Mixed-metal (Al,Ga)-MIL-53 materials were synthesised and enriched in ¹⁷O. An NMR crystallographic approach reveals the cation distribution on the atomic level, and the effect of this on the breathing behaviour of the framework.

The lithium-exchanged form of a merlinoite zeolite (MER) with Si/Al = 4.2 (unit cell composition Li6.2Al6.2Si25.8O64) possesses a strongly contracted framework when dehydrated (the unit cell volume decreases by 12.9% from the hydrated 'wide-pore' form to the dehydrated 'narrow-pore' form). It shows cooperative adsorption behaviour for CO2, leading to two-step isotherms with the second step at elevated pressure (>2.5 bar at 298 K). Partially exchanging Na and K cations to give single phase Li,Na-and Li,K-MER materials reduces the pressure of this second adsorption step because the transition from narrow-to wide-pore forms upon CO2 adsorption occurs at lower partial pressures compared to that in Li-MER: partial exchange with Cs does not reduce the pressure of this transition. Exsolution effects are also seen at K cation contents >2.2 per unit cell. The phase transitions proceed via intermediate structures, by complex phase behaviour rarely seen for zeolitic materials. The strongly distorted narrow-pore structures adopted upon dehydration give one dimensional channel structures in which the 2 percolation of CO2 through the material requires cation migration from their locations in ste sites. This is slow in Li3.4Cs2.8-MER where Cs cations occupy these critical ste cavities in the channels, causing very slow adsorption kinetics. As the partial pressure of CO2 increases, a threshold pressure is reached where cooperative adsorption and Cs cation migration occur and the wide-pore form results, with a three dimensionally connected pore system, leading to a sharp increase in uptake. This is far in excess of the increase of unit cell volume because more of the pore space becomes accessible. Strong hysteretic effects occur upon desorption, leading to CO2 encapsulation. CO2 remaining within the material after repeated adsorption/desorption cycles without heated activation improves sorption kinetics and modifies the stepped isotherms.

Small pore aluminosilicate zeolites are attractive targets for synthesis because of their activity as catalysts in important reactions, including ammonia-mediated selective catalytic reduction (SCR) of NOx in auto-exhaust emissions. Such a zeolite with SWY framework type, previously observed as a silicoaluminophosphate, has been prepared highly crystalline via designed syntheses employing organic 1,8-(1,4-diazabicyclo[2.2.2]octane)octyl (diDABCO-C8) and K + cations as templates. STA-30 (St Andrews microporous material 30) is an ABC-6 structure in the erionite-offretite family of zeolites that exhibits the 12-layer stacking sequence AABAABAACAAC. The framework, which can be prepared with controllable Si/Al ratio, possesses columns of alternating d6r units and can cages, the latter oriented to give an inter-column pore space comprising gme cages and swy cages connected via 8Rs. DiDABCO-C8 cations fill the swy cages of as-prepared STA-30 while K + cations display high occupancy in the can cages. Removal of template by calcination, followed by ammonium ion exchange 2 of K + cations residing outside the can cages and subsequent deammoniation, gives a highly crystalline zeolite (K3H6Al9Si72O144, P63/mmc, a = 12.9922(9) Å, c = 29.9624(12) Å) with solid acidity shown by solid state 1 H MAS NMR. Upon hydration, a portion of the Al adopts octahedral geometry, as demonstrated by two sharp resonances at −2.0 ppm and −3.1 ppm in the 27 Al MAS NMR. These octahedral species can be converted back to tetrahedral Al by ammonium exchange and are interpreted as distinct hydrated framework Al sites. The activated K,H-STA-30 is a small pore solid acid with a three-dimensionally connected micropore volume of 0.31 cm 3 g −1 . In the copper-loaded form it is an active catalyst for the SCR of NO by ammonia.