Effect of chromium and boron incorporation methods on structural and catalytic properties of hierarchical ZSM-5 in the methanol-to-propylene process

Effect of chromium and boron incorporation methods on structural and catalytic properties of hierarchical ZSM-5 in the methanol-to-propylene process

We introduced chromium and boron into the hierarchical structure of ZSM-5 by following an incipientwet impregnation and hydrothermal synthesis approach to enhance the performance of the catalystsin the methanol-to-propylene process. Crystal structure, preferred orientation, and crystal symmetry ofsynthesized zeolites were discussed using Rietveld refinement and revealed that all synthesized zeolitescrystallized in a monoclinic structure, whereas the boron-incorporated sample exhibited an orthorhombicsymmetry. Large-scale defect-free single-crystalline structures of hierarchical zeolite created by CTABand F127 mesoporogens are confirmed by electron microscopy and magic angle spinning nuclear magneticresonance (MAS NMR). The formation of surface metal oxides and extra-framework metal oxidescaused changes in the electronic structure of the components as visible in Si 2p and O 1s spectra. The predominantpresence of OH groups and the higher Cr (VI) /Cr (III) ratio account for the better performanceof impregnated chromium-ZSM-5 especially in the production of light olefins. The introduction of boronby impregnation further preserved the preferred growth orientation, hierarchical structure with highcrystallinity and caused surface acidity changes in favor of increasing propylene selectivity to 67% witha propylene/ethylene ratio of close to 8.

We introduced chromium and boron into the hierarchical structure of ZSM-5 by following an incipientwet impregnation and hydrothermal synthesis approach to enhance the performance of the catalystsin the methanol-to-propylene process. Crystal structure, preferred orientation, and crystal symmetry ofsynthesized zeolites were discussed using Rietveld refinement and revealed that all synthesized zeolitescrystallized in a monoclinic structure, whereas the boron-incorporated sample exhibited an orthorhombicsymmetry. Large-scale defect-free single-crystalline structures of hierarchical zeolite created by CTABand F127 mesoporogens are confirmed by electron microscopy and magic angle spinning nuclear magneticresonance (MAS NMR). The formation of surface metal oxides and extra-framework metal oxidescaused changes in the electronic structure of the components as visible in Si 2p and O 1s spectra. The predominantpresence of OH groups and the higher Cr (VI) /Cr (III) ratio account for the better performanceof impregnated chromium-ZSM-5 especially in the production of light olefins. The introduction of boronby impregnation further preserved the preferred growth orientation, hierarchical structure with highcrystallinity and caused surface acidity changes in favor of increasing propylene selectivity to 67% witha propylene/ethylene ratio of close to 8.