Effect of boron on ZSM-5 catalyst for methanol to propylene conversion

B-ZSM-5 catalysts were prepared by various modification methods with boric acid, including ion-exchange, impregnation and direct synthesis. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), NH₃-Temperature Programmed Desorption (NH₃-TPD), N2 adsorption-desorption, Fourier Transform Infrared spectrometry (FT-IR), ²⁷Al and ¹¹B MAS NMR spectra. The results revealed that the weak acidity of catalysts was significantly increased by modification. The catalytic activity was measured in a fixed bed at 460°C for methanol to propylene (MTP) reaction. The results of MTP reaction showed a great increment of the propylene selectivity for the boron modified samples, especially for the directly synthesized B-ZSM-5 which also displayed high activity and selectivity towards C₂ =-C₄ = olefins. It was found that the remarkable selectivity strongly depended on the intensity of weak acidity.