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Cation Gating and Relocation during the Highly Selective “Trapdoor” Adsorption of CO

DOI: 10.1021/cm404028f DOI Help

Authors: Magdalena Lozinska (University of St Andrews, U.K.) , John Mowat (University of St Andrews, U.K.) , Paul Wright (University of St Andrews, U.K.) , Stephen Thompson (Diamond Light Source) , Jose Luis Jorda Moret (Instituto de Tecnología Química, Spain) , Miguel Palomino (Instituto de Tecnología Química, Spain) , Susana Valencia (Instituto de Tecnología Química, Spain) , Fernando Rey (Instituto de Tecnología Química, Spain)
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.

Subject Areas: Chemistry, Materials, Environment

Instruments: I11-High Resolution Powder Diffraction

Added On: 23/10/2014 16:03

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