Ion-exchanged ETS-10 catalysts for the cycloaddition of carbon dioxide to propylene oxide

Alkali- and alkaline-earth-exchanged ETS-10 molecular sieve catalysts were investigated for the cycloaddition of carbon dioxide to propylene oxide to produce propylene carbonate. Adsorption microcalorimetry of adsorbed carbon dioxide was used to correlate reactivity to the strength and number Of CO2 adsorption sites. While carbon dioxide uptake for the ETS-10 and K-ETS-10 catalysts was the greatest for the catalysts investigated, these two catalysts were not as productive as Cs-ETS-10. The adducts formed between carbon dioxide and the charge-compensating cations appear to be prevalent in these materials and do not provide an appropriate CO, adsorption site for the reaction to occur. Yield of propylene carbonate was found to have an inverse relationship with the Sanderson elect ronegativity associated with the charge-compensating cation, indicating that surface basicity associated with the partial charge of the framework oxygen plays an important role in the catalyst effectiveness for the reaction. The alkali-exchanged samples were significantly more active than the alkaline-earth-exchanged catalysts on a per gram basis due to their higher strength CO2 adsorption sites as indicated by adsorption microcalorimetry. The Cs-exchanged ETS-10 molecular sieve gave conversions similar to those observed for basic NaX zeolites containing occluded alkali oxide species. (C) 2004 Elsevier Inc. All rights reserved.