Investigating the Impact of Synthesis Conditions to Increase the Yield and Tin Incorporation Efficiency for Lewis Acid Nano-Sn-MFI Zeolites

Abstract

Advances in the synthesis of Lewis acid zeolites have been bolstered by the synthesis of nano-zeolites to overcome diffusion limitations. Key challenges remain for the synthesis of Lewis acid nano-zeolites since current methods tend to result in a low tin incorporation efficiency (25%) and a low material yield (∼25%). In this work, insights on how to overcome these limitations are investigated through synthesizing nano-zeolite MFI with different tin precursors (n-Sn-MFI) and different ratios of water to silica and/or structure directing agent (SDA) to silica. The crystallization process is monitored using dynamic light scattering, and it is determined that the tin precursor has a minor impact on the final particle size, but the water and SDA concentrations did affect the final particle size. Compared to the standard synthesis (SiO2/SDA/H2O of 1:0.4:23), reducing the amount of SDA/SiO2 to 0.2:1 results in a larger particle size but increases the yield and tin incorporation efficiency. Reducing the amount of water (H2O/SiO2 of 19 and SDA/Si of 0.2) improves the tin incorporation efficiency over the standard case and results in small particles while achieving a yield of up to 78%. The resulting materials are characterized using several standard techniques to demonstrate that the materials are of high quality. The materials are tested for catalytic activity in the alcohol ring opening reaction of epoxide as a probe reaction and are found to have comparable activity. The rate of conversion of 1,2-epoxyhexane can be increased through synthesizing small crystals in high yield through decreasing the SDA/SiO2 ratio to 0.2:1 and reducing the H2O/SiO2 ratio to 19:1. Overall, the work demonstrates that the synthesis conditions can be tuned to increase the tin incorporation efficiency and increase the yield of the Lewis acid nano-zeolites while producing a highly active catalyst.