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 meso- and micropores. The rate and apparent activation energy of the catalytic probe reactions in zeolites possessing dual meso- and 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.