Multinuclear NMR Analysis of SAPO-34 Gels in the Presence and Absence of HF: The Initial Gel

Abstract

Gels prepared for the synthesis of SAPO-34, with morpholine as a structure-directing agent, have been characterized by multinuclear (1H, 13C, 19F, 27Al, and 31P), high-resolution NMR at room temperature. Less complex solutions are prepared and analyzed to aid in the peak assignment. Although some spectral features remain unresolved, the overall analysis is qualitatively consistent with the expected complex chemistry taking place in these solutions. Systems in the presence and absence of HF reveal significant spectral differences. It has been shown that pH can be monitored by the proton and carbon chemical shift of morpholine. In addition, 1H and 13C NMR spectra 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 27Al NMR, where it has been concluded that morpholine has a significant 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 aluminophosphate complexes are formed in the absence of HF and morpholine. No sign of interactions 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.