Some observations on the synthesis of colloidal beta zeolite from a clear precursor sol

The preparation of colloidal beta zeolite has been studied by the hydrothermal reaction of a concentrated but clear precursor solution. When the reaction temperature was below 100 °C, the obtained zeolite particles were smaller than 60 nm, but suffered from a low yield. The yield can be improved by the increase of reaction temperature or the reaction time, but the size of the zeolite particles also grew. In the best condition, a yield of 77% was achieved for ~80 nm beta zeolite particles. The amorphous residue in the synthesis solution existed largely as ~30 nm microporous nanoparticles showing similar IR spectrum as the cr ystalline products. High speed centrifugation and thorough wash are essential to remove the amorphous silicates from the truly crystalline product. It was difficult to alarm the contamination of amorphous materials in the obtained product by analysis such as XRD, IR and nitrogen adsorption. However, a marked difference between the zeolite and the amorphous nanoparticles was observed on the Temperature Program Desorption (TPD) of hexane isomers. For methylpentane and dimethylbutane, particularly, the peak desorption temperature measured with zeolite nanoparticles was about 100 °C higher than that with amorphous ones. Nevertheless, the peak desorption temperature of zeolite nanoparticles was still about 100 °C lower than that of micron size counterpart, suggesting a shorter diffusion path in the former.