Effect of (Si+Al)/CTAB ratio on crystal size of mesoporous ZSM-5 structure over methanol-to-olefin reactions

• Methanol conversion and light olefins showed a volcano-type dependency on crystal sizes.
• The highest methanol conversion and light olefins were obtained over moderate crystal size with hierarchical structure.
• Methanol conversion and selectivity of light olefins showed a dependence of reaction conditions such as temperature, WHSV.

Mesoporous ZSM-5 catalysts were prepared with different (Si+Al)/CTAB (cetyltrimethylammonium bromide) molar ratios and their applications in methanol-to-olefin (MTO) reactions were studied at various reaction conditions. It was found that methanol conversion and selectivity to light olefins showed a volcano-type dependency on (Si+Al)/CTAB molar ratios. The highest initial methanol conversion and selectivity of light olefins, catalyst stability were obtained over (Si+Al)/CTAB molar ratio of 15 due to its moderate crystal size with hierarchical structure. A higher C3=/C2= ratio was obtained over mesoporous ZSM-5 catalysts, which was ascribed to high Si/Al ratio and low diffusion hindrance of hierarchical structure.

With a decrease of (Si+Al)/CTAB molar ratios, the morphologies of mesoporous zeolites became more homogeneous and crystal sizes increased. The highest methanol conversion and light olefins were obtained over crystal size of 6–8 µm.Figure optionsDownload as PowerPoint slide