitation Excerpt :Silicon oxide has the characteristics of non-toxicity, highly ordered structure, large specific surface area, adjustable pore size, and high functionality. It has been widely used in drug delivery, catalysis, and storage (Fang et al., 2013; Li et al., 2009; Zhu et al., 2005). Huang et al. (2014b) first prepared ordered mesoporous silica hollow spheres doped with lanthanum.
Experimental study on plasma-catalytic synthesis of hydrocarbons from syngas
2019, Applied Catalysis A: GeneralPerformance of hierarchical ZSM-5 supported cobalt catalyst in the Fischer-Tropsch synthesis
2017, Ranliao Huaxue Xuebao/Journal of Fuel Chemistry and TechnologyFischer-Tropsch synthesis over a 3D foamed MCF silica support: Toward a more open porous network of cobalt catalysts
2016, Journal of CatalysisCitation Excerpt :Cobalt catalysts are preferred because of their low water–gas shift activity, low deactivation rate, and high selectivity to long-chain hydrocarbons. Ordered mesoporous materials, such as MCM-41[4], MCM-48 [5], SBA-15 [6–8], and HMS [9–11], have been used as supports in FTS. These mesostructured materials not only enhance the dispersion of the active phase but also decrease the deactivation rate [12].
Dehydration of d-xylose to furfural using different supported niobia catalysts
2014, Applied Catalysis B: EnvironmentalCitation Excerpt :These results are consistent with those previously reported by Gómez-Cazalilla et al. [49]. Nevertheless, an attenuation of the diffraction peak as the niobium loading increased (SBA-12Nb and SBA-20Nb) was detected, which could be explained by the partial disorder of the silica framework during calcination step, because of the exothermic decomposition of the large amount of oxalate precursor used for preparing these catalysts, as observed by Li et al. [50]. Regarding the XRD patterns in the high-angle region, the characteristic reflections of crystalline Nb2O5 phases were not found, pointing to the presence of either amorphous particles or small sized Nb species on the silica surface (Fig. 1B).