Size-dependent Ru/Al2O3 catalysts for promoting the rate-determining step in N-ethylcarbazole hydrogenation

The 8H-NEC was synthesized by different organic routes and used as the substrate for kinetic studies. • Ru/Al 2 O 3 catalysts with controllable Ru particle sizes were prepared. • Smaller Ru particles showed higher TOF and lower apparent activation energy. • Low-coordinated Ru line-edge sites enhanced 8H-NEC adsorption. N -ethylcarbazole (NEC) is a promising liquid organic hydrogen carrier (LOHC) for hydrogen storage, and Ru/Al 2 O 3 catalyst is one of the most widely used catalysts for NEC hydrogenation. However, previous studies have primarily focused on the chemical electronic effect of Ru/Al 2 O 3 catalyst, while neglecting the influence of geometric structure. In this work, Ru particle size effect on the rate-determining step of 8H- N -ethylcarbazole (8H-NEC) hydrogenation has been considered. Firstly, a series of Ru/Al 2 O 3 catalysts with controllable Ru particle sizes were prepared. After that, 8H-NEC was synthesized by different organic routes to serve as the substrate for catalytic and kinetic experiments. Results showed that as the Ru particle size increased from 1.4 to 5.3 nm, the turnover frequency (TOF) decreased from 59.7 to 32.2 min −1 and the apparent activation energy increased from 44.55 to 74.00 kJ·mol −1 . CO probe diffuse reflection infrared Fourier transform spectrum (CO-DRIFTS) and density functional theory (DFT) results demonstrated that superior catalytic performance of smaller Ru particles was associated with the exposure of more low-coordinated line-edge sites, which exhibited stronger adsorption toward 8H-NEC. This study offers new insights into the design of highly efficient catalysts of NEC hydrogenation. Download: Download high-res image (169KB) Download: Download full-size image