The role of external acidity of meso-/microporous zeolites in determining selectivity for acid-catalyzed reactions of benzyl alcohol

A comparison of selectivity in catalytic conversion of benzyl alcohol in mesitylene on hybrid lamellar-bulk MFI (HLBM) zeolite materials containing dual meso-/microporosity showed that the external Brønsted acidity in meso-/microporous MFI zeolites effectively impacts on selectivity of the parallel alkylation and etherification reactions. HLBM zeolites, consisting of crystalline bulk microporous core and lamellar mesoporous shell, not only catalyzed the parallel reactions on the external environments (external surface and mesopore) but also catalyzed the etherification reaction in the internal environment (micropore) as illustrated by the completely suppressed alkylation and retained residual etherification reactions after 2,6-di-tert-butylpyridine (DTBP) poisoning. A systematic study of HLBM zeolites with tunable meso-/microporous domain sizes achieved by a dual template assisted synthesis revealed that parallel alkylation and etherification reactions are tailored by the tunable external surface area and external acidity of the HLBM zeolites. The external alkylation and etherification reaction rates as a function of cumulative DTBP addition suggested the presence of Brønsted acid sites with different strengths on external environments of the HLBM zeolites, which influenced the external etherification reaction, but not as significantly as the alkylation reaction. The evidence shown here for the involvement of external acidity in catalyzing parallel reactions and for the role of external acidity with variable strengths in HLBM zeolite materials extends the scope of observed catalytic behaviors of meso-/microporous zeolite materials beyond those reflecting transport effects and accessibility of acid sites.