We have recently investigated ETS-10 molecular sieve catalysts for the cycloaddition of carbon dioxide to propylene oxide to produce propylene carbonate in a batch autoclave operating in a high pressure atmosphere of CO₂, a reaction which requires significant basicity to proceed. Our studies have shown that surface bound water enhances the cycloaddition reactivity for the ETS-10 catalysts and the rate of enhancement depends on whether the amount of water is above or below the ammount associated with the hydration level consistent with that initially found in the as-prepared material. This enhancing effect has also been observed for reactions performed with other microporous catalysts, such as X zeolites. Because of this enhancing effect of water, this investigation focuses on alternative reaction pathways for the cycloaddition reaction in which 1,2- or 1,3-propylene glycols, which have been detected in small quantities from our product analysis, are active reaction intermediates that are responsible for the enhanced reaction rates observed. Additional studies investigating isomers of propylene oxide as potential reaction intermediates that may be formed under reaction conditions, such as propionaldehyde and allyl alcohol, are also presented. The role microporosity plays will also be discussed.