Solvent-Free Zeolites

The zeolite family of microporous silica-alumina materials is an invaluable resource for industrial catalysis and separations. The materials are typically made using copious amounts of water or other solvent, which can reduce final yield and generate excessive polluted wastes. An international research team has now reported a simple and economical solvent-free approach to making multiple classes of zeolites that could significantly cut down on environmental concerns. The work was led by Xiangju Meng and Feng-Shou Xiao of Zhejiang University, in China, and Feng Deng of Wuhan Institute of Physics & Mathematics of the Chinese Academy of Sciences, and it included process research and engineering collaborators at BASF (J. Am. Chem. Soc. 2015, DOI: 10.1021/ja5124013). Solvent-free approaches to making zeolites are known, but they usually begin with the hydrated form of silica gel, which limits industrial applications because anhydrous materials are ultimately needed. The new approach involves grinding up anhydrous silica gel with ammonium fluoride and standard alkylammonium zeolite templates at room temperature and then heating the mixtures as high as 240 °C. The fluoride helps drive crystallization of anhydrous zeolites, the researchers note. Compared with conventional hydrothermal synthesis, the new solvent-free approach simplifies procedures and enhances yields.