Catalytic Behavior of Brønsted Acid Sites In MWW and MFI Zeolites

Zeolites possessing micro- and meso-porosity couple the catalytic features of micropores and the improved access and transport consequence of mesopores in a single material. The catalytic behavior of Brønsted acid sites in three acidic meso-/micro-porous zeolite materials (pillared MWW, pillared MFI, and 3DOm MFI) was studied using ethanol dehydration and monomolecular conversion of propane and isobutane as probe reactions. The pillared MWW (or MCM-36) consists of a zeolitic layer structure, with independent microporosity and mesoporosity within the layers and between the layers, respectively. Pillared MFI zeolite also contains a zeolitic layer structure, but with interconnected micropore and mesopore systems. 3DOm MFI contains nanometer-sized spherical elements forming an opaline structure, with highly interconnected meso- and micro-pores. The rate and apparent activation energy of the catalytic probe reactions in zeolites possessing dual micro- and meso-porosity was comparable to conventional microporous MCM-22 (MWW) and MFI materials. This similarity in kinetic behavior between materials possessing dual meso-/micro-porosity 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-/micro-porosity is preferentially dominated by the microporous environment possibly because it provides a better fit for adsorption of small alkane or alcohol reactant molecules.