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
Date
09/09/2021Author
Grant ID
EP/N024613/1
ep/l017008/1
BB/R013780/1
Metadata
Show full item recordAbstract
The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper-exchanged form of Rho and mixed Cu,H- and Cu,Na-forms have been prepared. EPR spectroscopy reveals that Cu2+ ions are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu-Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO2 rapidly at room temperature. Breakthrough tests with 10 % CO2/40 % CH4 mixtures show that Cu4.9-Rho is able to produce pure methane, albeit with a relatively low capacity at this pCO2 due to the weak interaction of CO2 with Cu cations. This is in strong contrast to Na-Rho, where cations in narrow elliptical window sites enable CO2 to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na-Rho materials was prepared to improve uptake and selectivity compared to Cu-Rho, and kinetics compared to Na-Rho. Remarkably, Cu,Na-Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na-Rho showed improved performance in CO2/CH4 breakthrough tests, producing pure CH4 with improved uptake and CO2/CH4 selectivity compared to that of Cu4.9-Rho.
Citation
Lozinska , M M , Jamieson , S , Verbraeken , M C , Miller , D N , Bode , B , Murray , C , Brandani , S & Wright , P A 2021 , ' Cation ordering and exsolution in copper-containing forms of the flexible zeolite Rho (Cu,M-Rho; M = H, Na) and their consequences for CO 2 adsorption ' , Chemistry - A European Journal , vol. 27 , no. 51 , 202101664 , pp. 13029-13039 . https://doi.org/10.1002/chem.202101664
Publication
Chemistry - A European Journal
Status
Peer reviewed
ISSN
0947-6539Type
Journal article
Description
Funding: UK Engineering and Physical Sciences Research Council. Grant Numbers: EP/N024613/1, EP/N032942/1, EP/L017008/1.Collections
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