Synthesis and characterization of all-silica DDR zeolite by microwave heating

All-silica zeolite DDR was prepared by microwave-aided hydrothermal synthesis and characterized by X-ray diffraction, scanning electron microscopy, infra-red spectroscopy, nitrogen adsorption , elemental analysis and thermal gravimetric analysis . Microwave-aided heating significantly reduced the synthesis time from 25 d to 3 d and crystal size from 8 μm to 2 μm. With the help of seeding, the synthesis time and crystal size were further reduced to 6 h and 0.7 μm respectively. The crystal size decreased with seed content. The fragmentation of seed crystals had positive impact on reducing crystal size and increasing product yield. The aging of mother liquor and decrease of H 2 O/SiO 2 had little impact on crystal size.