A New Practical Route to ZSM‐5 Nanoparticles and Optimization of Synthetic Parameters through D‐optimal Design of Experiments

A D‐optimal experimental design with three levels of SiO₂/Al₂O₃, template/SiO₂, H₂O/SiO₂, Na₂O/SiO₂ and TPABr/TPAOH ratio parameters has been used to optimize the experimental parameters by an analysis of variances (ANOVA). The effects of these ratios in the initial synthetic mixture on the size of the ZSM‐5 zeolite nanoparticles have been studied. XRD and FE‐SEM analyses were used to characterize synthetic samples. Fischer test results showed that H₂O/SiO₂ and TPABr/TPAOH ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variables were the interaction of template/SiO₂ and TPABr/TPAOH molar ratios. The average particle size was in the 34–79 nm range. Furthermore, a mathematical model for the synthesis of ZSM‐5 zeolite nanoparticles was derived using experimental results. The optimized gel composition is as follows: SiO₂/Al₂O₃₌91.20, template/SiO₂₌0.16, H₂O/SiO₂₌40.42, Na₂O/SiO₂₌0.0147 and TPABr/TPAOH=0.     

Ultrasonic pretreatment for hydrothermal synthesis of SAPO-34 nanocrystals

Synthesis of SAPO-34 nanocrystals which has been recently considered as a challenging task was successfully performed by sonochemical method using TEAOH as structure directing agent (SDA). The products were characterized by XRD, SEM, EDX, BET and TGA. The average crystal size of the final product prepared sonochemically is 50 nm that is much smaller than that of synthesized under hydrothermal condition and the morphology of the crystals changes from uniform spherical nanoparticles to spherical aggregates of cube type SAPO-34 crystals respectively. In the case of sample synthesized sonochemically with aid of hydrothermal condition, the surface area is significantly upper than that of obtained by the conventional static hydrothermal technology with almost the same crystallinity. SAPO-34 framework synthesized by just ultrasonic treatment is unstable and a significant part of SAPO-34 nanocrystals is transformed to the dense phase of AlPO₄ structure, i.e., Cristobalite. Contrary to hydrothermal method that at least 24 h of the synthesis time is required to obtain fully crystalline SAPO-34, sonochemical-assisted hydrothermal synthesis of samples leads to form fully crystalline SAPO-34 crystals taking only 1.5 h. In a sonochemical process, a huge density of energy for crystallization is provided by the collapse of bubbles which formed by ultrasonic waves. The fact that small SONO-SAPO-34 crystals could be prepared by the sonochemical method suggests a high nucleation density in the early stages of synthesis and slow crystal growth after nucleation.     

Application of D‐optimal experimental design in nano‐sized ZSM‐5 synthesis for obtaining higher crystallinity

D‐optimal experimental design with three levels of SiO₂/Al₂O₃, template/SiO₂, H₂O/SiO₂, SiO₂/Na₂O and TPABr/TPAOH ratio parameters was used to optimize the experimental parameters by the analysis of variance (ANOVA). The effects of above mentioned ratios in the initial synthetic mixture on the crystallinity of the ZSM‐5 zeolite were studied. The synthesized samples were characterized by XRD, FE‐SEM, and TEM analysis. Fischer test results showed that SiO₂/Al₂O₃ and H₂O/SiO₂ molar ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variable was that of template/SiO₂ and Na₂O/SiO₂ molar ratios. The optimum composition of the gel compound to achieve relative maximum crystallinity is SiO₂/Al₂O₃ = 99.96, template/SiO₂ = 0.16, H₂O/SiO₂ = 34.68, Na₂O/SiO₂ = 0.02 and TPABr/TPAOH = 1.44.