Acidity tuning of HZSM-5 zeolite by neutralization titration for coke inhibition in supercritical catalytic cracking of n-dodecane

Abstract 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/H2O suspension using dilute NaOH aqueous solution at room temperature was introduced to neutralize excessive Bronsted acid sites of HZSM-5 zeolite (Si/Al = 25). SEM, XRD, N2 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.