Structural characterization and hydrochlorofluorocarbon reactivity on zinc-exchanged NaX

Solid-state MAS NMR and synchrotron X-ray powder diffraction have been used to study the reactivity and structure of Zn2+-exchanged NaX. Dehydrated Zn X with a Zn:Na ratio of 3.6:1 was refined in the space group Fd3m. The zinc cations were located in four distinct positions all along the [111] direct ion, Residual sodium cations were found in the supercage at the site II pos ition. A tetrahedral extraframework aluminum species, AlO45-, was refined i n the center of the sodalite cage; this anion was also observed by Al-27 MA S NMR. The reactions of hydrochlorofluorocarbon (HCFC)-124a (CF2HCF2Cl) ove r NaX, and two Zn(2+-)exchanged NaX samples, were studied with NMR and a ma ss spectrometry (MS)-equipped catalysis unit. The products of both the dehy drofluorination and dehydrochlorination reactions are observed over all zeo lites: the unsaturated products (CF2CF2 and CF2CFCl) desorb from the zeolit es and are detected by MS. In contrast, saturated products are primarily ob served when the reaction is followed with F-19 NMR in sealed ampules. Both CF2CF2 and HFC-125 (CF3CF2H) are observed for reactions over NaX, while on Zn2+ exchange, CF2CF2 is no longer observed. Instead, a resonance is observ ed at -123 ppm, which is tentatively assigned to (CF2)(n) groups. No eviden ce is seen by Al-27 and F-19 NMR for attack of the zeolite framework when t he reactions are performed at low temperatures. An in situ X-ray diffractio n study of HCFC-124a loaded ZnX shows significant structural changes at the same temperature as the onset of HCFC reactivity.