An optimal trapdoor zeolite for exclusive admission of CO₂ at industrial carbon capture operating temperatures

Abstract

High purity molecular trapdoor chabazite with an optimal Si/Al ratio (1:9) was prepared from fly ash. Gas adsorption isotherms and binary breakthrough experiments show dramatically large selectivities for CO over N and CH, which are the highest among physisorbents at operating temperatures suitable for postcombustion carbon capture and natural gas separations.

Cation Ordering and Exsolution in Copper‐Containing Forms of the Flexible Zeolite Rho (Cu,M‐Rho; M=H, Na) and Their Consequences for CO2 Adsorption

“…Commercially available CuO was measured as a standard. The FWHM of the Ag 3d 5 peak at 368.4 eV is routinely below 0.55 eV with a similar value for Au 4f 7 at 84 eV and experimental drift as a function of time is negligible over a period of 24 h. The crystallinity of as-prepared, cation-exchanged and dehydrated samples was confirmed by laboratory powder X-ray diffraction (PXRD) using a Stoe STAD I/P diffractometer with Cu K α1 X-radiation (1.54056 Å). To determine the structure of dehydrated zeolites, the powders were loaded into 0.7 mm quartz capillaries and dehydrated at 623 K at 5 × 10 À 5 mbar on a glass vacuum line for 10 h. The PXRD patterns of the dehydrated samples were obtained from these loaded and sealed capillaries.…”

“…[1][2][3] Furthermore, advanced materials and chemical engineering research continues to drive improved performance in these and similar applications, [4] and also in CO 2 adsorption in natural gas and biogas upgrading (CO 2 /CH 4 ) [5,6] and carbon capture from power plant and industrial emissions (CO 2 /N 2 and CO 2 /CO,H 2 ). [7,8] The performance of zeolites in gas separation relates directly to their high chemical and thermal stability and also to their structural features: high internal surface area accessible via well-defined pores and the presence of extra-framework cations. These cations affect their adsorption properties in a number of ways.…”

“…There is also strong evidence that cations in single eight-membered ring (S8R) sites (8R refers to the size of the ring, which contains 8 tetrahedral Si or Al atoms and 8 O atoms) can exert trapdoor behaviour, where the cation must move to allow passage of adsorbates, leading to selectivity on the basis of the strength of cation -molecule interactions. [7,[9][10][11][12][13][14][15] The extra-framework cation composition can be modified by aqueous ion exchange. Many studies have investigated the adsorption behaviour as the cation type (and charge) is varied, typically examining the alkali and alkaline earth metal cations.…”

Synthesis of Discrete CHA Zeolite Nanocrystals without Organic Templates for Selective CO2 Capture

“…The selective adsorption of CO 2 in CHA zeolites containing various cations (K + , Rb + , or Cs + ) have been investigated demonstrating that the cations controlling the adsorption of CO 2 over CH 4 are the ones located at the center of the 8MR. Their high separation ability was attributed to cation gating behavior described as a molecular trapdoor mechanism [10–13] . Shang et al [6] .…”

“…Their high separation ability was attributed to cation gating behavior described as a molecular trapdoor mechanism. [10][11][12][13] Shang et al [6] proposed that CO 2 and CO interact strongly with the 8MR door-keeping cations (K + , Rb + , Cs + ) owing to their respective quadrupole and dipole moment and higher polarizability as compared to N 2 and CH 4 . This interaction displaces the door-keeping cations located at site SIII' (Figure 1 a) from the 8MR, allowing the selective entry of molecules into the super cage of the CHA zeolite.…”