Catalytic Behavior of Brønsted Acid Sites in MWW and MFI Zeolites with Dual Meso- and Microporosity

The catalytic behavior of Brønsted acid sites in three acidic zeolite materials (one MWW and two MFI zeolites) containing dual meso-/microporosity was studied using ethanol dehydration and monomolecular conversion of propane and isobutane as probe reactions. The meso-/microporous MWW zeolite, MCM-36 or pillared MWW, consists of a zeolitic layer structure, with independent microporosity and mesoporosity within the layers and between the layers, respectively. A meso-/microporous MFI (pillared MFI) zeolite also contains a zeolitic layer structure, but with interconnected micropore and mesopore systems. A different meso-/microporous MFI zeolite, three-dimensionally ordered mesoporous-imprinted (3DOm-i) MFI, contains nanometer-sized spherical elements forming an opaline structure, with highly interconnected mesoand micropores. The rate and apparent activation energy of the catalytic probe reactions in zeolites possessing dual mesoand microporosity was comparable to conventional microporous MCM-22 (MWW) and MFI materials. This similarity in kinetic behavior between materials possessing dual meso-/microporosity and their microporous analogues when assessed under conditions of strict kinetic control implies that the catalytic behavior of Brønsted acid sites in materials with dual meso-/microporosity is preferentially dominated by the microporous environment possibly because it provides a better fit for adsorption of small alkane or alcohol reactant molecules.