Ion exchange with Li + reduced the adsorption capacity and the Brunauer-Emmett-Teller (BET) surface area of SAPO-RHO. The degree of reduction was proportional to the extent of Li + exchange, as indicated by the number of exchange cycles (fig. and table. S4). Similarly, the 20 introduction of Na + , K + , or Cs + cations also decreased the adsorption capacity (fig. and table ) .