Nanocrystalline ZSM-5: A catalyst with high activity and selectivity for epoxide rearrangement reactions

Nanocrystalline ZSM-5 (∼20–50 nm) has been tested as a catalyst in the liquid phase rearrangement of 1,2-epoxyoctane, 2-methyl-2,3-epoxybutane and isophorone oxide together with a microcrystalline ZSM-5 sample (∼5 μm) employed as a reference. Whereas this last material shows a low activity for the three epoxide rearrangement reactions considered, nanocrystalline ZSM-5 leads in all cases to high epoxide conversion. This different catalytic performance is attributed to the differences in the accessibility of the reactant molecules to the catalyst active sites. The smallest crystal size of the nanocrystalline zeolite contributes favourably to both the formation of a high external surface area, with no steric constraints, and to a faster intracrystalline diffusion of the epoxide molecules towards the acid sites located within the zeolite micropores. When sterically hindered epoxides are tested, the catalytic rearrangement occurs mainly on the external surface of the nanocrystalline zeolite. Moreover, it is remarkable that for the three epoxides investigated the high catalytic activity observed over nanocrystalline ZSM-5 is accompanied by the attainment of high selectivities, typically around or over 80%, towards products with commercial applications.

Nanocrystalline ZSM-5 has been tested in the liquid phase rearrangement of different bulky epoxides, showing in all cases a high selectivity towards the desired products. Compared to a reference zeolite sample, nanocrystalline ZSM-5 presents a quite superior activity due to the improved accessibility to the active sites derived from its small crystal size.Figure optionsDownload high-quality image (166 K)Download as PowerPoint slide