(228d) Quantifying Active Catalytic Sites in Lewis Acidic Zeolite Sn-Beta

Sn-Beta is a promising catalyst for numerous reactions involved in biomass upgrading and fine chemical production. Interestingly, Sn-Beta is proposed to have two distinct catalytic sites: open and closed sites. The quantification of these different sites is important, as previous investigations suggest a correlation between specific types of sites and improved activity for certain reactions. Common techniques to quantify the fraction of open and closed sites in Sn-Beta include solid-state MAS NMR and diffuse-reflectance FTIR with probe molecules, but these methods do not provide insight into the activities associated with the different sites for a given reaction. This information can be obtained from site quantification experiments that involve the addition of a catalyst poison. Here, four Lewis bases are tested as poisons in site quantification poisoning experiments: triethylamine, pyridine, 2,6-lutidine, and trimethylphosphine oxide. The poisoning solution is introduced to the Sn-Beta to deactivate a certain fraction of the Sn metal sites prior to catalyzing the ring opening of epichlorohydrin by methanol. Results of the site quantification poisoning experiments using triethylamine indicate that approximately 80% of the catalytic sites in Sn-Beta are active for this reaction. As demonstrated experimentally, the results are robust with little to no effect of diffusion limitations on the data. Additionally, triethylamine is able to distinguish catalytic sites with different levels of activity by preferentially deactivating sites with higher activity, evidenced by the multi-slope decrease in turnover frequency. Ongoing work is demonstrating how the crystallization time impacts the fraction of active catalytic sites that are formed in Sn-Beta. The identification of appropriate poisons will contribute to the establishment of robust procedures for Sn-Beta site quantification, which in turn will enable the determination of effective Sn-Beta synthesis parameters.