Template free crystallization of zeolite Rho via Hydrothermal synthesis: Effects of synthesis time, synthesis temperature, water content and alkalinity

Four parameters affecting organic template free hydrothermal synthesis of Rho zeolite were investigated, including synthesis time, synthesis temperature, water content, and alkalinity. XRD and SEM techniques were applied to characterize the synthesized zeolite Rho powders. The results showed that synthesis time has a higher impact on the crystal size. The crystal size increases from 1.45 to 1.90 μm by increasing synthesis time from 4 to 10 days. Synthesis time is also effective on the crystals morphology and there is an extremum in the diagram of crystallinity versus synthesis time for zeolite Rho. In addition, synthesis temperature has high impact on morphology of the crystals and can change the zeolite phases. Besides, water content is also highly effective on crystallinity of the synthesized powders and with increasing water content the crystallinity decreases dramatically. At last, increasing alkalinity increases the nucleation and decreases the crystals size. At water content of 400 mol, pollucite phase was synthesized at two ratios of Na2O/Al2O3=6 and Cs2O/Al2O3=0.8, and also two ratios of Na2O/Al2O3=9 and Cs2O/Al2O3=1.2; and for these ratios the mean crystal sizes were 0.70 and 0.40 μm, respectively, confirming the negative effect of alkalinity on the mean crystal size.