Hydrogen-Bonded Aliphatic Amine Dimers as Organic Structure-Directing Agents in Molecular Sieve Synthesis

Abstract

Two novel silicon-rich silicoaluminophosphate (SAPO) molecular sieves with PHI and GIS topologies (designated as SAPO-PHI and SAPO-GIS, respectively) are synthesized using N,N-dimethylethylenediamine and N,N-dimethylpropylenediamine as organic structure-directing agents with Si/(Si + Al + P) ratios of 0.23, and 0.24, respectively. Single-crystal X-ray diffraction analysis on as-made SAPO-PHI reveals that the two identical organic moieties and one bridging water molecule are self-assembled through hydrogen-bonding thus construct a hydrogen-bonded dimer organic structure-directing agent. In addition, a combination of vibrational and multinuclear MAS NMR spectroscopies evidences the host-guest and guest-guest interactions within the two SAPO frameworks. Like the case of SAPO-PHI, SAPO-GIS exhibits the hydrogen-bonding interactions between water and organic molecules within itself, probably suggesting that they are also oriented to form a hydrogen-bonded dimer complex. Framework of both novel high silica SAPO materials is characterized by unprecedentedly high concentration of Si(OAl)4 species without any Si-rich domain, which can be attributed to the structure-directing of hydrogen-bonded aliphatic amine dimers.