Strontium(II) chabazite-type silicoaluminophosphate prepared via microwave synthesis and partial detemplation: A superior CO 2 adsorbent

Abstract

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 CO 2 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 Sr 2+ after partial detemplation and afterwards tested for CO 2 uptake at room temperature. Elemental analyses revealed superior Sr 2+ loadings per unit cell, probably due to the neat crystalline characteristics. As a result, the materials also exhibited superior CO 2 adsorption capacities, particularly at low partial pressures where the sorbent–sorbate interactions are predominant.