Al-MFI Nanosheets as Highly Active and Stable Catalysts for the Conversion of Propanal to Hydrocarbons

Abstract

The conversion of propanal to hydrocarbons is investigated over mesoporous aluminosilicate MFI nanosheets (Al-MFI-ns) of single-unit-cell thickness and conventional aluminum MFI zeolite (Al-MFI) at 673 K and atmospheric pressure. Al-MFI-ns exhibits a fivefold in- crease in stability attributed to the shorter diffusion path lengths and open architecture of the nanosheets, which minimizes pore blocking from fouling. The overall ratio of olefin to aromatic products is similar for Al-MFI-ns and Al-MFI at all conversion levels. However, the product distribution within each group shows that the Al-MFI-ns generate a fivefold increase in selectivity to C6-8 olefins and a twofold increase in selectivity to C9-10 aromatics compared to Al-MFI. The very high selectivity to C9- aromatic trimethylbenzene supports an aromatization mechanism involving sequential aldol condensation and dehydration sequences. The very short diffusion paths in the single-unit-cell thick nanosheets allows for the C9 aromatics to diffuse out of the pores before they can be converted to lighter aromatics or olefins. Al-MFI-ns shows no indication of irreversible deactivation, fully recovering its original activity after regeneration by calcination, and retaining similar deactivation rates and product selectivities as the fresh catalyst. Al-FMI-ns improves the production of aromatics from light oxygenates at mild conditions, a key feature for bio-oil upgrading.