Comparative Study of Acidic Properties of UZM-5 Nanosheets by Stepwise Adsorption Assisted by a Selective External Poisoning Approach

Abstract

UZM-5 zeolite was hydrothermally synthesized using a TMA+/TEA+ mixed-template as a structure-directing agent (SDA). The resulting sample displays a sheet-like morphology and a uniform particle size of 100–300 nm. The thickness of the particles is ca. 15 nm, corresponding to 5 unit cells. UZM-5 has an 8-membered ring (8-MR) micropore system with a pore diameter of 3.8 A, a secondary mesopore system with a narrow pore size distribution centered at 3.5 nm, specific surface area of 576 m2/g and significantly large external surface area of 122 m2/g. The nature and the location of acid sites were determined from the temperature-programmed desorption (TPD) of basic probes with various sizes and an FT-IR method, combined with topological analysis. It was found that the density of the acid sites on the external surface of particles is higher than that in the micropores. Regarding the acid sites on the external surface of particles, the highly exposed double 4-ring (D4R) units represent dominantly strong Bronsted-t...