Short communicationCore–shell structured Cu@m-SiO2 and Cu/ZnO@m-SiO2 catalysts for methanol synthesis from CO2 hydrogenation
Graphical abstract
Introduction
As a cheap, nontoxic and abundant C1 feedstock, chemical utilization of CO2 is a challenge and important topic. Synthesis of methanol from CO2 hydrogenation is of vital importance for both greenhouse gas control and fossil fuel substitution, if the needed hydrogen can be generated from water electrolysis with the energy from renewable and sustainable sources (solar energy, wind, hydroelectric, or even nuclear) [1], [2].
Cu/ZnO/Al2O3 catalysts are commercially used for methanol synthesis from syngas. However, the low activity and stability of Cu/ZnO/Al2O3 catalysts, which are partly ascribed to Cu sintering accelerated by the presence of the water vapor byproduct, create major barriers toward direct application to CO2 hydrogenation [3], [4]. Recently, various attempts have been made to improve the performance of Cu/ZnO-based catalysts for CO2 hydrogenation to methanol [4], [5], [6], [7]. It has been suggested that the high activity for CO2 hydrogenation was generated by the presence of surface defects of metallic Cu surface which can reduce the activation energy of hydrogen dissociation [8]. Rich surface defects can be achieved by decreasing the size of Cu nanoparticles with a simultaneous high dispersion. In addition, many researchers claimed that the copper particle size played an important role in the catalytic performance of copper-based catalysts [7], [9], [10]. Therefore, great efforts have been made to decrease the Cu particle size for Cu-based catalysts. However, the Cu nanoparticles are easily aggregated during reduction and reaction process, leading to deactivation and low stability.
Metal nanoparticles within a core–shell structure have important applications in catalysis [11]. The outer shells can prevent the sintering of core metal nanoparticles, even under harsh reaction, due to the confinement effects in those materials [12], [13]. Recently, considerable attention has been given to synthesizing core–shell nanocomposites using silicon dioxide (SiO2) as the shell, because SiO2 is easy to form uniform spheres with tunable sizes and possesses high thermal stability and good compatibility with other materials [14], [15]. Moreover, compared with conventional SiO2, mesoporous SiO2 (m-SiO2) favors metal dispersion and diffusion due to the higher specific surface area and enriched porosity [16]. Although many researches on SiO2 coatings on various core materials have been reported, the study of the Cu@m-SiO2 core–shell nanocomposites is – to the best of our knowledge – still lacking.
Herein, the core–shell structured Cu@m-SiO2 and Cu/ZnO@m-SiO2 nanocatalysts were prepared and tested for CO2 hydrogenation to methanol. For comparison, the mesoporous-SiO2 supported catalyst was also prepared by incipient wetness impregnation. The effect of the silica coating on the properties of Cu-based catalysts for methanol synthesis from CO2 hydrogenation will be investigated in detail.
Section snippets
Sample preparation
The synthesis for CuO@mesoporous-SiO2 nanocomposites was as follows, 0.49 g of Cu(Ac)2 was dissolved in 1350 mL ethanol under magnetic stirring, and then 9.8 g of polyvinylpyrrolidone (PVP) was added as a dispersant of nanoparticles. Afterwards, the solution was solvothermal treatment at 423 K for 8 h [17]. The obtained brown suspension was homogeneously dispersed in a mixture of distilled water (1350 mL), ethanol (1350 mL) and aqueous ammonia solution (28 wt%, 54 mL), then 4.92 g cetyltrimethylammonium
Textural and structural properties of the prepared nanocomposites
The actual metal composition of CuO@m-SiO2, CuO/ZnO@m-SiO2 and CuO/m-SiO2 materials deriving from ICP measurement is summarized in Table 1. It was evident that the copper content of the three materials was similar with each other, around 12 wt%. In addition, Zn content was 5.45 wt% for CuO/ZnO@m-SiO2 and the Cu2 +:Zn2 + atomic ratio was in close agreement with the nominal compositions (7:3) taken for the catalyst preparation.
The XRD patterns of the calcined and reduced CuO@m-SiO2, CuO/ZnO@m-SiO2
Conclusions
In summary, Cu@m-SiO2 and Cu/ZnO@m-SiO2 core–shell nanocatalysts were successfully synthesized with promising performance and high stability for CO2 hydrogenation to methanol. Several Cu or Cu/ZnO nanoparticles with a uniform particle size in around 5.0 nm were well encased within a silica shell, while each nanoparticle was separated by a thinner silica wall. The Cu dispersion of the core–shell nanocatalyst was much higher than those of the mesoporous-SiO2 supported catalyst. In addition, the
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (21503260), Strategic Priority Research Program of the Chinese Academy of Sciences (XDA02040602), and Shanghai Municipal Science and Technology Commission, China (14DZ1207600, 15ZR1444500).
References (35)
- et al.
J. CO2 Util.
(2014) - et al.
Appl. Catal. A Gen.
(2014) - et al.
Catal. Today
(2013) - et al.
J. CO2 Util.
(2013) - et al.
Appl. Catal. B Environ.
(2014) - et al.
Catal. Commun.
(2007) - et al.
Catal. Commun.
(2011) - et al.
J. CO2 Util.
(2015) - et al.
Catal. Commun.
(2014) - et al.
Catal. Commun.
(2010)
J. Catal.
Appl. Catal. B Environ.
J. Catal.
Appl. Catal. A Gen.
J. Mol. Catal. A Chem.
J. Catal.
Energy Convers. Manag.
Cited by (77)
Development of Silicalite-1 encapsulated Cu-ZnO catalysts for methanol synthesis by CO<inf>2</inf> hydrogenation
2024, Chemical Engineering JournalFrom catalyst development to reactor Design: A comprehensive review of methanol synthesis techniques
2024, Energy Conversion and ManagementAdvancement and State-of-art of heterogeneous catalysis for selective CO<inf>2</inf> hydrogenation to methanol
2023, Coordination Chemistry ReviewsLiquid phase methanol synthesis by CO<inf>2</inf> hydrogenation over Cu-Zn/Z catalysts: Influence of Cd promotion
2023, Journal of the Taiwan Institute of Chemical EngineersSynthesis, characterization and activity of CeO<inf>2</inf> supported Cu-Mg bimetallic catalysts for CO<inf>2</inf> to methanol
2023, Chemical Engineering Research and Design