Quantitative sorption experiments on Ti-zeolites and relation with α-olefin oxidation by H2O2

A tracer chromatographic method is used to study liquid-phase adsorption on TS-1, Ti-beta, and Ti-MCM-41. Partition coefficients for alkenes, alkanes, epoxides, and other polar products are strongly dependent on the carrier solvent. Linear alpha-olefins are concentrated inside the TS-1 micropores, particularly when methanol is the solvent, This agrees well with the superior initial rates of olefin epoxidation with TS-1 in methanol. Sorption also governs the relative reactivities of olefin substrates, especially in competitive experiments. Thus, under truly initial conditions, 1-hexene is less reactive than 1-octene or 1-nonene, For the latter substrates, however, deactivation is fast, especially in methanol. This process is related to the strong adsorption of higher 1,2-epoxyalkanes in TS-1 in methanol. Deactivation due to competitive epoxide adsorption is slower in acetone, making this a more suitable solvent than methanol for 1-nonene epoxidation with TS-1. Overall, physisorption effects play a dominant role in the small pore TS-1 catalyst, due to the close interaction of substrates such as alkenes with the pore wall. Wider-pore catalysts such as Ti-beta and especially Ti-MCM-41 do not adsorb olefins as selectively and hence intraporous olefin concentrations are much lower. (C) 1999 Academic Press.