MFI-type zeolite nanosheets for gas-phase aromatics chlorination: a strategy to overcome mass transfer limitations

The continuous gas-solid (environmentally-friendly) chlorination of deactivated arenes using trichloroisocyanuric acid (TCCA, C3N3O3Cl3) as a chlorination agent was chosen to compare the catalytic performances of various MFI-type catalysts in a reaction demanding a strong acidity. Mass transfer limitations were also evaluated by reacting either chloro-or nitrobenzene through a ZSM-5 zeolite porous network having different crystal sizes and morphologies. Whereas, the reaction rate was completely controlled by internal diffusion in 10-15 mu m-sized big ZSM-5 zeolite crystals (Weisz modulus, phi(big) crystals similar to 10), the impact of internal diffusion could be ruled out for ZSM-5 nanocrystals (200-400 nm) and in stacked ZSM-5 nanosheets (thickness 2 nm). Based on reactivity differences in arene halogenation between the two nano-sized ZSM-5 zeolites, we were able to estimate the quantity of mild acidic silanol groups in ZSM-5 nanosheets to roughly 1/3 of the total amount of BrOnsted acid sites.