27Al and 19F Solid‐State NMR Studies of Zeolite H‐β Dealuminated with Ammonium Hexafluorosilicate.

Abstract

The dealumination of zeolite H-β by ammonium hexafluorosilicate (i.e., (NH4)2SiF6, AHFS) treatment was investigated by 27Al and 19F solid-state NMR, combined with 27Al/19F double resonance NMR. The NMR results demonstrated that the experimental conditions of AHFS dealumination, that is, in the presence and absence of ammonium acetate (NH4OAc), strongly affected the amount, state, and nature of extraframework aluminum (EFAl) species. Different aluminum fluoro-complexes after dealumination were detected. 19F and 27Al NMR results revealed that the essential part of the dealumination process carried on with AHFS in the presence of NH4OAc was that most of the extracted Al3+ reacted with F- to form (NH4)3AlF6 species that were evident from the signals at 0 ppm in the 27Al spectrum and −143 ppm in the 19F spectrum, respectively. In the absence of NH4OAc, a resonance at 13 ppm and a broad pattern spread from −20 to −90 ppm in the 27Al spectrum were observed, indicating the presence of two different forms of alumi...