Potassium-promoted single-atom Co-N-C catalyst for direct dehydrogenation of ethylbenzene

Alkali metals have been widely used as promoters of metal catalysts in various applications, yet the atomic understanding of the promotional mechanism remains elusive. In this work, we for the first time report the significant promotional effect of potassium to the Co-N-C single-atom catalyst for the direct dehydrogenation of ethylbenzene. K cation was introduced by impregnation of Co-N-C with KCl followed by calcination at 600 °C, which resulted in the bonding of K to the Co-O moiety of the Co-N-C catalyst as revealed by X-ray absorption spectroscopy in combination with theoretical calculations. The formation of Co-O-K moiety led to the increase of electron density at the O atom due to electron transfer of K to O, and consequently facilitated the heterolytic cleavage of the C–H bond of ethylbenzene across the Co-O moiety. The promotional effect of K was found to be a volcano-function with the K/Co ratio and became the greatest at the K/Co ratio of 1.36, which resulted in the highest steady-state reaction rate of 9.7 mmol_EB·g_cat⁻¹·h⁻¹ reported thus far. Moreover, the catalyst exhibited excellent stability during 100 h time on stream.