On the use of 1-butene double-bond isomerization as a probe reaction on cesium-loaded zeolite X Original Research Article

Oxides of cesium and potassium were synthesized in the supercages of zeolite X by impregnation and decomposition of acetate precursors. The alkali-loaded zeolites were characterized by N2 adsorption, CO2 adsorption microcalorimetry and stepwise TPD of CO2. For a loading of about two alkali metal atoms per zeolite supercage, the majority of CO2 adsorption sites at 373 K were characterized by a −ΔHads of about 80–100 kJ mol−1. The initial turnover frequency (TOFi) for 1-butene isomerization, based on excess cesium atoms, followed the order CsOx/CsX, CsOx/KX, KOx/KX, which parallels the expected ranking of base strength based on composition. For CsOx/CsX, the TOFi was independent of Cs loading, which suggests that active sites were non-interacting and that heat and mass transfer artifacts were absent in the kinetic data. Studies of catalyst deactivation showed that trace impurities in the feed were the likely cause of activity loss with time on stream. Selective poisoning of active sites with CO2 indicated that only about 5% of the sites counted by CO2 adsorption at 373 K were active for butene isomerization. Evidently, the very low active site density made these catalysts vulnerable to trace impurities in the feed.