Synergetic effect of H-ZSM-5/Silicalite-1@Pt/Al2O3 core–shell catalyst to enhance the selective hydrogenation of p-xylene

• A bi-layered H-ZSM-5/Silicalite-1@Pt/Al2O3 core–shell catalyst was synthesized.
• This catalyst combined the effect of isomerization and shape-selective hydrogenation.
• High PX hydrogenation conversion and selectivity of 90.8% and 97.2% were obtained.

A H-ZSM-5/Silicalite-1@Pt/Al2O3 core–shell catalyst that combined para-directed isomerization and shape-selective hydrogenation was synthesized by coating MFI membranes onto the surface of Pt/Al2O3 pellet. The binary p/m xylene mixture was performed as the feed to evaluate the enhanced selective hydrogenation property of this bi-layered core–shell catalyst. In the hydrogenation of xylene isomers, the hydrogenation efficiency and selectivity of p-xylene over the H-ZSM-5/Silicalite-1@Pt/Al2O3 core–shell catalyst exceeded those over the monolayer H-ZSM-5@Pt/Al2O3 and Silicalite-1@Pt/Al2O3 core–shell catalysts, while maintaining the tiny formation of the unexpected hydrogenation products of m- or o-xylene. The effect of reaction temperature was also investigated on the H-ZSM-5/Silicalite-1@Pt/Al2O3 catalyst. The p-xylene hydrogenation conversion and 1,4-dimethylcyclohexane selectivity of as high as 90.8% and 97.2%, respectively, were achieved at 300 °C. The isomerization on the H-ZSM-5 shell and the selective hydrogenation on the Silicalite-1@Pt/Al2O3 cooperated concertedly and promoted mutually. This bi-layered core–shell catalyst, with the synergetic effect of equilibrium shift and shape-selectivity, might have great potential to develop into a novel approach for xylenes separation.

A H-ZSM-5/Silicalite-1@Pt/Al2O3 core–shell catalyst was successfully synthesized by coating one inner Silicalite-1 layer and one outer H-ZSM-5 layer onto the surface of Pt/Al2O3 catalyst. The bi-layered core–shell catalyst, with the synergetic effect of equilibrium shift and shape-selectivity, showed enhanced efficiency for the selective hydrogenation of p-xylene in comparison with monolayer core–shell catalysts.Figure optionsDownload high-quality image (170 K)Download as PowerPoint slide