Encapsulated Ni Nanoparticles within Silicalite-1 Crystals for Upgrading Phenolic Compounds to Arenes

Abstract

About 3–5 nm Ni nanoparticles were significantly encapsulated within different crystal sizes of a silicalite-1 matrix through tailoring the hydrothermal synthesis conditions and ratios of feeding materials, which were applied in the upgrading of phenolic compounds to arenes via the hydrogenolysis route. The smaller the sizes of Ni@silicalite-1 crystals with similar Ni contents and nanoparticles, the more obvious the active centers could be characterized. The enhancement in both phenol/m-cresol conversion and benzene/toluene selectivity was obtained with the decrease in crystal sizes of Ni@silicalite-1, which originated from the selective elimination of the hydroxyl group, hindrance of further hydrogenation of aromatics, and the formation of methane. Furthermore, Ni@silicalite-1 was first reported for its superior stability for more than 300 h during m-cresol conversion, which maintained a high conversion from 78.4% at 8 h to 76.2% at 334 h and aromatics yield from 73.1% at 8 h to 72.6% at 334 h. Therefore, Ni@silicalite-1 provided an alternative methodology for terminal priority to achieve selectivity control different from hydrogenation on phenyl rings via a thermodynamically favorable flat mode. Ni nanoparticles encapsulated within zeolites provided a new method to regulate the adsorption mode of reactants to modify aromatic selectivity steric effects originating from shape selectivity of the silicalite-1 matrix, which also contributed to much better stability of Ni nanoparticles.