Na⁺ and K⁺-Exchanged Zirconium Phosphate (ZrP) as High-Temperature CO₂ Adsorbents

In this contribution, the high-temperature CO₂ capture performance of zirconium phosphates (ZrPs) and their cation exchanged forms were investigated for the first time. Two phases of ZrPs, i.e., α-ZrP and γ-ZrP and K⁺ (or Na⁺) exchanged α-ZrP were characterized in detail using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). After K⁺ or Na⁺ exchange of α-ZrP (α-ZrP-K or α-ZrP-Na), the interlayer distance of the corresponding ion exchanged α-ZrP was increased from 7.6 Å to 9.0 and 8.4 Å, respectively. γ-ZrP showed a higher CO₂ capture capacity (0.09 mmol/g) than α-ZrP (0.06 mmol/g) at 350 °C. The CO₂ capture capacity of K⁺ and Na⁺ exchangedα-ZrPs was 0.13 and 0.14 mmol/g, respectively, at 350 °C. As increasing the adsorption temperature from 350 to 550 °C, the CO₂ capture capacity slightly increased from 0.13 to 0.15 mmol/g. Our result suggested that K⁺ or Na⁺ exchange of α-ZrP could be a good candidate for CO₂ capture in the temperature range of 400–500 °C, enabling the sorption enhanced hydrogen production processes more viable.