The effects of varying the starting silica source on the synthesis of molecular sieve zeolite NaX were investigated, while all other reaction parameters were kept constant. The silica sources were all powders of varying types and purity. Characterizations of the silica sources, the silicate solutions, and the synthesis products were completed by powder X-ray diffraction, electron microscopy, particle-size analysis, n.m.r, spectroscopy, laser light scattering, and elemental analysis. The use of different silica sources significantly influenced the outcome of the synthesis experiments. There were large differ- ences in the results from the various batch synthesis mixtures, even though the batch compositions were all the same (neglecting impurities). The experiments, all conducted at 115°C in sealed 6 ml autoclaves, yielded products of different particle sizes, different amounts of impurity zeolite phases, and different conversion rates to zeolite NaX. The n.m.r. spectra of the dissolved silica sources were all effectively the same; however, the levels of trace impurities were very different. The extent to which nuclei formed in these experiments was shown to correlate to the impurity level of any one of several elements in the silica sources, but not to the turbidity of the filtered solutions as noted by a simple light-scattering measurement.
- Zeolite X crystallization
- silica source