Synthesis and Rietveld Refinement of the Small-Pore Zeolite SSZ-16

摘要

Recent research efforts invested in the synthesis of new high-silica zeolites have yielded several novel materials with medium (～5.6 A) and large (～7.2 A) pores. Examples include new zeolites with intersecting 10 and 12 member rings-i.e., pores bounded by 10 and 12 tetrahedral (T) atoms respectively-like SSZ-26, NU-87, SSZ-37, SSZ-25, MCM-22, CIT-1(CON), and the aluminophosphate-based DAF-1 (DFO). However, except for the zeolites SSZ-28 (DDR) and SSZ-13 (CHA), to the best of our knowledge, no new high-silica zeolites with small pores have been reported. High-silica small-pore zeolites could be potentially useful for several catalytic reactions including the synthesis of dimethyl-amine, the reduction of NO_x from combustion gases and the dewaxing of fuels for octane upgrading. We present here the synthesis and structural characterization using Rietveld refinement of synchrotron X-ray powder diffraction data of the zeolite SSZ-16. SSZ-16 was first reported as being crystallized in the , presence of a diquaternary ammonium compound, derived from connecting two quinuclidine units together with a polymethylene bridge (see Figure 1, molecule I). A typical synthesis is carried out dissolving 1.89 g of 1,4-bis(1-azoniabicyclo[2.2.2]octane)butyl dibromide in 6 mL of H_2O and mixing with 5 g of sodium silicate solution (Banco 38.3% solids, SiO_2:Na_2O = 3.22) in a Teflon-lined Parr autoclave. A second solution containing 0.25 g of Al_2(SO_4)_3·18 H_2O and 0.67 g of concentrated NaOH dissolved in 6 mL of H_2O is prepared.