Quantitative analysis of framework Al at channel intersections of HZSM-5 zeolite by toluene adsorption-desorption

Precise analysis of the framework Al (AlF) at channel intersections of HZSM-5 zeolite is the basis of fine tuning of the spatial distribution of active sites within different pores which is critical to promote the catalytic performance in various applications. However, existing technologies cannot provide reliable quantitative results either in theory or practice due to the co-existence of Al pair and single Al. Here we report a new method based on toluene adsorption-desorption. As a promising probe, toluene can be preferentially adsorbed on AlF at channel intersection under low loading (<= 4 molecules/unit cell) due to spatial matching and energetic heterogeneity. After strengthening the toluene/AlF affinity through replacing H+ by Na+ and designing a new stepwise TPD technique (toluene-STPD), the contents of AlF atoms at channel intersections of HZSM-5 samples were successfully calculated by counting the desorbed toluene molecules based on the 1:1 stoichiometric relationship between adsorbed toluene and AlF.(c) 2022 Elsevier Inc. All rights reserved.