Abstract
Nanoporous crystalline aluminosilicates, zeolites, are synthesised by solvothermal method producing three-dimensional (3D) crystals. An alternative, more controllable approach of zeolite synthesis - ADOR - can be used for preparation of isoreticular zeolites with tuneable porosity.
Zeolites porosity allows their wide use as isomerisation catalysts due to their shape selectivity effects. Selective isomerisation of m-xylene towards p-xylene is an industrially important reaction due to a high demand for the latter as a substrate for terephthalic acid production.
In this work, we investigated the influence of pore size (shape selectivity effect) on the isomerization of m-xylene using a system of isoreticular Al-containing zeolites. These materials, prepared by ADOR approach (UTL, IPC-7, IPC-2, IPC-6, and IPC-4) had different layers connectivity, and therefore various channel systems.
We tracked the influence of the pore systems of ADOR zeolites (8- up to 14-ring channels) on the catalytic performance in gas-phase m-xylene isomerisation. We investigated the crystallinity and interlayer distances, phase purity, textural properties of prepared materials, their crystals morphology, and aluminium content.
M-xylene isomerisation was carried out in a fixed-bed reactor at 350 °C. ADOR catalysts were compared with standard ZSM-5 zeolite.
We show the dependence of zeolite porosity on the performance in isomerisation of m- to p-xylene. Smaller pore zeolites: IPC-4 (8- and 10-ring channels) and IPC-6 (8-, 10- and 12-ring channels) exhibited the lowest conversions, while the highest conversion and p-xylene yields were observed for IPC-2 (10-and 12-ring channels).
Presence of extra-large, 14-ring channels (IPC-7 and UTL) resulted in the drop of selectivity due to the xylene disproportionation.