Designed Synthesis of STA-30: A Small-Pore Zeolite Catalyst with Topology Type SWY

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 with high crystallinity 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 a controllable Si/Al ratio,
possesses columns of alternating d6r units and can cages, of which the latter are 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 the template by calcination, followed
by ammonium ion exchange 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 1H MAS NMR. Upon hydration, a portion of the Al adopts octahedral
geometry, as demonstrated by two sharp resonances at −2.0 and
−3.1 ppm in the 27Al 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 cm3 g–1. In
the copper-loaded form, it is an active catalyst for the SCR of NO
by ammonia.