Strontium(II) chabazite-type silicoaluminophosphate prepared via microwave synthesis and partial detemplation: A superior CO2 adsorbent

A silicoaluminophosphate with a chabazite-type framework (SAPO-34) was synthesized via a microwave heating assisted hydrothermal method. The effect of variables such as crystallization time and aging time on the microwave-assisted synthesis was investigated in detail. X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma mass spectrometry (ICP-MS), solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) measurements, porosimetry and pure component CO2 gas adsorption were used to characterize the materials structural and textural properties. High purity and small size cubic crystals (0.2–1 μm) of Na-SAPO-34 with large surface area were successfully synthesized by microwave heating after 42 h, compared to 8 days required via the conventional method. It has been discovered that a short aging time of 8 h favors formation of small crystals, plausibly due to an enhanced nucleation. In addition, MAS NMR spectra showed that framework silicon atoms are present mainly as Si(4Al), which evidences a framework with minimal amount of faults. As-synthesized materials were ion exchanged with Sr2+ after partial detemplation and afterwards tested for CO2 uptake at room temperature. Elemental analyses revealed superior Sr2+ loadings per unit cell, probably due to the neat crystalline characteristics. As a result, the materials also exhibited superior CO2 adsorption capacities, particularly at low partial pressures where the sorbent–sorbate interactions are predominant.

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► In this study we obtained smaller SAPO-34 crystals with narrow size distribution.
► When combined with partial detemplation, the synthesis produces better Sr2+ loadings.
► The materials exhibit outstanding CO2 adsorption loadings at low partial pressures.