Cation gating and relocation during the highly selective “trapdoor” adsorption of CO2 on univalent cation forms of zeolite rho

DOI: 10.1021/cm404028f

Authors: Magdalena M. Lozinska (University of St Andrews) , John P. S. Mowat (University of St Andrews) , Paul A. Wright (University of St Andrews) , Stephen P. Thompson (Diamond Light Source) , Jose L. Jorda (Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia) , Miguel Palomino (Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia) , Susana Valencia (Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia) , Fernando Rey (Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials , VOL 26 (6) , PAGES 2052 - 2061

State: Published (Approved)
Published: March 2014
Diamond Proposal Number(s): 9027

Abstract: Adsorption of CO 2 and CH 4 has been measured on the Na-, K-, and Cs-forms of zeolite Rho (0 - 9 bar; 283 - 333 K). Although CH 4 is excluded, CO 2 is readily taken up, although the uptake at low pressures decreases strongly, in the order Na + >K + >Cs + . Structural studies by powder X-ray di ff raction (PXRD) suggest that cations in intercage window sites block CH 4 adsorption; however, in the presence of CO 2 , the cations can move enough to permit adsorption (several angstrom s). Determination of time- averaged cation positions during CO 2 adsorption at 298 K by Rietveld re fi nement against PXRD data shows that (i) in Na-Rho, there is a small relaxation of Na + cations within single eight-ring (S8R) sites, (ii) in Cs-Rho, D8R cations move to S8R sites (remaining within windows) and two phases of Cs-Rho ( I 4 3 m , Im 3 m ) are present over a wide pressure range, and (iii) in K-Rho, there is relocation of some K + cations from window sites to cage sites and two phases coexist, each with I 4 3 m symmetry, over the pressure range of 0 - 1 bar. The fi nal cation distributions at high P CO 2 are similar for Na-, K-, and Cs-Rho, and adsorption in each case is only possible by “ trapdoor ” -type cation gating. Complementary studies on K-chabazite (Si/Al = 3) also show changes in time-averaged cation location during CO 2 adsorption.

Journal Keywords: Adsorption; Cations; Molecules; Physical and chemical processes; Zeolites

Diamond Keywords: Carbon Capture and Storage (CCS); Gas Separation

Subject Areas: Chemistry, Materials, Environment


Instruments: I11-High Resolution Powder Diffraction

Added On: 23/10/2014 16:03

Discipline Tags:

Zeolites Earth Sciences & Environment Climate Change Chemistry Materials Science Chemical Engineering Engineering & Technology Inorganic Chemistry

Technical Tags:

Diffraction X-ray Powder Diffraction