Direct modification of pelletized 13X zeolite by atomic layer deposition toward effective CO₂ capture from flue gas

As a promising sorbent material for post combustion CO₂ capture, 13X zeolite has been broadly investigated in pressure/vacuum swing adsorption (P/VSA). However, recent P/VSA process simulation studies have posited that some metal organic frame works (MOFs) with reduced CO₂ and N₂ adsorption affinities and adsorption enthalpies can enable process level improvements, suggesting that the CO₂/N₂ adsorption strength in 13X may be stronger than what is optimal for post combustion CO₂ capture (PCC) via P/VSA. Via preferential H₂O adsorption on strong adsorption sites in 13X zeolite, we found that temporarily passivating these sites led to enhancements in CO₂ working capacity (5–15 kPa CO₂, 30 °C) and CO₂/N₂ separation factor (5–15 kPa CO₂, 1–85 kPa N₂, 30 °C) by 12 % and 94 %, respectively. To permanently weaken the adsorption strength in 13X, we employed H₂O/TiCl₄ atomic layer deposition (ALD) to “passivate” the strong adsorption sites and thus fabricate a novel adsorbent, Ti-13X, and investigated the effect of selective inhibition of high adsorption strength sites on the thermodynamic CO₂/N₂ adsorption properties. The modification technique resulted in suppressed CO₂ and N₂ adsorption affinity, manifesting in a 10 % and 133 % increase in the CO₂ working capacity (5–15 kPa, 30 °C) and CO₂/N₂ separation factor (5–15 kPa CO₂, 1–85 kPa N₂, 30 °C), respectively. CO₂ microcalorimetry experiments showed a suppressed and homogenized CO₂ heat of adsorption in Ti-13X versus pristine 13X, indicating that high enthalpy CO₂ adsorption was inhibited while the CO₂ physisorption behavior was preserved. When evaluated using the General Evaluation Metric (GEM), Ti-13X scored similarly to promising MOFs and significantly outscored pristine 13X, suggesting its merit for future investigation.