Synthesis and application of HZSM-5@silicalite-1 core–shell composites for the generation of light olefins from CH3Br

• Nonacidic silicalite-1 was contiguous coated on HZSM-5 to yield core–shell composites.
• The composites exhibit light olefins selectivity up to 80% and higher stability in CH3Br conversion.
• The good stability is ascribed to shell that hinders HZSM-5 from deactivation.

To improve activity and hinder deactivation, nonacidic polycrystalline silicalite-1 was contiguously coated on HZSM-5 to yield HZSM-5@silicalite-1 composites using a hydrothermal synthesis method. The obtained samples were examined as catalysts for the generation of light olefins (ethylene and propylene) from CH3Br, and found to show high catalytic activity, stability and high selectivity to the desired products. The excellent performance is attributed to the silicalite-1 shell which causes passivation of acid sites on the external surface of HZSM-5. It was observed that the HZSM-5@silicalite-1 composite with thicker coating (ZS-2) shows much higher stability and selectivity to light olefins (up to 80%) than that with thinner coating (ZS-1), indicating that the surface of HZSM-5 crystals of the latter was less covered. Based on the characterization results, it is deduced that the catalytic stability of ZS-2 is due to the silicalite-1 shell that hinders HZSM-5 from deactivation as a result of surface coking.

Figure optionsDownload as PowerPoint slide