Stabilizing large pores
Zeolites with very large cages, such as zeolite Y, are rare but extremely useful in processing the large hydrocarbons in petroleum. Lee et al. report a route for preparing thermally stable forms of the large-cage phosphate-based molecular sieves UCSB-6 and UCSB-10 (see the Perspective by Xie). They used mainly sodium and cesium ions as inorganic structure-directing agents, along with an organic molecule, in their charge-density mismatch approach. These zeolites were used as diesel-cracking catalysts at 600┬░C.
Science, abi7208, this issue p. 104; see also abj1834, p. 28
Abstract
UCSB-6 (framework type SBS) and UCSB-10 (SBT), two three-dimensional phosphate-based molecular sieves with supercages accessible through 12-ring (circumscribed by 12 tetrahedral atoms) windows, are structurally similar to the hexagonal and cubic polytypes of faujasite or zeolite Y, an industrially relevant catalyst, but the cage structures are substantially different. Nonetheless, their inherent thermal instability has precluded any catalytic application so far. By using multiple inorganic cation and charge density mismatch approaches, we synthesized PST-32 and PST-2, a thermally stable aluminosilicate version of UCSB-10 and the hypothetical SBS/SBT intergrowth family member, respectively. This study suggests that many hypothetical cage-based zeolite structures with multidimensional channel systems can be synthesized as compositionally robust forms by systematically exploring the synergy effect of inorganic and organic structureтАУdirecting agents.
