Importance of the Nature of Acidic Sites of Different Aluminosilicates on Fixation of Carbon Dioxide with Styrene Oxide.

Abstract

The nature of acidic sites in commercially available aluminosilicates, zeolite Na-Y, zeolite NH4 + -ZSM-5, and as-synthesized Al-MCM-41 have been investigated by employing them as catalysts for capturing CO2 by styrene oxide. The catalysts, in tandem with tetrabutylammonium bromide (TBAB), produce styrene carbonate, and the yield of the product is observed to be governed by the acidity of the catalysts and hence, the Si/Al ratio. All these aluminosilicate frameworks have been characterized by IR, BET, TGA, and XRD. XPS, NH3 -TPD, and 29 Si solid-state NMR studies have been carried out to analyze the Si/Al ratio and the acidity of these catalysts. According to TPD studies, the number of weak acidic sites of these materials follow an order as NH4 + -ZSM-5 < Al-MCM-41 < zeolite Na-Y, which is just in accordance with their Si/Al ratios and the yield of the cyclic carbonates obtained, i. e., 55.3 %, 68 %, and 75.4 % respectively. The TPD data and the yield of the product carried out with calcined zeolite Na-Y indicate that not only the weak acidic sites but also the role of strong acidic sites might appear crucial in the cycloaddition reaction.