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

[Display omitted] • Al F at channel intersection of HZSM-5 was identified by toluene adsorption. • The affinity of toluene/Al F was enhanced by the ion exchange of H+ by Na+. • Stepwise TPD (STPD) method was designed to quantitate the toluene desorbed from Na+. • The toluene-STPD method is not affected by the coexistence of Al pair and single Al. Precise analysis of the framework Al (Al F) 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 Al F at channel intersection under low loading (≤4 molecules/unit cell) due to spatial matching and energetic heterogeneity. After strengthening the toluene/Al F affinity through replacing H+ by Na+ and designing a new stepwise TPD technique (toluene-STPD), the contents of Al F 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 Al F. [ABSTRACT FROM AUTHOR]