Synthesis And Characterization Of Morphology-Controlled Mordenite Zeolites

Mordenite as one of the earliest zeolite in human knowledge. Mordenite is widely used in the field of separation, adsorption and catalysis because of its thermal resistance, acid resistance and water resistance. The morphology of zeolite has a substantial effect on performance, therefore it is still a challenge to fabricate suitable morphology-controlled mordenite due to the complicate relationship between zeolite morphologies and synthetic conditions. The advantages of the mordenite aggregated with small-sized crystals include simple operation, easy separation, low wear degree and convenient recovery of catalytic application. Furthermore, zeolites with this morphology is conducive to the increase of the specific surface area due to the accumulation of small grains. Moreover, we reduced the synthesis time of mordenite reduced to 18 h successfully, and improved the synthesis efficiency. The main conclusions are summarized as follows:1. The structure directing agent as a high-activity silicon source was introduced into the synthetic system. The synthesis by using two silicon sources resulted in mordenite crystals with different morphologies. The influences of synthesis parameters on mordenite morphology, such as proportion of SiO2 in two silicon sources, molar composition of the starting synthesis gel, crystallization time, had been systematically investigated. A series of mordenite crystals with different morphologies were obtained from the two silica sources system without any additives, and characterized by XRD, SEM, FT-IR and N2 physisorption. The results indicated that morphologies of mordenite crystals can be controlled by adjusting the synthetic conditions, and the increase in the proportion of the structure directing agent can accelerate the nucleation, shorten the crystallization time and improve silicon aluminum ratio of the products. The optimum conditions of smooth large prismatic mordenite was the starting gels composition of SiO2/Na2O/H2O/Al2O3=35/10/750/1 (crystallized at 180 ℃ for 18 h) by n= 0.83 (n:silica molar ratio of the structure directing agent and TEOS in starting gels). When the starting gels composition was SiO2/Al2O3/Na2O=35/1.4/10 with n= 0.13 (crystallized at 180 ℃ for 48 h) by water content from 250-1750, we had successfully synthesized mordenite. This illustrated that the addition of the structure directing agent can also broadened the range of water content used for the mordenite synthesis. We also successfully prepared circular pies were aggregated with small-sized rod-like crystals, and the synthesis conditions was the starting gels composition of SiO2/Na2O/H2O/Al2O3=35/10/750/1.4 (crystallized at 180 ℃ for 18 h) by n= 0.13. The nitrogen sorption isotherm of the sample showed a BET surface area and pore volume of 266.85 m2g-1 and 0.12 cm3g-1, respectively.2. In the single silicon source system of preparing mordenite, a series of experimental parameters which can influence the morphology and structure of the zeolite were discussed. The obtained experimental results indicated that mordenite with micro-nanostructure can be synthesized by using TEOS as silicon source, and the synthesis conditions was the starting gels composition of SiO2/Na2O/H2O/Al2O3=25/5/800/1 (crystallized at 180 ℃ for 96 h). The addition of CTAB in the synthesis system produced the mordenite with better dispersion.