Methylcellulose-Directed Synthesis of Nanocrystalline Zeolite NaA with High CO₂ Uptake.

Dilshod Shakarova,Arto Ojuva,Lennart Bergström,Farid Akhtar

doi:10.3390/ma7085507

Dilshod Shakarova, Arto Ojuva + Show 2 more

Open Access

https://doi.org/10.3390/ma7085507

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Journal: Materials	Publication Date: Jul 28, 2014
Citations: 48	License type: CC BY 3.0

Affiliation: Stockholm University, Luleå University of Technology

Abstract

Zeolite NaA nanocrystals with a narrow particle size distribution were prepared by template-free hydrothermal synthesis in thermo-reversible methylcellulose gels. The effects of the amount of methylcellulose, crystallization time and hydrothermal treatment temperature on the crystallinity and particle size distribution of the zeolite NaA nanocrystals were investigated. We found that the thermogelation of methylcellulose in the alkaline Na2O-SiO2-Al2O3-H2O system played an important role in controlling the particle size. The synthesized zeolite nanocrystals are highly crystalline, as demonstrated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) shows that the nanocrystals can also display a well-defined facetted morphology. Gas adsorption studies on the synthesized nanocrystalline zeolite NaA showed that nanocrystals with a size of 100 nm displayed a high CO2 uptake capacity (4.9 mmol/g at 293 K at 100 kPa) and a relatively rapid uptake rate compared to commercially available, micron-sized particles. Low-cost nanosized zeolite adsorbents with a high and rapid uptake are important for large scale gas separation processes, e.g., carbon capture from flue gas.

Highlights

Zeolites are porous aluminosilicates with a high surface area and a high thermal stability and are used in applications such as catalysis [1,2], ion exchange [3,4] and in separation and purification processes [5,6]
Nanocrystalline zeolite A has been hydrothermally synthesized in solutions containing thermo-reversible methylcellulose
The dynamic light scattering (DLS) measurements indicate a slightly smaller change in the average particle size than the scanning electron micrographs indicate, e.g., NZ040 and NZ080 are reported by DLS as having an average size of 100 ± 20 nm and 150 ± 50 nm, respectively, but Figure 1e (NZ040)

Summary

Introduction

Zeolites are porous aluminosilicates with a high surface area and a high thermal stability and are used in applications such as catalysis [1,2], ion exchange [3,4] and in separation and purification processes [5,6]. Low-cost nanosized zeolite adsorbents that can combine a high adsorption capacity and good selectivity with rapid adsorption kinetics are of importance for carbon capture from flue gas. While the capacity and selectivity are primarily determined by the chemical and topological features of the pores, the uptake kinetics can be controlled by reducing the diffusion length, e.g., by decreasing the particle size. A number of approaches have been developed to synthesize zeolite nanocrystals with and without the use of structure-directing agents [13,14,15,16,17]: Valtchev et al showed that zeolite A nanocrystals with a size of 100–300 nm could be obtained by a slow (three days) room temperature, template-free synthesis in the system of Na2O-SiO2-Al2O3-H2O [14]. The well-faceted crystal morphology was obtained for crystals averaging 400–500 nm after prolongation of synthesis time to

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