Search

[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]

[Display omitted] • Neutralization titration can reduce the acid density and strength of HZSM-5 zeolite. • The neutralization reaction just occurs in liquid phase rather than in solid phase. • Nature of neutralization titration is solid phase ion exchange between Na+ and H+. • Neutralization method facilitates the removal of extremely strong acid sites. • Both coke amount and harmfulness per unit mass of coke can be suppressed. Reducing the acid density and strength of HZSM-5 zeolite are typical strategies to inhibit coke deposition during catalytic cracking reactions. Herein, direct titration of HZSM-5/H 2 O suspension using dilute NaOH aqueous solution at room temperature was introduced to neutralize excessive Brønsted acid sites of HZSM-5 zeolite (Si/Al = 25). SEM, XRD, N 2 adsorption and n -propylamine temperature-programmed decomposition confirmed that simultaneous acid strength weakening and acid density reducing were achieved without obvious influence on crystalline or textural property. The evolution of the surface charge during the titration process tracked by Zeta-potential measurement reveals that the mechanism of such neutralization is: liquid phase neutralization between H+ and OH− & solid phase ion exchange between Na+ and H+. Supercritical catalytic cracking of n -dodecane over a series of partial neutralized HZSM-5 catalysts showed that moderate neutralization can enhance the conversion of n -dodecane by alleviating both the coke amount and harmfulness per unit mass of coke. [ABSTRACT FROM AUTHOR]