MFI Type Zeolite Aggregates with Nanosized Particles via a Combination of Spray Drying and Steam-Assisted Crystallization (SAC) Techniques

Abstract

Hydrothermal synthesis is the state-of-the-art technique for the preparation of zeolites and related porous solids. However, when it comes to the preparation of nanosized zeolites, this technique is limited by low yields, separation problems and high amounts of waste. In this work, we utilized the strengths of a combination of spray drying and steam-assisted crystallization (SAC), also known as dry gel conversion, to reduce these problems. At spray drying temperatures between 300 and 400 °C, it was possible to convert all the amorphous material via SAC into zeolite particles without extra addition of template. Kinetic studies of SAC revealed that about 4 to 8 days are needed to achieve the formation of a 100% crystalline product. The newly formed crystalline phase was crystallized on the surface of the nanosized zeolites and led to a slight increase in the primary particle size while the macroscopic morphology of the spray-dried aggregates was preserved. This work demonstrates that the combination of spray drying and SAC are useful tools in supplementing the hydrothermal synthesis of nanosized zeolites.

Anomalous Temperature-Induced Particle Size Reduction in Manganese Oxide Nanoparticles

“…42 According to their results, the particle sizes are deduced varying from 120 and 40 nm for heated samples at 300 and 400 °C, respectively. 42 A similar case was reported by Fievet et al, 43 where the sizes of nickel, cobalt, and copper decreased along with the temperature increasing, all falling below 200 °C and suggesting a higher saturation level in such a polyol system during the hydrothermal process. In our system, the saturation level is as low as 150 °C, resulting in high solubility among metal salt, distilled water, and reducing agent NaOH.…”

“…However, we also note a similar observation of an unusual trend that was also reported by Machoke et al related to the synthesis of Al-zeolite using the hydrothermal method with spray-drying and steam-assisted crystallization. 42 According to their results, the particle sizes are deduced varying from 120 and 40 nm for heated samples at 300 and 400 °C, respectively. 42 A similar case was reported by Fievet et al, 43 where the sizes of nickel, cobalt, and copper decreased along with the temperature increasing, all falling below 200 °C and suggesting a higher saturation level in such a polyol system during the hydrothermal process.…”

“…Indeed, we find that temperature mostly governs the particle growth direction, which causes the particle size to increase, as reported by various literature works (Table ). However, we also note a similar observation of an unusual trend that was also reported by Machoke et al related to the synthesis of Al-zeolite using the hydrothermal method with spray-drying and steam-assisted crystallization . According to their results, the particle sizes are deduced varying from 120 and 40 nm for heated samples at 300 and 400 °C, respectively .…”