Insight into interactions among P, Zn and ZSM-5 during bi-component modification on ZSM-5

Abstract

Zn/P/ZSM-5 catalysts were selected to demonstrate interactions among Zn, P and ZSM-5 during bi-component modification on ZSM-5 and their corresponding effects on the catalytic performance. The status of impregnated Zn and P species, as well as the framework Si and Al species in Zn/P/ZSM-5 were systematically investigated by X-ray diffraction (XRD), ²⁷Al, ³¹P and ²⁹Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR), NH₃ temperature-programmed desorption (TPD) and Fourier transform infrared (FTIR) spectroscopy. It is important to verify that ZnO could be transformed into Zn₃(PO₄)₂ and Zn₂SiO₄ in the presence of P and framework Si species respectively, leading to a decrease in aromatization performance. More significantly, Zn₃(PO₄)₂ could also hinder the coordination between P and framework Al, leading to deteriorated acidity and poor hydrothermal stability. A clearer insight into the interaction among species in bi-component modified zeolites would provide a general proposal for better optimization on the catalytic performance of bi-modified zeolites.