Samples of high-silica SSZ-13, ion exchanged with protons and alkali-metal cations Li(+), Na(+), and K(+), were investigated using adsorption isotherms of CO(2) and N(2). The results show that Li-, Na-SSZ-13 have excellent CO(2) capacity at ambient temperature and pressure; in general, Li-SSZ-13 shows the highest capacity for N(2), CO(2) particularly in the low-pressure region. The effect of cation type and Si/Al ratio (6 and 12) on the adsorption properties was investigated through analysis of adsorption isotherms and heats of adsorption. The separation of CO(2) in a flue gas mixture was evaluated for these adsorbents in the pressure swing adsorption and vacuum pressure adsorption processes.

The increased carbon dioxide concentration in the atmosphere caused by combustion of fossil fuels has been a leading contributor to global climate change. The adsorption-driven pressure or vacuum swing (PSA/VSA) processes are promising as affordable means for the capture and separation of CO₂. Herein, an 8-membered-ring zeolite ZK-5 (Framework Type Code: KFI) exchanged with different cations (H⁺, Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺) was synthesized as novel CO₂ adsorbent. The samples were characterized by SEM, energy-dispersive X-ray spectroscopy (EDAX), XRD, and gas adsorption (CO₂ and N₂). The Toth adsorption model was used to describe the CO₂ adsorption isotherms, and the isosteric heats of adsorption were calculated. CO₂ capture adsorbent evaluation criteria such as working capacity, regenerability and CO₂/N₂ selectivity were applied to evaluate the zeolite adsorbents for PSA/VSA applications. The in situ FTIR CO₂ adsorption spectra show that physisorption accounts for the largest fraction of the total CO₂ adsorbed. The CO₂ adsorption analysis shows that Mg-ZK-5 is the most promising adsorbent for PSA applications with the highest working capacity (ΔN(CO₂)=2.05 mmol g⁻¹), excellent selectivity (α(CO₂/N₂)=121), and low isosteric heat. Li-, Na- and K-ZK-5 with good working capacity (ΔN(CO₂)=1.55-2.16 mmol g⁻¹) and excellent selectivity (α(CO₂/N₂)=103-128) are promising CO₂ adsorbents for the VSA working region.

A dual template synthesis strategy was employed to achieve one-step design of meso- and microporous MFI nanosheet assemblies with tailored morphology, mesoporosity, and catalytic activity. A molecular template (tetrapropylammonium hydroxide, TPAOH) and a polyquaternary ammonium surfactant ([C22H45–N+(CH3)2–C6H12–N+(CH3)2–C6H13]Br2, C22–6–6) were used as cotemplates in the synthesis with a composition of 30Na2O/1Al2O3/100SiO2/10C22–6–6/xTPAOH/4000H2O/18H2SO4. By tuning the concentration of TPAOH (x) from 0 to 20, the morphology of the as-obtained MFI nanosheet assemblies changed from intertwined, to house-of-cards-like, and to dense packing plates. The N2 isotherms showed the hysteresis loop at the range of P/P 0 = 0.45–1.0 increases, reaches a maximum, and then decreases with increasing x values, indicating a systematic tailoring of the mesoporosity with TPAOH concentrations. Under strict kinetic control, the rates and apparent activation energies of the ethanol activation in zeolite nanosheet assemblies were comparable. The catalytic conversion of benzyl alcohol in mesitylene showed that the activity of as-obtained MFI zeolites increases, reaching a maximum, and then decreases with increasing x values. The consistency in the variation of morphology, mesoporosity, and catalytic activity with varying x values in the synthesis indicates TPAOH can be used as a secondary template to tailor the textural and catalytic properties of MFI nanosheet assemblies primarily guided by C22–6–6.

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CO2 adsorption in Li-, Na-, K-CHA (Si/Al=6,=12), and silica chabazite zeolites was investigated by powder diffraction. Two CO2 adsorption sites were found in all chabazites with CO2 locating in the 8-membered ring (8MR) pore opening being the dominant site. Electric quadrupole-electric field gradient and dispersion interactions drive CO2 adsorption at the middle of the 8 MRs, while CO2 polarization due to interaction with cation sites controls the secondary CO2 site. In Si-CHA, adsorption is dominated by dispersion interactions with CO2 observed on the pore walls and in 8 MRs. CO2 adsorption complexes on dual cation sites were observed on K-CHA, important for K-CHA-6 samples due to a higher probability of two K(+) cations bridging CO2. Trends in isosteric heats of CO2 adsorption based on cation type and concentration can be correlated with adsorption sites and CO2 quantity. A decrease in the hardness of metal cations results in a decrease in the direct interaction of these cations with CO2.