Macroscopic nanodiamonds/β-SiC composite as metal-free catalysts for steam-free dehydrogenation of ethylbenzene to styrene

Abstract

Nanodiamonds (NDs), a typical sp3-like carbon, have an average size less than 10nm with a large surface-to-volume ratio, which contributes to a high surface activity than other types of carbon. However, the powder form of the material renders it difficult to use in large-scale applications, especially in the field of heterogeneous catalysis in which high pressure drop across the catalytic bed and difficulty of handling powder are the main drawbacks. In this work, a new hybrid structure consisting of nanodiamond-decorated porous β-SiC foam matrix has been investigated as a metal-free catalyst in the steam-free dehydrogenation of ethylbenzene into styrene. The hybrid foam catalyst displays an excellent catalytic specific rate and stability in the direct catalytic dehydrogenation of ethylbenzene (EB) to styrene. The dehydrogenation activity (12.87mmolST/gND/h, moles styrene products per gram of nanodiamonds per hour) is about 10 times higher with respect to the commercial K-Fe-based catalyst and 3.8 times higher than that of powder-form NDs without losing styrene selectivity (SST=98%) and thus demonstrates the high catalytic efficiency of this metal-free catalyst for the studied reaction. This study shows a new development towards the practical use of such structured composite catalysts in the field of catalysis where high performance and stable catalyst are still under scrutiny.