Multinuclear NMR analysis of SAPO-34 gels in the presence and absence of HF: The initial gel

Gels prepared for the synthesis of SAPO-34, with morpholine as a structure- directing agent, have been characterized by multinuclear (H-1, C-13, F-19, Al-27, and P-31), high-resolution NMR at room temperature. Less complex sol utions are prepared and analyzed to aid in the peak assignment. Although so me spectral features remain unresolved, the overall analysis is qualitative ly consistent with the expected complex chemistry taking place in these sol utions. Systems in the presence and absence of HF reveal significant spectr al differences. It has been shown that pH can be monitored by the proton an d carbon chemical shift of morpholine. In addition, H-1 and C-13 NMR spectr a suggest that the structure-directing agent is an inactive species at room temperature independent of the presence or absence of HF. This is contrary to the Al-27 NMR, where it has been concluded that morpholine has a signif icant influence on the aluminum coordination, giving tetrahedral Al when HF is absent. The existence of octahedral aluminophosphate-fluoride complexes is evident in the presence of HF, while several octahedral aluminophosphat e complexes are formed in the absence of HF and morpholine. No sign of inte ractions between aluminum and silicon, silicon and phosphates, silicon and morpholine, phosphates and morpholine, or morpholine and fluoride has been observed within the concentration range studied. Some time-resolved studies have revealed that the aging is shown to influence the type and the amount of species present in the solutions.